Submitted to: American Society of Agricultural and Biological Engineers
Publication Type: Abstract Only
Publication Acceptance Date: 8/22/2016
Publication Date: N/A
Technical Abstract: Since mid 1990s, there have been a rapid development and application of crop growth models such as APEX (the Agricultural Policy/Environmental eXtender) and RZWQM2 (Root Zone Water Quality Model). Such process-oriented models have been designed to study the interactions of genetypes, weather, soil, and management practices as well as their impact on crop yield and water use efficiency (WUE). Those models have been widely applied to development of soil water and irrigation management practices for optimum yield and water use of many crops in diverse regions. Irrigated area in the mid-south USA has increased steadily in recent years, most regions will face a serious shortage of water for agriculture if improved irrigation techniques and management are not developed and implemented. Soybean is an important crop in the US, approaching the economic values of $40.29 billion, or 30% of the total production value of major field crops in 2014. In the Mid-south, Mississippi’s soybean producers harvested 2.2 million acres with $2.81 billion value, accounting for 51% the total production value of all crops in 2014. Producers eager to learn irrigation management tools and practices, however, little irrigation research has occurred in the region. Therefore, a STELLA decision support tool that we developed, APEX and RZWQM2 model were applied to nine dominant types of soils in Noxubee county of Mississippi for optimizing the use of rain, soil water and irrigation for soybean production. Objectives of this study were to 1) investigate rain water deficit and irrigation demand; 2) determine yield potential (Yp) and the amount, timing and number of irrigations required for achieving the potential; 3) estimate maximum increase in yield by supplemental irrigation and its cost-return. The simulation of STELLA tool using long-term weather data (1895 to 2014) found that soybean did not need irrigation for only 12 years across the 120-yr period in the humid region. The average amount of irrigation water requirement was 180 mm yr-1. Irrigation was required from June 29 to September 7, particularly between critical water sensitive growth stages of R3 to R7, when the crop appeared to require a minimum of five irrigation events. Stages R5 and R6 had the highest probability to irrigate. Grain yield simulated by APEX model under rainfed condition from 2002 to 2014 varied broadly from 2.24 to 6.14 Mg ha-1 across the nine soil types. Simulated Yp without water stress for nine soil types ranged from 4.47 to 6.51 Mg ha-1 over the 13 years. The total WUE of the nine soil types under non-limiting water conditions ranged from 10 to 14 kg ha-1 mm-1, the average irrigation water use efficiency ranged from 2 to 8 kg ha-1 mm-1. The yield gap (Yg, between Yp and rainfed yield) was 1.58, 0.60 and 0.71 Mg ha-1 for dry, normal and wet years, respectively. There is a great potential for yield increase if supplemental irrigation is provided during critical water stress period (R4, R5 and R6). Griffith, Sumter and Demopolis soils had the highest average Yg over 13 years, ranging from 1.37 to 1.60 Mg ha-1. Irrigation can greatly increase soybean yield on those soils. Compared with a rainfed condition, average net return of irrigated soybean increased by $89 per hectare among nine soil types.