Farmland protection and delimitation in the urban fringe considers not only natural factors but also the spatial characters and site factors. Taking Daxing District, Beijing in China as a case study, this paper used landscape ecology and power-law methods to analyze and evaluate farmland loss during the period of 2004-2007 based on the interpretation results of SPOT5 remote sensing images in 2004 and 2007. At the patch level, we selected four landscape indices, namely patch size, shape index, the nearest neighbor distance between farmland and construction land (including residential land and other construction land), and cropping type, to evaluate the risk of farmland loss and establish a farmland site analysis indicator system. The results showed that patch size and shape index have a significant positive correlation with farmland loss, whereas the distance to construction land has a clear negative correlation with farmland loss. As regards cropping type, fallow farmland is much easier for non-agricultural use than cultivated farmland. The relative transition ratio among vegetable land, fallow farmland and cultivated farmland is 1︰5.6︰1. The patch size of lost farmland follows a power-law distribution, indicating that not only small parcels but also large parcels can be lost. Patch size less than 4 ha or more than 15 ha is in high loss risk, between 4 ha and 10 ha in medium loss risk, and larger than 10 ha and less than 15 ha in low risk. Farmland with a more regular shape has a higher likelihood of loss. Patch shape index less than 2.0 is in high loss risk, between 2.0 and 3.0 in medium loss risk, and larger than 3.0 in low risk. Construction land has a varying impact on farmland loss, the residential land effected distance is 1000 m, and that of the other construction land is 2000 m. This analysis showed the relationships between site factors and farmland loss, and the analysis framework can provide support and reference for farmland protection and delimitation of prime farmland in China.
As the climate worsens and the demand for food grows,so does the interest in nanoagriculture.The interaction between plants and nanomaterials(NMs)has been extensively and intensively examined.However,stopping at the outcome of a phenomenon is often insufficient.Therefore,we introduce three important processes of nanoparticleplant interactions:translocation,transformation,and plant metabolism.During the migration of nanoparticles,size and surface electrical properties are the main determining factors.Additionally,the interaction of nanoparticles with cell membranes is another key aspect of research.The transformation of nanoparticles in plants is mainly due to redox substances.The way that nanoparticles affect plant metabolism may be able to shed light on the interaction of nanoparticles with plants.This review adds to the existing knowledge on the design of nanoagrochemicals and summarizes the mechanism of interaction of NMs with plants.In this way,NMs can be used for their beneficial effects and thus contribute to the maintenance of food security and sustainable development.
