HEIGHTENING SORGHUM NITROGEN UPTAKE WHILE MAINTAINING OPTIMAL SOIL NUTRIENT LEVELS THROUGH MINERAL FERTILISER APPLICATION

Improving nutrient management of soils is important in subsistence farming systems in the tropics due to declining soil fertility resulting from continuous cropping coupled with inadequate nutrient replenishment. Balancing nutrient inputs with crop removal is crucial in reducing the build-up of nutrients and minimises nutrient losses through different pathways, thus reducing the cost of production. This study aimed at evaluating the effect of N and P fertiliser on sorghum N uptake at Kampi ya Mawe (KYM) in Makueni County and Katumani (KAT) in Machakos County, Kenya. Two factors (nitrogen and phosphorus) each at two levels (0 and 75 kg ha-1) were evaluated, resulting in four treatments, each replicated thrice. At KYM, N content in sorghum tissues increased by 24.2% in comparison with the control following application of N at 75 kg ha-1. At KAT, plots amended with N and P at 75 kg ha-1 resulted in the highest N content in sorghum tissues at the three sorghum development stages assessed. At the seedling stage, an increase of 18.8% was observed. Sole N application led to an increase in N content in sorghum tissues of 17.6% at the seedling stage. A positive linear relationship between NO3- N and N content in sorghum tissues was also observed. The study showed that soil N uptake was higher in the early growth stages of sorghum. The results of this study are essential to farmers and extension officers as a guide to ensure timely fertiliser application to ensure optimum utilisation of nutrients during crop growth.