Mineral nitrogen dynamics in soil during sugar beet and winter wheat crop growth

Abstract

Nitrogen (N) is the crop nutrient which most directly influences the production and quality of sugar beet ( Beta vulgaris subsp. vulgaris L., SB) root. It is therefore important to accurately estimate the amount of N to be supplied to the crop. Past research has focused on predicting the amount of N available at the beginning of the growth season, whereas the amount of N in soil during crop growth is less considered. The aim of this work was to improve our knowledge of N availability for SB during the crop growth season, by monitoring the mineral N content in the cultivated soil layer in the spring-early summer period. The N dynamics in soil under rain-fed SB was compared to that under winter wheat ( Triticum aestivum L., WW). Three experiments were carried out in three locations of the Po Valley, North Eastern Italy, on silty clay (San Prospero, Modena, 2004), silty clay loam (Rovigo, 2006), and loam (Bovolone, Verona, 2008) soils. The experimental design was a strip-plot, with crops (SB, WW) in the main plots and three N rates in the sub-plots (0, 40 and 80 kg N ha −1 for SB and 80, 120 and 200 kg N ha −1 for WW, at San Prospero; 0, 60 and 120 kg N ha −1 for both crops, at Rovigo and Bovolone). Increasing N rates did not influence crop N removal, or only slightly increased it. In the period of simultaneous crop growth, in the three locations, the mean mineral N content of the soil samples under SB was on average more than twice that under WW, even though crop N removal by SB was on average higher than that of WW (more than twice, at Rovigo, and up to three times, at Bovolone). Our results suggest that N recommendations should be formulated by taking into account, besides the usually considered N balance terms, the soil N availability linked to specific crop management and growth patterns.