Apparent fertilizer nitrogen recovery and residual soil nitrate under continuous potato cropping: Effect of N fertilization rate and timing

Abstract

Adequate nitrogen (N) fertilization is crucial to optimize yield and quality of potato and also to minimize N environmental losses. Effects of rates and timing of N fertilizer on residual soil nitrate (RSN) [NO3-N, 0-0.7 m], soil solution nitrate (SWN) concentrations and apparent fertilizer nitrogen recovery (Nrec) by potato (Solanum tuberosum L.) tubers were evaluated from 1999 to 2001. Two sites representative of the management zones (MZ) previously delineated by apparent soil electrical conductivity and differing in soil water availability were selected. The MZ differed primarily with depth to a clayey substratum, with average values of 1.06 m and 1.34 m in the shallow MZ (SMZ) and in the deep MZ (DMZ), respectively. At each site, a trial with 21 treatments including five rates of ammonium nitrate (0–200 kg N ha-1 in 1999; 0–240 kg N ha-1 in 2000 and 2001) was conducted. Each N rate was applied according to five application timings (100, 75, 50, 25 or 0% of N applied at planting with the remainder at hilling). The effects of N rates and timing on Nrec, RSN and SWN sometimes differed between sites. The Nrec was less responsive to N rates and timing in the SMZ site compared with the DMZ site. Application of the same rate of fertilizer N generally resulted in higher values of RSN at harvest in the SMZ site compared with the DMZ site. Measured SWN was higher in the DMZ than in the SMZ on several occasions in 1999 and 2001, indicating greater nitrate (NO3) leaching in the DMZ site compared with the SMZ site. Different site-specific N management regimes could thus be used at the two sites to improve N use efficiency and to limit the risk of NO3 leaching. However, the temporal variability in the measured parameters, influenced mainly by climatic conditions, was greater than the spatial N variability and this emphasizes the fact that a dynamic model of the N status based on the soil and/or the plant is a prerequisite to help growers to adjust the N fertilizer application within fields and seasons. Key words: Solanum tuberosum, apparent soil electrical conductivity, suction lysimeter