Soil Depth and Moisture in Relation to Barley and Chickpea Growth and Uptake

Abstract

While drought is the major crop-limiting factor in Middle Eastern agriculture, nutrients for such as phosphorus (P) are inherently deficient and need to be added as fertilizers; the amounts of P required are theoretically related to critical soil test values derived from field calibration studies. Soil test values for P recommendations are based on shallow sampling (e. g., 0-20 cm) and do not consider profile or rooting depth, an important factor in rainfed cropping where soil moisture is invariably limited. Under field conditions, soil depth controls the soil’s water-holding capacity and the potential of plant roots to exploit soil moisture and available nutrients such as P. While field crop responses to applied P have been observed to vary with soil depth and available moisture, the interaction between these variables can only be assessed under a controlled environment. Two successive crops, barley (Hordeum vulgare) and chickpea (Cicer arietinum), were grown to maturity in a greenhouse in a P-deficient (3. 2 mg kg-1 Olsen P) clay soil (Chromic Calcixerert) in tubes (15-cm internal diameter) of variable depth (15, 30, 45 cm) and moisture (33, 66 and 100% of the water required for field capacity), with applied P (0, 30, 150 mg kg-1) as monocalcium phosphate. In most cases, the response was highly significant at 30 mg kg-1, with relatively smaller increases thereafter. While growth responses increased with increasing soil moisture, soil depth had a major influence, with growth directly related to rooting depth. For chickpea, relative responses to P increased with soil depth and with soil moisture at any depth. Barley showed less consistent trends, but the relative increase was inversely related to depth, especially at low soil moisture. Thus, in addition to crop variation, both soil depth and moisture, which controls rooting depth, are also important considerations in the interpretation of critical test values and thus P fertilizer response.