Response of green grams to fertilizer Nitrogen, chicken manure application and Rhizobal inoculation
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A field experiment was conducted at the University of Nairobi, Kabete Field Station between April, 2000 and March 200 1 to determine the effects of nitrogen source (organic, inorganic or combination) and rhizobium inoculation on growth, biological nitrogen (N) fixation (BNF) and yield of green grams (Vigna radiata (L.) Wilczek). Nitrogen was applied at a rate of 100 kg N/ha as calcium nitrate (Ca(N03)2), urea, chicken manure (CM), 50 kg Nlha Ca(N03)2 + 50 kg N/ha CM, 50 kg N/ha urea + 50 kg Nlha CM and no N application. The grams were either inoculated or not inoculated. Wheat was grown as reference crop to determine BNF by difference method. The experiment was laid out in randomized complete block design with three replications. The results showed that total, leaf and stem dry matter, leaf area index (LAI), solar radiation interception, root nodulation, biological nitrogen fixation (BNF) and seed yield were significantly influenced by N sources. The numbers of leaves/plant, branches/plant, seeds/pod, harvest index (HI) and 1000-seed mass were not significantly affected by N sources or rhizobium inoculation., Ca(N03)2 application increased total dry matter (TDM, g/m"), photosynthetically active radiation (PAR) interception and LAI and seed yield relative to other N sources. Nodulation and BNF were significantly increased by rhizobium inoculation but were reduced by fertilizer N application. Nitrate N source gave the highest economic returns but was more costly to purchase. Chicken manure led to high economic losses due to high cost of buying the manure and low seed yield observed. The gross margin increased 6.5 times in plants that were inoculated with rhizobium without fertilizer N application, compared to non-inoculated. Farmers with limited financial resources could use Rhizobium while those not limited by finances may use nitrate N source to increase profits in green gram production.