Measuring pH for Cannabis Plants has never been easier with these special devices made for easy and simple pH measuring. Models for all kinds of growers. Reducing pesticide application in agricultural land is a major challenge for the twenty-first century. Responses of weed seed’s germination and seedling’s early development to chemical soil conditions around the seed may be a promising way to aid weed control in a no-till system. Thus, the objective of this work was to test, under controlled conditions, whether different chemical conditions affect the germination and development of horseweed [Conyza canadensis (L.) Cronquist]. We used, as treatment, solutions containing different nutrients (P, K, Ca, and Mg), separately and in combination, and at two pH levels (4.8 and 6.5). Phosphorus alone inhibited horseweed seed germination at ~ 7 times while had ~ 4 times reduction in final germination percentage and germination speed index for both pH tested. Other nutrients tested had a no-effect in germination speed index compared to the control treatment. Potassium alone or associated with other ions (P, Ca, and Mg) at pH 4.8 had a synergistic effect on seedling development (root and shoot length). In the same way, K associated with Mg was synergistic to the root length at pH 6.5. Seeds in the control treatment (distilled water) presented a high germination speed index at pH 6.5, while at low pH this parameter was higher when in association with KMg, PMg and Ca. The findings demonstrate that seed germination traits and seedling development of horseweed depend on nutrient kind exposure and pH conditions in the seed environment. This work suggests that adequate topsoil management (i.e., pH and nutrient availability) may aid to reduce weed germination, because, it consists of an important factor of weed occurrence in agricultural areas. The water pH level that you use to grow your cannabis seeds is important to the healthy growth of the plant. There is some variation in the PH level …
Cannabis pH and Watering your Plants
When growing cannabis, and almost any other type of plant, there are various factors that influence how they grow and the quality of the final product such as the quality of the air, water, sun and soil. Any sort of issue with the quality or presence of these parameters will generally produce poorly plants that are likely to catch more illnesses and/or be infested by insects or fungi. That’s why we’re going to be talking about pH for cannabis plants; pH is one of the most determining factors when it comes to feeding cannabis plants and having them absorb everything you give them.
What is pH?
pH is used to measure acidity and alkalinity of a liquid or dissolved solid. pH levels can range from anywhere between 0.0 and 14.0; substances with a pH lower than 7 are considered acidic, whereas those with a pH higher than 7 are considered more alkaline. If the solution is exactly 7.0, it’s pH neutral. A great example of an acidic substance is hydrochloric acid, which has a pH of 0.0, whereas caustic soda (washing soda) is highly alkaline, with a pH of 14.0. Water is the best example of neutral substances, as it tends to sit at around 7.0 pH.
The Importance of Measuring Cannabis pH Levels
When you put a lot of work and effort into growing cannabis in the hopes of obtained the best possible results. pH is an incredibly important factor when it comes to making sure that your plants are absorbing everything you give them via their roots. If your plants’ roots are not being given substances with the right pH, they won’t be able to absorb certain types of nutrients, and in a matter of time they may end up showing signs of deficiencies or excess, as certain types of minerals build up in the growing medium, creating a toxic environment for your plants’ roots while also stopping other nutrients from being absorbed.
If you manage to keep pH levels under check when watering, you still may end up with deficiencies or overwatering, although the probabilities of this happening are much lower and they’ll be much easier to fix if the pH is right.
What Should pH be for Cannabis Plants
For a cannabis plant to grow to the best of its abilities, you need to keep in mind that pH levels shouldn’t always be exactly the same; depending on the strain grown, the stage in which it is in (germination, growth, pre-flower, bloom), the growth medium and whether you’re growing organically or using minerals, the pH level of your water should vary slightly.
You can grow cannabis by keeping the pH at a constant level, although it’ll need to range between 5.5 and 7.0. This allows for decent results, although you won’t be making the most out of your seeds nor the nutrients you’re using to feed your plants. Plus, you may end up with feeding and nutritional issues further down the line.
These are the ideal pH values for growing cannabis in hydroponic and aeroponic settings including other inert substrates:
- First weeks: 5.8 – 5.9 pH
- Pre-bloom: 6.0 – 6.2 pH
- Real bloom: 6.0 – 6.3 pH
These are the ideal pH values for growing cannabis peat mixes or straight in the ground:
- First weeks: 5.5 – 6.0 pH
- Pre-bloom: 6.0 – 6.2 pH
- Real bloom: 6.2 – 6.5 pH
Adjusting pH for Cannabis Plants
Figuring out how to adjust the pH in your water isn’t that complicated at all. You need to discern between watering using nutrients and only water, and there will be a difference between using automatic watering systems and watering manually.
Using just water
Fill your tank or bottle, let the water sit for a few minutes and then measure the pH in the water using a pH meter. If needed, follow the instructions provided by the manufacturer of your pH Up or Down products. If there is no recommendation, add an extremely small amount to your water tank or bottle, dilute properly and let it sit before measuring it again. Repeat this process as many times as necessary until pH levels are as desired.
Water with nutrients
This process varies depending on the fertilizers used; some brands recommend adjusting the pH before adding their products, whereas others recommend measuring and adjusting the pH after adding them to your water. If the manufacturer has not left any specific instructions, we recommend dissolving your nutrients one by one, mixing thoroughly. Then, you’re going to need to let it sit for a few minutes in order for the pH to balance out. This way you can measure and adjust accordingly without any fluctuations.
When it comes to automatic watering systems, a large tank is usually used alongside an automatic pipe system which usually contains water and nutrients, enough to feed your plants for about one to two weeks. In order to adjust the pH and keep it balanced within the recommended pH value, we recommend using pH and temperature monitors so that you can have an eye on the pH at all times. This allows you to easily and quickly adjust the pH when needed – all you have to do is keep an eye on it and you’ll be able to fix it before anything goes wrong.
Note: in order to avoid taking too long to adjust the pH in your water, we recommend writing down the original pH of your water and then writing down how much product was needed to get it to the right value. This will save plenty of time down the line.
How to adjust the pH in Water |The Best pH for Cannabis
Adjusting the pH in your water can be so simple that it gets complicated if you don’t have the proper tools and they aren’t in decent condition. In order to do this correctly, you’ll need to use a pH meter as well as specific liquid products used to adjust pH upwards or downwards. We’re going to have a quick look at pH meters and liquids used for adjusting pH.
pH meters are measuring instruments that are quite easy to use; most of the time, all you have to do is switch it on and place the sensor end in the water in order to analyze its pH. In order to avoid bad readings and issues with the meter itself, we recommend cleaning it after every use as well as adjusting them when necessary. Also, you’ll want to keep the sensor moist using a maintenance solution.
Liquids used to reduce or increase the pH in nutrient solutions contain either acidic or alkaline ingredients, which can be organic and/or mineral. Plus, depending on the manufacturer, some pH adjusters can be specific for the growth period or for the bloom phase.
Mineral pH adjusting products are generally made using the following ingredients:
- Nitric acid: depending on the ratio, you can use this to increase or decrease pH levels, plus it’s perfect for the growth period thanks to its high Nitrogen count.
- Phosphoric acid: this is used to lower the pH and it’s ideal for the flowering period thanks to its high phosphorus content, although it can also be used in the growth period.
- Potassium hydroxide: this is used to increase the pH in water. Thanks to its high potassium content it can be used in the growth and flowering periods.
Organic pH adjusters tend to contain the following components:
- Humic acids: these acids increase the pH in your water and can be used during the entire growing period, although we recommend using it during the growth period as humic acids can actually decrease THC yield.
- Citric acid: this is used to decrease pH and it can be used during the entire growth and flowering process.
The main difference between organic and mineral pH adjusters is that the minerals tend to harm any natural life in the soil, so you need to rebuild it after every use. Organic products don’t have the same reaction, although you’ll need to use slightly more product than mineral products in order to get the desired levels.
Cannabis pH Meter Types
pH Testing Drops
This type of pH measuring kit is one of the easiest kits to use; all it contains is a vile, liquid reagent, and a color chart. In order to figure out the pH in your water, all you have to do is fill up ¾ of the vile using the water you want to analyze. Add in a couple of drops of the liquid reagent, and then place the lid on the vile straight away. Shake thoroughly for a few seconds and then text the color using the included color chart – this allows you to figure out the pH in your water.
We highly recommend keeping in mind that this type of reagent liquid can only be used in water without any nutrients or additives, as it will end up giving a false reading in such cases.
pH 600 ECO Milwaukee Meter
This is one of the most used pH meters on the market when it comes to indoor and outdoor growing rooms, as it’s the most affordable one and it provides good results. It’s a great way to get started when it comes to growing cannabis if you’re on a budget. You’ll need to calibrate it by using a calibration liquid – first, adjust it to 7.0 pH and then adjust it down to 4.0 pH. In order to adjust the pH to your calibration liquid, you need to turn the small screw that it has while checking the screen to make sure you’re adjusting it right.
The only downside to this meter is that you’re going to need to keep the sensor clean and humid/moist by using a pH meter maintenance liquid – if not, your meter will most likely start producing erroneous results when compared to other meters. You’ll also need to take into account that this device is not water-resistant, so do not let it fall into the water when using it.
ADWA pH AD-100 Meter
This pH meter is slightly more sophisticated than the previous model; as well as offering precise data, it can also adjust itself automatically when using pH 7.0 and 4-0 calibrators, which come included. It also has an automatic temperature compensation feature, which makes for much more precise measurements. This particular model is much stronger and more trustworthy as times goes on, although just like with any other meter, you’ll need to keep it humid and in good condition to avoid bad readings. The only inconvenience here is that it isn’t waterproof; all you need to do is place the tip of the sensor in the water.
ADWA pH AD-11 Meter
This AD-11 ADWA meter is a semi-professional model that, apart from precisely measuring the pH in your water thanks to automatic temperature compensation, also indicates the temperature of the water and can emerge unscathed if dropped in the water. This doesn’t mean that it’s entirely waterproof, and you still need to use the sensor part when measuring pH values. These water-resistant ADWA meters are quite prone to sensor issues, as they’re quite delicate, but you can easily get your hands on a replacement sensor. This allows you to keep one on hand just in case it breaks and your plants are at a delicate period.
In order to calibrate it, you’ll need to hold the ON/OFF button for a few seconds while it’s on until the letters CAL come up on the screen. Next, the meter itself will let you know what calibration liquid is needed – first, you have to use pH 7.00 and next you’ll need to use pH 4.00. In order to keep it in decent shape, you’ll need to clean it after every use and use maintenance solution when storing it to keep it working well and for much longer.
Guardian Bluelab Monitor
The Guardian Bluelab Monitor is, without a doubt, the most sophisticated, professional and precise pH meter found in this post; it’s a pH, EC and temperature meter that works continuously; it’s a great idea for hydroponic and aeroponic grow set-ups, as these types of grows tend to need a lot more control when it comes to the water used.
In order to use this continuous pH, EC and temperature meter correctly, all you have to do is place the monitor at head-height so that you can easily take a look at it, and then you’ll need to adjust the pH and EC in your water, depending on your plants’ needs and the period that they’re in. It also has a visual alarm system (a blinking light) that lets you know when the pH or EC in your nutrient tank aren’t at the right values, allowing you to correct almost any fluctuation instantly.
When you use any type of continuous pH monitor, you’ll end up saving loads of time when it comes to watering, allowing you to make the most of your cannabis plants’ potential. Keep in mind that the sensors can be replaced in case one of them breaks or is worn – you can easily replace them. In as far as its calibration system, it’s super easy – only the pH sensors needs to be calibrated in the exact same way as the rest of pH meters on the market. We recommend cleaning the sensors after every grow and storing them in maintenance liquid.
In order to learn more about the pH meters for growing cannabis plants in this post, you can go straight to their product page by clicking on their picture, allowing you to visualize the product better thanks to their concise, simple descriptions that make them incredibly easy to understand. Plus, we stock many more models that you can have a look at!
Nutrient availability and pH level affect germination traits and seedling development of Conyza canadensis
Reducing pesticide application in agricultural land is a major challenge for the twenty-first century. Responses of weed seed’s germination and seedling’s early development to chemical soil conditions around the seed may be a promising way to aid weed control in a no-till system. Thus, the objective of this work was to test, under controlled conditions, whether different chemical conditions affect the germination and development of horseweed [Conyza canadensis (L.) Cronquist]. We used, as treatment, solutions containing different nutrients (P, K, Ca, and Mg), separately and in combination, and at two pH levels (4.8 and 6.5). Phosphorus alone inhibited horseweed seed germination at ~ 7 times while had ~ 4 times reduction in final germination percentage and germination speed index for both pH tested. Other nutrients tested had a no-effect in germination speed index compared to the control treatment. Potassium alone or associated with other ions (P, Ca, and Mg) at pH 4.8 had a synergistic effect on seedling development (root and shoot length). In the same way, K associated with Mg was synergistic to the root length at pH 6.5. Seeds in the control treatment (distilled water) presented a high germination speed index at pH 6.5, while at low pH this parameter was higher when in association with KMg, PMg and Ca. The findings demonstrate that seed germination traits and seedling development of horseweed depend on nutrient kind exposure and pH conditions in the seed environment. This work suggests that adequate topsoil management (i.e., pH and nutrient availability) may aid to reduce weed germination, because, it consists of an important factor of weed occurrence in agricultural areas.
The reduction of pesticide application is a major challenge in modern agriculture for the twenty-first century. No-till system (NT) implemented in the 1970s decade promoted better soil quality since soil cover, crop rotation, low soil disturbance, adequate traffic load, and adequate dose and fertilization method were practiced 1 . However, when these aspects are mismanaged, agricultural areas are subject to soil degradation 2 , low productivity and weed occurrence 3 , increasing pesticide uses 4 , and environmental risks 5 . Weeds present high seed production, dissemination, and cropland infestation capacities, causing mainly yield reduction. The species ability to complete germination and grow in a large range of edaphic conditions engender competitive advantages to the weeds over crops 6 . It is a key mechanism of success in plant establishment in different environments 7 , but the seed germination process can be affected by several factors such as light regime, temperature, and soil moisture 8 .
From an agronomic perspective, the genus Conyza Less. is responsible for decreasing soybean yields up to 30% 9,10 . The species of this genus are easily found in no-till system, where they became a great issue in the cereal crop production worldwide 3,8 . Recently, agronomists have found Conyza spp. biotypes with herbicide resistance mechanisms to several herbicide molecules, including glyphosate 4,11 . In South Brazil, 78% of the Conyza spp. biotypes showed herbicide resistance to glyphosate 4 . In summary, a good chemical horseweed control became arduous 4,12,13 . Furthermore, because this species is stress-tolerant and strong competitors 10,14 , alternative management strategies should be considered in the no-till system. Those strategies based on the species biology/ecology and soil management applied in an integrated manner seem to be promising to reduce the pollution pressure on the environment 8,15,16 . In this sense, Conyza sp., a dicot weed of the Asteraceae family commonly known as horseweed, stands out among weed species because can produce large quantities of easily disseminated seeds 8,15 . Germination is stimulated by light and may occur on bare topsoil in all seasons 8,17,18 . The wind may carry horseweed seeds over a hundred meters 15 , while seeds can migrate from infested fields to new areas a few thousand kilometers distant attached to cattle hair 19 . Horseweed seeds reach cropland topsoil easily, enriching the soil seed bank 8 . The horseweed seeds in the soil seed bank may germinate under favorable conditions from few years to decades 8 . The horseweed germination may occur by neutral to alkaline pH, saline and not disturb soil conditions, but maybe disturbed in the presence of Aluminum (Al) and when temperature and humidity conditions are out of the ideal range 3,8,18,20,21 . Furthermore, the species respond to factors such as salinity (NaCl) 7 , nutrient availability (N, P, and K), elements’ toxicity, and soil pH 7,22,23,24,25 . Thus, we expect that other nutrients available in soil may favor weed establishment and their dominance 26,27 .
These studies suggested then that different cations affect the germination process. However, scarce literature reports on germination of horseweed at acid conditions (low pH) and in presence of macronutrients found commonly in fertilizer and lime products 28 . This is particularly important to the no-till system, which has been receiving lime and fertilizer products on the topsoil, promoting a nutrient enrichment a few centimeters of soil surface. This scenario was not yet been studied face to the Conyza canadensis (L.) Cronquist var. canadensis germination and development. Thus, we expected that horseweed seeds may have a variable germination percentage and seedling establishment caused by exposure to different nutrients and pH levels, as suggested in the literature for other species 7,25,26,29,30 . In this study, we pay attention to two basic questions: which are the nutrients and pH level that act preponderantly in the germination and development of horseweed? and; what are the implications for horseweed management and fertilization practices on the field conditions? In this direction, studies on the factors involved in horseweed germination and establishment may allow improvement in management practices to avoid weed infestations in no-till system, reducing pesticide products as a control agent. We hypothesize that seed exposure to different nutrients and pH levels affects seed germination traits and seedling development. We expected also that eutrophic conditions present three possibilities of effects: synergistic, antagonistic, or no-effect. Identifying whether nutrients drive C. canadensis germination and plant establishment is essential to provide a better knowledge on fertilization in agricultural areas to help weed control and diminish pesticide application.
Thus, this study aimed to evaluate the seed germination traits and seedling development of horseweed in different chemical environments with a range of nutrient availability and pH conditions. For this, horseweed seeds were exposed to several nutrients (P, K, Ca, and Mg, alone and in combination) under two pH levels (4.8 and 6.5). The nutrients and their concentrations as well as the pH conditions were chosen to simulate field conditions of fertilization and liming commonly practiced in soybean crop under no-till system in south Brazil.
Overview on anova
The nutrients, as a factor of variation (F1 Factor), affected significantly all the parameters evaluated (Table 1). The pH (F2 factor) did not affect horseweed’s final germination percentage and germination speed index and root length, except for seedling length and root:shoot ratio. The interaction between nutrients and pH (F1 vs F2) affected all variables.
Final germination percentage (FGP) and nutrients
Different nutrients affected the FGP by the average of both pH levels (Fig. 1a,b). Two effects were observed (i.e., no-effect and antagonistic effect). In both pH (4.8 and 6.5), two effects were observed (i.e., no-effect and antagonistic effect) on FGP. At low pH (pH 4.8), nutrients alone or in combination did not differ from the control treatment (FGP of 25.5%), except for the treatment with P that presented the lowest C. canadensis final germination percentage (6%) (Fig. 1a). This indicates an antagonistic effect of P (4.25 times) on the final germination percentage compared with the control. At high pH (6.5), the treatment with P alone presented the lowest value, 3.5% (Fig. 1b). As the treatment had a reduction in germination around 7.28 times compared to the control, they had an antagonistic effect. In addition, all other nutrients alone or in combination had no-effect because did not differ from the control (distilled water).
Final germination percentage (FGP) of Conyza canadensis in response to the nutrients (alone or in combination) under solutions at pH 4.8 (a) and at pH 6.5 (b). Bars with the different colours, comparing means among treatments, are significantly different, according to the Tukey’ test (p < 0.05). Different letters represent a statistical difference for the same treatment between the two pH tested while ns represents not significant; The results in the Bars represent means, while error bar marks represent standard deviation (n = 4) from the mean value.
Final germination percentage and pH levels (acidity)
The pH alone did not influence final germination percentages. On average, the FGP was not sensitive to the pH levels and their values were similar, 25.3% and 26.8% to high and low pH tested, respectively. Furthermore, the pH presented interaction with only Ca and PMg treatments. The final germination percentage was higher for Ca (29%) at low pH than at pH 6.5 (17.5%), while PMg treatment was higher at pH 6.5 (24.5%) than at pH 4.8 (16%) (Fig. 1a,b).
In summary, P alone inhibited horseweed seed germination in 4.25 and 7.28 for both pH tested, 4.8 and 6.5.
Germination speed index (GSI) and nutrients
For germination speed index (GSI), different nutrients had different effects at each pH level (Fig. 2a,b). At low pH (4.8), nutrients produced no-effects on the GSI (Fig. 2a). At high pH (6.5), two effects were observed (i.e., no-effect and antagonistic effect) (Fig. 2b). All treatments (Ca, Mg, K, CaMg, PCa, KCa, KMg, KCaMg, PCaMg, PKCa, PKCaMg, and, PCa) presented similar GSI values to the control treatment, indicating no-effect of nutrients compared to the control. Phosphorus alone presented the lowest GSI value (0.56, au), indicating an antagonistic effect comparatively to the control. The GSI reduction was 6.96 times in the GSI, comparatively to the control.
Germination speed index (GSI) of Conyza canadensis in response to the nutrients (alone or in combination) under solutions at pH 4.8 (a) and at pH 6.5 (b). Bars with the different colours, comparing means among treatments, are significantly different, according to the Tukey’ test (p < 0.05). Different letters represent a statistical difference for the same treatment between the two pH tested while ns represents not significant; The results in the Bars represent means, while error bar marks represent standard deviation (n = 4) from the mean value.
Germination speed index and pH levels
In the average of all nutrients, the GSI was not affected following the pH levels. In addition, pH interacted with KMg, Ca, PMg, K, and control treatment. At pH 4.8, the GSI values were higher for the KMg (4.69), Ca (3.8), K (5.2) presenting 1.20, 1.53, 1.78, and 1.34 times greater than pH 6.5, respectively. At pH 6.5, PMg (4.08) and control (3.9) treatments were higher compared to the pH 4.8, presenting 2.02 and 1.51 times greater, respectively.
Briefly, phosphorus alone had an antagonist effect, reducing GSI in both pH conditions by an average of ~ 5.6 times (Fig. 2).
Seedling length (SL) and nutrients
For SL, different nutrients had different effects follow the pH levels (Fig. 3a,b). At low pH (4.8), nutrients produced three effects (i.e., synergistic, no-effect, and antagonistic effect) (Fig. 3a). The PK combination and K alone presented the highest SL values (9.34 mm and 8.65 mm, respectively), comparatively with the control (5.35 mm). This indicated a synergistic effect of PK and K nutrients on SL compared to the control, increasing the values in 1.74 and 1.62 times, respectively. All other nutrients (Mg, Ca, K, PK, PCa, PMg, PKCa and, PCaMg, KMg, KCa, CaMg and PKCaMg) differed from the control, indicating an antagonistic effect. Phosphorus and PMg presented the lowest SL values, representing a 19.8 times reduction compared to the control treatment. At high pH (6.5), no-effect was observed among the treatments compared with the control (Fig. 2b). All treatments presented similar SL values among them.
Seedling length in aerial part (SL) of Conyza canadensis in response to the nutrients (alone or in combination) under solutions at pH 4.8 (a) and at pH 6.5 (b). Bars with the different colours, comparing means among treatments, are significantly different, according to the Tukey’ test (p < 0.05). Different letters represent a statistical difference for the same treatment between the two pH tested while ns represents not significant; The results in the Bars represent means, while error bar marks represent standard deviation (n = 4) from the mean value.
Seedling length and pH levels
The pH had an interaction with some nutrients (Fig. 3). On average, the SL at low pH (2.76 mm) was higher than at pH 6.5 (1.22 mm). Comparing SL between both pH, the treatments control, PK, K and, KCa presented 8.05, 7.30, 6.93 and, 2.12 times greater at pH 4.8 than at pH 6.5, respectively. In opposition, the PMg treatment presented 4.47 times greater SL at pH 6.5 than at pH 4.8 (Fig. 3).
Briefly, K alone or in combination with P was synergistic for shoot length (SL) at low pH, while all other combinations were antagonistic at low pH. At pH 6.5, a wide range of combinations of nutrients ad no-effect on SL.
Root length (RL) and nutrients
The different nutrients affected the parameter in each pH level (Fig. 4a,b). In both pH (i.e., low and high), two effects on RL were observed (i.e., synergistic and no-effect). At low pH (4.8), the PKCaMg treatment (combination from all nutrient tested) presented the highest RL value (4.32 mm) comparing to the control (1.28 mm), indicating a synergistic effect of nutrients. Furthermore, all other treatments: P, Mg, Ca, K, PK, PCa, PMg, KMg, KCaMg and, PCaMg presented similar SL values to the control, indicating no-effect of these nutrients (Fig. 4a). At high pH (6.5), the treatment KMg presented the highest RL value (5.23 mm), comparing to the control (1.09 mm), indicating a synergistic effect of nutrients (Fig. 4b). The KMg treatment presented RL 4.84 times greater than the control. All other nutrients: alone or in combination presented RL values similar to the control, indicating no-effect of nutrients.
Root length (RL) of Conyza canadensis in response to the nutrients (alone or in combination) under solutions at pH 4.8 (a) and at pH 6.5 (b). Bars with the different colours, comparing means among treatments, are significantly different, according to the Tukey’ test (p < 0.05). Different letters represent a statistical difference for the same treatment between the two pH tested while ns represents not significant; The results in the Bars represent means, while error bar marks represent standard deviation (n = 4) from the mean value.
Root length and pH levels
The pH presented an interaction with nutrients. KCa treatment, presenting higher RL values (3.32, times, respectively) greater at pH 4.8 than at pH 6.5. The KMg, PCa and PMg treatments presented higher RL values (1.72, 2.14, 8,72 times, respectively) greater at pH 6.5 than at pH 4.8.
Root:shoot ratio (RSR) and nutrients
At low pH (4.8), nutrients produced three effects (i.e., synergistic, no-effect, and antagonistic effect) on RSR (Fig. 5a). The treatments PCa, PKCa, PCaMg, KCa, CaMg, and PKCaMg presented high RSR indicating a synergistic effect comparing with the control. Phosphorus presented the lowest RSR value, characterized as an antagonistic effect compared to the control treatment. All other treatment presented no-effect because did not differ to the control (5.35 mm). At high pH (6.5), no-effect was observed among the treatments (Fig. 2b), except for the P treatment that demonstrates an antagonistic effect compared with the control.
Root:seedling ratio (RSR) of Conyza canadensis in response to the nutrients (alone or in combination) under solutions at pH 4.8 (a) and at pH 6.5 (b). Bars with the different colours, comparing means among treatments, are significantly different, according to the Tukey’ test (p < 0.05). Different letters represent a statistical difference for the same treatment between the two pH tested while ns represents not significant; The results in the Bars represent means, while error bar marks represent standard deviation (n = 4) from the mean value.
Root:shoot ratio and pH levels
The high pH (6.5) presented higher RSR values for KMg, PMg, PCa, PK and, K and control treatments compared with the same nutrients at low pH (Fig. 5b).
The principal component analysis (PCA)
The PCA represented the association degree among studied variables. The first and the second principal components of PCA explained 66.9% and 26.2% of the data variations, for pH 4.8; and 76.6% and 22.0% for pH 6.5 (Fig. 6). Principal component analysis pointed that frequently K alone or in combination with Ca and Mg had a high positive association (vectors in the same directions) with seed final germination percentage, and root length and shoot length of C. canadensis. However, P resulted in an antagonistic response for these variables (vectors in opposite directions). Phosphorus associated with the K or Mg was the most prominent nutrients generating contrasting plant responses for germination speed index and seedling development (shoot length) depending on the pH level. Phosphorus showed a greater antagonistic effect, which was a low seed germination percentage; however, P allows a good development of C. canadensis seedling. Potassium had a positive correlation with the final germination percentage and root length of C. canadensis seeds, especially under low pH.
Principal component analyses considering nutrients (alone and in combination) under solution at pH 4.8 and 6.5. G = Final germination percentage; GSI = germination speed index; SL = seedling length in their aerial part; RL = root length; Data set used for each pH level (n = 60; treatments × replications). The principal components (i.e., axes PC1 and PC2) explain the magnitudes in percentage of data variability.
Nutrients and pH as factors to seed germination traits and horseweed seedling development
Overall, the studied species had important requirements to germinate, considering the germination traits (FGP and GSI) verified in the control treatment (~ 36%), suggesting an average ability to complete germination. In the same way, the seedlings may develop in a wide range of chemical conditions (pH and nutrients). Then, our study reinforces the literature which this species can easily get establish itself in several topsoil conditions 8 . Two agronomic/environmental reasons can be emphasized as major issues concerning the horseweed management: i) this species has a low control in no-till system and has a great capacity to reduce crop yield 3,8 and, ii) the no-till system has been receiving annually large amounts of fertilizers (nutrients) and lime on topsoil 28 , regardless the consequences for the weeds’ communities. The present work argues on the early plant development stage (germination and seedling development) because it seems to be a crucial plant stage for better understand the occurrence and establishment of C. canadensis in cropland areas. The results evidenced that nutrients, alone or in combination, play a role in germination traits and development of C. canadensis, while pH had an influence only under interaction with certain nutrients (Figs. 1, 2, 3, 4, 5). Below, we will present a discussion based on the synergistic effect, no-effect, or antagonistic effect that nutrients and pH had on seed germination and the development of C. canadensis. We will discuss also the finding implications on weed management at field conditions.
Nutrient as factor conditioning horseweed germination and seedling development
In the literature, nitrogen is one of the most studied nutrients that affect the horseweed germination process 31 , 32 , 33 , while studies on other nutrients are scarce. Here, the findings clearly show that the exposure of horseweed seeds to different nutrients affected the final germination percentage and initial development of C. canadensis (Figs. 1, 2, 3, 4, 5). Furthermore, a large range of nutrient combinations had no-effect on the germination traits and development of horseweed. Phosphorus had an antagonistic effect on the following parameters: FGP, GSI, SL (at pH 4.8), and RSR for both pH (4.8 and 6.5). The P alone seems to inhibit germination and early horseweed development, probably due to the imbalance of nutrients in the seeds 34 . However, P exposure in combination with K or Ca and Mg allowed a synergistic effect on C. canadensis seedling development (SL and RL). Our study evidenced that P inhibited germination process, but the seedling development was busted with the P presence in combination with other nutrients.
The exposure of certain nutrients such as N, or metals such as Al, promotes a competition of nutrients out and inside the seeds, degrading the cell’ seeds 34 . However, when salt stress (Cl – ) was tested with different cations (Mg, Na, and Ca), the germination traits were also affected 20,21,35 . As horseweed seeds do not undergo dormancy 33 , the germination process starts immediately when seeds fall out on topsoil in any crop season 14,36 . Thus, the conditions surrounding the seeds become determinants to germination trait responses 37 . In addition, the same nutrient may act equally or differently on the C. canadensis germination and seedling development processes depending on the pH, as clearly evidenced here for P alone or in combination with others ions (Figs. 1, 2, 3, 4, 5). As nutrients and pH conditions affected the horseweed germination, several physiological mechanisms may be involved as follow: seed nutrient balance, physiological seed deterioration, osmotic stress, and nutrient toxicity 34,38 . However, these mechanisms need to be better explored in future studies to answer how nutrients act in the germination process. The answer requires an understanding of the seed germination response beyond temperature and moisture substrate conditions, considering ion competition and pH conditions that influence seed deterioration/germination 34 . It is known that chemical osmotic effects from nutrient exposure easily led to changes in metabolic and physiological seed behavior 14 . Woodstock et al. 39 found that seed quality was associated with seed capacity for ion releases, as a response to adverse conditions. The mechanism is then associated with the physical integrity of seed membranes, which ensures high germination potential but may be altered by nutrient availability of the growing media.
In our study, seeds exposed to different ions varied the final germination percentage and seedling development, sometimes having no-effect on the germination and sometimes decreasing when compared to the control (distilled water only). Phosphorus exposure presented an antagonist effect on germination probably because the ion balance affected other mandatory ions of physiological importance, such as Zn inside the seed, which is an important nutrient for the seed’s germination process 40 . In contrast to the P, other nutrients alone or combined with Ca, Mg and K presented no-effect on germination. Yamashita and Guimarães (2011a) found Al at 1.5 cmolc Kg of soil (low Al contents) diminishes C. canadensis germination by 24%. In addition, calcium chlorate affects C. canadensis germination and GSI in concentrations higher than 6 cmolc L -1 and 2 cmolc L -1 , respectively 20 . These studies suggest that seed responses depend on the ion companion in the salt molecule, as reinforced here. Finally, our study provided a large range of nutrients which produced different responses on germination and development of horseweed species.
The synergistic effect on RSR was observed when several nutrients were combined at low pH. When a large nutrient availability (P, K, Ca, Mg) is offered to the horseweed the plant allocates nutrients in the root system. Kuchenbuch & Jung (1988) stated that a non-restrictive nutrient condition reaches a high RSR – high root system comparatively with shoots. Thus, adequate soil/substrate chemical conditions tents to increase RSR. On the other hand, P availability had an antagonistic effect on RSR. It seems that P availability promoted a shoot allocation comparatively to the root allocation 41 .
Even under unfavorable edaphic conditions, horseweed development was assured when a large variety of nutrient was available except for P, that had an antagonistic effect. It reinforces that horseweed is able for surviving in adverse and eutrophic soil conditions, as reported by Concenço and Concenço (2016) 10 .
Acidity as factor conditioning horseweed germination and seedling development
Few studies were produced on horseweed testing chemical conditions (nutrients vs pH) on germination process 20,21,40 . The literature shows that horseweed germination is favored by neutral pH conditions even under saline conditions 18,20,21 . Here, two pH levels were tested, which pH affected only SL values as a single factor. However, pH presented interaction with some nutrients alone or in combination (K, Ca, P, and Mg). Low pH (4.8) associated with Ca presented higher values for FGP and GSI. Furthermore, seedling elongation seemed to be benefited at pH 4.8, regardless of the nutrient combination studied. At pH (6.5), PMg nutrients combination presented higher values for FGP and RL, SL and RSR than a pH 4.8. pH 6.5 associated with the nutrients reached high values for the majority parameter evaluated, excepting SL. In the control treatment (only with distilled water), GSI and RSR values were higher at 6.5 than at pH 4.8 while for SL was the value was higher at pH 4.8.
In the literature, different pH levels (4.7, 5.7, 6.7, and 7.7) and nitrogen concentration in eight species at Spain 35 (covered the following families: Fabaceae, Onagraceae, Apiaceae, Poaceae, and Polygonaceae) were tested and it was found that the germination process is greatly dependent of N amounts and forms, but is not associated with pH levels. The pH influences the germination process but depends on the species 29 . Laghmouchi et al. (2017) 3125 , did not find evidence of pH effects on the seed germination of Origanum compactum and Capsella bursa-pastoris in a large range of pH. However, Gentili et al. (2018) 32 studying an Asteraceae species (Ambrosia artemisiifolia) suggests that low soil pH (5.0) affects positively the growth and development while neutral pH limited it. Furthermore, contrasting pH effects have been described on germination dependence on the species studied 31,42 . In this sense, the germination of many species responds rather to salt stress and nutrient availability than pH levels 43 .
Our findings indicate that pH is not a critical factor for germination traits when taken into account as an isolated factor, but in combination with nutrients assumes a relevant role. Thus, this study provides good knowledge on the effect of ions on the C. canadensis germination and seedling development, which allows us to plan adequate soil management to reduce the weed pressure in croplands since the knowledge in the literature is scarce 14,18,22,36 .
Findings implication for horseweed management on field conditions
Here, it was demonstrated that different ions affected the germination traits of C. canadensis. Light, temperature, and water availability were controlled in our laboratory’s experiment, varying only nutrients availability and pH conditions. In addition, the doses used for the treatments are compatible with the doses of Ca, Mg, P, and K normally receipt as fertilizers on topsoil from no-till system cropped with soybean. Thus, we expected that the findings found here can be a subsidiary under the field situation, concerning only the pH and nutrients availability.
In this sense, the P nutrient stood out as the most important nutrient in germination trait and seedling growth, and secondly, the pH was determinant mainly in combination with nutrients. Despite this study has been conducted under controlled conditions, our results showed that P alone or in combination with Ca inhibited horseweed seed germination percentage around 7.28 and 1.64 times compared to the control. However, after seed germination, the combination of P with other nutrients (eutrophic conditions) had a synergistic effect on seedling development. In addition, P alone had a reduction of 4.28 times in GSI.
From the agronomic perspective, our study suggests that topsoil chemical conditions should be taken into account to develop effective and integrated alternatives for C. canadensis control. Tudela-Isanta et al. (2018) stated that low pH promoting increases in soil aluminum contents, but pH is micro factor stress controlling seed germination niche in habitat management 44 . It is well-known that liming regulates soil acidity and by consequence species ability for land invasion 27 . Thus, the occurrence, distribution, and hazardousness of weed species may be handling partially by soil chemical factors 37 .
Our approach became mandatory for horseweed control in no-till systems because (i) the ecological and physiological species characteristics favor their occurrence in croplands 15 , including high soil seed bank 8 (ii) the low chemical horseweed control efficiency due to the herbicide resistance mechanisms of C. canadensis 4,12,13 and, (iii) the low quality of a major no-till system practiced, including low crop residue 3 , topsoil P and K fertilization, which produces an intense soil eutrophication 28 .
As seed germination is one of the main mechanisms of alien species to invade and establish on agricultural areas 43 , handling ecological aspects of this mechanism may aid plant management 23 . The final germination percentage of horseweed varied from 6 to 35.5% following the nutrient available. This behavior may indicate the amplitude in the control effectiveness associated with fertilizer management in no-till system. In general, the species had a high capacity for land invasion when the seeds find favorable conditions (adequate temperature, moisture, and chemical environment). Although the species produce large quantities of seeds that are easily disseminated 15 , an adequate chemical environment may contribute to diminish the weed establishment. In this sense, the fertilization method commonly used in no-till system areas for furnish Ca and Mg (under lime product), P and K (under triple superphosphate and potassium chloride) transformed the topsoil in eutrophic condition 28 . This information may answer why in areas under no-till system in Brazil there is a high abundance of this weed species 4 . Thus, the manner of fertilization and liming should be revisited because it may favor the occurrence and establishment of horseweed in this system.
Although our results were obtained in laboratory conditions, they suggest that the topsoil with low nutrient contents and low pH level consists in an adequate edaphic condition for reaching low germination percentage and speed germination of C. canadensis. Furthermore, we state that adequate fertilization in no-till areas may improve crop nutrition efficiency and may assist in effective weed control, reducing pesticide use, and improving environmental quality. In addition, a good NT system must be properly conducted, observing the adequate straw quantity and quality, a good crop rotation to minimizes soil disturbance diminishing seed quantities in the soil seed bank, which follows recommendations of several authors 2,39,45 . These ideas are not novelty; classical studies in phytosociology, in which species ecology and edaphic conditions control the occurrence of species in environments, are readily available 6,8,23,24,27,39,44 .
Finally, our results contribute to an integrative strategy in weed management, in which nutrient management may be used to diminishing horseweed germination in no-till areas that present a high germination percentage 8,45 . Thus, we expected that low horseweed germination results in low horseweed occurrence and pressure on crops, reducing environmental pressure 9 .
Conclusions and implications
This work corroborates the hypothesis in which the seed exposure to nutrients, alone or in combination, and different pH levels (4.8 and 6.5) are important factors controlling seed germination traits and seedling development of horseweed seeds. Regarding the nutrient effect, the phosphorus alone has an antagonistic effect on the final germination percentage of horseweed in both pH tested. However, nutrient richness, including P, surrounding horseweed seeds shows a synergistic effect the seedling development (root length and shoot length). Medium acidity (pH level) is a secondary factor influencing the germination traits, but pH 4.8 promotes horseweed seedling development (increasing shoot length). The pH is a preponderant factor when in interaction with certain nutrients, presenting a high germination speed index at pH 6.5 in the control treatment and associated with K and at pH 4.8, when in association with Ca, KMg, and PMg.
These findings suggest that chemical topsoil conditions favor or inhibit seed germination traits and seedling development of horseweed species. Thus, chemical edaphic status aid to explain the weed occurrence in agricultural areas. The implication of our findings fills a scientific gap and fits as a useful approach to integrate future strategies of weed control, improving the substantiality in modern agriculture.
Materials and methods
Local of study
The present study was carried out under controlled conditions at the University of Passo Fundo, State of Rio Grande do Sul, Brazil and complies with local and national regulations. The experiment used Canadian horseweed seeds (Conyza canadensis (L.) Cronquist var. canadensis) bought from a commercial farmer and distributer (Agrocosmos 13,165–970, São Paulo, Engenheiro Coelho, Brazil). The seeds were originated from the owner production (the year of 2018) at São Paulo State (tropical climate regime). The seeds were managed at the Seed Analysis Laboratory by the Passo Fundo University, with Accreditation in the ISO/IEC 17,025—general requirements for the competence of testing and calibration laboratories, under the responsibility of Dr. Nadia Canali Lângaro. An aliquot of seeds used in this study (~ 10 g) was deposited in an herbarium of the Program of Post-graduation in Agronomy of the University of Passo Fundo (504–302,224—2019), for public access. The seeds were then submitted to the germination process in different nutrient solutions, in an environmentally controlled chamber.
Experimental design and assay conditions
We used 14 nutrient solutions containing P, K, Ca, and Mg, alone and in combination 46 . These elements were chosen because they are normally used in topsoil liming and fertilization under no-till crop system. The nutrient quantities used in topsoil follow in decreasing order Ca, Mg, K, and P. Each solution was divided into two aliquots: the pH of the first aliquot was adjusted to 4.8 with chloric acid (HCl), and the pH of the second aliquot was adjusted to 6.5 with sodium hydroxide (NaOH). Thus, the trial was divided into two parts according to pH, with 14 treatments each, plus the control (distilled water) (Table 2). We assume that pH levels were maintained or had low variation during the assay. Additionally, all material used in the experiment was sterilized with ethanol (70%, v:v).
We prepared nutrient solutions according to recommended lime/fertilizer doses used in the field for soybean crop 47 . In the field soybean crop, the fertilizer formulas and doses commonly used are: potassium chloride (KCl) at the dose of 80 kg/ha, or 25.6 kg of K per ha, and triple superphosphate at the dose of 40 kg/ha, or 35.2 kg of P per ha. For Ca and Mg, the formulas and doses were based on the lime practice at 2 ton/ha of dolomitic limestone applied on the topsoil. Thus, the doses per hectare of Ca is 992 kg, while Mg is 592.2 kg. A more detailed explanation of the doses for each treatment is given in Table 2.
In the laboratory, the nutrient solutions were prepared using distilled water combined with phosphoric acid (H3PO4) as a P source, potassium sulfate (K2SO4) as a K source, calcium hydroxide (Ca(OH)2) as a Ca source, and magnesium oxide (MgO) as a source of Mg. High chemical purity reagents were used (P.A. Merck Co). The doses were calculated taken into account the surface area of plastic boxes for germination test—gerbox (10 cm × 10 cm × 3.5 cm).
Germitest paper (J. Prolab, São José dos Pinhais, PR, Brazil) placed in gerbox plastic boxes received 10 mL of nutrient solutions and 50 horseweed seeds per replicate. These composed the experimental units, which were incubated, in quadruplicate, in controlled climate chambers (volume capacity: 354 L) for 15 days at 24 °C (± 0.5 °C) in light 12/12-h photoperiod (Light characteristics: four OL T8, 8 W, 6500 k led lamps). The boxes were covered using plastic film to maintain the similar moisture during the assay.
Over 10 days, the gerbox treatments were daily monitored to estimate the final germination percentage (FGP) and germination speed index (GSI). The seeds with root length over 2 mm were considered as a seed that accomplished their germination process and were recorded daily. The experiment was conducted based on the protocol proposed by the official seed analysis from the Brazilian government 48 .
The final germination percentage was calculated following Eq. (1), and is expressed as a percentage. The germination speed index (GSI) was evaluated using Eq. (2).
where FGP is the total seeds that accomplished their germination process (Ʃn1) in relation to the total of seeds used in the assay (NSi);
where, G1, G2, Gn are the number of seeds that accomplished their germination process for the day and N1, N2, Nn are the number of days after the assay start.
Seedling shoot length (SL) and root length (RL) were evaluated at the end of the experiment (15 days after the start of the assay). The root:shoot ratio values were calculated using data of RL and SL.
The data is presented to show which nutrients (alone or in combination) present a synergic, no effect, or antagonist effect compared with the control (distilled water). Thus, the synergistic effect is when average values were statistically higher than control treatment; no-effect means that there was no statistical difference, and antagonistic effect means low values compared with the control treatment.
This manuscript consists of original research that has not been published before and is not currently being considered for publication elsewhere. Besides, the manuscript has been read and approved by all named authors.
Consent to participate and for publication
The authors consent for the participation in this publication.
Table 1 Summary of two—way analysis of variance (F and p—values) of germination traits of C. canadensis (final germination percentage; germination speed index) the seedlings traits (seedling and root length, root:shoot ratio) of nutrients and pH levels.
We supplied all data. All data used in this study were included in the Supplementary Information File.
Final germination percentage
Germination speed index
Seedling length in the aerial part
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We thank the National Council for Scientific and Technological Development—CNPq [Brasilia/Brazil: 304676/2019-5 for ECB] and Coordination of Superior Level Staff Improvement—CAPES by the PROSUC fellowships received by APH.
CNPq [Brasilia Brazil: 304676/2019-5; ECB fellowship] and CAPES by the fellowships received [CAPES/PROSUC fellowship].
Authors and Affiliations
University of Passo Fundo, Campus I, BR 285, km 292, Passo Fundo, Rio Grande do Sul, 99052-900, Brazil
Caroline Maldaner Follmer
Postgraduate Program in Agronomy, University of Passo Fundo, Campus I, BR 285, km 292, Passo Fundo, Rio Grande do Sul, 99052-900, Brazil
Ana Paula Hummes, Nadia Canali Lângaro & Claudia Petry
Federal Institute of Education, Science and Technology of Rio Grande Do Sul, Osvaldo Aranha, Bento Gonçalves, Rio Grande do Sul, 540, 995700-000, Brazil
Diovane Freire Moterle
Laboratory of Land Use and Natural Resources, University of Passo Fundo, Campus I, BR 285, km 292, Passo Fundo, Rio Grande do Sul, 99052-900, Brazil
Water pH levels for cannabis seeds
The water pH level that you use to grow your cannabis seeds is important to the healthy growth of the plant. There is some variation in the PH level based off of the medium/medium you’re using to grow seeds:
Soil: 6 – 7 pH range – there’s not a set number within the range and some natural fluctuation within the window is good for the plant
Soiless and hydroponics: 5.5 – 6.5 pH – some natural fluctuation within the window is good for the plant but keep in mind that huge fluctuations are more of a risk here then with soil
If you need to lower or rise your pH, there are pH Up and pH Down products that you can get. If anyone knows of specific brand names please do share!