The bearing capacity of the soils of Ahero irrigated rice fields under the exposure to land preparation traffic
Investigations for the causes of immobility of tractors during land preparation and the possibility of re-introducing the Double Cropping System (DCS) of rice production at the Ahero Pilot Scheme CAPS) were carried out between December 1990 and May 1991. The area of study is used for irrigation of rice and is mainly covered by heavy clay soils with a clay content of more than 60 % . The parameters that were monitored during the study were meteorological factors, soil moisture content (SMC) and penetration resistance (PR) - as an indicator of the soil bearing capacity measured. Meteorological parameters were monitored on daily basis while SMC and PR were monitored on average once or twice a week. The study was conducted in three blocks of the scheme that had shown persistent mobility problems over a long period. In each block, the experiment was replicated four times. Sampling was carried out at the drain, middle and feeder sides of each plot (replicate) and under ashes or straw heaps. Sampling was also carried out in the field nurseries. At each location the sampling depths were 0-5, 15,30,45 and 60 em. Simulation equations for predicting SMC and PR were developed with the help of the data collected and the soil drying model of Thornthwaite and Mather. Through the simulation equations, it was found that with the given climatic conditions and the rice varieties grown at APS, DCS of rice production is impossible as the soils do not attain adequate strength by the time of land preparation. The major causes of mobility problems were attributed to be the management of land preparation and of straw after harvesting rice and lack of a hardpan. The effect of ashes or straw cover reduced PR by about 3.6 times as compared with the no-cover situation.