Rain water deficit and irrigation demand for row crops in Mississippi Blackland Prairie

Authors: Feng, Gary; OUYANG, YING - US Department Of Agriculture (USDA); Adeli, Ardeshir; Read, John; Jenkins, Johnie

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2017
Publication Date: 3/22/2018
Citation: Feng, G.G., Ouyang, Y., Adeli, A., Read, J.J., Jenkins, J.N. 2018. Rain water deficit and irrigation demand for row crops in Mississippi Blackland Prairie. Soil Science Society of America Journal. 82:423-435. https://doi.org/10.2136/sssaj2017.06.0190.
DOI: https://doi.org/10.2136/sssaj2017.06.0190

Interpretive Summary: Although irrigation has rapidly increased in the Mid-South, rain water deficit, crop water requirement and irrigation demand of soybean, corn and cotton are still poorly understood. Such knowledge can play vital roles in irrigation scheduling, water resources distribution planning and optimization, soil and water conservation and cropping system design. A STELLA dynamic model was developed to workout various daily soil water balance components including runoff, drainage, evapotranspiration (ETc), soil evaporation, rainfall, irrigation and soil water content in root zone. The model was applied to determine when and how much irrigation should be applied to the three major crops over the last ten decades using long-term weather data from 1895 to 2014 in the Blackland Prairie region, east central Mississippi. The average annual rainfall of century long record was 1300 mm. The probability of occurrence of annual rainfall = 1,125 mm is 75%. Mean monthly rainfall over 120 years ranged from 86 to 126 mm, the difference between the lowest and the highest monthly rainfall in the same month varied from 171 to 233 mm in this region. The 120 years were classified as 30 wet years with annual rainfall <25th percentile of the rainfall, 30 dry years with annual rainfall >75th percentile, and 60 normal years with annual rainfall between 25 and 75 percentile. Annual rainfall of wet, normal and dry years ranged from 1465 to 1931 mm, 1129 to 1463 mm and 802 to 1125 mm, respectively. Rainfall during growing season of soybean, corn and cotton accounted for 32%, 40% and 36% of annual rainfall in the normal years, and 27%, 37% and 30% of annual rainfall in the dry years. Mean water requirement of soybean, corn and cotton during entire growing season over 120 years was 542 mm, 569 mm, and 563 mm. Thus the growing season water requirement was not fulfilled by rain water. The STELLA model estimated effective rainfall deficit of 200 mm yr-1, 217 mm yr-1, and 184 mm yr-1 for soybean, corn and cotton, respectively, as averaged over all 120 years. It was revealed that effective rain water deficit of soybean, corn and cotton was 209 mm yr-1; 238 mm yr-1, and 163 mm yr-1 in normal years, while 340 mm yr-1; 324 mm yr-1, and 327 mm yr-1 in dry years. Weekly effective rainfall deficit ranged from 8-26 mm during peak period of high water requirements of the three crops. The three crops required irrigation in all dry years, they did not need irrigation for only 2 out of 60 normal years. The STELLA model determined that 180 mm yr-1; 167 mm yr-1, and 175 mm yr-1should be irrigated to soybean, corn and cotton on average over 120 years. During dry years, soybean, corn and cotton required irrigation as high as 266 mm yr-1; 229 mm yr-1, and 258 mm yr-1. Soybean required irrigation between June 29 and September 7, five and more times of irrigation were needed from R3 to R7 critical water sensitive stage. Corn needed irrigation from June 8 to August 17, peak irrigation requirement occurred from June 8 to July 26. Cotton required irrigation from August 3 to September 9. This study provides a STELLA model and serves as a demonstration for analysis of crop water requirement, rain water deficit and irrigation demand in other region.

Technical Abstract: Irrigated area in the Mid-South has increased greatly, however, there was little irrigation research occurring in the region. Knowledge on rain water surplus and deficit, crop water requirement, and irrigation demand are of great importance to water resources planning, irrigation system design, and irrigation scheduling. This study is the first attempt to determine rain water deficit and irrigation demand for soybean, corn and cotton in the Blackland Prairie of east central Mississippi. A STELLA soil water balance model was developed and long-term weather data (1895-2014) were utilized by the model to investigate characteristics of rain water deficit and determine irrigation demand for the three major crops in the previous 120 years. The long-term analysis showed annual rainfall in excess of 1125 mm was at probability of 75%. Rainfall over 50% frequency ranged from 226 to 412 mm, 283 to 505 mm, and 220 to 472 mm during soybean, corn and cotton growing season, accounted for 30%, 39% and 33% of annual rainfall in the normal and dry years. Total effective rain water deficit of 200 mm, 217 mm, and 184 mm was found during entire growing season for soybean, corn and cotton over 120 years, respectively. During dry years, as more as 340 mm yr-1; 324 mm yr-1, and 327 mm yr-1 effective rain water deficit was determined for soybean, corn and cotton. This study revealed that soybean, corn and cotton did not need irrigation for only 12, 17 and 14 out of 120 years. Average amount of required irrigation was 180 mm yr-1; 167 mm yr-1, and 175 mm yr-1 accordingly. Soybean required irrigation from June 29 to September 7, five and more times of irrigation were needed from R3 to R7 critical water sensitive stage.