Effects of intercropping arrangements and fertilizer application on growth and yield of African nightshade (Solanumnigrum L.) in Kisii County, Kenya

The study evaluated effects of intercropping arrangements and fertilizer combinations on growth and yields of Solanum nigrum L., soil nutrient balances and gross margins. The study was carried out at Kenya Agricultural and Livestock Research Organization (KALRO) in Kisii County for two seasons in the short rains 2015 and long rains 2016. The experiments were laid out in a randomized complete block design with a split plot arrangement replicated thrice. The main plots were intercropping arrangements of spider plant: African nightshade rows (intercrop ratios of 0:16, 1:14, 1:2, 1:3, and 1:4) and sub plots were fertilizer combinations of Farm Yard Manure (FYM), urea (NPK: 46-0-0) and triple super phosphate (NPK: 0-46-0). Data on number of branches per plant, number of leaves per plant and fresh leaf yield were measured. The total fresh leaf yield was used for gross margin analysis. Nutrient status and balances were determined for pH, Organic carbon, N, P and K analyzed before planting and after harvesting using nutrient monitoring (NUTMON) tool box. The results indicated that fertilizer combinations had a significant (P=0.05) effect on the number of branches and leaves per plant. The application of urea (60kg N ha-1) +TSP (40kg P ha-1) resulted in the highest number of branches and leaves (10 branches and 32 leaves per plant) while application of FYM (60kg N ha-1+ 36 kg P ha-1)resulted in the lowest number of branches and leaves ( 6 branches and 21 leaves per plant). On total fresh leaf yield, sole African nightshade supplied with Urea (60kg N ha-1) + TSP (40Kg P ha-1) resulted in the highest fresh leaf yield (35.1 tons ha-1). This however was not significantly different from sole African nightshade supplied with urea (40 kg N ha-1) + TSP (30 kg P ha-1) + FYM (20 kg N ha-1+ 9 kg P ha-1) that resulted in 32.5 tons ha-1. An intercrop ratio of 1:2 supplied with FYM (60 kg N ha-1+ 36 kg P ha-1) resulted in the lowest fresh leaf yield (8.9 tons ha-1). The results further showed that intercropping arrangements and fertilizer combinations had a significant (P=0.05) effect on soil nutrient status and balances. In terms of nutrient status, plots containing sole African nightshade and 1:4 intercrop ratio supplied with FYM (60 kg N ha-1+ 36 kg P ha-1) had a soil pH of 6.3 while plots with intercrop ratios of 1:2, 1:4, 1:3 and 1:14 supplied with urea (60 kg N ha-1) + TSP (40 kg P ha-1) had a pH of 5.58. Further an intercrop ratio of 1:14 supplied with FYM (60 kg N ha-1+ 36kg P ha-1) resulted in 0.46% N while an intercrop ratio of 1:2 supplied with urea (40 kg N ha-1)+ triple superphosphate (30 kg P ha-1)+FYM (20 kg N ha-1+ 9kg P ha-1)or urea (60 kg N ha-1)+ triple superphosphate (40 kg P ha-1) resulted in 0.3% N and a phosphorus content of 11.7ppm after harvest. Further, plots containing sole African nightshade as well as intercrop ratios of 1:3 1:4, and 1:14 supplied with FYM (60 kg N ha-1+ 36 kg P ha-1) resulted in 8 cmolkg-1K and 3 % C while plots supplied with urea (60 kg N ha-1) + triple superphosphate (40 kg P ha-1) or urea (40 kg N ha-1) + triple superphosphate (30 kg P ha-1) + FYM (20 kg N ha-1+ 9 kg P ha-1)resulted in 4 cmol kg -1 P across all intercropping arrangements. Further, Sole African nightshade supplied with FYM (60 kg N ha-1+ 36 kg P ha-1) recorded nutrient balances of -9 kg N, -9.9 kg P and -5.4 kg K ha-1 yr-1 while an intercrop ratio of 1:2 with an application of urea (60 kg N ha-1)+ triple superphosphate (40 kg P ha-1) recorded nutrient balances of -36.5 N, -25.2 P and -34.2 kg K ha-1 yr-1. On gross margin analysis, African nightshade grown at an intercrop ratio of 1:4 supplied with urea (60 kg N ha-1) + triple superphosphate (40 kg P ha-1) resulted in highest gross margin of KES 294,243 followed by sole African nightshade supplied with urea (60 kg N ha-1) + triple superphosphate (40 kg P ha-1) that resulted in KES 276,091 while an intercrop ratio of 1:2 supplied with FYM(60kg N ha-1+ 36 kg P ha-1) gave the lowest gross margins of KES 37,354. It can therefore be concluded that intercropping arrangements and fertilizer application influenced growth and yield of African nightshade, nutrient balances and gross margins. Further increase in spider plant population and/ or farm yard manure with the corresponding reduction of inorganic fertilizer resulted in low yields of African nightshade with low nutrient losses compared to when only inorganic fertilizer was used. However, combined yields for both vegetables with high ratios of inorganic fertilizer gave the highest gross margins. Therefore for a profitable vegetable enterprise, farmers should grow African nightshade at an intercrop ratio of 1:4 with nutrients supplied from urea (60 kg N ha-1) + triple superphosphate (40 kg P ha-1) to maximize on gross margins but for farmers who opt to grow a mono crop of African nightshade then nutrients must be supplied from only inorganic fertilizers. However, for those farmers who cannot afford inorganic fertilizers, can grow African nightshade at an intercrop ratio of 1:2 supplied with FYM (60 kg N ha-1; 36 kg P ha-1) since it is also profitable and facilitates reduction in soil nutrient losses. Although these technologies will empower small scale farmer economically, more has to be done to realize the most compatible vegetable intercrops with African nightshade, that will enhance nutrient use efficiency, reduce production costs and maximize gross margins.