Relationships between combined and individual field crops’ biomass and planting density

Abstract

ContextField crops, irrigated and rain-fed, constitute the majority of cropland worldwide. An important agricultural variable determining their biomass production is planting density. ObjectiveThe objective of the study was to explore the relationships between the biomass (dry matter) and planting density for either major individual field crops or all field crops, combined, and to suggest empirical models describing them. MethodsThis article describes a meta-analysis of the literature data on biomass per unit area or plant versus planting density for 8 major field crops: 4 cereals (corn, wheat, sorghum, and pearl millet) and 4 forbs (soybean, sunflower, rapeseed, and buckwheat). ResultsWhen data from all 8 field crops are combined, it seems that areal biomass production is practically independent of planting density, apparently obeying the constant final yield hypothesis. By contrast, analyzing each of the 8 crops separately, there is a clear rising trend of areal biomass with increasing planting density, with a mean intraspecific allometric exponent of about 0.25, and individual exponents that increase systematically with a decrease in the average planting density. ConclusionsApplying a planting density-dependent allometric exponent improves the predictability of the interspecific biomass–planting density relationship for field crops. A bounding, exponential model that describes the biomass–planting density relationship in the agricultural range of 1–1000 plants per m2 better than power-law allometric equations is proposed. Although the biological meaning of a derived generic expression relating areal biomass to single-plant biomass for field crops is not clear, the deviation of the outliers probably reflects already utilized or remaining breeding potential for increased areal biomass and agricultural yields. ImplicationsA good understanding, quantification, and prediction of the biomass–planting density relationship is essential for both plant breeding and management of crop production. Plant breeders need this knowledge to choose between strategies for either increasing the single-plant biomass or increasing the plants’ tolerance to high planting density. Agronomists and extensionists need it to optimize planting density for a particular variety under given environmental and agricultural (GxExM) conditions.