pH and nutrient uptake

pH in the nutrient solution determines the uptake of nutrients, and as a result the crop development

Introduction

Regular pH control is essential, in the nutrient solution and in the root environment. You should pay extra attention to pH control when the irrigation strategy has been changed in autumn and spring. So both high and low pH in the nutrient solution inhibits the uptake of nutrients and does not improve the root development.

pH influence of your crop

When a plant root takes up positive ions (cations) like calcium, it also excretes positive ions (H+) into the root environment. When a plant root takes up negative ions (anions) like nitrate, it also excretes negative ions (OH-) into the root environment. The roots take up nutrients (cations and anions) continuously, the crop stage determines in which ratio they are being taken up. The balance between positive and negative ions taken up by the roots influences the pH in the substrate. More cation rather than anion uptake will cause pH raise. More anion rather than cation uptake will cause a decreasing pH.

Nitrogen influence on pH

Nitrate is a suitable nutrient to regulate the pH in the nutrient solution, being applied as NO3- ion and NH4+ ion. Both ions can be taken up by the roots easily. A high NH4+ concentration in the nutrient solution reduces the pH, but can also inhibit the uptake of calcium, magnesium and iron. Therefore it is better to choose for a little higher pH in the root environment when you grow crops/cultivars sensitive for calcium deficiency. Crop (leaf) sampling in that case can be a proper way to determine where you can draw the line.

Crop reaction on pH

Roses require a relatively low pH in the root environment with regard to growth, number of shoots, shoot length and weight. Moreover relatively high NH4+ concentrations are necessary to keep the pH low. In a recirculating system this comes down to 15-20% of the total nitrogen concentration, almost 1 mmol/l. Roses and other cut flowers also have better vase life when they were grown at moderate to low pH.

pH fluctuations

There are several reasons for pH fluctuation. The most important ones are mentioned in the table below.

  • Decreasing pH
  • Increasing pH
  • Slow growth (fall, winter)
  • Quick growth (spring, summer)
  • Much flowers
  • Few flowers
  • Low HCO3 (bicarbonate) concentration in the nutrient solution
  • High HCO3 (bicarbonate) concentration in the nutrient solution
  • In case of a recipe with acids; dripping with a higher EC than prescribed
  • In case of a recipe with acids; dripping with a lower EC than prescribed
  • pH and nutrient uptake by the roots

    Phosphate precipitates at high pH and as a result we measure low P concentrations. The P level in the nutrient solution does not have to be increased when you lower the pH. At low pH micronutrient solubility improves. At too low pH micronutrient excesses can develop in the plant. Especially manganese is dangerous. In a vegetative and generative stage you have important information available on nutrient requirements of your crop when you analyze both substrate and crop nutrient levels. Those data can be taken into consideration while calculating fertilizer recommendations.

    So, check the pH in the root environment regularly because it determines both growth and (leaf) color.

    Please contact us when you have questions about this news letter.