Yield and soil fertility variations of soil catenas along transect

The spatial variation of soils in the KADA region shows the occurrence of typical topohydro-sequence on various landscapes. The Tok Yong series and Chempaka series occupy the upper slope position, Lating series occur in midslope positions as a narrow band while Jabil series is found on the lower slope position. The Sendong series is found in the low areas in the bottom slope position. The soil positions, along with their drainage status, have marked influence on the yield of rice. A study was therefore conducted to investigate varitions in soil fertility parameters and yield in the various soil series along some selected transects. Three tansects on contrasting landscapes were selected. Grain yield variations along the various transects was assessed, with and without nitrogen fertilizer applications over 3 to 4 consecutive rice growing seasons. Plant analysis were conducted at two growth stages i.e. maximum tillering and harvest, and soil analyses after harvest of each crop. Irrespective of transect, texture fineness increased down the slope in contrast to pH which decreased. Soils of lower elevations had high organic carbon contents. Available phosphorus content differed among transects. The total nitrogen status and cation exchange capacity for all transects were low. Despite the dominance of exchangeable calcium in the cation exchange complex, the soils of the transects studied were inadequate in the supply of calcium for optimum rice growth. Soil exchangeable K was also inadequate. Changes in soil fertility characteristics with 2 to 4 consecutive croppings were minimal. However, an increase in organic carbon content was observed. Seasonal variations in yield were observed for all soil types in the three transects. Irrespective of transects, soils at higher elevation larger yield enhancement in response to nitrogen fertilizer application. The yield enhancement of soils at higher elevations was about 1.4 t/ha compared to 0.8 t/ha at lower elevations. The Tiong and Tanjung Puri transects had higher mean yields exceeding 5 t/ha. Among soil types, Tok Yong series and Chempaka series have potential to provide yields greater than 6 t/ha.