Adaptability of irrigated rice to temperature change in sahelian environments

To assess genotype adaptability to variable environments, we evaluated five irrigated rice genotypes, three new varieties, WAS161, a NERICA, IR32307 and ITA344, and two controls: Sahel 108, the most popular short-duration variety in the region, and IR64. In a field experiment conducted at two locations, Ndiaye and Fanaye, along the Senegal River, rice was sown on 15 consecutive dates at one month intervals starting in February 2006. Yield (0–12.2 t ha-1) and crop cycle duration (117–190 days) varied with sowing date, genotype and site. Rice yield was very sensitive to sowing date and the associated temperature regimes. Spikelet sterility due to cold stress (T 35 °C) resulted in spikelet sterility when sowing took place in April (Ndiaye and Fanaye) and May (Fanaye). For all experiments the source and sink balance was quantified and showed that yield was most limited by sink size when sowing between July and October. Variety WAS 161 was least affected by genotype × environment interactions, resulting in lower interactive principal component values. An increase in minimum temperature of 3 °C could decrease spikelet sterility from 100 to 45%. These changes in temperature are likely to force rice farmers in the Senegal River to adjust the cropping calendar, e.g. to delay planting or to use heat-tolerant genotypes

Release of CO2 and CH4 from lakes and drainage ditches in temperate wetlands

Shallow fresh water bodies in peat areas are important contributors to greenhouse gas fluxes to the atmosphere. In this study we determined the magnitude of CH4 and CO2 fluxes from 12 water bodies in Dutch wetlands during the summer season and studied the factors that might regulate emissions of CH4 and CO2 from these lakes and ditches. The lakes and ditches acted as CO2 and CH4 sources of emissions to the atmosphere; the fluxes from the ditches were significantly larger than the fluxes from the lakes. The mean greenhouse gas flux from ditches and lakes amounted to 129.1 ± 8.2 (mean ± SE) and 61.5 ± 7.1 mg m-2 h-1 for CO2 and 33.7 ± 9.3 and 3.9 ± 1.6 mg m-2 h-1 for CH4, respectively. In most water bodies CH4 was the dominant greenhouse gas in terms of warming potential. Trophic status of the water and the sediment was an important factor regulating emissions. By using multiple linear regression 87% of the variation in CH4 could be explained by PO4 3- concentration in the sediment and Fe2+ concentration in the water, and 89% of the CO2 flux could be explained by depth, EC and pH of the water. Decreasing the nutrient loads and input of organic substrates to ditches and lakes by for example reducing application of fertilizers and manure within the catchments and decreasing upward seepage of nutrient rich water from the surrounding area will likely reduce summer emissions of CO2 and CH4 from these water bodie

Root, soil water and nitrogen dynamics in a catch crop - soil system in the Wageningen Rhizolab

Catch crops (winter rye [Secale cereale] and fodder radish [Raphanus sativus]) were grown on lysimeters with rhizotron facilities in Wageningen, Netherlands, from September-March (1993-94) and August-March (1994-95) in order to study root growth and water and nitrogen dynamics under different regimes of irrigation and N supply. Catch crops took up 20-30 g N/msuperscript 2, of which 37-48% was present in dead leaves in March. Rooting depth increased by 2.6 cm/day for both species at the start of the growing season. Catch cropping reduced the NO-3-N concentration in the soil considerably, initially in the top layers and then further down the soil profile. The reduction in total leached N was similar to the total crop N uptake. Nitrate-N concentrations in leached water were reduced by 49-85 mg/litre (62-99%), depending upon N availability and irrigation. Due to catch cropping the NO-3-N concentration in the percolate decreased with increasing irrigation (or precipitation), whereas the amount of N leached increased with irrigation. Evapotranspiration from a catch cropped soil was close to the potential evapotranspiration under optimal growth conditions

Root, soil water and nitrogen dynamics in a catch crop-soil system in the Wageningen Rhizolab.

Catch crops (winter rye [Secale cereale] and fodder radish [Raphanus sativus]) were grown on lysimeters with rhizotron facilities in Wageningen, Netherlands, from September-March (1993-94) and August-March (1994-95) in order to study root growth and water and nitrogen dynamics under different regimes of irrigation and N supply. Catch crops took up 20-30 g N/msuperscript 2, of which 37-48% was present in dead leaves in March. Rooting depth increased by 2.6 cm/day for both species at the start of the growing season. Catch cropping reduced the NO-3-N concentration in the soil considerably, initially in the top layers and then further down the soil profile. The reduction in total leached N was similar to the total crop N uptake. Nitrate-N concentrations in leached water were reduced by 49-85 mg/litre (62-99%), depending upon N availability and irrigation. Due to catch cropping the NO-3-N concentration in the percolate decreased with increasing irrigation (or precipitation), whereas the amount of N leached increased with irrigation. Evapotranspiration from a catch cropped soil was close to the potential evapotranspiration under optimal growth conditions