SUMMARYA study was conducted to evaluate performance of two rice (Oryza sativa L.) varieties under water saving irrigation through alternate wetting and drying in sandy clay loams of Southern Malawi. The varieties, Nunkile and NERICA 4, are adapted to upland and lowland irrigated conditions, individually, and commonly grown by farmers. Four irrigation regimes were used in the study: (1) continuous flooding with surface water level kept at approximately 5 cm throughout crop duration (CFI), (2) alternate wetting and drying up to start of flowering after which continuous flooding was applied (AWD1), (3) alternate wetting and drying up to start of grain filling after which continuous flooding was applied (AWD2) and (4) alternate wetting and drying throughout the crop duration (AWD3). While seasonal crop water requirement was 690 mm, total irrigation depths were 1923.61, 1307.81, 1160.61 and 807.87 mm for the four regimes respectively. The CFI treatment used 32%, 40% and 58% more water than AWD1, AWD2, and AWD3 regimes respectively. In the same treatment order, the average yields per treatment for Nunkile were 4.92, 4.75, 4.74, and 4.47 t ha−1 with significant yield differences among CFI, AWD2 and AWD3 treatments. The average yields per treatment for NERICA 4 were 3.93, 3.75, 3.75, and 3.71 t ha−1 with significant yield differences only between CFI and all AWD treatments. Crop water productivity (CWP) was higher for Nunkile compared with NERICA 4 across all irrigation treatments, while CWP for CFI treatment was superior to all three AWD treatments grown under either variety. Thus, CWP was not increased with AWD irrigations. AWD till flowering and grain filling did not significantly differ with respect to yield and CWP. It is suggested that for similar conditions and where water is scarce, rice can be grown by AWD till grain filling as it saved more water. An important part of the research is to extend the initial results beyond the climate and soils of study.
A comparative study was carried out of annual ridge tillage (RT) and short-term effects of conservation agriculture (CA) on soil properties in fields of small-scale farmers. Soil samples were collected at depths of 0–10 and 10–20 cm from a total of 12 fields which had been under CA for two and four seasons, respectively, and from adjacent RT fields for direct comparisons. CA fields were converted from fields previously under continuous RT. Soil organic carbon, total nitrogen and available phosphorus were greater in CA fields while extractable potassium, pH and salt content were moderated under CA. Conversion of long-term RT to CA did not significantly influence bulk density and aggregate stability (geometric mean diameter) although structural stability was greater under CA practices. Total porosity, macroporosity and matrix porosity, and volumetric water content at saturation, field capacity and permanent wilting point did not substantively respond to tillage effects. Relative water capacity and air–water storage parameter, hfc/PORt, were significantly greater after 4 yr of CA. Soils under CA showed greater values for field-saturated hydraulic conductivity compared with RT fields. With the highest loadings in a principal component analysis, this work suggests that variables related to volumetric water content and aeration of the soil matrix, organic carbon, available phosphorus and soil texture were the most useful indices for future field comparison of RT and CA practices
In this study, panel linear models were used to develop an empirical relationship between metered household water use and the independent variables plot size and theoretical irrigation requirement. The estimated statistical model provides a means of estimating the climate-sensitive component of residential water use. Ensemble averages of temperature and rainfall projections were used to quantify potential changes in water use due to climate change by 2050. Annual water use per household was estimated to increase by approximately 1.5% under the low emissions scenario or 2.3% under the high emissions scenario. The model results provide information that can enhance water conservation initiatives relating particularly to outdoor water use. The model approach presented utilizes data that are readily available to water supply utilities and can therefore be easily replicated elsewhere.
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