Response of slender leaf (Crotalaria brevidens and Crotalaria ochroleuca) to different phosphorus levels

Abstract

Crotalaria brevidens and Crotalaria ochroleuca are the two most promising slender leaf species that are used as vegetables in Kenya. The young leaves and shoots of the slender leaf have been reported to be a good dietary source of provitamin A, carotenoids, vitamin C, iron, calcium, and proteins. Slender leaf is commonly cultivated and consumed throughout East Africa and to a limited extent in West Africa. Malnutrition is a major challenge in Kenya mostly affecting women and children, and this could be reduced if indigenous vegetables are consumed such as slender leaf. Although slender leaf is commercially produced in Kenya, only 2-4 tons per hectare have been harvested, yet it has the potential of producing 10-12 tons per hectare. This low production has been caused by poor quality seeds, lack of technical production packages and declining soil fertility instigated by continuous cultivation without addition of essential macronutrients such as phosphorus. Although the effect of nitrogen on the growth of slender leaf has been studied in Kenya, limited studies on the effect of phosphorus on the growth of slender leaf have been carried out in Kenya. Thus a study was carried out at Jomo Kenyatta University of Agriculture and Technology farm to evaluate the effect of different phosphorus rates on two Crotalaria species in a greenhouse pot study and in the field. The objectives of the study were to evaluate the effect of different phosphorus levels on the growth of two slender leaf species and to determine the effect of phosphorus on the nutritional content of the two slender leaf species at vegetative, reproductive and maturity stages. Eight levels of phosphorus 0, 0.28, 0.56, 0.84, 1.12, 1.40, 1.68 and 1.96 g/pot equivalent to 0, 15, 30, 45, 60, 75, 90, 105 kg P2O5 ha-1were added to the pots filled with red soil and sand mixture in the ratio of 5:1. These were then replicated four times in a completely randomized design. The field study was laid out in 1m x 7 m sq. plots, in split plot design with the species as the main plot factor and fertilizer treatments as sub-plot factor. Watering was done thrice per week to field capacity, while weeding was done to ensure healthy growing plants. Data on the plant height, the number of leaves, the number of branches, the number of pods, was taken

fortnightly. Data on seed weight and seed yield was collected after seeds matured. Leaves for nutritional content analysis were harvested at vegetative, reproductive and maturity stages of growth and kept at 100 Celsius awaiting the determination of nutrient content. The protein and nitrogen content were determined using semi micro Kjeldah method. Beta carotene content was analyzed using column chromatography and UV Spectrophotometry. Determination of minerals was done using dry ashing and atomic absorption spectrophotometry method. Data collected was subjected to the analysis of variance (ANOVA) using SAS 9.1.3 software to establish if the treatments had a significant effect on growth parameters considered and the nutrient content. Results of the study showed that phosphorus had a significant effect on all growth parameters in the greenhouse at p≤0.05 but not in the field. A significant interaction was found between phosphorus levels and species as far as plant height, number of leaves, number of branches, number of pods and seed weight and seed yield were concerned in the greenhouse study but not in the field. The effect of phosphorus on the nutrient content was only significant (p≤0.05) for beta carotene but not all other nutrients studied. From the results of this study, it can be concluded that P application had a significant effect on growth in the greenhouse pot study but not in the field conditions. Relatively higher levels of potassium phosphorus, zinc and iron were observed in the vegetative stage of growth. Significantly higher levels of nitrogen, protein magnesium calcium and beta carotene were observed at maturity stage of growth. Significantly higher beta carotene levels were observed in the second field experiment conducted in the months of November 2013-March 2014. Crotalaria ochloreuca had significantly higher levels of beta carotene and seed weight than Crotalaria brevidens. Application of 60 kg P205 ha-1 is recommended for enhanced leaf growth in the two slender leaf species