A modified parametric index to estimate yield potentials for irrigated alfalfa on soils with gypsum in Quinto (Aragón, Spain)

Abstract

A modelling approach is described to assess potential productivity of soils with gypsum in Quinto (northeastern Spain) for irrigated alfalfa, taking into account the environmental conditions, described during a detailed soil survey, and different management levels. The soils assessed in this article are: Xeric Torrifluvents, Xeric Torripsamments, Typic Haplogypsids, and Typic Haplocalcids. The methodology considers only two hierarchically ordered production situations. The simplest or highest situation is an alfalfa cropping system in which the production potential depends on radiation and temperature regime during the crop cycle. As these factors cannot normally be manipulated, the yield of alfalfa is only determined by its physiological characteristics, the prevailing level of irradiance and the temperature regime. Calculation of this climatic production potential (CPP) is based on the crop growth model of FAO AEZ-project. Water availability is considered optimal under irrigation, therefore yield potential in the second hierarchical production situation is determined by reducing the CPP for unfavourable soil conditions, including gypsum content, and by considering different management levels. The effect of unfavourable soil characteristics on the final land production potential (LPP), is expressed by a soil index, calculated using a parametric approach. The correlation between predicted yields and actual reported yields suggests a close resemblance between the simulated production environment and the situation in which alfalfa grows. The proposed model is useful in assessing comparative land productivity and allows an evaluation of the impact of the considered soil characteristics on the final crop production. Quantification of the major constraints allows estimation of the required inputs to increase productivity.