How Biochar Affects Nitrogen Assimilation and Dynamics by Interacting Soil and Plant Enzymatic Activities: Quantitative Assessment of 2 Years Potted Study in a Rapeseed-Soil System.

Zaid Khan,Junguo Bi,Lijun Luo,Kangkang Zhang,Liyong Hu,Mohammad Nauman Khan,Kunmiao Zhu

doi:10.3389/fpls.2022.853449

Zaid Khan, Junguo Bi + Show 5 more

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https://doi.org/10.3389/fpls.2022.853449

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Abstract

The amendment of biochar has been proposed to improve soil fertility and crop yield. However, consolidated information lacks explaining the role of biochar on soil and plant enzymatic activities involved in nutrients cycling in soil and accumulation in plants improving utilization of applied inorganic fertilizer and crop growth. In the current study, we evaluated the integral effects of biochar levels (B0:0, B15:15, B3:30, and B60:60 t ha–1) and nitrogen fertilizer levels (N0:0, N75:75, N225:225, and N450:450 kg ha–1) on soil physicochemical properties, enzymatic activities, nitrogen use efficiency (NUE) and grain yield of rapeseed for 2 years in the pots during 2020 and 2021. The findings revealed that compared to control (B0 + N0), a combination of B30 + N450 increased soil urease activity by 73 and 75%, and B60 + N450 increased activities of soil catalase by 17 and 16%, and B60 + N225 increased alkaline phosphatase by 17 and 19%, respectively, in the first and second year. Moreover, a single application of high nitrogen at 450 kg ha–1 reduced the activities of plant nitrogen metabolism-related enzymes, however; the integration of biochar at 30 t ha–1 compensated the high nitrogen toxicity and improved the activities of nitrate reductase (NR), nitrite reductase NIR, glutamate synthase (GS) and glutamine synthetase (GOGAT) at seedling stage (SS) and flowering stage (FS) in both years. The integration of biochar at 30 t ha–1 with nitrogen at 450 kg ha–1 induced synergetic effects on rapeseed growth through sorption of excessive nitrogen in soil and significantly improved the plant height up to 11 and 18%, pods plant–1 39 and 32% and grain yield plant–1 54 and 64%, respectively, during the first and second year. Moreover, biochar at 15 t ha–1 along with nitrogen at 225 kg ha–1 resulted in the highest NUE of 29% in both years suggesting that biochar can also offset the deficiency of lower nitrogen. This study highlighted the ameliorative effect of biochar suppressing high nitrogen toxicity and decreasing lower nitrogen deficiency effects on rapeseed growth by improving nitrogen use efficiency via enhancing soil conditions, enzymatic activities and soil nitrogen utilization potential and thus improving rapeseed growth and yield.

Highlights

In the recent past, global food production has greatly increased with applying chemical nitrogen (N) fertilizers
In the range of 0–60 t ha−1 biochar application, the results showed that soil chemical and physical properties were improved more significantly under biochar application at 30–60 t ha−1 in the first season; in the second season, the higher biochar at 60 t ha−1 reduced the availability of available forms of nitrogen (NO−3 and NH+4 ) compared to pots amended with biochar 30 t ha−1
In the first season of rapeseed, biochar application treatment B60 + N225 significantly increased soil pH by 12%, soil organic carbon (SOC) by 359% in B60 + N225, NO−3 by 198% in B30 + N450, NH+4 by 134% in B60 + N450, TP by 68% in B60 + N450 and AK by 64% in B60 + N225 treatment compared to control (B0 + N0) (Table 2)

Summary

Introduction

Global food production has greatly increased with applying chemical nitrogen (N) fertilizers. In China, a 70% increase in crop production has been recorded with a threefold increase in chemical N fertilizers since 1980 (Guo et al, 2010). Lower nitrogen use efficiency and poor soil fertility in many developing countries accelerate food insecurity to meet the food demand of the world’s growing population. The seed production of rapeseed per unit N applied is equal to the half of cereals, which ascribe it as a lower N-efficient crop (Sylvester-Bradley and Kindred, 2009). It is imperative to apply nitrogen fertilizers along with organic amendments to prevent nitrogen fertilizer loss, lower the economic cost of production, alleviate environmental pollution and improve nitrogen use efficiency (NUE) and yield of rapeseed on a sustainable basis

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