Cowpea (Vigna unguiculata) is a major source of dietary protein and essential component of the cropping systems in semi-arid regions of Sub-Saharan Africa. However, yields are very low due to lack of improved cultivars, poor management practices, and limited inputs use. The objectives of this study were to assess the effects of rhizobia inoculant and P on nodulation, N accumulation and yield of two cowpea cultivars in Mozambique. Field study was conducted in three contrasting environments during the 2013/2014 and 2014/2015 seasons using randomized complete block design with four replications and four treatments. Treatments consisted of seed inoculation, application of 40 kg P2O5 ha-1, inoculation + P, and a non-inoculated control. The most probable number (MPN) technique was used to estimate the indigenous bradyrhizobia populations at the experimental sites. The rhizobia numbers at the sites varied from 5.27 × 102 to 1.07 × 103 cells g-1 soil. Inoculation increased nodule number by 34–76% and doubled nodule dry weight (78 to 160 mg plant-1). P application improved nodulation and interacted positively with the inoculant. Inoculation, P, and inoculant + P increased shoot dry weight, and shoot and grain N content across locations but increases in number of pods plant-1, seeds pod-1, and 100-seed weight were not consistent among treatments across locations. Shoot N content was consistently high for the inoculated plants and also for the inoculated + P fertilized plants, whereas the non-inoculated control plants had the lowest tissue N content. P uptake in shoot ranged from 1.72 to 3.77 g kg-1 and was higher for plants that received P fertilizer alone. Inoculation and P either alone or in combination consistently increased cowpea grain yield across locations with yields ranging from 1097 kg ha-1 for the non-inoculated control to 1674 kg ha-1 for the inoculant + P treatment. Grain protein concentration followed a similar trend as grain yield and ranged from 223 to 252 g kg-1 but a negative correlation between grain yield and protein concentration was observed. Inoculation increased net returns by $104–163 ha-1 over that for the control. The results demonstrate the potential of improving cowpea grain yield, quality and profitability using inoculant, although the cost-benefit for using P at the current fertilizer price is not attractive except when applied together with inoculant at low P site.

Soybean cultivars are generally adapted within a narrow north‐south geographical zone for full‐season growth due primarily to photoperiod response. The areas of adaptation were empirically defined more than three decades ago and re‐examination is needed. The accuracy of adaptation area determination can be improved by utilizing updated information, including changes in production practices and new technologies. The objective of this paper was to use current soybean yield data from experiments conducted across soybean producing states in the US to develop optimum zones of adaptation for soybean maturity groups (MGs) in the continental US. Data from state soybean variety trials conducted in 1998‐2003 were obtained from 139 locations, and were used to create regional adaptation map using ArcGIS. The MG 0 cultivars are adapted best to the region north of latitude 46°N, whereas succeeding groups are adapted further south. Each of the MGs 0 to III is adapted best within approximately two degrees latitude covering an area equivalent to 220 km wide from north to south. The zones of adaptation for MGs IV, V, and VI are wider than those for the earlier maturing cultivars. Overall, the regions of adaptation for the early‐maturing cultivars (MG 0 to III) have not changed; however, the adapted zones for MGs IV, V, and VI are much broader than previously thought. Groups VII and VIII, which dominated production areas in the South decades ago are now planted on a limited basis.

HighlightsBiological nitrogen fixation (BNF) is a key process for soybean production in Africa.The selection of elite African indigenous soybean Bradyrhizobium strains is a feasible strategy.Eighty-seven isolates were obtained from soybean nodules in Mozambique.Isolates fit into the Bradyrhizobium (75%) and Agrobacterium-Rhizobium (25%) clades.Five Bradyrhizobium isolates with outstanding symbiotic performance were obtained.

HighlightsThe effect of inoculation was evaluated in 2082 on-farm soyabean trials across Africa.Significant but moderate responses were observed.Variability was high and largely unexplained by considered environmental factors.Promiscuous varieties had similar yields but lower responses than specific types.Strong responses coincided with better uninoculated yields of promiscuous varieties.

Double-cropping soybean [Glycine max (L.) Merr.] after harvesting wheat (Triticum aestivum L.) is an important production system in the mid-southern USA. Field studies were conducted at Stoneville, MS (33°269 N lat) to evaluate the seed yield and net returns from early soybean maturity groups grown in a double-crop system under limited irrigation and to compare the results with those from a full-season system. Soybean cultivars from maturity groups (MG) III, IV, and V were used. Double-cropped soybean yields ranged from 2055 to 3767 kg ha 21 and were 10 to 40% lower than their full-season counterparts. For both systems, the average yield and net returns from MG IV, in particular the late IV cultivars, were among the highest, whereas those from MG III and late V were generally the lowest. The net returns from the full-season soybean averaged $85 to 274 ha 21 higher than those from the double-cropped soybean; however, the net returns from the double-cropped wheat more than compensated for these differences. The 3-yr average wheat yield was 5170 kg ha 21 and accounted for more than 60% of the combined net returns from the double-crop system. These results indicate that yields and net returns from double-cropped MG III or IV soybean could be equal or greater than MG V cultivars, but the late MG IV provided the highest yield and economic return. The data indicated that wheat-soybean doublecrop system using MG III or IV under limited irrigation was more profitable than the full-season soybean system.