Effects of manuring on physico-chemical properties of soil.

About one hectare of virgin land having very low nutrient status has been selected for conducting such long-term research work. Most of the top soils have been removed during land leveling resulting the exposure of C horizon in some cases. Due to uneven distribution of top soils during land leveling, the field soils became very heterogeneous in nutrient content. The soil was silty clay loam in texture. The five different manuring treatments chosen for first application in March, 1988 were cowdung at the rate of 25 t/ha (Cd), compost (made of rotten rice straw, cowdung, cattle urine etc.) at the rate of 25 t/ha (Cp); Ipil leaves at the rate of 5 t/ha (Gm); water hyacinth at the rate of 15 t/ha and the controlled one (Mo). The second application of manures in November, 1988 included some minor changes. Cowpea plants were grown and incorporated to the soil of Gm plots at the age of 45 days. Rice straw were incorporated to the soil of Ml plots at the rate of 1.43 t/ha. The three crops grown were (a) corn (March-July, 1988), (b) T. Aman (July-October, 1988) and (c) wheat (November, 1988-March, 1989). Three different doses of nitrogen including a controlled one were chosen in each crop to find the interaction of manures and different doses of nitrogen. Application of manures resulted in the improvement of soil physical properties. Solid phases of soil decreased substantially in surface layer (0-5 Cm). Infiltration rates of water increased by manure application. The dispersion ratios of soil reduced abruptly from 92% to 76% by addition of manures. Soil texture, particle density, and saturated hydraulic conductivity (HC) did not change by addition of manures. Lowest valves of HC were found in 10-15 cm soil layer in all the treatments (1.0 X 10(-7) to 6.3 X 10(-7) cm/sec). Plasticity index was found to be 36. Nitrogen, organic carbon and phosphorus contents of the virgin soil were found to be 0.33%, 0.03% and 0.001% respectively and the Ph was recorded to be 6.2. Exchangeable Ca, Na, K and Mg were found to be 2.4, 0.32, 0.27 and 0.89 me/100 g respectively. Addition of different doses of N had direct impact on the yield of grains. There was no positive affect of manures in nitrogenous plots. Rice cultivation deteriorated the soil physical properties.