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

A modelling approach is described to assess potential productivity of soils with gypsum in Quinto (northeastern Spain) for irrigated alfalfa, taking i nto 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 Ty pic Haplocalcids. The methodology considers only two hierarchically ordered production situations. The simplest or highest situation is an alfalfa cro pping system in which the production potential depends on radiation and tem perature regime during the crop cycle. As these factors cannot normally be manipulated, the yield of alfalfa is only determined by its physiological c haracteristics, the prevailing level of irradiance and the temperature regi me. Calculation of this climatic production potential (CPP) is based on the crop growth model of FAO AEZ-project. Water availability is considered opt imal under irrigation, therefore yield potential in the second hierarchical production situation is determined by reducing the CPP for unfavourable so il conditions, including gypsum content, and by considering different manag ement levels. The effect of unfavourable soil characteristics on the final land production potential (LPP), is expressed by a soil index, calculated u sing a parametric approach. The correlation between predicted yields and ac tual reported yields suggests a close resemblance between the simulated pro duction environment and the situation in which alfalfa grows. The proposed model is useful in assessing comparative land productivity and allows an ev aluation 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. (C) 1998 Elsevier Science B.V. All rights reserved.