Predicting Yield Prospects for the 1989 Kansas Grain Sorghum Crop Based upon Soil Moisture Levels Prior to Planting

Abstract

Because most of the management decisions for growing a dryland crop are made by the time the crop is planted, unpredictable and variable climates present obstacles to obtaining consistently profitable yields. Years of weather extremes further complicate crop management because of producer lack of practical experience under those conditions. Crop growth models provide a method of evaluating yield prospects and examining alternate management practices over a range of possible weather conditions. The lack of rainfall across much of Kansas from the spring of 1988 to the spring of 1989 led to a serious reduction in soil moisture levels by the 1989 planting season. Doubts were raised about the chances of obtaining crop yields capable of returning a profit. Crop growth models are the only means available to answer questions of this type with an accurate assessment of the probabilities. The SORKAMI grain sorghum growth model was used to evaluate yield probabilities at five locations. Soil moisture levels, either measured or estimated, were used along with climatic data for the past 32 years to simulate sorghum yields. These yields were compared to yields simulated with normal soil moisture levels to demonstrate the likely effects of 1989 soil moisture levels at planting on final grain yields. The model showed significant yield reductions for all locations where soil moisture was below normal. Reductions were greatest in years with below average rainfall and least in years with above average rainfall. Yields simulated with 1989 soil moisture data ranged from 16 to 100 percent below those simulated using normal soil moisture inputs. This study demonstrates that regardless of the historical rainfall pattern experienced, low soil moisture levels at planting, such as those experienced in Kansas in 1989, will significantly lower the yield potential of grain sorghum. Contribution No. 91-141-J. From the Kansas Agric. Exp. Sta., Manhattan 66506. ' SORKAM-software program acronym. This content downloaded from 157.55.39.8 on Wed, 30 Nov 2016 05:02:52 UTC All use subject to http://about.jstor.org/terms VOLUME 94, NUMBERS 1-2 59 100 100 90 32 year avg. 90 32 year avg. 80 ..----1988-89 80 ..... 1988-89 70 E 70 ,60 6050 50 4....... 40 40 30 230Cl 20 ... Garden City 20-Colby 0 I1 0 -I JAN MAR MAY JUL SEP NOV JAN MAR JAN MAR MAY JUL SEP NOV JAN MAR