Optimizing Slow-Release Fertilizer Rate for Crop and Soil Productivity in Kimchi Cabbage Cropping Systems in the Highlands of Gangwon Province

Abstract

Slow-release fertilizer (SRF) improves Kimchi cabbage (KC) productivity in the Highlands of Gangwon Province in South Korea; however, optimum rates for the region are not established. This study investigated the optimum and most economical rate of SRF that maximizes KC yield, nutrient uptake and nitrogen use efficiency (NUE) and enhances soil quality in two experiments at the Highland Agriculture Research Institute. Post-harvest soil N (mg kg−1), P2O5 (mg kg−1), K, Ca and Mg (cmolc kg−1), pH (1:5), electrical conductivity (EC; dSm−1) and organic matter (OM; g kg−1) were measured to assess soil quality. Added net returns (ANR) of treatments were evaluated. Recommended N rate (238 kg ha−1) for KC production was the basis for treatment applications. Treatments included no fertilizer control (‘nf’), full N recommendation SRF (SF1), ½ N recommendation SRF (SF0.5), double N recommendation SRF (SF2) and full N recommendation conventional fast fertilizer (FF). Results showed that SF0.5, SF1 and SF2 influenced the highest KC marketable yield in both experiments (66–74 and 42–66 Mg ha−1, respectively). SRF rates between 0.5 and 1 times the N recommendation produced the highest possible linear increases in marketable yield; and the most economical, with ANR > KRW 83 million ha−1 in the first experiment and > KRW 22 million ha−1 in the second. Crop N, P, K, Ca and Mg uptakes were highest among the three SRF rates in both experiments. SF0.5 influenced the highest (91%) NUE in the first experiment; however, it left 8 mg kg−1 N by the end of this experiment compared to the start-up 27.2 mg kg−1 N. Thus, nutrient mining occurred. Soil N increased between 23 and 135 mg kg−1 by SF 1 and 2 in both experiments. Soil EC spiked to 0.6 dSm−1 from the initial level of 0.2 dSm−1 by SF2 in the first experiment. Soil pH, P2O5, K, Ca and Mg levels post-harvest were comparable among treatments in both experiments. SF0.5, 1 and 2 increased soil OM by 7–16% above pre-experimental levels in the second experiment. In conclusion, SRF rates between 0.5 and 1 for KC produced the maximum corresponding KC yield and were the most economical. SRF rates ≤ 0.5 pose risks of nutrient mining, which could jeopardise native soil fertility. SF1 and 2 improved some soil quality indices (N and OM). However, SF2 potentiates risks of soil salinity and large P losses, and it is less economical. Therefore, for holistic sustainability of the cropping system, the optimum SRF rate should lie between 0.5 and 1 N recommendation.