Effect of N-fertilizer and farmyard manure application, rhizobium inoculation and irrigation on performance of snap bean (phaseolus vulgaris L.) in central Kenya

Nitrogen nutrient deficiency is a limiting factor for snap bean production and ought to be supplied in a sustainable way. Two field experiments were conducted at Mwea in Central Kenya between April and December 2006. The objective of the study was to investigate the effect of different combinations of farmyard manure and inorganic N fertilizers, Rhizobium inoculation and irrigation regimes on growth and yield of snap bean. In the first experiment, four levels of inorganic fertilizer and four levels of farmyard manure were tested in a factorial experiment laid out in a randomized complete block design with three replications. The inorganic N fertilizer levels were: 0, 30,60, and 90 kg N/ha, while the farmyard manure (FYM) levels were: 0,4,8, and 12 t/ha. A farmer practice comprising of: 100 kg N/ha + 50 kg P20s/ha was included in each of the replicates. The crop was grown under furrow irrigation which was done twice a week supplying 50mm of water in each irrigation. In the second experiment, the treatments were: three irrigation regimes (irrigating once a week, irrigating twice a week (or farmer practice) and irrigating three times a week) at 50mm of water per irrigation and three inputs (rhizobia inoculated, uninoculated and supplied with 60 kg N/ha). These treatments were tested in a split plot design experiment laid out in a randomized complete block design with three replications. The irrigation regimes were in the main plots while the input treatments were in the sub-plots. There was a farmer practice comprising of 100 kg N/ha + 50 kg P20s/ha in each replicate where irrigation was done twice a week only at 50mm per irrigation. The parameters measured in both experiments included: % crop emergence, % flowering rate, % pod set, plant height, nodule numbers, nodule dry weight, root dry weight, shoot dry weight, total pod yield, graded pod fresh weight and pod moisture content. The results showed that fertilizer improved germination and podding rates in both experiments. Application of 60 kg N/ha had the highest significant crop emergence rates compared to the farmer practice (100 kg N/ha + 50 kg P20s/ha) and 90 kg N/ha. Plots treated with 60 kg N/ha also had the highest plant height at flowering in experiment I while the farmer practice treatment gave the tallest plants in experiment II. There was no significant effect on nodulation in experiment I while the Farmer practice treatment suppressed nodulation in experiment II. Applying 4t/ha, 8t/ha and 12 t/ha FYM gave increasing root dry weight in experiment I while the same was not significant in experiment II. The farmer practice treatment (100 kg N/ha + 50 kg P20slha) increased shoot dry weight significantly in both experiments. The interaction between FYM and N-fertilizer improved both marketable yield as well as total pod yield as compared to the farmer practice treatment. Plots with 30 kg N/ha and 8 t/ha FYM had the highest extra-fine yield, while those treated with 60 kg N/ha and 4 t/ha FYM produced the highest fine yield in experiment I. Overall, combining both FYM and N-fertilizer at the rate of 60 kg N/ha and 4 t/ha FYM produced the highest total pod yield. In conclusion, plots treated with both farmyard manure and fertilizer combinations did better than the farmer practice in terms of yield and plant biomass. In the second experiment, farmer practice seemed to perform better in terms of total as well as marketable pod yield than rhizobia and N-treatments. Irrigating twice a week improved extra-fine yields significantly while irrigating three times a week improved the fine yield. Overall, plots treated with the farmer practice (100 kg N/ha + 50 kg P20s/ha) and those treated with 60 kg N/ha produced significantly higher pod yield compared to the inoculated and uninoculated plots. Rhizobia inoculation was not effective in this study.