Response of maize to selected productivity traits and biological nitrogen fixation in cowpea-maize combinations under conservation farming system.

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Simunji, Simunji
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The University of Zambia
Maize productivity among the smallholder farmers in Zambia is generally low, resulting in average national grain yield of 2.3 tons per hectare. This challenge is mainly attributed to low and erratic rainfall, low soil fertility, and poor farming practices. This study was conducted to (i) evaluate the grain yield performance of selected drought and Low N tolerant maize varieties under conventional and conservation farming systems. (ii) evaluate the performance of cowpea genotypes for Biological Nitrogen Fixation (BNF) in conservation farming system. (iii) identify maize – cowpea combinations that result in high water use efficiency (WUE) and nitrogen use efficiency (NUE) for high maize productivity under CF system. The trials were conducted for two seasons at two sites of different soil types, fertility status and rainfall patterns. The three maize varieties (GV 640, GV 635 and ZMS 606) were evaluated in maize – cowpea rotation. Four cowpea genotypes used for rotation were Lutembwe (LTPRT) Bubebe (BBPRT), LT 11-3-3-12 (LT) and BB 14-16-2-2. The experimental designs used were split plot for objective(i) and (iii) and Randomized Complete Block Design for objective (ii). 15N and 13C discrimination isotopic technics were used to determine NUE, BNF, d13C and WUEi. Soil moisture storage (SMS) was measured using Divinner 2000 at the Chisamba site and the HH soil moisture meter at Batoka site. The maize grain yields of 8203 kg ha-1 and 4996 kg ha-1 under the conservation farming system (CF) at Chisamba and Batoka respectively were significantly higher (P<0.05) than 6987 kg ha-1 and 2281 kg ha-1 under conventional farming system (CONV) respectively. The yield of maize from CF was 17.4 % more than from CONV practice at the well- endowed fertile site (Chisamba) whereas at the poorer and drought-prone site (Batoka), yields from CF were 119 % more than from CONV practice. Maize variety ZMS 606 that yielded 7973 kg ha-1 was superior over GV 640 and GV 635 during the 2015/2016 season. GV 640 had the highest yield of 9539 kg ha-1 during the 2016/2017 season. Cowpea genotype LT 11-3-3-12 exhibited highest Biological Nitrogen Fixation of 86.1 kg N ha-1 and 16.5 kg N ha-1 followed by genotype BB 14-16-2-2 that fixed 57.9 kg N ha-1 and 4.5 kg N ha-1 at Chisamba and Batoka sites respectively. The nitrogen use efficiency (NUE) was significantly (P<0.001) higher under the conservation farming system (CF) with mean values of 26.48 % and 13.90 % than conventional system (CONV) at Chisamba and Batoka respectively. Under CF, water use efficiency of 10.16 kg ha-1 mm-1 at Batoka and 18.84 kg ha-1 mm-1 at Chisamba was superior over CONV attributed to cowpea genotype BB 14-16-2-2. The soil moisture storage at 10 cm and 20 cm soil depths under CF was higher than under CONV by 10.3 % at the well-endowed fertile site (Chisamba) whereas at the poorer and drought-prone site (Batoka), was higher under CF than CONV by 22.7 %. Cowpea genotype LT 11-3-3-12 was most effective for moisture storage in the soil at both sites. Maize variety GV640, genotypes LT 11-3-3-12 and BB 14-16-2-2 could be most efficient for intrinsic water use as indicated by lowest discrimination of 13C values of -12.13 ‰, -27.71 ‰ and -27.51 ‰ respectively. Therefore, the study identified ZMS 606 and GV 640 with high yielding, NUE and WUE as efficient drought and low N varieties for rotation with cowpea genotypes BB 14-16-2-2 and LT 11-3-3-12 with high dry biomass and BNF to ensure improved maize productivity under CF among smallholder farmers in Zambia. Keywords: 13C, conservation farming, cowpea genotypes, 15N, nitrogen fixation, nitrogen use efficiency, water use efficiency
Organic farming. , Cowpea genotypes. , Conservation farming system--Zambia. , Sustainable agriculture.