The Effects of Some Soil Fertility Improvement Technologies on the Chemical Characteristics of a Sandy Soil and Yields of Two Maize Varieties

Abstract

Low and declining soil fertility has been shown to be the fundamental root cause of low food per capita in sub-Saharan Africa (SSA). Coastal Kenya is therefore not an exception. Soil fertility improving technologies have therefore been developed in the region to increase crop yields and reduce food poverty levels in coastal Kenya. The long-time effects of these technologies on the environment or their sustainability have however not been evaluated. This study carried out on a sandy soil classified as Acrisol to Luvisol therefore looked at the long-time effects of four (4) soil fertility improving technologies The study was conducted at KARI's Regional Research Center (RRC)-Mtwapa with Pwani hybrid 1 and 4 (PH 1 & 4) maize varieties were the test crop. The experiment was conducted for a period of 6 seasons or 3 years. Continuous use of inorganic fertilizers (DAP and CAN) lowered the soil's cation exchange capacity (CEC), pH and organic matter (OC) content while extractable P was increased. Total nitrogen (N) does not seem to be a good parameter to measure the effect of inorganic fertilizers on soil N levels. Since soil OC is necessary for a soil to have a good workability and increased CEC, the results appear to confirm farmers' observations that continuous use of inorganic fertilizers adversely affects soil physical characteristics (hard to till). The other 3 technologies resulted in increased soil. CEC, phosphorus (P) levels and OC content. The soil pH either remained the same or was slightly increased by the 3 soil improving technologies. Therefore the 3 soil improving technologies boosted or sustained the soil chemical characteristics which are vital for sustained crop productivity. Pwani hybrid 4 grain yields decreased with seasons reaching levels almost similar to those of PH 1 in the final season. On the other hand, PH 1 yields remained the same except during the first season where inadequate rainfall lowered them. The continued decrease in yields of PH 4 with successive seasons even when soil fertility improving technologies are used calls for further investigation on the nutrition of the maize variety. Nutrients needs of PH 1 are shown to be adequately supplied by the 4 technologies used.