Soil Science: Confronting New Realities in the 21st Century

The effects of selected contour cultural practices on soil and water conservation and crop water use efficiency were compared under a rainfed highland agricultural system. The field trial was conducted during 2000 and 2001 on a 35% hill slope (latitude 19��33'47"N, longitude 98��12'9"E, altitude 780m) in Maehongson province, Northern Thailand. A completely randomized design, with four treatments and three replicates, used a cropping sequence of maize, followed by lablab bean, was conducted from May 2000 to April 2002. The treatments were (i) conventional contour planting, CC, (ii) contour ridge cultivation without mulching, CR, (iii) contour ridge cultivation with polythene sheet + straw mulch, INCOPLAST or CRP and (iv) alley cropping with mango-hedgerow tree and ground surface cover with Graham Stylo, AL. Soil water stored within 1700 mm was monitored every 2-3 weeks by neutron moisture meter. Runoff and erosion were measured after every rain storm. Soil sampling and analysis were conducted one month after sowing and one month before harvesting maize. Crop development was measured as total dry biomass at different growth stages and maize and lablab bean yields were harvested as total dry-matter and yields. Results obtained during the two experimental years (2000-2001) showed that alley cropping (AL) was the most effective treatment in decreasing runoff and erosion, while CRP was the second best at erosion control. However, CRP had the highest rate of runoff and erosion under high intensity rainfall during the early growing season. Generally, CRP protected the soil surface from the splash erosion and had better soil physical properties, leading to the highest crop water use efficiency, and had the highest growth rate of Lablab bean. Crop yields under CRP and AL were relatively high andcomparable compared with either CC or CR during the dry season of both years