Nitrogen fixation potential and residual effects of selected grain legumes in a Kenyan soil

<p>Based on their performance attributes, butter bean (variety Ex-kasuku) and grass pea (Selection 1325) have been<br>identified as potential alternative legumes for the maize-based cropping system in the cold semi-arid region of<br>Laikipia County in Kenya. However, their nitrogen fixation potential and nitrogen residual effects have not been<br>established. A green house experiment was therefore conducted to determine the nitrogen fixation potential and<br>residual effects of the introduced legumes (butter bean and grasspea) relative to the local checks (common bean<br>cv. Katumani 330 and chickpea cv. Desi). The legume seeds were planted in perforated polythene bags,<br>measuring 14 cm diameter and 20 cm high, containing 3.6 kg air dried soil collected from Matanya in Laikipia<br>County, Kenya. Barley, a non-nitrogen fixing reference crop, was also planted in polythene bags and used to<br>determine the amount of nitrogen fixed according the N-difference method. Butter bean and grass pea<br>significantly out-performed chickpea in total nodule number, active nodule number, total nodule dry matter,<br>total plant dry matter, dry matter N yield, amount of N-fixed, percent N derived from the atmosphere and<br>residual N effect, but were comparable to common bean in all these attributes. There was a significant, positive<br>linear relationship between quantity of N-fixed and quantity of total plant biomass accumulated. Butter bean,<br>grass pea and common bean significantly increased soil mineral nitrogen while chickpea had no influence on soil<br>nitrogen. Butter bean and grasspea can therefore provide N to cropping systems in the cold semiarid region<br>through biological N fixation.