Analysis and modeling of dry matter production rate by soybean [Glycine max] community: Curvilinear response to radiation intensity

The linear relationship between the amount of absorbed radiation and dry matter production by crop communities has long been known, and the proportionality constant between them is known as the radiation use efficiency (RUE). To analyze and predict crop production using RUE, the assumption is often made that RUE is not sensitive to radiation intensity and that dry matter production rate (DMPR) is a linear function of radiation intensity.However, there is evidence in opposition to this assumption, including reports of increasing RUE in shade tests, and hyperbolic response of photosynthetic rate to radiation intensity. The following model was developed and used to analyze the response of DMPR and RUE to daily radiation R_S : DMPR = DMPR_max(R_S) * g(α) where DMPR_max (R_S) is the DMPR of a hypothetical soybean community absorbing all radiation, and g(α) represents the effect of radiation absorptivity (α). A hyperbolic curve and a straight line were employed for DMPR_max (R_S) and g(α), respectively. Field experimental data including shade tests were used to determine the parameters for the model. Two sets of parameters were required to cover the entire experimental period. DMPR_max (R_S) had an apparent curvilinear relationship with R_S. The model successfully described dry matter production under successive low radiation conditions, which could not be estimated by a model with RUE insensitive to radiation. (author)