Assessing Nitrogen Use Efficiency in Sugar Beets Grown Under Variable Fertilizer and Drip Irrigation Rates.

Assessing Nitrogen Use Efficiency in Sugar Beets Grown Under Variable Fertilizer and Drip Irrigation Rates

The unique physiology of sugar beets (beta vulgaris) enables the root crop to search deep within the soil profile for nitrates that would otherwise be unavailable to shallow rooted crops. With the advent of nitrogen management plans (NMP) and increasing efforts to minimize nitrate leaching, the quest for a cropping system that maximizes nitrogen use efficiency (NUE) is at an all-time high. In this study, sugar beets were grown under three different irrigation and fertilizer regimes to determine which agronomic practices offered the greatest NUE. The beets were grown on a clay loam soil in the Central San Joaquin Valley located at the University of California West Side Research and Extension Center (WSREC). The experimental design was a split-plot with three replications of irrigation as the main treatment (100% ET surface-drip, 70% ET surface-drip, and 100% ET flood) and nitrogen rate as the sub-treatment (0, 100, 150, 200 lb N/ac). Soil samples were collected on three different dates throughout the growing season: one pre-planting, one mid-season, and one post-harvest. Samples were analyzed for nitrates using a Seal© AQ2 Auto Discrete Analyzer. In addition, petiole samples were taken at the time of each soil sampling and harvest to measure N uptake. Data from the first and second growing season shows that irrigation did have an effect (P < 0.05) on root nitrate concentrations. Fertilizer rates also had an effect on petiole nitrate concentrations, particularly with the early and mid-season sampling. A highly significant interaction between fertilizer and irrigation treatments was detected (P=.007) during the second growing season. NUE was calculated as a function of several parameters including root and sucrose yield. The greatest NUE, measured as sucrose yield per pounds of N apllied, was observed under the 100 lb/ac fertilizer rate.