Daily Crop Evapotranspiration, Crop Coefficient and Energy Balance Components of a Surface-Irrigated Maize Field

Abstract

Irrigation water shortage is affecting many areas of the world. This is the case in Nebraska and in other areas of the USA High Plains. In Nebraska, field maize (Zea mays L.) is the primary irrigated row crop and is one of the most important drivers of the state’s economy. The most typical cropping rotations in Nebraska are continuous maize and maize following soybeans. With the development of ethanol and bio-fuel industries, continuous maize farming practices are increasing. Over-pumping of groundwater for irrigation, coupled with recent drought conditions, and increasing continuous maize production are causing serious concerns about the future availability and sustainability of water resources. Increasing fuel prices, which increases pumping costs should provide an economic incentive for farmers to match irrigation applications to crop water requirements. Accurate determination of actual crop evapotranspiration (ETc) can improve utilization of water resources through welldesigned irrigation management programs. Reliable estimates of ETc are also vital for developing criteria for in-season irrigation management, water allocations, long-term estimates of water supply, water demand and use, design and management of water management infrastructures, and the effect of changes in land use and management on water balances (Irmak and Irmak, 2008). Water shortage is creating a need for growers to produce crops using less water. An option is to use more efficient irrigation systems, which has already occurred to a large extend over the last four decades in the USA Midwestern states by converting from surface irrigation to overhead sprinkler systems. For example, water and labour shortages have already driven growers in Nebraska to switch from surface irrigation to more efficient overhead sprinkler irrigation systems (mainly center pivots). Currently, of the 3.5 million ha of irrigated land, 75% is irrigated using center pivots and 25% still uses surface irrigation, mainly furrow irrigation. Adoption of more efficient drip systems, like subsurface drip irrigation, to irrigate maize, however, has been limited due mainly to their high initial cost and maintenance