Fate of 15N fertilizer applied to trickle-irrigated grapevines.

摘要

15-N enriched ammonium and nitrate fertilizers were applied in the spring through a trickle irrigation system to six Thompson Seedless vines in a vineyard on the West Side of the San Joaquin Valley of California. At fruit harvest, all above-ground plant parts were removed and analysed for 15N. Soil around each vine was also sampled and analysed for 15N in the inorganic and organic N fractions. Spatial patterns of fertilizer N for soil inorganic and organic N were analysed using a median polish technique which indicated large variability with respect to direction, distance, and depth. There was a greater tendency for the fertilizer N from NH4 to be located directly beneath emitters than that from the NO3. N from the NH4 application penetrated to only the 150-cm depth, whereas some N from the NO3 application reached 210-240 cm. Most of the organic fertilizer N for both NO3 and NH4 applications was in the top 60 cm of soil where the vine roots were likely of greatest density. Overall recovery of fertilizer N was also quite variable, probably due to variability in soil physical properties and uneven surface application of water and fertilizer due to local surface ponding. Although not statistically significant, uptake of fertilizer N by above-groundplant components was slightly higher for the NH4 application (24.2% of applied N) than for the NO3 application (21.5%). Soil organic N had significantly more N from NH4 (19% of applied N) than from NO3 (13%). This probably occurred due to longer residence time of N from NH4 within the top 60 cm, where the bulk of roots and microbial activity existed, than for NO3. Overall, about 67-79% of the fertilizer N applied in spring remained in the soil at harvest, and the vines took up the rest. There was no indication of significant N leaching below 2.4 m or denitrification of fertilizer N for the trickle-irrigated vines during the growing season.