Study On Improvement Of Cropland Multiple Cropping Potential

The total food production is the function of crop yield,cropland area and multiple cropping frequency.Due to the limited space for the improvement of crop yield and the difficulty in expanding the cropland area,reducing the multiple cropping gap through increasing multiple cropping frequency on the basis of the existing cropland has become the key approach to improving the cropland potential and food production.And the reduction of multiple cropping gap is closely related to the crops.Therefore,combining with multiple cropping frequency and crop growth duration,this study considers the differences of multiple cropping observation with various resolution remote sensing data as well as evaluates the effects of various crop growth durations on multiple cropping gap and its utilization,which can provide scientific basis for improving cropland intensification and safeguarding national food security.Jinxian County,one of the core county of China's grain production in Jiangxi province,was selected as the study region and the local typical multiple cropping was taken as the study object.The MODIS product,GF-1/WFV images and agricultural statistics were used as the main study datasets to explore the improvement potential of multiple cropping.Firstly,the multiple cropping intens ity was estimated.Based on three NDVI datasets with different spatial and temporal resolutions(i.e.MODIS,GF and GF-MODIS),the actual multiple cropping frequencies were extracted by the quadratic difference algorithm,and the uncertainties about multiple cropping observation brought by different temporal and spatial resolution data were explored.Secondly,multiple cropping potential was improved.Based on the GF-MODIS dataset with the highest accuracy,the crop growth durations were extracted by dynamic threshold method,and the remained cropland growth durations were calculated.Four types of crops(i.e.generic crop without regard to crop growth duration,crop with the growth duration of 60 days,crop with the growth duration of 90 days,crop with the shortest growth duration within the pixel)with different growth durations were used to fill,and the effects of cropping system and crop growth duration on multiple cropping potential were explored.The main conclusions of this study are as follows:(1)Most of the correlation coefficients between the fusion images obtained based on STARFM model and its corresponding real image are more than 0.7,which indicates the fusion results are generally good.The initial input high spatial resolution images have a large quantity and homogeneous intervals,which contributes to improving overall fusion accuracy.The fusion image can reflect the time series change advantage of MODIS images as well as the space details distribution advantage of GF-1/WFV images.Therefore,the high spatial-temporal fusion image obtained by the model can not only effectively supply missing time series images of coarse temporal resolution images,but also effectively refine space details of coarse spatial resolution images.(2)Among the multiple cropping observation results based on MODIS,GF and GF-MODIS datasets,the GF-MODIS result performed the best,which not only had the highest spatial accuracy,but also were the closest to the regional value.Single cropping all dominated the study region in the three results.And the proportion of single cropping was descending in MODIS,GF and GF-MODIS results,while the proportions of double cropping and triple cropping are ascending respectively.Therefore,the coarse spatial resolution images can observe the most primary cropping system in the region,while the high spatial resolution images can better identify the multiple cropping practices in the region.(3)The spatial resolution of MODIS images is relatively coarse so that mixed pixels appear obviously in large spatial heterogeneity areas.The interannual rotation system,the frequent interchanges of multiple cropping and the fragmentation of small fields in the study region led to the situation that most MODIS pixels with single cropping system corresponded to multiple cropping system.This indicates that high spatial resolution is the first necessity for mapping the multiple cropping frequency in south China,where the agricultural landscape is extremely fragmented.GF images have a coarse temporal resolution and its information of GF images in the critical growth duration was pretty little.Owing to the complex cropping structure,frequent cloudy/rainy weather and changeable land cover in the study region,the GF-MODIS result was more accurate.This indicates that high temporal resolution is also important to capture multiple cropping practices along with rapid changes in land use.(4)The multiple cropping potential of the study region was triple cropping.When the crop growth duration was not taken into consideration,the multiple cropping gap of all single cropping pixels were 2,the multiple cropping gap of all double cropping pixels were 1,and all triple cropping pixels had no multiple cropping gap.While considering cropland growth duration,the remained cropland growth durations were different in different pixels in spite of the same cropping system.If filled by different types of crops with various growth duration(i.e.generic crop without regard to crop growth duration,crop with the growth duration of 60 days,crop with the growth duration of 90 days,crop with the shortest growth duration within the pixel),the actual multiple cropping gaps were disparate.Furthermore,the actual multiple cropping gap combining with crop growth duration would be far less than theoretically potential multiple cropping gap.(5)Under the three GAP-filling schemes,there was a signif icant difference in the multiple cropping gap of single cropping pixels.However,the multiple cropping gap of double cropping pixels were analogous and the multiple cropping gap of triple cropping pixels were all the same under the three schemes.This indicates that the actual multiple cropping gap is greatly affected by the growth duration of the filling crop.In addition,through reducing the multiple cropping gap reasonably,farmers can strength cropland use intensification sustainably as well as increase food production effectively.Simultaneously,the crop phenology information can also assist crop classification.