Effectiveness of rock wall terraces on soil conservation and crop performance in a southern Honduras steepland farming system

Abstract

The effect that rock wall terraces have on soil and water conservation and crop production was studied on a steepland farm in southern Honduras during the 1995 growing season. The research compared a site with 10 year old rock terraces with an adjacent portion of the field that had no terraces. Soil was collected at I m intervals between rock walls and at random locations within the unterraced field. At every sample location soil samples were taken in 15 cm depth increments from 0 to 75 cm. These samples were analyzed to compare soil physical and chemical properties between sites. Runoff plots were installed on the terraced (35% slope) and unterraced (50% slope) sites to determine differences in sediment yield and runoff. The upslope portion of the 1 m tall rock walls had completely filled in with sediment over the previous decade, thus they were no longer useful for retaining newly eroded material. Indeed, erosion from the terraces was not significantly different from unterraced land. However, total runoff from unterraced sites exceeded total runoff from the terraced field by about 87 mm. Standing crop of maize and sorghum were also measured along transacts between terraced and on unteffaced land. The terraced sites had significantly greater standing crop. Standing crop yield on terraced sites was 59% greater compared with the unterraced field. Sorghum grain yield was 70% greater in terraced field. Within each terrace, the crop yields were highest in areas immediately above the rock wall where the most soil deposition had taken place. The results of the chemical soil analysis indicated that soil organic matter was significantly greater on the terraced sites (P < 0. 1). Nitrogen content was significantly greater on the terraced sites. The low nitrogen content in unterraced fields may explain in part the lower biomass and grain yield. The levels of phosphorus, potassium, calcium, magnesium, sodium, sulfur and pH were generally not statistically different between terraced and unterraced fields. The results of the soil physical analysis indicated that terraced fields tended to have lower bulk density. There was no consistent difference in soil texture between terraced and unterraced sites. This study shows that the use of rock walls combined with minimum tillage and mulch residue, can control soil erosion and maintain crop yield in steep land areas of southern Honduras.