The effect of potassium fertilization on kale (brassica oleraceae var acephala) production

Abstract

In Kenya, decline in food production has been a major problem facing smallholder farmers. The main production constraint being declining soil fertility. It is believed that judicious management and balanced application of plant nutrients is a strategy that can be employed to overcome soil fertility decline constraints. This strategy was incorporated in this study. Balanced fertilization of nitrogeneous, phosphatic and potassium fertilizers were used to improve yield and quality of Kale, Brassica oleraceae var acephala. A randomized complete block experiment was set up m 2001 in the greenhouse at the National Agricultural Research Laboratories (NARL) at Kabete with an overall objective of determining agro-economic potassium application levels (rates) in the production of Kales. The first specific objective was to determine the potassium fertilizer application on the growth, yield and quality of kale and to what extent its omission limited yields. The second objective was to determine K uptake and partitioning following K fertilization and its effect on quality of Kale. Field and greenhouse experiments were conducted to determine the effects of various treatments. One field experiment was conducted at Kerugoya while two greenhouse experiments were conducted using Mumias and Kerugoya soils, respectively. Soils from Mumias and Kerugoya sites were markedly contrasting with respect to agro-ecological and physico-chemical conditions. Kerugoya soils were better than Mumias in terms of soil fertility resulting in better performance of kale. Results obtained indicated that under optimum Nand P soil status, 75 - 100 and 25 - 50 kg/ha K20 were the agronomic and economic rates of K application, respectively. Higher K levels were needed in the field experiment while lower levels were needed in the greenhouse experiment. These rates resulted in superior plant growth (stem diameter, height and leaf expansion) and yield (number and weight of fresh leaves). Higher nutrient use efficiencies were obtained on Kerugoya than on Mumias soils per kilogram of K applied. The quality of Kale followed similar trends like the yields. There was an increase in leaf size with K application. Mineral nutrient contents of elements such as K, Ca and Mg also increased in the roots, stems and leaves with optimum amounts being obtained at 75 kg ha-1 K20 in the Kerugoya field experiment. Economic analysis showed that the optimum profit was obtained at application of 25 and 50 kg ha-1 K20 on the Kerugoya and Mumias soils in the greenhouse experiments and at the Kerugoya field experiment, respectively. These fertilizer levels were lower than the optimum yield levels implying that at the present fertilizer and kale prices it pays very little to use the K fertilizer and cheaper sources of K should be considered