I. Evaluation of seed treatments and nitrogen on soybean nodulation and grain yield.

Abstract

Soybeans (Glycine max) are known to form symbiotic relationships with soil microbes and conduct biological nitrogen fixation (BNF). However, only 50-60% of the crop's nitrogen (N) requirement is met through this process. Previous work has suggested that the use of seed inoculants and molybdenum (Mo) can improve the plant's ability to fix nitrogen (N) thus potentially improving grain yield. Therefore, the objective of this study was to evaluate different seed treatments as well as fertilizer N applications and their effect on soybean nodulation, tissue N concentration, grain yield, and protein and oil concentration. The seed treatments evaluated include a standard inoculant rate, double inoculant rate, Mo and combinations of all products in addition to an at-planting N application of 45 kg N ha-1. It was noted that nodule counts were improved at most locations when a seed treatment was applied. Alternatively, nodule counts commonly significantly decreased when N was applied at planting. Significant increases in grain yield were observed in 4 of the 7 site years when inoculants were used, particularly in higher yielding environments. Similar findings were noted with seed protein. Although, applying N at planting commonly decreased nodule counts, grain yield was not largely impacted. In conclusion, higher rates of seed inoculants can increase plant nodule counts and boost grain yield in certain environments and perhaps provide additional profitability for producers.

Winter wheat (Triticum aestivum) is extensively grown throughout the state of Oklahoma. Producers commonly apply nitrogen (N) and phosphorus (P) fertilizers each season; however, pre-plant N and P interactions are not well understood. The objective of this study was to evaluate the effects of N, P and their interactions on winter wheat grain yield, grain N, and N uptake. To evaluate these effects, Experiment 702 was established in 1996 at the Cimarron Valley Research Station near Perkins, OK. This experiment was designed as a randomized complete block design with a complete factorial treatment structure consisting of four pre-plant N rates (0, 56, 112, 168 kg ha-1) and three P rates (0, 14.8, 29.6 kg P ha-1). Twenty years of yield data from this trial were analyzed in addition to grain N and N uptake when data was available. Analysis was first conducted separately for each year and then under different environmental grain yield and in-season precipitation (ISP) parameters. Results indicated that N and P interactions were more common among high yielding environments.