[Research advances in water-fertilizer effect on dry land farmland].

Water and fertilizer are the keys in improving dry land productivity, and the main factors limiting the agricultural development in dry land regions. For our food security and agricultural sustainable development, it' s of significance to bring the effect of water and fertilizer on increasing yield into full play. This paper introduced the design principles of several commonly used methods in researching the effect of water and fertilizer, e.g., irrigation experiment, rainproof-shed experiment and long-term experiment, compared their advantages and disadvantages, and discussed the mechanisms and models of water-fertilizer interaction on dry land farmland, based on the sum-up of the achievements of related qualitative and quantitative researches. It was indicated that under appropriate conditions, there was a positive interaction between water and fertilizer on grain yield, but the effect differed with research method and natural condition. The development trend of the researches on the water-fertilizer effect on dry land farmland in light of the characteristics of agro-ecosystern was also prospected.

[K fertility and K deficit index of aquic brown soil under different fertilization systems].

A 15-year fertilization experiment was conducted on an aquic brown soil to study the variations of its K fertility and the index of K deficit under different fertilization systems. The results indicated that no K application accelerated the depletion of soil K, representing a certain decrease of soil available and slow-release K. Applying K alone could not keep soil K in balance, still having a decrease of soil available and slow-release K. The application of recycled compost combined with appropriate amount of fertilizer K could compensate soil K expenditure to a certain degree, and keep the concentrations of soil available and slow-release K somewhat constant. The statistic analysis on the past years test results showed that the critical values of soil available K in corn- and soybean fields obtained by crossing method were all 73 mg x kg(-1).

[Decomposition process and residual rate of organic materials C and N in soils].

By using nylon mesh bags and sand filter tubes, this paper studied the decomposition of organic materials in the soils at Shenyang and Hailun eco-experimental stations of CAS to investigate the dynamic changes of their organic C and N during decomposition. The results showed that the decomposition process could be divided into two phases, i.e., quick phase and slow phase. The organic N in the materials had an obviously lower decomposition rate than organic C, and thus, had a higher residual rate. The decline of C/N ratio could be also divided into quick and slow phases. After 3-5 years decomposition, the C/N ratio of all test materials tended to be stable. The C/N ratio of the residual organic materials with an initial lower C/N (such as pig manure) approached to that of soil humus, being about 10, which indicated that the humification process was completed, while that of the residual organic materials with an initial higher C/N was about 25, being available to the activities of soil microbes, which would benefit the increase of soil organic matter and the improvement of soil fertility.