ABSTRACT

Umudike (05 29 N. 07 33 E). a typical rainforest agro- ecological zone, was assessed for suitability for the growth and production of an Indian sub-continent originated mungbean ( Vigna radia'a.L. Wilczek) as food legume using systems approach. Simulation modeling was used to predict the potential yield (Ymp) and maximum cvapo-transpiration of the crop (ETm) in the zone. Validation of the models involved field experiments at the Teaching and Research Farm of Michael Okpara University of Agriculture Umudike. In the first field trial four mungbean varieties (NM-92, NM-94, VC 6372 and VC 1163 from Asian Vegetable Research and Development Centre (AVRDC) were evaluated at three sowing dates (April, June and September) each in 2003 and 2004. The experiments were laid out in split- plot pattern in a randomized complete block design (RCBD) with four replications. The second fieldwork assessed the response of mungbcan varieties to varying doses of NPK fertilizer. Four levels of NPK Fertilizer (N0—P0 K(); N1 -P -K20, N —P6cr K., and N40- P80- K60 kg/ha) and two varieties of mungbean (NM-92, and VC 6372) were arranged in a factorial in randomized complete block design with three replications. The third field trial was a planting geometry experiment which had as treatment two row directions North-South (N-S) and East- West (E-W) ail-four inter- and intra- row spacing (20 cm x20 cm ; 28 cm x14 cm; 40 cm x 10 cm, and 56 cm x7 cm). Treatments were placed in a factorial in randomized complete block design with four replications. Results show that 2.4-3.6 cycles of rainfed mungbean could be cultivated between April-October. Simulation modeling indicated a mean crop evapotranspiration of 300 mm, while the mean effective rainfall was 400 mm. A mean potential maximum grain yield (Ymp) of 3.5 t/ha/period with a range from 3.2 -3.8 tfhalperiod. The highest potential grain yield of 3.8 t/halperiod predicted for April sowing date coincided with the period of highest mean solar radiation of 421calIcm/day. In the variety and sowing date trial, early season (April sowing) mungbean produced the highest yield of 0.84 t/ha, while the late season (September sowing) recorded the lowest significant yield of 0.14 t/ha. The variety VC 6372 and NM-92 were statistically at par 0.82 and 0.81 t/ha respectively but significantly out yielded Nm 94 (0.48t1ha) and VC 1163(0.42 t/ha). A yield gap analysis revealed 78-86% variation between potential and realized grain yield indicating the quantum of work needed to bridge the gap. Mungbean response to variety and fertilizer application indicated significant (P<0.01) varietal effect only in total dry matter and pod length with VC 6372 being superior while NM-92 showed superiority in 1000 seed caught. All physiological parameters [leaf area index (LAL), crop growth rate (CGR), net assimilation rate (NAR), relative growth rate (RGR)], morphological characters, [plant height, total dry matter (TDM), and harvest index (HI)J as vcIl as seed yield and other yield components were significantly (P<0.0 I) enhanced by fertilizer application. NPK rates of 30-60-40 kg/ha elicited the highest seed yield at 1.2-1.3 t/ha significantly surpassing the control by 40-41%. Planting geometry experiment showed that both spacing and row orientation influenced anthesis, height at maturity and dry matter distribution. Crops in N-S row direction produced significantly (P <0.01) higher seed yield of 1.4 tlha compared to 1.38 tfha obtained for crops in E-W row direction. Combined analysis for the two years showed that 20 cm x20 cm produced the highest seed yield of 1.4 1./ha while 56 cm x7 cm recorded the lowest significant seed yield (1.30 tlha). Soil beneath canopies of plant in rectangular spacing of 28 cmx 14 cm in N-S orientation maintained significant (P< 0.05) lowest temperature (28.36 °C) compared to other treatments while its seed yield was statistically at par with plants in equidistance distribution of 20 cm x 20 cm that recorded the highest seed yield. It is concluded that mungbean cultivars VC 6372 and NM 92 evidently thrived and flourished in Umudike thereby validating the results of the modeling studies which predicted the suitability of Umudike for mungbean growth and production. Sowing in April presents the best growth condition, while NPK fertilizer at 30-60-40 and rectangular spacing of 28 x 14 cm in N-S row orientation increases seed yield. There is need for more research work that integrates the crop into the farming systems in many locations in the zone.