Using an allometric model for the accumulation of mineral nutrients in crops under saline and water stress: A field experience in fertigation

Abstract

Simulating accumulation of mineral nutrients in crops is useful for scheduling fertigation under ideal conditions, but doing so under saline and water stress would be a double beneficial tool. First, fertilization can be scheduled to fit mineral requirements while crops grow, and, second, fertilizers can be limited to the level determined by the stress condition, thus avoiding additional salinization by fertilizer not used by crops. The model considers crop development in a thermal timescale, in which the total crop period is obtained by integration in time of the thermal response equation. This integral is a constant value for a specific crop and cultivar. Biological age is then defined as a fraction of the current thermal time accumulated at any time to the total thermal time required. Using this relative time, the accumulation of mineral nutrients can be calculated as an allometric equation dependent on thermal time. It also considers crop biomass at any biological age, the total biomass of a crop and other specific parameters of the crop and the mineral nutrient being quantified (Misle J Plant Nutr 36:1327-1343, 2013). Thermal time dependence allows this model to follow daily variations of temperature in order to adjust the forecast of the accumulation of mineral nutrients to thermal variations on growth. The model is then coupled with already published equations for water and saline stress. As these restrictions are added to growth, total biomass will not be the maximum attainable for certain agro-climatic conditions, so that restrictions can be transmitted to the nutrient accumulation forecast (Misle and Garrido Determination of crop nutrient accumulation under water or saline stress through an allometric model, El-Zaiem Press, Cairo, Egypt, 2008). In this chapter we contextualize the problem, describe the theoretical background and analyse field experience from 1998 on crops fertigation, following stages of the model development and discussing growth restrictions imposed by saline and water stress to the nonrestricted forecast.