Mapping management zones in a sandy pasture soil using an objective model and multivariate techniques

Abstract

Soils occupied by dryland pastures usually have low fertility but can exhibit a high spatial variability. Consequently, logical application of fertilisers should be based on an appropriate knowledge of spatial variability of the main soil properties that can afect pasture yield and quality. Delineation of zones with similar soil fertility is necessary to implement sitespecifc management, reinforcing the interest of methods to identify these homogeneous zones. Thus, the formulation of the objective Rasch model constitutes a new approach in pasture felds. A case study was performed in a pasture feld located in a montado (agrosilvopastoral) ecosystem. Measurements of some soil properties (texture, organic matter, nitrogen, phosphorus, potassium, cation exchange capacity and soil apparent electrical conductivity) at 24 sampling locations were integrated in the Rasch model. A classifcation of all sampling locations according to pasture soil fertility was established. Moreover, the infuence of each soil property on the soil fertility was highlighted, with the clay content the most infuential property in this sandy soil. Then, a clustering process was undertaken to delimit the homogeneous zones, considering soil pasture fertility, elevation and slope as the input layers. Three zones were delineated and vegetation indices (normalized diference vegetation index, NDVI, and normalized diference water index, NDWI) and pasture yield data at sampling locations were employed to check their diferences. Results showed that vegetation indices were not suitable to detect the spatial variability between zones. However, diferences in pasture yield and quality were evident, besides some key soil properties, such as clay content and organic matter.