基于GIS的长江中游油菜种植区土壤养分及pH状况

摘要

Objective]Rapeseed is one of the most important oil crops in China,and the Yangtze River Valley is a major oilseed rape production region of the country,accounting for over 20% of the world’s mean of annual rapeseed planting area and total rapeseed yield. Farmers in the Yangtze River Valley plant two or three crops a year to form a rotation system. Rapeseed is planted in winter in rotation with rice, cotton or soybeans. As a result of such an intensive cropping system,the farmlands are quickly deprived of soil nutrients and do not have enough time to get recovered in soil fertility. Besides,farmers apply nitrogen (N),phosphorus(P),potassium(K)and boron(B)fertilizers randomly without taking into account the demands of the crops for nutrients. Consequently,the farmlands vary sharply in soil fertility or soil nutrient content from area to area. In this paper an attempt has been made to explore characteristics of the spatial distribution of soil nutrients and pH as affected by crop rotation system and area in the middle reaches of the Yangtze River Valley with the aid of geostatistics and GIS technology,so as to provide some technical support to the efforts of establishing a region-scaled scientific fertilization system for the crop of rapeseed aiming at high yield,high efficiency and eco-environment safety,and realizing sustainable development of the agriculture in the region.[Method]Based on the database of the soil survey and sampling carried out in Hubei,Hunan and Jiangxi provinces during the period of 2013-2014,a total of 5463 soil samples collected from these provinces were analyzed for six soil indices,such as soil organic matter(SOM),total N(TN), available P(AP),available K(AK),available B(AB),and soil pH. With the aid of the GIS platform and Kriging method,the farmlands in these provinces were evaluated and sorted into six grades by referring to the standards for grading of the six indices set for the Second National Soil Survey. In the light of complicate topography and high diversity of soil types,the region was divided into four cropping zones,i.e.,plain area with double cropping system(PⅡ),mountain area with double cropping system(MⅡ),plain area with triple cropping system(PⅢ),and mountain area with triple cropping system(MⅢ).[Result]Results show that SOM,TN,and AP contents were obviously higher in the areas with triple cropping system than in those with double cropping system,which is attributed to the higher multiple cropping index of the former and resultant higher root residue in the field,increasing SOM. Especially in MⅢ,SOM,TN and AP reached as high as 28.8 g kg-1,1.60 g kg-1 and 16.2 mg kg-1,respectively. In terms of SOM,63.3%~76.1% of the farmlands were sorted into Grade Ⅲ;in terms of soil TN,about 90.2% or 11 061 000 hm2 were in Grade Ⅱ(1.5~2.0 g kg-1)and Ⅲ(1.0~1.5 g kg-1);in terms of soil AP,70.2% or up to 8 601 000 hm2 of the farmlands were in Grade Ⅲ(10~20 mg kg-1),and 17.5% and 12.3%,in GradeⅡ and Grade Ⅳ, respectively. Soil AK did not vary much between zones,ranging from 93.6 to 95.8 mg kg-1. However,the region still had 182 000 hm2 of farmlands deficient in K(<50 mg kg-1). Soil AB did not either,ranging from 0.42 to 0.47 mg kg-1. It is quite clear that measures should be taken to raise soil AB content in the region,especially in the areas with triple cropping system,where about 13.6%~20.4% of the farmlands were in Grades Ⅴ and Ⅵ. According to the standard for grading in the Second National Soil Survey,the region was quite high and could be sorted into Grades Ⅱ and Ⅲ in SOM,TN,and AP,but quite low and in Grade Ⅳ in soil AK and AB. Most of the farmlands in the region were around 6.0 in soil pH,but in areas with triple cropping system,a relatively high proportion or about 35.7% of the farmlands varied in the range of 4.5~5.5 in soil pH.[Conclusion]To sum up,in the middle reaches of the Yangtze River Valley,soil nutrient status varies from area to area. Especially in the areas with triple cropping system,quite a large proportion of farmlands need to be raised in soil boron content and ameliorated in soil acidity.%为了掌握长江中游油菜种植区土壤养分状况，在湖北、湖南、江西三个省份调查和取样分析5463份土壤数据的6个指标（土壤有机质、全氮、有效磷、速效钾、有效硼和pH），基于ArcGIS平台，采用Kriging插值法分析4个不同油菜种植区域（二熟制山地区、二熟制平原区、三熟制山地区、三熟制平原区）的土壤养分状况。结果表明，长江中游油菜种植区土壤有机质、全氮和有效磷均处于适宜/丰富的含量水平，基本没有5级和6级水平的有机质、全氮、有效磷分布。从不同区域来看，以上3个养分指标总体均表现为三熟制地区养分含量高于二熟制地区。长江中游仍有1.82×105 hm2区域土壤速效钾处于缺乏的水平（30～50 mg kg-1）。土壤有效硼含量仍有待提高，尤其是在三熟制地区，土壤有效硼缺乏（5级和6级）的比例仍高达13.6%～20.4%。土壤pH多集中在6.0左右，但是三熟制地区仍然有较高比例（约35.7%）的土壤pH处于4.5～5.5。综上所述，长江中游不同种植区域土壤养分性状存在差异，尤其是三熟制地区仍有相当比例需要提高土壤有效硼和改良酸性土壤。