Soil-phosphorus distribution and availability as affected by greenhouse subsurface irrigation

Abstract

Vertical distribution and plant availability of soil P under subsurface irrigation were investigated in a 5-year tomato-grown-greenhouse experiment. Irrigation was applied when soil water condition reached the predefined maximum allowable depletion (MAD) for different treatments, e.g., -10 kPa, -16 kPa, -25 kPa, -40 kPa, and -63 kPa. Results show that P distribution with soil depth was significantly affected by irrigation schedules. The general trend is that concentrations of soil total P and inorganic P were greater in topsoil than in subsoil, whereas the concentrations of soil organic P were larger at the depths of 0-10 cm, 30-40 cm, and 40-60 cm than at other soil depths. Comparison of different irrigation schedules indicates that more soil organic P was retained in the soils under the MAD of -25 kPa, -40 kPa, and -63 kPa, implying that irrigation of relatively low frequency and large water quantity of each irrigation event favored the accumulation of organic P in soils. In addition, we found that the concentrations of plant-available P decreased with soil depth and were largest under the MAD of -16 kPa and -25 kPa. This result suggests that irrigation of relatively high frequency and low water quantity of each irrigation event led to greater P availability for plant uptake. Overall, this study suggests that the transformation and plant availability of soil P can be manipulated, to some degree, by soil-water management. Maximum allowable depletion controlled between -16 kPa and -25 kPa could result in high availability of soil P in clay-textured soils. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.