Nitrogen use in cereal crops with Pivot Bio ProvenTM inoculant

Abstract

Nitrogen (N) fertilizer is a significant input of many cropping systems. Additionally, N losses pose environmental concerns and represent a loss of resources for the farmer. ProvenTM , an N-fixing bacterial inoculant for cereal crops is expected to fix ~20-33 kg N ha⁻¹ over a growing season. Bacterial inoculants that fix N reduce leaching, denitrification, and volatilization losses compared to fertilizer N, resulting in increased N use efficiency. Biological N fixation in cereal crops is novel and has the potential to increase N efficiency and decrease N loss. The objective of this study was to determine the N benefit provided by ProvenTM and determine the effect of ProvenTM on NUE in cereal crops. Field trials with corn for two years and sorghum for one year evaluated the efficacy of ProvenTM. The corn experiment was a split-plot design with four replications in 2019 and six replications in 2020. The main treatment was N fertilizer applied as urea at planting at 0, 56, 112, and 168 kg N ha⁻¹ in 2019, with an additional 140 and 154 kg N ha⁻¹ in 2020. The sub plot was the presence or absence of ProvenTM. Preplant and post harvest soil sampling to 90 cm depth quantified soil inorganic N (IN). In addition, the soil was sampled during selected growth stages to 30 cm for inorganic N. In-season plant measurements included NDVI, SPAD, and green leaf count. Plant N uptake was determined at R6. At harvest, grain moisture, test weight, and yield were measured. Nitrogen use efficiency was calculated with and without ProvenTM to determine the N benefit from ProvenTM at the different N rates. The sorghum experiment was a split plot design with six replications planted in 2020. The main treatment was N fertilizer applied as urea ammonium nitrate at planting at 0, 34, 67, 101, and 135 kg N ha⁻¹, with and without ProvenTM as the sub plot factor. Grain yield, moisture, test weight, and grain N were collected from the sorghum experiment at harvest. In 2019 there was a trend for greater average corn N uptake with ProvenTM than without at all N rates, with a 10.9 kg N ha⁻¹ benefit of ProvenTM at 0 kg N ha⁻¹, although this difference was not statistically significant. Corn N uptake and yield were significantly affected by the N rate. No significant effects of ProvenTM or an N rate and ProvenTM interaction were found for yield or total plant N for corn in either year ([alpha]= 0.05). Sorghum grain N and yield were significantly affected by N rate but not by ProvenTM or a ProvenTM by N rate interaction. ProvenTM appeared to be a source of 18 kg N ha⁻¹ in 2019. Nitrogen Use Efficiency (NUE) calculations generally followed the expected N rate response. NUE calculations were not significantly affected by ProvenTM in 2019. In 2020, N apparent recovery efficiency (NARE), total N balance index (TNBI), and N recovery efficiency (NRE) were significantly affected by a ProvenTM by N rate interaction. There was little evidence that ProvenTM provided a significant amount of N or increased NUE in corn or sorghum.