Parallel Session 1: Irrigation Management
THE ROLE OF MESOSCALE DATA NETWORKS IN IRRIGATION SCHEDULING FOR RURAL WATER RESOURCE MANAGEMENT
F G KOCH1, M D BRUSBERG2 and R L ELLIOTT3
1ARC-ISCW, 600 Belvedere St, Arcadia, Private Bag X79, Pretoria, 0001 South Africa
2US Dept of Agriculture, Room 6832 USDA South Bldg, Washington DC 20250-3800, USA
3Oklahoma State University, 116 Agricultural Hall, Stillwater, OK 74078-0497, USA
Water availability is the number one constraint to successful agricultural planning and utilization of natural resources in arid regions. Whenever possible, the desire to irrigate must be tempered by the necessity for conservation of precious water reserves, highlighting the delicate balance between regional food production and water usage. In recent years, the advent of mesoscale (state or provincial level) weather networks has fostered advances in both crop-water usage modeling and operational aspects of irrigation scheduling. Researchers with the Oklahoma Mesonet, a statewide network of more than 110 automated weather stations, have devised a system to provide real-time irrigation scheduling information to farmers based upon "on-farm" rainfall observations and estimates of crop-specific evapotranspiration. In the Republic of South Africa, officials at the Agricultural Research Council's Institute for Soil, Climate, and Water (ARC-ISCW) have formed a partnership with the Oklahoma Mesonet and have begun to expand and upgrade their existing network of automated weather stations. New telecommunication equipment has already yielded positive results toward improving the capacity to retrieve data from remote observation points. In addition, a pilot program to add soil moisture sensors to the current instrument array shows particular promise in the development of new techniques for the management of irrigation reserves. The ultimate goal of the ARC-ISCW system upgrade is to provide timely weather data to researchers and the agricultural community, particularly to the formerly disenfranchised rural farmer, in support of the utilization of the region's fragile environmental resources.
ORANGE RESPONSE AT DIFFERENT PERCENTAGES OF WETTED SOIL
A PANNUNZIO1, J GENOUD2, F COVATTA3, B TEXIDOR3 and A AGULLA4
1Irrigation and Drainage Section, Faculty of Agronomy, Univ of Buenos Aires, Argentina
3Fruit Section, Faculty of Agronomy, University of Buenos Aires;
4Statistics Section, Faculty of Agronomy, University of Luján, Argentina
Trickle Irrigation has improved the production of Washington Navel Orange (Citrus Sinensis L. Obseck) in research conducted in northern Buenos Aires province, Argentina. The work reported here, focused on determining optimum percentage of surface area irrigated in relation to the shaded canopy area. Experiments comparing different areas of coverage in four varieties of orange are summarized. Increasing the irrigated area resulted in greater yields. The magnitude of increase varied with the percent of shaded areas covered by irrigation water. The response was not the same in all varieties. Juice quality results were not consistent with treatment. The relationship between fruit size and wetted area was different for each variety. These data can allow the prospective citrus irrigator to determine the expected yield increase as a result of trickle irrigation, and to determine the type of system to select with respect to the volume of root zone irrigated, depending on varieties in the northern Buenos Aires province.
NITROGEN BALANCES IN TRICKLE IRRIGATED SUGARCANE
P J THORBURN1, I K DART2 and CP BAILLIE2,3
1CSIRO Tropical Agriculture & CRC for Sustainable Sugar Production, 120 Meiers Rd, Indooroopilly Q 4068
2Bundaberg Sugar Ltd and CRC for Sustainable Sugar Production, P O Box 500, Bundaberg Q 4670
3Current address; Canegrowers, P O Box 953, Bundaberg Q 4670, Australia
Trickle irrigation/fertigation can be a more efficient means of applying crop nutrients, so nutrient application rates should be reduced in trickle irrigated crops. However, there is little information on the extent of the possible reduction for trickle irrigated sugarcane, an important irrigated crop in northern Australia. An experiment was established to determine partial balances of applied nitrogen (N) under five different N application rates (0-240 kg/ha/yr N), which spanned that recommended for conventional irrigation systems (160 kg/ha/yr N). N removed in the crop and changes in soil mineral N were determined annually for three crops. In the treatments where N was applied, between 262 and 595 kg/ha of applied N were unaccounted for (lost to the environment) in the balance over the three crops. The losses increased linearly with increasing applied N. However, N sources other than applied fertilizer would have accounted for much of the lost N. In the treatment with no N applied, a total of 239 kg/ha of N was removed in the three crops. The sources of this N would have been net mineralization of soil organic matter and N in irrigation water and rainfall that would have also been present in the other treatments. At application rates of 80-120 kg/ha/yr, losses of fertilizer-derived N were minimal. Additionally, cane yields at these application rates were not significantly lower than in treatments receiving more N. The experiment has shown that productivity can be maintained and N losses to the environment minimized in fertigated sugarcane with a 25-50 % reduction in N fertilizer compared with that applied in conventional systems.
WATER AVAILABILITY AND YIELD RESPONSE TO HIGH-FREQUENCY MICRO-IRRIGATION IN SUNFLOWERS
E SEGAL1, A BEN-GAL1,2 and U SHANI1,2
1Dept of Soil and Water Sciences. Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Israel
2Arava Research and Development, Mobile Post Eilot 88820, Israel
Micro-irrigation enables the increase of irrigation frequency from weeks to daily or even shorter time periods, and enables management of soil water so that conditions of relatively high water content can be maintained. Discrete water application outlets give rise to a non-uniform but well ordered spatial pattern of water distribution. The spatial fluctuations in water content enable plants to concentrate roots in and extract water from zones where water content is higher than field capacity, without the growth inhibiting effects of poor aeration. We hypothesize that augmented mass flow in the soil caused by the high water content found in high-frequency irrigation regimes increases water availability due to higher water potential and hydraulic conductivity.
Sunflower (Helianthus annuus) was grown in two sizes of lysimeters and irrigated with equal quantities of total water given at different frequencies. High-frequency irrigation resulted in greater water consumption and greater yields. Continuous irrigation resulted in even greater growth than irrigation consisting of 8 pulses per day. The positive effect of high-frequency irrigation was found for systems with one-dimensional wetting patterns as in flood or sprinkler methods as well as for systems with radial distribution patterns as with drip irrigation.
IRRIGATION SCHEDULING OF DRIP IRRIGATED POTATOES
J M STEYN1, H F DU PLESSIS1, P FOURIE1 and T ROOS2
1ARC-Roodeplaat, Private Bag X293, Pretoria, 0001 South Africa - E-mail: firstname.lastname@example.org
2Northern Province Dept of Agriculture, P O Box 243, Pietersburg, 0900 South Africa
Worldwide water stress and high temperatures are recognized as the most important factors that hamper the yield and quality of potatoes. In South Africa many potato producers have switched to irrigated potato production. However, yields obtained are still low (average 35 t ha-1), although some producers regularly obtain yields of 60 t ha-1 and higher. The lack of proper irrigation management was identified as a major reason for low yields.
Improved water-use efficiency by effective irrigation scheduling and the use of more efficient irrigation systems are two possible options to improve on water-use efficiency. Drip irrigation is highly efficient, but is not commonly used on potatoes. Over irrigation seems to be a common problem encountered with drip irrigation.
The use of different irrigation scheduling methods on drip irrigated potatoes was investigated in a field trial. The long-term goal was to supply potato producers with new information with regard to drip irrigation management and irrigation scheduling techniques for potatoes.
Three irrigation scheduling methods (producers' method, reference crop evaporation with crop coefficients and Soil Water Balance model) and two irrigation frequencies (pulse and non-pulse irrigation) were evaluated in a field trial.
Total tuber yield was highest for the Soil Water Balance scheduling method. Irrigation frequency influenced yield differently for the different scheduling methods. Tuber relative density was improved by pulse irrigation. The amount of water applied ranged from 463 mm ha-1 for the Eoxf method to 640 mm ha-1 for the producer's scheduling method. Highest water-use efficiencies were obtained for the Eoxf and SWB methods (between 132 and 142 kg ha -1mm-1), while the producer's method consistently had the lowest efficiencies (108 kg ha-1 mm-1).