Summer crop rotational effects on carinata nitrogen management in the southeastern USA.

Growers in the United States (US) southeast are often recommended to reduce nitrogen (N) fertilization after peanut (Arachis hypogaea L.) by cooperative Extension services. However, these guidelines are not supported by the scientific literature. An experiment was conducted to quantify N contributions from peanut residues to a subsequent carinata (Brassica carinata) crop. A 3 (history: cotton [Gossypium hirsutum L.], peanut, fallow) × 5 (N rates: 0, 34, 67, 101,134 kg N ha−1) factorial randomized complete block split‐plot design was conducted over four site‐years during the 2018–2019 and 2019–2020 seasons at Jay, FL, USA. Peanut and cotton were planted under strip tillage, whereas carinata was drilled into peanut and cotton residues and weed‐free fallow plots. Although peanut residues accumulated 54–78 kg N ha−1, inorganic N content behind former peanut plots at the 0–15 cm depths, ranged from 6 to 8 and 8 to 11 kg N ha−1 in 2018–2019 and 2019–2020 season, respectively. Cropping history differences for carinata normalized difference vegetation index (NDVI) were pronounced at lower N rates in one out of four site‐years during which NDVI behind former cotton plots was lower than former peanut and fallow plots. Carinata seed yield behind former peanut plots was similar to unfertilized fallow based on four site‐years of data. Nonlinear regression models predicted that N rates required to optimize carinata seed yield following peanut would exceed 134 kg N ha−1 thereby indicating negligible peanut N credits. These results support a growing body of literature that suggests minimal N credits after peanut under humid southeastern US conditions. Core Ideas: Early season carinata NDVI differences behind peanut, cotton, and fallow plots diminished later in the season.Carinata seed yield behind former peanut plots was similar to unfertilized fallow plots across all N rates.Peanut N credits to subsequent crops were not detected. [ABSTRACT FROM AUTHOR]