Summer fallow increases loss of residual nitrogen fertilizer in dryland of the Loess Plateau: a 15 N-labeled method

Abstract

Summer fallow is very common in dryland agriculture to conserve rainwater and replenish soil fertility. However, bare land and intensive rainfall during summer fallow might result in a potential risk of N loss. We used a ¹⁵N-labelling method to study the loss of residual N fertilizer during summer fallow and its use by next wheat in the Loess Plateau. Our study included three treatments: without the addition of N (N₀W₀), with the addition of 50 kg ha⁻¹ N (NW₀) and with the addition of 50 kg ha⁻¹ N plus 35% more water (NW). The N fertilizer (K¹⁵NO₃) in solution was injected into the soil at a depth of 35 cm of the polyvinyl chloride (PVC) columns in field. The fates of ¹⁵N were followed after summer fallow and in the next season's wheat (Triticum aestivum L.). The summer fallow of this study was a dry summer; however, fertilizer ¹⁵N was still leached down to 40-cm depth for the NW₀ treatment; and for the NW treatment, the peak of ¹⁵N fertilizer was approximately 20 cm deeper. After summer fallow, the loss of the initially applied ¹⁵N was 26% in the soil profile for the NW₀ treatment; and for the NW treatment, it increased to 37%. Soil ¹⁵N abundance in 0–20 cm of the NW₀ and NW treatments was higher than the N₀W₀ treatment, indicating the upward movement of ¹⁵N in summer fallow. After the next wheat harvest, ¹⁵N uptake by wheat in the NW treatment decreased from 21.0 to 18.6% compared to the NW₀ treatment. High rainfall during summer fallow increased residual N loss during summer fallow but decreased its use by the next crop.

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