Gerd Dercon

Differential 13C isotopic discrimination in maize at varying water stress and at low to high nitrogen availability

The relationships between 13C isotopic discrimination and water stress are well documented for C3 and C4 plants. However, the application in the field is hampered by complex interaction patterns with other common stress factors, such as nutrient deficiency. In addition, questions arise if temporal reductions in water availability during crop growth can be traced back using δ13C data in the field. The objective of this study therefore is to assess the potential use of δ13C observations to quantify water stress and its dynamics in maize (Zea mays L.) grown under low to high nitrogen availability, and to develop tools based on δ13C values for its diagnosis in the field. In a pot experiment, carried out in a screen house in Ibadan, Nigeria, we grew maize for 60xa0days under four watering regimes, (i) optimum (at field capacity) during 60xa0days, (ii) optimum from 0 to 30xa0days and stressed (50% field capacity) from 30 to 60xa0days, (iii) stressed from 0 to 30xa0days and optimum from 30 to 60xa0days, and (iv) stressed throughout the 60xa0days. Nitrogen was applied at three rates (none, moderate (45xa0kgxa0Nxa0ha−1) and high (120xa0kgxa0Nxa0ha−1)). Plants were sampled after 30 and 60xa0days. At 60xa0days, leaves developed during the first 30xa0days were sampled separately from those developed between 30 and 60xa0days. Shoot production showed a clear water–nitrogen interaction. Nitrogen response increased with decreasing water stress, in particular from 30 to 60xa0days. δ13C values ranged from −12.42‰ to −10.80‰. Overall, a clear and significant water and nitrogen effect (P<0.0001) on the isotopic discrimination in maize was observed, opposite in direction from C3 plants. δ13C values decreased with increasing water stress, but increased with decreasing nitrogen availability, particularly when combined with limited water supply. In addition, isotopic discrimination was observed to be variable within plant, and could be related to a water stress in that growth period, in which the plant parts were developed. This shows that δ13C values measured in different plant parts at harvest can be used as a historical account on how water availability varied during the entire cropping cycle.

DOES CROP-LIVESTOCK INTEGRATION LEAD TO IMPROVED CROP PRODUCTION IN THE SAVANNA OF WEST AFRICA?

Integrated crop-livestock farming in the Guinea savanna of West Africa is often assumed to lead to synergies between crop and livestock production, thereby improving the overall productivity and resilience of agricultural production. Whether these synergies actually occur remains poorly studied. On-farm trials were conducted in northern Nigeria over a period of four years to assess the agronomic and economic performance of maize-legume systems with and without the integration of livestock (goats). Groundnut-maize rotations with livestock achieved the highest carry-over of nutrients as manure from one season to the next, covering approximately one-third of the expected N, P and K uptake by maize and reducing the demand for synthetic fertilizers. However, the advantage of lower fertilizer costs in rotations with livestock was offset by higher labour costs for manure application and slightly lower values of maize grain. Overall, no clear agronomic or economic benefits for crop production were observed from the combined application of manure and synthetic fertilizer over the application of synthetic fertilizer only, probably because the amounts of manure applied were relatively small. Legume-maize rotations achieved higher cereal yields, a better response to labour and fertilizer inputs, and a higher profitability than maize-based systems with no or only a small legume component, irrespective of the presence of livestock. Livestock at or near the farm could nevertheless make legume cultivation economically more attractive by increasing the value of legume haulms. The results suggested that factors other than crop benefits, e.g. livestock providing tangible and non-tangible benefits and opportunities for animal traction, could be important drivers for the ongoing integration of crop and livestock production in the savanna

Balanced Nutrient Management System Technologies In The Northern Guinea Savanna Of Nigeria: Validation And Perspective

Based on experimental evidence that combining mineral fertilizers with organic matter may address poor soil fertility status and result in added benefits, farmer-managed demonstration trials were initiated in 9 villages in the northern Guinea savanna (NGS) of northern Nigeria. The trials had four treatments: (i) a farmers control in which the farmer grows maize according to his usual practice, (ii) the maize technology being promoted by the NGO Sasakawa-Global2000 (SG2000), involving hybrid seeds, proper plant density and fertilizer application practice, and fertilizer application rates that are relatively high for the region (136 kg N, 20 kg P, and 37 kg K ha-1), (iii) the Balanced Nutrient Management Systems (BNMS) manure technology that follows the SG2000 package for maize, except that part of the fertilizer quantity is replaced by animal manure; and (iv) a soybean-maize rotation, again with reduced fertilizer rate to the maize.