Reuse of domestic wastewater treated in macrophyte ponds to irrigate tomato and eggplant in semi-arid West-Africa: Benefits and risks

The scarcity of freshwater resources is a critical problem in semi-arid zones and marginal quality water is increasingly being used in agriculture. This paper aimed at evaluating the physico-chemical and biological risks on irrigated soils and fruits of macrophyte treated wastewater (TWW), the nutrients supply, and the effect on tomato and eggplant production in semi-arid Burkina Faso. During three years of experiments, treated wastewater was used, with fresh water as control, in combination with or without mineral fertilizer application at recommended rate (140 kg N/ha + 180 kg P2O5/ha + 180 kg K2O/ha). The study revealed that the treated wastewater provided variable nutrients supply depending on year and element. The treated wastewater without mineral fertilizer improved eggplant yield (40% in average) compared to the freshwater. Both crops responded better to mineral fertilizer (52% for tomato and 82% for eggplant) and the effects of the treated wastewater and fertilizer were additive. As the N supply of TWW was very unsteady (8-227% of crop need), and P2O5 supply did not satisfy in whole crop need (3-58%) during any of the three years of experiment, we recommended that moderate N and P2O5 fertilizers be applied when irrigating with TWW in semi-arid West-Africa. On the contrary, the K2O supply was more steady and close to crop requirement (78-126%) over the three years of experiment and no addition of K fertilizer may be needed when irrigated with TWW. Faecal coliforms and helminth eggs were observed in treated wastewater and irrigated soils at rate over the FAO and WHO recommended limits for vegetable to be eaten uncooked. Tomato fruits were observed to be faecal coliform contaminated with the direct on-foliage irrigation with treated wastewater. Our results indicate that treated wastewater can effectively be used as both nutrients source and crop water supply in market gardening in the semi-arid Sub-Saharan West Africa (SSWA) where freshwater and farm income are limiting. Yet consumers should properly cook or disinfect treated-wastewater irrigated vegetables before eating, and market gardeners should also be careful manipulating treated wastewater to avoid direct health contamination in this environment.Treated wastewater Irrigation Freshwater Nutrients supply Pathogen health risks Tomato Lycopersicum esculentum Mill. Eggplant Solanum melongena L.

Variability in maize yield and profitability following hill-placement of reduced mineral fertilizer and manure rates under smallholder farm conditions in northern Benin

Whereas the decision to promote a given agricultural intensification technology has hitherto been largely based on its average agronomic or economic performance, it is increasingly being recognized that the variability in the performance must also be taken into account in order to develop more meaningful and flexible recommendations. This is true in particular for microdose fertilization which is being actively promoted in sub-Saharan Africa as a means to increase crop productivity, profitability and fertilizer use efficiency. To this end, a total of 51 onfarm maize trials were carried out in northern Benin in 2014 and 2015. The performance of two microdose fertilization options (MD1=23.8 kg N, 4.1 kg P, and 7.8 kg K ha−1; MD2=33.1 kg N, 8.2 kg P, and 15.6 kg K ha−1) applied alone or combined with hill-placed manure (FYM) at 3 t ha−1 was compared to an unfertilized control and a broadcast fertilizer treatment at the recommended rate (RR; 76 kg N, 13.1 kg P, and 24.9 kg K ha−1). On average, microdose fertilization alone increased maize grain yields by 1145 kg ha−1 (+105%), compared to the unfertilized control (1096 kg ha−1). There was no significant difference in yields between MD1, MD2 and RR in both years. Combining microdose fertilization with manure further increased yields by 848 kg ha−1 (+40%) on average. There was a large variability in yields among farmers, from 420 to 1687 kg ha−1, 1419 to 3418 kg ha−1 and 1834 to 4475 kg ha−1 for the control, sole microdose (MD1 and MD2) and microdose+FYM treatments, respectively. Variability tended to be lowest in the control treatment. Absolute yield response to microdose fertilization tended to decrease with increasing yields in the control plots and was well explained by the combination of some measured soil parameters (clay and/or silt, total carbon, exch-Mg, pH) and weed pressure. Based on the value-cost ratio (VCR), the economic performance of the RR treatment was less than that of the microdose treatments (alone or combined with manure) despite the higher labor cost associated with the latter treatments. MD1 should be favored over MD2 because yields were not significantly different yet the risk of achieving low VCRs was lower in MD1. Despite the greater variability compared to the control, the risk of no return on investment was nearly nil for MD1 (6%) and MD1+FYM (2%) as a result of the strong increase in yield. Despite the overall good performance of fertilizer microdosing, more effort is needed to better understand crop response to microdose fertilization for a broader range of environmental conditions in Benin in order to fine tune recommendation domains

Hill-placement of manure and fertilizer for improving maize nutrient- and water-use efficiencies in the northern Benin

Optimizing the use of organic and mineral fertilizer in rain-fed maize production is crucial for sustainable food production in sub-Saharan Africa. This study investigates the effect of hill-placement of two nutrient sources (farmyard manure and synthetic fertilizer) on nutrient- and water-use efficiencies of maize crops i.e. recovery efficiency (NUEre), internal utilization efficiency (NUEie) and water use efficiency (WUE). A four-year trial was conducted in the tropical sub-humid zone of the northern Benin with a factorial combination of farmyard manure at three levels (0, 3 and 6 t ha−1, hereafter NM, 3M and 6M, respectively) and three levels of fertilizer [0% (NF), 50% (50F) and 100% (100F) of the recommended rate (76 kg N + 13.1 kg P + 24.9 kg K ha−1) by the national center for agricultural research. The NUEre decreased with increasing rate of manure and/or fertilizer, but the decreasing rate was lower under combined manure and fertilizer application. However, the NUEie increased with the increasing manure and fertilizer amounts. The WUE was significantly higher in 3M and 6M treatments than in NM treatment, and higher in 50F and in 100F than in NF treatments. The combination of 3000 kg ha−1 farmyard manure with half recommended fertilizer rate (100 kg ha−1) could be suggested as an optimal nutrient management practice for maize production in the Northern Benin. Future studies should target the other agro-ecological zones in Benin, and also consider other widely cultivated crops in the study area for reducing yield gaps and promote food security