基于无人机高光谱遥感的冬小麦全氮含量反演

氮素是作物生长发育必需的营养元素之一,作物的全氮含量是表征其氮素状况的主要指标。田块尺度的冬小麦全氮含量空间分布监测可以辅助其精准定量追肥,减少环境污染。无人机高光谱遥感具有分辨率高、时效性高、成本低等优势,可为作物长势信息反演提供重要数据源。XGBoost(extreme gradient boosting)作为一种新兴集成学习算法,运行效率高,泛化能力强,可以有效的应用于构建冬小麦全氮含量遥感反演模型,预测田块尺度冬小麦全氮含量空间分布。以农业部蒙城砂姜黑土生态环境站内拔节期冬小麦为研究对象,开展以下工作:(1)以低空无人机搭载高光谱成像仪获取冬小麦拔节期冠层成像光谱影像,结合地面采样数据,获取126个样点全氮含量数据;(2)分析拔节期冬小麦冠层光谱特征,并根据Person相关系数分析176个波段的光谱反射率与全氮含量之间的相关性;(3)构建基于XGBoost算法的不同土壤肥力条件下拔节期冬小麦全氮含量无人机高光谱反演模型。结果表明:(1)176个波段(400~1000 nm)的光谱反射率与冬小麦全氮含量之间具有较强的相关性,除了735.5 nm外其他波段光谱反射率与全氮含量之间的相关系数均大于0.5;(2)基于XGBoost算法构建的拔节期冬小麦全氮含量无人机高光谱遥感反演模型具有较高的反演精度(R^(2)=0.76,RMSE=2.68);(3)基于XGBoost算法的冬小麦全氮含量反演模型可以获取不同土壤肥力条件下田块尺度的全氮含量空间分布图,总体上呈现较为显著的空间差异。该研究可为冬小麦精准定量追肥提供一定的科学依据,也为发展无人机高光谱遥感的精准农业应用提供了参考。

The impact of nitrogen amendment and crop growth on dissolved organic carbon in soil solution

Dissolved organic carbon(DOC) is an important component of the terrestrial carbon cycle.However,the sources and controlling factors of DOC in soils remain uncertain.In this study,the effects of nitrogen(N) amendment and crop growth on DOC in soil solution were examined at a maize-wheat rotated field located in the central Sichuan Basin in southwestern China.Nitrogen treatments in this study included 150 kg N ha-1 season-1,200 kg N ha-1 season-1 and the control without any fertilizer application.During the whole experimental period,we observed significant decreases(p<0.05) in DOC concentrations in the sampled soil solutions associated with increase in N inputs at the bare soil plots,but no change in DOC at the plots with crop growth.The estimated average contributions of plantderived DOC were 16%,24% and 32% of total DOC in the summer maize season and 21%,32% and 38% in the winter wheat season along with the gradient of N fertilizer application rates.The results implied thatthe crop growth could play a key role in the soil DOC production,and the N input enhanced DOC production by increasing crop growth.The relationship between the DOC concentrations and the crop root biomass was statistically significant for both the maize and winter wheat seasons.Our observations indicated that crop growth exerted greater influence on the seasonal variability of DOC concentration in soil solutions at the experimental site,which overwhelmed the effect of soil native organic matter decomposition on DOC concentrations in soil solutions.

Assessment of Soil Organic Carbon Stock in the Upper Yangtze River Basin

Soil organic carbon is of great importance to terrestrial ecosystems.Studies on the amount and spatial distribution of soil organic carbon stock in various types of soil can help to better understand the role of soil in the global carbon cycle and provide a scientific basis for the assessment of the magnitude of carbon stored in a given area.Here we present estimates of soil organic carbon stock in soils in the upper reaches of the Yangtze River based on soil types as defined by Chinese Soil Taxonomy and recently compiled into a digital soil database.The results showed that the total soil organic carbon stock of the upper Yangtze River to a depth of 100 cm was 1.452×1013kg.The highest soil organic carbon stock was found in felty soils(2.419×1012kg),followed by dark brown soils(1.269×1012kg),and dark felty soils(1.139×1012kg).Chernozems and irrigation silting soils showed the lowest soil organic carbon stock,mainly due to the small total area of such soils.The soil organic carbon density of these major soil types ranged from 5.6 to 26.1 kg m-2.The average soil organic carbon density of the upper reaches of the Yangtze River was 16.4 kg m-2,which was higher than that of the national average.Soil organic carbon density indicated a distinct decreasing trend from west to east,which corresponds to the pattern of increasing temperature from cold to subtropical.