Nutrient placement and tillage: A few things to consider
Department of Crop Sciences
Graduate Research Assistant
Department of Crop Sciences
Competition for resources between crop plants is not a good, or bad, phenomenon; rather it is an process. Seed yield is maximized when the competitive relationship is properly balanced to match its environmental parameters. One of the benefits of growing soybean as a crop is soybean plants have tremendous ability to regulate, or compensate, the primary yield components in response to a wide range of plant density. If soybean plants are in a dense plant stand, they will only grow as a single, primary stem and set few pods on main stem nodes only. However, when the plant stand is sparse, soybean plants will grow secondary branches, which cause the plants to ‘bush’, and subsequently pods will also develop on nodes of the secondary branches which can account for significant proportions of the overall seed yield.
Soybean seeding rates in Illinois have typically ranged from 150 to 200% of the number of plants needed at harvest (75,000 to 100,000 plants/acre) to maximize yield. High seeding rates provide ‘insurance’ against conditions that reduce soybean emergence. Historically, the cost of soybean seed was a relatively minor expense to the cropping operation, so the practice of dramatically over-seeding was a good decision from both an agronomic and economic point-of-view. However, soybean seed costs are five-fold greater today than 15 years ago. These higher seed costs have increased interest in reducing seeding rates in order to maximize economic return.
As a background to this research, data were compiled from three different experiments representing 50 site-years of data. These fifty site-years represent many different locations all throughout Illinois, several different growing seasons ranging from 1998 to 2009, multiple row spacings (7.5”, 15”, and 30”), and some different fungicide seed treatment applications. In all cases, data were balanced and interactions were non-significant; therefore, pooling all these data to analyze for yield response to seeding rate was statistically valid. These results show a rather wide variation around an expected yield given any seeding rate in the range of 50,000 to 200,000 seeds/acre over a wide range of conditions. Most importantly, the variation of the data across the whole range of seeding rates was constant. Meaning, there is just as much yield variation at the high seeding rates as the low seeding rates suggesting there is not that much greater ‘insurance’ for starting with higher seeding rates.
Unfortunately, sometimes pests or adverse weather events like hail can reduce plant stands long after establishment. Plant stands that are reduced to similar final harvested plant densities may have much different yield expectations in relation to initial starting densities and the timing of plant reductions. The objective of this current research is to understand the ability of plants to produce seed yield, and compensate extra yield, when competition is reduced by plant removal under different initial density environments, and at different soybean growth stages. This study compares two soybean cultivars (AG3205 and AG3803); sown at four initial seeding rates (60,000; 120,000; 180,000; 240,000), and plant densities are thinned at four soybean growth stages (V3; V6; R1; R4). The current seeding rate recommendation is to plant enough to have a minimum plant density of 100,000 plants per acre to maximize yield. How these different environments affect yield expectations under these scenarios will be discussed.
Soybean yield data for seeding rates ranging from 50,000 to 200,000 seeds per acre collected from 50 site years from 1998 to 2009 throughout Illinois including drilled (7.5”), 15”, and 30” row spacings, and different fungicide seed treatments.