Evaluation of Peanut Residue Nitrogen Contributions to Wheat in a Conservation Tillage Cropping System.

Cooperative Extension Services throughout the southeastern USA recommend a 20-45 kg N ha-1 credit to row crops planted after peanut (Arachis hypogaea L.), but information is generally not provided regarding the cultural practices or environmental conditions used to make these recommendations. The objective of this study was to quantify N contributions from peanut and cotton (Gossypium hirsutum L.) to wheat (Triticum aestivum L.) in a conservation tillage system. Preliminary results (2016-2017) from Citra and Jay, FL are presented. A split-plot design was used with summer crop (peanut, cotton, or weed-free fallow) as main plots, and mineral N application on wheat (0, 34, 67, 101 kg N ha-1) as subplots. Cotton was included to assess performance of wheat following a non-legume row crop fertilized with mineral N. Wheat was planted four and seven weeks after peanut and cotton harvest in Citra and Jay, respectively. Erratic precipitation delayed planting in Jay. Peanut and cotton accumulated 71-94 kg N ha-1 and 36-56 kg N ha-1, respectively. Soil inorganic N (0-15 cm depth) at wheat planting was higher in plots where peanut was grown compared to cotton and fallow at both sites. However, weekly normalized difference vegetation index (NDVI) readings on wheat were not affected by summer crops at either site suggesting that higher soil inorganic N after peanut did not lead to greater N uptake by wheat. Summer crops did not affect wheat biomass accumulation or grain yields at either site. However, both biomass accumulation and grain yields peaked with 67 kg N ha-1, which is below the recommended rate of 101kg N ha-1 for the region. These preliminary results suggest that peanut N credits recommended for subsequent crops by Cooperative Extension Services are not warranted.