Abstract: Under the support of Potash and Phosphate Institute of Canada and Natural Science Foundation of China, with the close co-operation of nine research institutions headed by Institute of Agricultural Resources and Regional Planning of Chinese Academy of Agricultural Sciences, following researches were conducted: the potassium status and potassium supply capacity of main soil types in north China; the potassium transformation characteristics in crop-soil system under main cropping systems in north China; the status of potassium and its change trend in different areas and soils and the conditions and technical measures of potash application effectively in varied areas and crops. Twenty five site-fixed field trials were established to study the circulation of potassium within crop-soil system selecting typical soil types and cropping systems. Soil samples were collected from each trial location to study the existing forms of soil potassium, the plant availability of each form of soil potassium, the capacity of adsorption and fixation of soil to applied potassium, the release characteristics of native soil potassium and the dynamics of adsorption to applied potassium and its release. The potassium circulation characteristics and related adjustment and control technology were also studied within soil-crop system in main cropping systems of 25 field trial locations. At the same time, a great deal of field experiments and demonstrations were set up in chief provinces and cities mainly in northeast and northern China, the potassium requirement characteristics, the response to potash application, the condition and technology of efficient potash application were studied systematically in corn, wheat, paddy rice and vegetables. More than 8 500 plough layer soil samples were collected from main soil types of different provinces and regions to study the soil potassium status and supply power. A complete and comprehensive evaluation was put forward to the soil potassium status and supply power in north China. Large economic benefit was gained by extension of this technology. And this technology was prized as National Second Award of Science and Technology Progress in 2000.

Key words: Form of potassium , North China soil , Potassium supply capacity , Potash application technology , Cropping system , Potassium requirement characteristics of crop