Peanut Yield and Nodulation Response to Inoculation and Starter N-Fertilizer Application.

Nodulation is important for peanut to maximize yield and grade.  Starter fertilizer applications have proven beneficial in numerous agronomic crops, and are commonly used at-planting with peanut in some countries.  But, excessive available N in the soil can be detrimental to nodulation and overall plant nutrient status.  The objective of this study was to determine if nodulation, yield, and grade of peanut would be affected using different combinations of inoculants and N-fertilizer rates at planting.  A randomized complete block design with a 4x4 factorial of commercially available inoculants (untreated, Optimize Lift [liquid], Vault Liquid, and Vault SP [sterile peat]) x N rates (0, 17, 34, and 67 kg N ha^-1) was used with four replications in 2008-2009 on a field previously planted to 25+ consecutive years of corn.  Significant differences among inoculants were observed for yield, with liquid products (2008 = 6150-6160; 2009 = 5800-5840 kg ha^-1) providing superior results over the sterile peat (2008 = 5260; 2009 = 5880 kg ha^-1) in one year and consistently over the control (2008 = 5010; 2009 = 5340 kg ha^-1).  Among N rates, the 67 kg N ha^-1 rate decreased nodulation by 51% compared to applying no N, and also increased total plant biomass by 27% in 2008.  Thus, there was more vegetative tissue as a sink for nutrients, but less nodules providing a source of N during reproductive growth once the initial boost of N was gone.  For this reason, it is not recommended to apply N-fertilizer at-planting with peanut, as it can be an added expense that is only a detriment to production.