Effect of supplementary soil nitrogen on yield of Vicia villosa Roth harvested at different maturity stages

Abstract

A study was conducted in Naivasha, Kenya over a period of 15 weeks to determine the effect of supplementary soil nitrogen (SSN) on yield of Vetch (Vicia villosa Roth) under Kenyan climatic condition. After field preparation, representative soil samples were taken for mineral profiling. Sixty plots of 2 x 2 sq. m size were then demarcated and further divided into 5 similar units comprising 4 blocks of 3 plots each. The plots in each block were independently allotted to 3 treatments in a randomized complete block (RCB) design. Treatments were T1 – control (without SSN), T2 and T3 are manure and inorganic fertilizer (as sources of SSN), respectively. All the 4 blocks (weed free) in each of the five (randomly distributed) units were planted on the same day. Harvesting was done at 6, 8, 10, 12 and 14 weeks in a sequential manner starting with unit 1 to 5. All the blocks in each unit were harvested on the same day (at 5 cm height). All the freshly harvested materials, per plot, were weighed. Representative grabs of the material were made, chopped to pieces of 2 cm length, mixed and 2 composite samples (500 g each) were taken for dry matter (DM) determination and chemical analysis. DM, Ash and Crude protein (CP) were determined according to standard procedures. Fresh matter yield (FMY), DM yield (DMY), organic matter yield (OMY) and crude protein yield (CPY) per 4m2 and hectare were determined. Data was stored in MS-Excel and analyzed using SAS (2002) analytical models to determine the differences between treatments. Results showed that, at the age of 6 weeks, FMY and DMY (kg 4m-2) in T3 (1.83 and 0.24) were 23.6 and 34.1% higher (p>0.05) than T1 (1.48 and 0.179). Similarly, T2 (1.53 and 0.183) and T1 were also not different (p>0.05) at this age. At the 14th week however, the mean FMY in T1 (19.38) and T2 (22.51) were different (p<0.01, r2 = 0.705) and that of T3 (22.88) was 18.1% higher (p<0.01, r2 = 0.807) than that of T1. At this age, the mean FMY for T2 and T3 were not different (p>0.05, r2 = 0.028). When translated to an acreage yield equivalent, the differences between the 3 treatments were not strongly evident. T1, T2 and T3 recorded 48.4, 56.3 and 57.2 ton FMY ha-1 and 9.5, 10.9 and 12.1 ton DMY ha-1, respectively. A similar trend was observed with OMY and CPY, with T2 and T3 (8.3 and 9.2 ton OM ha-1, respectively), which were 13.7 and 26% higher than T1 (7.3) respectively. The results also showed strong correlation of yield parameters studied. In overall however, ANOVA outputs showed that, SSN and cutting stage had effect on yield. It was therefore concluded that provision of SSN could enhance initial growth but not the overall yield of V. villosa.

Keywords: Vicia villosa; manure; inorganic fertilizer; dry matter; organic matter; crude protein

International Journal of Natural and Applied Sciences Vol. 2 (3) 2006: pp. 157-163