ABSTRACT
Among other ways of effective water management strategies is the use of drip irrigation system and adoption of deficit irrigation schedulling strategy which is not common in the study area. Effective water management is a key to improving agricultural water management, enhancing crop production and improved sustainability of irrigated agriculture. In the past, outcome of any water management strategy could only be known after field experiment, in recent times, means of evaluating the implications of irrigation schedules without field experiment is fast gaining grounds with the use of models. However, there is need for proper evaluation of developed irrigation schedulling options with the use of models for optimal water management and crop response, before recommendation can be made to relevant bodies. This research work presents scenarios studies for different developed irrigation schedulling options for a drip irrigated maize crop at the Institute for Agricultural Research (I.A.R) irrigation farm Samaru-Nigeria during 2012/2013 and 2013/2014 cropping season using a computer-based model. The experiment consisted of eight (8) treatments replicated three times and laid in a randomized complete block design. The water application was regulated at selected crop growth stages. The test crop was SAMMAZ 14 early maturity maize variety. AquaCrop, a decision support model was calibrated and validated with data obtained from the field, and later used to simulate impact of developed schedulling strategies on yields, soil water balance and water productivity of a drip irrigated Maize. It was further, used to generate scenario of different irrigation schedulling outcome which were interpreted. A drip irrigation setup with 72 laterals each 5m long and 16 mm diameter with inline emitters was used in the experiment. The results of the hydraulic characteristics were: The average variation of the emitter flow rate was found to be 19.7% the emission uniformity calculated was 92%, while the distribution uniformity was 91.9% which signified an even distribution of water through the system. The average discharge coefficient of variation was 6.34 % and the average coefficient of variation uniformity was calculated as 93.6 %. The overall application efficiency of the system was 92.2% and the overall average dripper discharge was found to be 0.557 l/hr. Grain and biomass yields, harvest index, seasonal evapotranspiration and crop water productivity were determined. The grain and biomass yields ranged from 1.56 to 3.52 t/ha and 5.63 to 11.53 t/ha, respectively, while the seasonal evapotranspiration varied from 280 to 483 mm across seasons. The general trend of the results suggests that skipping regular irrigations may be advantageous if such is done at grain-filling stage, though most of the time this stage is intercepted by rain. Performance evaluation was carried out, The CRM shows that the model has a tendency to over -predict grain and biomass yield at harvest by 3 and 4 % and under- predict seasonal evapotranspiration by 2%, over-predict grain water productivity by 3% and biomass water productivity by 24%. The modelling efficiencies for grain water productivity and biomass water productivity were 50 and 90%. The scenario studies shows that the peak grain and biomass yield value of 3273 and 10492kg/ha was recorded when 20mm WAD with 3-day irrigation interval was applied across all the growth stages; the irrigation water productivity with respect to grain yield and biomass yield were 0.83 kg/m3 and 2.65 kg/m3, which implies that about 830 g of maize grain and 2.65 kg of dry matter was produced from every cubic meters of water. Increasing the interval from 3 - 6 days led to grain yield reduction of 14.3, 30.8 and 48%, respectively, while the biomass yield reduction were 15.4, 31.3 and 45%, respectively. Imposing deficit at three growth stages led to grain and biomass yield reduction ranging from 14.3 - 30.8%. .There was percentage grain yield increase value of 0.21, 1.84, and 1.22% for the following plant densities, 55,556 74,074 and 66,667, while percentage reduction value of 0.95% was recorded when 44,444 plants/ha was adopted.