Research Article: Quantitative study on the fate of residual soil nitrate in winter wheat based on a 15N-labeling method

Date Published: February 7, 2017

Publisher: Public Library of Science

Author(s): Jing-Ting Zhang, Zhi-Min Wang, Shuang-Bo Liang, Ying-Hua Zhang, Shun-Li Zhou, Lai-Qing Lu, Run-Zheng Wang, P. Pardha-Saradhi.

http://doi.org/10.1371/journal.pone.0171014

Abstract

A considerable amount of surplus nitrogen (N), which primarily takes the form of nitrate, accumulates in the soil profile after harvesting crops from an intensive production system in the North China Plain. The residual soil nitrate (RSN) is a key factor that is included in the N recommendation algorithm. Quantifying the utilization and losses of RSN is a fundamental necessity for optimizing crop N management, improving N use efficiency, and reducing the impact derived from farmland N losses on the environment. In this study, a 15N-labeling method was introduced to study the fate of the RSN quantitatively during the winter wheat growing season by 15N tracer technique combined with a soil column study. A soil column with a 2 m height was vertically divided into 10 20-cm layers, and the RSN in each layer was individually labeled with a 15N tracer before the wheat was sown. The results indicated that approximately 17.68% of the crop N derived from RSN was located in the 0–2 m soil profile prior to wheat sowing. The wheat recovery proportions of RSN at various layers ranged from 0.21% to 33.46%. The percentages that still remained in the soil profile after the wheat harvest ranged from 47.08% to 75.44%, and 19.46–32.64% of the RSN was unaccounted for. Upward and downward movements in the RSN were observed, and the maximum upward and downward distances were 40 cm and 100 cm, respectively. In general, the 15N-labeling method contributes to a deeper understanding of the fates of the RSN. Considering the low crop recovery of the RSN from deep soil layers, water and N saving practices should be adopted during crop production.

Partial Text

Nitrogen (N) fertilization is a common practice in agricultural production, and it plays a key role in achieving the desired crop yields because soils do not have sufficient N in available forms to support production levels. However, the N use efficiency (NUE) is low in many soils, usually at <50% globally [1]. The apparent NUE may be 30 to 35% for agricultural production in China [2], and it averaged only 33% in relation to cereal grain production [3]. Low N recovery by a crop is associated with N loss by leaching, volatilization, denitrification, and soil erosion. Air contamination by ammonia (NH3), nitrous oxide (N2O) and the other N oxides (NO and NOx) and groundwater contamination by nitrate have been recognized as major concerns for humanity. The application of mineral fertilizers in agriculture is the principal source of those contaminants [4]. There is a great deal of reported evidence to show that agricultural activities are associated with the nonpoint source pollution of groundwater by nitrate [5–8] and the emission of greenhouse gases related to N [9–12].   Source: http://doi.org/10.1371/journal.pone.0171014

 

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