Efficient urea-N and KNO3-N uptake by vegetable plants using fertigation

Vegetable production demands high nitrogen inputs. Fertigation is a means to increase fertilizer-N use by plants. However, the effect of different N sources and doses, and how they relate to the total available N in soils are poorly known. In this study we applied 15N-labeled fertilizers to green pepper in the field using a drip irrigation system during the dry summer. KNO3-N and urea-N were applied at a total of 6, 12 and 18 g plant−1. Our results show that urea was as effective as KNO3 as a N source. The fertilizer-N utilization efficiency was dramatically reduced at higher N doses, from 48% for the 6 g N plant−1 dose to 36% and 26% for the 12 and 18 g N plant−1 doses, respectively. However, the N in plants derived from fertilizer consistently exceeded 60%, indicating high availability of fertilizer-N even at the lowest dose. Negative added nitrogen interactions – the effect of added N on the fate of soil-N – were observed, particularly at high fertilizer-N doses. The fertilizer-N utilization efficiency calculated by the difference method was lower compared with the 15N enrichment method. This clearly indicates luxury N applications and excess N availability brought about by precise localized placement of fertilizer-N that leads to limited uptake of the available soil-N. N leaching risks in the following rain period should therefore be based on both the residual fertilizer-N and the increased amounts of residual soil mineral-N