Maize is the main crop in western Jilin Province. Water is a major constraint on maize production. How to effectively utilize the limited water resources to ensure maize production needs to be solved urgently. Formerly the irrigation water was as the key indicator to measure the water consumption during crop production. However, it neglected the consumption of soil water and water pollution. Water footprint connects the physical and virtual forms of water, which covers blue water, green water and gray water. It can truly reflect water demand and its sources. Recently, the most studies regarding water footprint are to investigate the water footprints of consumer products and products trade between regions or countries. Whereas researching the water footprint in the production process is little.
According to the field experiments of maize, we explore the impact of different sowing dates on the source and consumption of green water, to determine the satisfactory degree of precipitation on maize growth and achieve the optimum matching relationship between sowing date and precipitation and temperature in maize growing season under the background of global warming. Results of 3-years experiments showed that either in the rainy year of 2005, or in the drought year of 2006 and extreme drought year of 2007, the green water consumption was the main water requirement in the maize production, which took the ratio over 98%. The green water footprint of maize production was mainly the effective precipitation in 2005 and soil water in 2006 and 2007. Effective precipitation in the green water footprint of the first three sowing dates accounted for 80.4%, 87.6% and 89.1% during 2005, 41.3%, 43.3% and 46.6% during 2006, and 34.2%, 35.5% and 36.5% during 2007, respectively. It implied that late sowing could gain more precipitation and higher temperature in maize growing stages. Water and thermal resources matched well, which was beneficial to maize production. Moreover, the effective precipitation took large ratio in the green water footprint. Therefore, late sowing is useful to enhance the rate of rainwater utilization, keep the soil water balance and promote the agricultural sustainable development.
In the current studies of virtual water and water footprint, the basically method was statistics calculation and analysis. However the statistics do not reflect the differences within the region, the practical production and the water consumption. Field experiments, from the microscopic view, can break through the limitations that the studies of virtual water, water footprint are only from the view of macro- and meso-scale. This paper investigates the regularity of the green water footprint of maize in different sowing dates under the same conditions of soil and cropland management, and provides the basis for the further subdivision of green water and the improvement of green water utilization.