Ingénierie des systèmes d’irrigation et de drainage

Maize (Zea mays.L) farmers in the traditional irrigation schemes in middle Mkoji sub-catchment, Tanzania observes three irrigation scheduling practices. This paper presents a simulation study of the impacts of these scheduling practices on yield and soil water balance of the maize crop. The three scheduling practices include irrigating at 5 days and 7 days intervals throughout the crop growing season, respectively; and irrigating at 7 days interval from planting to vegetative growth stage and 5 days interval from flowering to crop maturity stages. ISIAMOD, a crop growth cum irrigation simulation model, was used to simulate grain yield, soil water balance components and crop water productivity responses for the three scheduling practices over a range of water application depths. Simulated grain yield varied from 1338 to 4023 kg/ha. Seasonal water applied and deep percolation varied from 425 to 1800 mm, and 50 to 113 mm, respectively. The crop water productivity in terms of water applied varied from 0.22 to 0.57 kg/m3. These values closely agree with field measured values reported by some researchers for the study area. Irrigating maize fields at 5 days interval throughout the crop growing season or at flowering to crop maturity gave higher water productivity output only when application depths per irrigation did not exceed 30 mm. Water application beyond this depth only led to very high deep percolation losses without appreciable difference in crop yield compared to irrigating at 7 days interval throughout the crop growing season. Moreover, the productivity of water applied dropped by about 30 and 50 %. This implies that farmers who irrigate at 5 days interval because of they have access to water do not have any advantage (in terms of yield and water productivity) over those who irrigate at 7 days interval except they minimize water applied to their fields. Water application depth for higher productivity under the 7 days irrigation interval for the maize crop in the study area was 40 to 45 mm depth. Beyond this depth, there was no appreciable increase in grain yield but a fall in productivity of applied water and a buildup of deep percolation. To avoid over irrigation and the consequences associated with it, maize farmers at any sector of the irrigation scheme in the study area are advised to observe 7-day irrigation interval and keep water application depth within 40-45 mm per irrigation.

The natural processes and man-made disturbances in the watershed have influenced the micro climate and in turn affect the hydrology of the watershed along the time scale. The increase in emission of greenhouse gases into the atmosphere might induce variation in climatic pattern in the future. In hydrological models, the climatic parameters remain to be deterministic variables in simulating the surface water or groundwater components. In the recent past, climatological cycle and its variability have been incorporated into water resources systems modeling by many researchers. In this study, an attempt has been made to study the influence of climatic variability on irrigation water requirements in an arid region on a temporal scale, which will help in the water resource planning and management of an irrigation system. A climate crop water requirement (CCWR) integrated framework has been developed to estimate the irrigation requirement in Manimuthar river basin, Tamilnadu, India, incorporating variation in climatic parameters over temporal scale. Based on the existing land use pattern and economic development prevailing in the study area, the most likely climatic scenario has been identified as A1B. From the results, it is inferred that the irrigation water requirement is likely to increase by 5% from 2010 to 2020.

Land application of treated wastewater is increasing particularly in areas where water stress is a major concern. The primary objective of this study was to quantify the effect of irrigation with aerated lagoon treated wastewater on soil properties. Core and bulk soil samples were collected from areas under the canopies of mesquite and creosote and intercanopy areas from each of the three plots. Irrigation water quality from 2006 to 2008 showed that average sodium adsorption ratio (SAR), electrical conductivity (EC) and pH of irrigation water were 37.16, 5.32 dS m-1 and 9.7, respectively. The sprinkler uniformity coefficients of irrigated plot-I was 49.34 ± 2.23 % and irrigated plot-II was 61.57 ± 2.11 %. Within irrigated and between irrigated and un-irrigated plots, most soil physical properties remained similar except saturated hydraulic conductivity (Ks) which was significantly higher under mesquite canopies than in the intercanopy areas. Chloride (Cl-) concentrations below 60 cm depth were higher under creosote than mesquite canopies in irrigated plots indicating deeper leaching of Cl-. Nitrate (NO3 -) concentrations below 20 cm depth under canopy and intercanopy areas were low indicating no leaching of NO3 -.The average SAR to 100 cm depth under shrub canopies was 18.46 ± 2.56 in irrigated plots compared to 2.94 ± 0.79 in the un-irrigated plot. The Na+ content of creosote was eleven times higher un-irrigated than un-irrigated plot and Na+ content of herbaceous vegetation was three times higher in the irrigated than unirrigated. Thus irrigation with high sodium wastewater has exacerbated the soil sodicity and plant Na+ content. Since the majority of mesquite roots are found within 100 cm, and creosote and herbaceous vegetation roots are found within 25 cm from soil surface, a further increase in sodicity may threaten the survival of woody and perennial herbaceous vegetation of the study site.

The experiment was carried out to study the response of Sapota (Achraszapota) crop under drip irrigation and plastic mulch. Three levels of irrigation water applied through drip, ring basin irrigation method in combination with plastic mulch were experimented with five replications on Sapota plants. Reference evapotranspiration was estimated using FAO-56 Penman Monteith approach. The Sapota crop water requirement was estimated using reference evapotranspiration data and crop co-efficient for different crop growth stages. The irrigation water was applied at 60%, 80% and 100% of the crop water requirement. Irrigation intervals were at 2 and 5 days respectively in drip and ring basin irrigation treatments. The water requirement of Sapota crop varies between 2.14 mm (10.71 L) per day per plant in winter season and 6.89 mm (34.44 L) per day per plant in summer season for 100% water requirement treatment at peak growth stage. To investigate the effect of plastic mulch on soil, the physico-chemical analysis of soil was performed for the soil samples collected from three different depths (0-30, 30-60, 60-90 cm). The soil chemical analysis indicated increase in organic carbon, organic matter, humic acid, microbial count, available potassium, available phosphorus, total nitrogen content and C:N ratio for the soil covered with the plastic mulch treatment. The pH and available nitrogen was found to decrease in the soil covered with plastic mulch. The biometric observations (canopy, height, girth, no. of branches) of Sapota plants showed positive influence of the irrigation and plastic mulch treatments on growth of Sapota crop. Due to mulch alone the increase in Sapota yield varied from 7.62% to 41% in different treatments. Yield of Sapota crop was found to increase by 21.05% due to drip in comparison to ring basin irrigation.

System of Rice Intensification (SRI) is a holistic agro-ecological crop management technique seeking alternatives to the high-input oriented agriculture and one among the scientific management tool of allocating irrigation water based on soil and climatic condition to achieve maximum crop production per unit of water applied over a unit area in unit time. System of rice intensification was the main focus technology demonstrated by Water Technology Centre (WTC), Tamil Nadu Agricultural University (TNAU) under Irrigated Agriculture Modernization and Water Bodies Restoration and Management (TN-IAMWARM) Project. In general, an increase in rice productivity under SRI over the conventional system of rice cultivation was observed in all the demonstrations. The widespread adoption of SRI showed increasing trend in yield (from 28.3% in 2007-08 to 32.4% in 2010-11). The results of beneficiary wise analysis indicated that more beneficiaries reaped 40-50% yield increase followed by 20-30% yield increase over conventional. The data obtained from large scale demonstrations clearly indicated that the water requirement was less under SRI (885 mm) as compared to conventional (1180 mm). The demonstration of SRI technologies registered higher grain yield and Water Use Efficiency (WUE) of 6,406 kg ha-1 and 7.31 kg ha-1 mm-1, respectively as compared to conventional (5,284 kg ha-1 and 4.51 kg ha-1 mm-1). The water productivity in SRI was found to be 1,398 as against 2,274 lit. kg-1 in conventional irrigation.