Evaluation of Soybean Maturity Group and Planting Date in a Soybean-Rice Rotation on Overall Crop Productivity

Little is known about the effects of soybean (Glycine max L.) management techniques on soil-nitrogen (N) credit development and its impact on the subsequent rice (Oryza sativa L.) crop’s success. This study was conducted to determine how soybean maturity group (MG) and planting date effect overall soybean productivity and its influence on the following rice crop. Various soybean planting dates (optimum and late) and MGs (3.5, 4.7, 5.4, and 5.6) were grown and followed in rotation with a rice crop. Six rates of pre-flood fertilizer-N (0, 44, 89, 134, 179, 224 kg N ha-1) were applied to the rice crop. Soybean grain yield was significantly different amongst MGs in both 2016 (P = 0.0012) and 2017 (P = 0.0004), with the 4.7 relative MG consistently yielding the highest. Soybean total N uptake (TNU) increased with increasing grain yield (P = 0.0167) when all site years were analyzed together. The net N returned to the soil through biomass residue was not significantly influenced by planting date (P = 0.7796) or MG (P = 0.3475). The rice grown in clay soil produced a higher grain yield when following a 5.4 MG soybean (P < 0.0001). On a silt loam soil the interaction of both planting date and MG of the previous soybean crop influenced the maximal grain yield achieved of the rice crop (P < 0.0001) and the N rate needed to achieve 95% relative grain yield (P = 0.0007). At an optimum planting date, soybean MG had little effect on the rice crop but should be selected to achieve the highest soybean grain yield. However, when the soybean crop is planted late, a determinate cultivar should be selected to achieve the highest rice crop TNU, maximal grain yield, and require the lowest rate of fertilizer-N to achieve 95% relative grain yield. Soybean crop management decisions can be highly influential when producing a soybean-rice rotation in Arkansas to maximize overall crop rotation productivity and profitability. ACKNOWLEDGMENTS I would like to extend my sincere appreciation to my academic advisor, Dr. Trenton Roberts, for all time, patience, and friendship shared. You have set an example of excellence as a researcher, mentor, and role model. Thank you for all the opportunities and experiences, I am so grateful for everything you have done for me, taught me, and the shared laughs. Special thanks are extended to the N-STaR family for their guidance and support. The wonderful lab technicians Stephanie Williamson, Carri Scott, and Joe Schafer as well as my fellow graduate students Kyle Hoegenauer, Kelsey Hoegenauer, Chester Grueb, Julia Fryer, Robyn Mulloy, Drew Kirkpatrick, and Bradley Hurst all of whom I could not have done this without. I would also like to thank the undergraduates who helped facilitate my research, especially Trent Frizzell. These people have constantly inspired me to be the best I can be and surrounded me with support and encouragement. I would also like to thank my family for their constant love and support through it all. My mother and role model, Helen Ortel, has taught me how to work hard and never give up. My sister, Laura Ortel, who constantly challenges me to be my best self. And my dad and step mom, Marc and Denise Ortel, who have continually loved and encouraged me. Although previously mentioned, all the hard work put in by Kyle Hoegenauer warrants a special thank you. All the long days downstate, missed classes, and shared ideas have not gone un-noticed. Thank you for going above and beyond to help me complete this research and thesis. This project was made possible by the generous funding from the Arkansas Rice Research and Promotion Board, which I am ever grateful for. This research study has been an adventure I could not have done alone, thank you to everyone who has supported and inspired