Abstract:
On-farm study was carried out for two seasons on sandy clay soil of southwest Kenya in 2004.
The objective was to determine effect of different application rates of mucuna green manure on its
decomposition pattern, available soil N and distribution in rooting zone of maize, in the season when the
biomass is incorporated into the soil. The treatments were mucuna applied at rates of 0, 30, 60, 120, 240 and 480
kg N haG and inorganic fertilizer-urea at 30, 60 and 120 kg N haG included for comparison. The approaches1 1
employed in evaluating the treatments were: Field incubation using micro-lysimeter technique and, direct field
sampling method. Randomized complete block design with three replications was used. Results showed that
mucuna decomposition pattern remained same irrespective of application rate. Soil available N (SAN) increased
over time after application of either source of N. The SAN level reached a significantly higher peak at 2 weeks
after application (WAA). Direct field sampling showed that at 2 WAA most of the N accumulated at 50–100 cm
depth, regardless of the N source. Significant differences in SAN level attributed to application of the
various rates of mucuna and fertilizer were notable at 2 WAA, but had disappeared by 4 WAA. At the 2 WAA,
mucuna and fertilizer applied at 60 and 120 kg N haG , respectively showed comparable SAN level and had1
non-significant effect on it at 0-15 and 15–30 cm depths. It required 240 kg N haG equivalent of mucuna, or 1201
kg N haG of inorganic fertilizer to substantially increase SAN level over the control.
