Managing inoculation failure of field pea and chickpea based on spectral responses

Abstract

Pulse crop production is expanding in semiarid regions of the Northern Plains, and depends on successful biological N2-fixation. Inoculation failure, resulting in plant N deficiency and economic crop loss, might be alleviated by remedial N fertilizer application. The experiment was conducted using no-till management at two dryland sites in Montana in 1999 and 2000, where field pea and chickpea were grown in cereal stubble. Shoot biomass, shoot biomass N concentration, seed yield and seed N concentration were measured for uninoculated and inoculated controls and compared with remedial fertilizer N applied 0, 4, 6, and 8 wk after seeding. Spectral reflectance was compared for the inoculated and uninoculated controls. For field pea and chickpea, the critical period for fertilizer N application to prevent yield loss occurred within 6 wk of seeding (P ≤ 0.05). Logistic regression models derived from spectral reflectance had overall accuracies of 84 and 60% for detecting uninoculated control treatments in field pea and chickpea, respectively. The field pea model had a high degree of accuracy 6 wk after seeding, indicating it was capable of assisting a decision to apply remedial N fertilizer. Spectral reflectance provided a window of opportunity of 1 wk to apply remedial N fertilizer to attain full yield potential.