Temporal stability of soil moisture in irrigated carrot crops in Northeast Brazil

Abstract

Abstract Soil water content plays an important role on crop productivity, mainly in the semiarid zones of the world. Given the importance of water resources to agricultural systems, investigations of soil moisture spatio-temporal variability can contribute to soil management, especially at highly heterogeneous irrigated soils occurring in alluvial valleys of the Brazilian northeast. In this sense, techniques which allow identifying and reducing the number of samples for soil moisture analysis are required. Additionally, the impact of management alternatives to control soil water losses by evaporation, such as mulching, on moisture temporal dynamics must be addressed. In this study, the temporal behavior of soil moisture was evaluated for an irrigated plot in the semiarid region of northeast Brazil. A pilot area of 1800 m 2 was cropped with carrots, and irrigated daily adopting two management treatments: one with mulch (using beans residues), and another without mulch. A total of 101 access tubes for neutron probe readings were installed in a 5 m × 5 m grid, with measurements at 20 and 40 cm depths. Readings were taken twice a week during the 96-day crop cycle, comprising 20 measurement campaigns. These data were evaluated by descriptive statistics and temporal stability methods (relative difference and Spearman's rank correlation). Mulching proved to be efficient in retaining soil moisture and reducing variation coefficient, thus decreasing soil water spatial variability. In addition, the values of the Spearman's correlation coefficients were high among the measurement campaigns results, indicating temporal dependence along the entire crop cycle. Based on the relative difference technique, locations at the sampling space could be identified which reproduced the average soil moisture pattern of the pilot area, representative of alluvial valleys of the Brazilian semiarid region. Temporal stability is an important issue in crop fields, in terms of reducing costs and time for adequate water management in irrigated areas.