HYDRAULIC CONDUCTIVITY OF SALINE-SODIC SOIL AFTER GYPSUM APPLICATION AND CROPPING

Slow internal drainage is a major problem in the reclamation of saline-sodic soils. This field experiment was conducted on a low-permeability, saline-sodic soil (a fine-loamy, mixed, thermic Typic Natrustalf) near Lahore, Pakistan, to compare field saturated hydraulic conductivities (K-fs) after various treatments. Treatments were: (i) deep-rooted perennial alfalfa (Medicago sativa L.), (ii) sesbania [Sesbania bispinosa (Jacq.) W.F. Wright]-wheat (Triticum aestivum L.)-sesbania rotation, (iii) incorporated wheat straw at 7.5 Mg ha(-1), and (iv) a fallow control. These four treatments were each combined with and without 25 Mg ha(-1) of gypsum, subsoiling to 0.45 m, and open-ditch drainage. The K-fs of the soil under each treatment was measured in each 20-cm increment to 120 cm after 6 mo and 1 yr. Gypsum applications increased the K-fs of the top 20-cm soil layers. Compared with uncropped plots, K-fs of the 0- to 20-cm depth as cropped plots with gypsum increased about twofold after 6 mo and about fourfold after 1 yr. The crop rotation significantly increased the K-fs of the 0 to 20-cm (with and without gypsum) when compared with wheat straw or fallow treatments. The K-fs on plots with alfalfa plus gypsum were significantly greater to 80 cm than the K-fs, on fallow plots. Neither subsoiling nor open-ditch drains improved soil permeability. Gypsum plus sesbania-wheat-sesbania rotation most increased permeability of the surface layer; gypsum plus alfalfa was best to improve the permeability of the deeper layers.