Developing Guidelines for Replanting Grain Sorghum: II. Improved Methods of Simulating Caryopsis Weight and Tiller Number

Abstract

Enhancing the yield prediction accuracy of SORKAM, a growth model for sorghum [Sorghum bicolor(L.) Moench], requires improving the simulation of grain growth and the relationship between tiller number and minimum temperature. A new grain growth equation, developed from 1990 data collected at Manhattan, KS, relates grain‐filling rate to the rate of change of plant dry matter per caryopsis during the effective filling period. Additional functions are specified for the lag and leveling‐off phases of caryopsis growth, resulting in a new submodel, which was tested against data from Kansas and two Australian sites. The tiller number calculation was revised using three years of Manhattan data. After incorporating the new submodels, SORKAM outputs were compared with observed yields and yield components in three Kansas regions. The R2 values for yield increased from 0.27, 0.46, and 0.79 to 0.76, 0.69, and 0.90 for eastern, central, and western Kansas, respectively. Caryopsis weight comparisons showed that the revised model accounted for 48 to 72% of observed variability, up from 15 to 57% for the original model. Tiller number predictions also improved, although modestly.

Seeding Practices, Cultivar Maturity, and Irrigation Effects on Simulated Grain Sorghum Yield

“…Also, common biotic pressures, such as weed competition, insect injury, soil fertility, or planting moisture effects on emergence and stand uniformity, are not considered by SORKAM when simulating crop growth and yield and therefore may have contributed to these yield overestimates. Based on this and related work (Heiniger et al, 1997; Xie et al, 2001), we determined that SORKAM simulates crop growth and grain yields throughout a broad range of climate stress conditions and cultural practices including hybrid characteristics.…”

Genotype and Environment Effects on Dynamics of Harvest Index during Grain Filling in Sorghum

“…The variations in slope of linear increase in HI (0.014–0.025 d −1 ) and time at cessation of that increase (0.61–0.85) due to effects of genotype (i.e., maturity) and environment (i.e., temperature) in this set of experiments were largely explained by variations in assimilation during grain filling and remobilization of preanthesis assimilate. Recent studies (Heiniger et al, 1997) have developed simple methods for predicting grain growth that are based on considerations of supply of, and demand for, assimilate during grain filling. In this method, remobilization and HI are emergent consequences of the balance between supply and demand.…”

Modeled El Niño‐Southern Oscillation Effects on Grain Sorghum under Varying Irrigation Strategies and Cultural Practices

“…Inferring alternative cultural practice effects on grain sorghum growth, yield, and water use efficiency is critically dependent on the validity of SORKAM to simulate plant responses under variable growing conditions. In addition to numerous reports validating SORKAM (Rosenthal and Gerik, 1990;Heiniger et al, 1997;Xie et al, 2001), Baumhardt and Howell (2006) also validated SORKAM calculated grain sorghum yields for the Pullman soil at Bushland using location recorded weather and actual cropping conditions (e.g., planting date). Their simulated grain yields averaged ~4% more than observed yields (r 2 = 0.70, RMSE = 903.5 kg ha -1 ) of the corresponding similarly planted late-and medium-maturity hybrids from a 1984-1998 wheat-sorghum-fallow rotation study (Jones and Popham, 1997).…”