High irrigation frequency: The effect on plant growth and on uptake of water and nutrients

The objective of the present research was to explore the effects of frequent irrigation and fertilization on the uptake of water and nutrients by lettuce and bell pepper plants. The daily fertigation frequency induced a significant increase in yield, especially at low nutritional levels. Yield improvement was primarily related to enhanced uptake of nutrients, especially P. It was suggested that the reduced yield obtained at low frequency resulted from deficiency of nutrients rather than of water, and that high irrigation frequency could compensate for nutrient deficiency. Consequently, an increase in fertigation frequency enables the concentrations of immobile elements such as P, K and trace metals in irrigation water to be reduced, so reducing environmental pollution. The main two mechanisms involved were the frequent replenishment of nutrients in the depletion zone near the root surface and the enhancement of mass flow transport. However, modification of the NH ₄/NO₃ ratio is recommended while the irrigation frequency is increased because of NH₄ toxicity. Time-dependent processes such as nitrification reduce the temporal NH₄ concentrations in the rhizosphere and hence, the actual NH₄concentrations increase as the time interval between consecutive fertigations is reduced. Adjustment of the NH₄/NO₃ ratio at high irrigation frequencies is recommended, in order to diminish the risks of NH₄ toxicity in sensitive crops.