Small cylinders were filled to a depth of 20 cm with Ludas sand to which different organic wastes, viz. sewage sludge, press mud, green manure and farmyard manure had been added up to a maximal rate equivalent to 827, 1043, 1370 and 542 t/ha. The cylinders were set in the ground and kept moist. At the end of 308 days' equilibration period, the samples were used for measuring soil water retention, saturated hydraulic conductivity as well as the horizontal infiltration with 0.01 M CaCl2 and alcohol. An apparent advancing contact angle was calculated from the last two measurements. The incorporation of all the organic wastes caused an appreciable increase in the amount of water retained at a given pressure potential. Increase in available water was caused by the application of sewage sludge and press mud only. Hydraulic conductivity, penetration coefficient and cumulative horizontal infiltration decreased markedly with additions of these materials. The maximum decrease in hydraulic conductivity was in case of press mud (93%), whereas the maximum decrease in penetration coefficient was in case of farmyard manure (81%). The contact angle, which plays an important role in penetration of water into porous materials, increased more in conventional organic manures (green manure and farmyard manure) than in municipal and industrial wastes (sewage sludge and press mud).

The leaching behaviour of a highly saline-sodic, moderately permeable, sandy-loam soil was evaluated under continuous and intermittent submergence conditions in a longterm field study in the presence of rice and subsequent wheat and sesbania crops. Leaching curves with respect to both desalinization and desodification showed that leaching efficiency was considerably higher with intermittent than with continuous submergence. The curves were useful in determining the amount of leaching water needed for a given mode of water application to reduce harmful levels of salinity and sodicity to acceptable ones. Empirical equations were determined to fit the experimental data. Their comparison with another empirical equation from published bare-field data of this site showed that leaching efficiency under crops was higher than under fallow. From the desodification leaching curve, it is concluded that in reclamation of these soils there is no need of the application of any amendment like gypsum. The soil salinity and sodicity data recorded at different growth stages and crop yields showed that leaching during the rice growing season, under intermittent submergence without previous leaching, decreased salinity and sodicity throughout the top 100 cm of the soil to levels safe for the successful cultivation of rice and subsequently the relatively deep-rooted crops of wheat and sesbania.

Spatial variability of NO3, K, Mg and organic C of a loess field was studied by using a geostatistical concept, known as theory of regionalized variables. Fifty measurements were made at the nodes of a 30 m × 30 m grid for each of 0‐30, 30‐60 and 60‐90 cm depths. Semivariograms determined from the data showed that NO3 observations were spatially independent, and hence could be analyzed only by classical methods. Semivariograms of K, Mg and C showed these parameters to be correlated over space for a separating distance between two observations well exceeding 150 m. Their semivariograms were then used in an interpolation method called kriging, which takes into account the correlation between adjacent samples while estimating the interpolated (kriged) value without bias and with minimum variance. Means and estimation variances calculated by punctual kriging were compared to those obtained by classical theory assuming random sampling (i.e., no interdependence between observations). We obtained 1.4 to 3 fold gains in efficiency over that estimated by classical theory. One can, therefore, be sure that the estimation variance of the mean obtained in classical manner will overestimate the real variance unless the sample sites are so far apart that they are spatially independent. The kriged estimates were used to draw contour maps of the properties. Usefulness of such maps and the kriging technique as a whole is discussed to provide better options for management decisions. Finally, a method for determining sample sizes (i. e., number of observations), and hence sample spacing, is developed, taking account of spatial dependence. By this method, sample sizes can be chosen to achieve any desired precision. The sampling effort determined this way in less, and can be very less when based on block or universal kriging, than would have been judged necessary using the classical approach.

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