Variability of light interception and radiation use efficiency in maize and soybean

Variability of light interception and its derivatives are poorly understood at the field-scale in maize (Zea mays L.) and soybean [Glyine max (L.) Merr.]. Quantifying variability can provide reliable estimates of field-scale processes and reliable methodology. A field study was conducted during the 2005 growing season in a 31 ha maize and 23 ha soybean field rotated annually near Ames, IA to measure variability of cumulatively intercepted photosynthetically active radiation (CI-PAR) and radiation use efficiency (RUE) by deploying eight line quantum sensors in each field. Cumulative mean PAR interception for soybean was 575 MJ m−2 ending on day of the year (DOY) 249 compared with 687 MJ m−2 in maize ending on DOY 244. Soybean standard error (sX) for a single sensor was 4.48% and with six sensors was 1.83% of the final CI-PAR. Maize sX for a single sensor was 5.29% and with eight sensors was 1.87% of the final CI-PAR. Crop biomass was quantified weekly by collecting four 1 m2 samples. Soybean RUE using all sensors was 1.44 ± 0.06 g MJ PAR−1. The highest CI-PAR from a single sensor had RUE of 1.32 and the lowest was 1.55 g MJ PAR−1. Maize RUE using all sensors was 3.35 ± 0.09. The highest CI-PAR from a single sensor had RUE of 2.87 and the lowest was 3.70 g MJ PAR−1. Reliable transmitted PAR and RUE estimates are obtainable at the field-scale in maize and soybean with four and three sensors, respectively, assuming that crop biomass is accurately measured.

Research highlights▶ Cumulative mean PAR interception for soybean was 575 MJ m−2 and 687 MJ m−2 in maize. ▶ Soybean standard error for a single sensor was 4.48% and with six sensors was 1.83% of the final cumulative intercepted PAR and maize standard error for a single sensor was 5.29% and with eight sensors was 1.87% of the final cumulative intercepted PAR. ▶ Soybean RUE using all sensors was 1.44 ± 0.06 g MJ PAR−1 with a range of 1.32–1.55. ▶ Maize RUE using all sensors was 3.35 ± 0.09 with a range of 2.87–3.70. ▶ Reliable transmitted PAR and RUE estimates are obtainable at the field-scale in maize and soybean with four and three sensors, respectively.