Impact of Methods of Administering Growth-Stage Deficit Irrigation on Yield and Soil Water Balance of a Maize Crop (SAMAS TZEE)

Field experiments were conducted in 2009/10 and 2010/11 irrigation seasons at the Institute for Agricultural Research, Samaru Zaria, to assess the impact of two methods of administering Growth-stage deficit irrigation scheduling (GSDIS) on yield and soil water balance of an early maturing maize variety. The two methods include reducing water application depth at selected crop growth stages and skipping regular irrigation interval at selected crop growth stages. The test crop was SAMAS TZEE early maturing maize variety. Grain yield, biomass yield, harvest index, seasonal water applied, evapotranspiration and deep percolation and crop water productivity were determined. Grain and biomass yields ranged from 2.12 to 3.01 t/ha and 7.57 to 10.0t/ha, respectively, while seasonal evapotranspiration varied from 366 to 486.8 mm across the seasons. Thisstudy reveal that at vegetative growth stage of the maize crop, it is better to skip weekly irrigation (to irrigation every other week) and apply water to meet full water requirement than to maintain regular weekly irrigation butapply water at half water requirement. A grain filling to maturity stage, it is more advantageous to reduce irrigation water application by half water requirement than to skip weekly irrigation. Grain yield, biomass yieldand seasonal evapotranspiration from such scheduling were not significantly different from that which received weekly irrigation throughout the crop growing season. Moreover, the productivity of water applied was higher while water loss to deep percolation was drastically reduced.Keywords: Deficit irrigation scheduling, Economic net return, Maize crop, Irrigation water managemen

Field-based crop coefficients (Ke) for a maize crop under deficit irrigation scheduling

This study presents crop coefficient (Kc) values ofTMVl-ST maize variety cultivated under deficit inigation scheduling in Mkoji sub-catchment, Tanzania. Field experiments consisting of eight (8) treatments were conducted in 2004 and 2005 irrig~tion seasons. The treatments variation was irrigation . intervals. The control treatment was irrigated on weekly basis while the other treatments were irrigated every other week at one or more growth stages of the maize crop. Surface irrigation method was used and. soil moisture contents were monitored weekly throughout the crop growing season from which weekly crop actual evapotranspiration was computed. Weather data of the study location were used to compute wee~y reference evapotranspiration based on the FAO-PenmanMonetieth model. Crop coefficients were ·computed as the ratio of crop actual evapotranspiration of the different treatments to reference evapotranspiration on weekly basis. Water stress coefficients were also computed. The crop coefficients . had similar trend in the two seasons which m~e them reliable. The average crop coefficient (Kc) of the fully irrigated treatment for the two seasons for the establishment, vegetative, flowering and grain filling stages were 0.53, 0.82, 1.10, and 1.06, respectively, while the average crop coefficients of the deficit irrigated treatments (Kc') forthe two seasons for the establishment, vegetative, flowering and grain filling stages were 0.53, 0.75, 0.94, and 0.78, respectively. Withholding regular irrigation at any crop growth stage reduced crop coefficient by between 17 to 30 %, while withholding regular irrigation at two or more successive growth stages of the maize crop reduced crop coefficient by about 40 %. The water stress coefficient (Ks) resulting from deficit irrigation at any one growth stage only of the maize crop were found to range from 0. 74 to 0.83, while deficit irrigation at two or more successive growth stages ranged from 0.68 to 0.77. The crop and water stress coefficients developed from this study could be used in irrigation systems planning and design for the study area in Tanzania. .Keywords: Irrigation scheduling, deficit irrigation, crop coefficient, water stress,maize, Tanzani

Evaluation of a simulation model for predicting soil-water characteristics of selected agricultural fields

The ability of the Soil Water Characteristics-Hydraulic PropertiesCalculator (SWC-HPC) model in predicting soil-water characteristics ofagricultural fields in Zaria, Nigeria, was tested and reported in this study. The goal was to establish the predictability and reliability of the model, and hence, its use in determining water characteristics of soils in the study area. Fortty soil samples collected from four irrigation sites were used in the evaluation. The soils particle size distribution (specifically, percent clay and sand) and organic matter contents were inputted into the model to simulate soil moisture status at saturation, field capacity and wilting point, soil bulk density and saturated hydraulic conductivity.The model outputs were statistically compared with observed parameters from laboratory tests using root mean square error (RMSE), coefficient of variation (CV), modeling efficiency (BF) and coefficient of residual mass (CRM). The model accurately simulated the observed bulk densities of the soil tested, satisfactorily simulated soil moisture content at field capacity, and moderately simulated moisture content at saturation and wilting point. The model however, poorly simulated saturated hydraulic conductivity of the soils tested. The SWC-HPC may therefore be used only to simulate soil bulk densities and moisture status at saturation, field capacity and wilting point inthe study locations. Keywords: Simulation, SWC-HPC model, Field capacity, wilting point, bulkdensity, saturated hydraulic conductivit