Effects of nitrogen and early irrigation on root development and water use by wheat on two soils

Abstract

Modelling water uptake by crops for water-use/yield relations requires quantitative information on progressive root development as affected by management practices on a given soil. This study reports the effects of applied nitrogen and one light early-season irrigation on root development of wheat on loamy sand and sandy loam soils. Progressive root length index ( rli, km root m −2 surface area in the rooted profile) and depth of rooting (m) differed with the management practices and soil but conformed to the logistic growth relation y = a/(1 + b exp ct) wherein t is time (days) in all cases. The proportion of root length in different depth segments of the rooted profile was independent of soil and treatment at all times, and was adequately explained by exponential function of time and depth segments and their cross-product. Root development was more extensive and rapid in the sandy loam than in the loamy sand. Treatment effects on root growth also varied with soil. Whereas the increases in root growth with early irrigation and applied N were comparable in the sandy loam, the former had much larger effect than the latter in the loamy sand. Combined effects of the two treatments on rli were slightly lower than their additive effects on both the soils. However, the priming effect on water use of the combination in N and irrigation was greater than their additive effects. Soil water-depletion profiles under different treatments matched well with the fitted root-density profiles.