Effect Of Long-Term Irrigation Methods On Soil Phosphorus Leaching Potential In Greenhouse.

Water shortages within the northern China are resulting in the adoption of water-saving agricultural practices in greenhouse within this region. Among the many possible methods for saving water in agriculture, the adoption of suitable irrigation method provides a potential solution to the problem of low water use efficiency. The objectives of this 13-year field study were to evaluate the impact of irrigation methods on phosphorous forms and distribution in the soil profile of tomato cultivated greenhouse. In this study, surface drip irrigation (SUR) and subsurface drip irrigation (SDI) were applied, with furrow irrigation (FI) as control in greenhouse. 45 soil cores were collected from different treatments and analyzed for forms of phosphorous, organic matter (OM), Fe, Al, Ca, pH, and total phosphorous (TP).  Soil P was fractionated into H₂O-P_i, H₂O-P_o, NaHCO₃-P_i, NaHCO₃-P_o, NaOH-P_i, NaOH-P_o, HCl-P, and Residual-P. Results showed TP content were 871.5 to 3180.1 mg kg^-1, 1062.3 to 2456.3 mg kg^-1, and 830.2 to 2348.8 mg kg^-1 for the soil profiles of the FI, SUR, and SDI, respectively. The ranking order of TP content was FI > SUR > SDI at the same soil layer within 0-30 cm. SUR treatment had the highest TP content and SDI had the lowest content within 30 to 60 cm. The top layer (0 to 20 cm) for FI treatment had 319.3mg kg^-1 available P, while SUR and SDI had 272.2 mg kg^-1 and 251 mg kg^-1 available P, respectively. The available P content at the depths of 20 to 60 cm followed the order of SUR > FI > SDI. The P in the soils was mostly bound to Ca, Fe, Al oxide phases or adsorbed on the soil surface for the three irrigation methods. Water soluble P was correlated negatively with pH, and it was correlated positively with OM. Residual-P was correlated with OM and exchangeable Ca. Moderately resistant P was only correlated with exchangeable Ca.

Key words: surface drip irrigation; subsurface drip irrigation; furrow irrigation; soil phosphorus forms, greenhouse