长期覆膜会降低黄土高原土壤有机碳储量吗？

Does long-term plastic film mulching really decrease sequestration of organic carbon in soil in the Loess Plateau?《长期覆膜会降低黄土高原土壤有机碳储量吗？》2017.4.10兰州大学生命学院李凤民投稿EJA

Highlights

•Plastic film mulching showed more positive impact than without mulching on SOC.

•Plastic film mulching increased productivity alleviated the risk of SOC loss.

•When aridity index between 0.15–0.4, SOC more likely to benefit from mulching.干旱指数0.15-0.4的地区，覆膜更有利于SOC积累。

Abstract

Plastic film mulching (PM) is used extensively in China to increase the productivity of food crops, especially in the arid and semi-arid regions, although a recent concern is whether the practice decreases soil organic carbon (SOC). 覆膜在中国广泛使用以增加粮食产量，尤其是干旱和半干旱区域，最近覆膜是否会降低土壤有机碳引起关注。

A process-based biogeochemical model applied in the Loess Plateau, where PM is widespread, examined the status of SOC over 30 years of maize cultivation with PM. 用基于过程的生物地球化学模型模拟黄土高原玉米覆膜30年的SOC变化。

The model explained 96% of the observed variance in SOC. 模型可解释96%的实测变异。

The root mean square error was 0.39 g kg−1, the mean absolute error was 0.32 g kg−1, and the bias value from the SOC simulation was −0.006 g kg−1. 均方根误差、平均绝对误差和偏差。

The model’s projections showed that PM has no significant impact on the overall average content of SOC across the entire study area compared to the fields without mulching, or control (CK), assuming that 5% of the crop residue was ploughed back into soil. 模型结果表明，和CK相比，覆膜对整个区域的SOC无显著影响。

However, based on individual simulation points in the 0–50 cm soil profile after 30 years of PM, 59.29% of the points, mainly on the western parts of the Loess Plateau, showed significantly higher SOC than that in CK, 8.30% showed significantly lower, and 32.41%, mainly on the south-eastern part of the Plateau, showed no significant difference between sites with PM and without it. 但单点模拟表明，覆膜30年后59%（主要位于黄土高原西部）0-50cm土壤SOC显著高于CK，8%显著降低，32%（主要位于黄土高原东南部）和CK无显著差异。

Mulching increased the biomass, rhizodeposition, and the speed of turnover of SOC significantly, compared to the corresponding values in CK. 和CK相比，覆膜显著增加了生物量、根际沉积和SOC周转速度。

High biomass in PM led to more carbon (C) being retained in soil and lowered the depletion of SOC. 高生物量导致更多的C保持在土壤中，降低了SOC消耗。

Ploughing the crop residues back into soil increased SOC, the greater the percentage of residue thus returned to soil, the higher the SOC. 秸秆翻压还田增加SOC，还田比例越高，SOC越高。

For a given residue return percentage, PM could increase more SOC than the CK. 在固定的还田比例下，覆膜增加SOC高于CK。

At 15%, which is the current average residue return ratio in the Loess Plateau, SOC levels remained stable or even increased in 77% of the study area if it adopted PM; in CK, the corresponding figure was only 63%. 黄土高原目前平均秸秆还田比例为15%，在该水平下覆膜使77%（而CK使63%）的研究地区SOC保持稳定或增加。

In regions such as the Loess Plateau where biomass is in great demand as a fuel or animal feed, PM provides greater biomass, which also means that more of it is available to be returned to soil—PM thus promotes the sequestration of SOC. 黄土高原秸秆生物量常用于燃料和饲草，覆膜可提高生物量，这意味着更多生物量还田，因此覆膜可促进SOC积累。