[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.

[A conjecture on the fertilizer recovery measurement by field experiment].

The measurement of fertilizer recovery either by isotope tracer technique or by field experiment with plots fertilized and unfertilized, both were suspected unreliable and reasons were discussed. Based on some reasonable presumptions, an alternative way of estimating fertilizer recovery by field trials was proposed in this paper, but further examination on it's reliability is needed.

[Research on mineralization process of organic phosphorus in black soil in Northeast China].

Buried bag and incubation experiments were conducted to study mineralization process of organic phosphorus in black soil in Northeast China under different time sequences. The results showed that both the content and mineralized velocity of organic P decreased gradually as time went on, the cumulative mineralized rate increased step by step, whether it was used by the method of incubation or buried bag. Under incubation, two treatments' mineralized velocity reached the maximum at first month (31.67, 38.75 mg x kg(-1) x month(-1), respectively), and their cumulative mineralized rate and mineralized velocity at six months were 7.94%, 13.26 mg x kg(-1) x month(-1) and 9.24%, 17.99 mg x kg(-1) x month(-1), respectively. Under buried bag, the mineralized velocity of five treatments all reached the maximum at first year (55.67, 55.65, 49.60, 19.71, 22.52 mg x kg(-1) month(-1), respectively), and the cumulative mineralized rate and mineralized velocity of maize root and wheat root treatments at three years both were approximately 50% and 35 mg x kg(-1) x month(-1), which were higher than those under soybean root andgrass root treatments. From two methods of studies on the mineralization process of organic P, it could be seen that the original content of organic P influenced its mineralized rate and mineralized velocity: the higher of the original content of organic P, the higher of its mineralized rate and mineralized velocity.

[Comprehensive evaluation of cultivated black soil fertility].

Black soil is one of the main soil types in northeastern China, and is a valuable soil resource of this country. Based on the analysis of the physical and chemical properties of soil samples collected from the north-south transaction of black soil, the index system of black soil fertility was established, the fertility level was evaluated and classified by Fuzzy and Factor Analysis, and the fertility map of black soil zone was drawn with GIS software ArcInfo. It was found that the humus layer in black soil region was thick in north and thin in south, which was due to the climatic condition and soil-forming process. The soil fertility level was high in east and low in west. From north to south, it was decreased in the order of central part > northern part > south part. In most part of this region, soil fertility level was medium, and the area accounted for 73.6% of the black soil area.

[Research advance in soil organic phosphorus].

Soil organic phosphorus (P) plays an important role in the material cycling in agro-ecosystem, and its research is vital for understanding the characteristics of P cycle in soil-plant system. This paper summed up the latest research achievements at home and abroad about soil organic P content and its affecting factors, soil organic P forms, their fractionation and determination methods, effects of fertilization on soil organic P forms, and mineralization of soil organic P. The existing problems in soil organic P study and its hotspots in future were also discussed.

[Relationships between water-stable aggregates and nutrient status in black soil after reclamation].

The study on the dynamics of water-stable aggregates in black soil after reclamation and its relation to soil nutrient status showed that the contents of soil water-stable aggregates decreased significantly at initial reclamation stage, but the declining became small with time. > 0.25 mm water-stable aggregates had a significant correlation with soil organic C, total N, total P and CEC, the correlation coefficients being 0.7625, 0.6794, 0.6084 and 0.8134, respectively, and also had a significant correlation with soil exchangeable Ca, Mg, K, Na. A closer relationship of the aggregates was found with soil organic C and CEC than with other fertility properties, while no evident correlation existed between the aggregates and soil total K, available P, available K and slow-release K. In order to maintain a good aggregate structure of black soil, it is of most importance to concern a proper balance of soil organic C.

[Contribution of fertilization development to yield production and its geographic differentiation].

The results of long-term field experiments at three stations in different areas of China indicated that the contribution of fertilization to crop yield was significantly affected by the thermal condition of climate and the fertilization system. In the case of optimum fertilization, the largest contribution rate was 0.31 (average of fourteen years) at Hailun Station (in temperate zone), 0.39 (average of twelve years) at Shenyang Station (in warmer-temperate zone), and 0.42 (average of eleven years) at Taoyuan Station (in subtropical zone), which showed that the existence of geographic differentiation was caused by the thermal condition of local climate. Therefore, keeping the optimum fertilization systems, the largest contribution rate to crop yield could be estimated from 30% to 50%, depending on the local climate condition. The interaction of fertilization and thermal factor between Shenyang and Taoyuan was much bigger than that between Shenyang and Hailun. The interaction between organic manure and thermal condition of local climate was bigger than that between chemical fertilizer and thermal condition of local climate.

[Long-term trial on fertilization and on use of recycled nutrients in farming systems V. Response of crop yields to fertilization in different precipitation years and estimates of water and nutrient interaction].

According to the responses of crop yields under fertilizations in 1996 with normal precipitation (456 mm in crop growth season) and in 1998 with higher precipitation (598 mm in growth season), the effect of water and nutrient interaction on crop yields in semihumid-semiarid region of west Liaoning Province were estimated. Under N application and sufficient water supply (more rainfall), the increase of crop yields was 3,056 kg.hm-2, of which, 1,996 kg.hm-2 was estimated from water-nutrient interaction, while in NP and compost treatment with sufficient water supply, the yield increase was 4,703 kg.hm-2, of which, 1,554 kg.hm-2 was estimated from water-nutrient interaction.

[Advances in studies on accumulation and leaching of nitrate in farming soil].

Nitrate leaching in farming soil is the main reason resulting in ground water pollution of nitrate. The main factors, which can affect nitrate accumulation and leaching greatly, include fertilization, precipitation, irrigation, soil characteristics, and cultivation system. Superfluous nitrogen in soil caused either by using chemical fertilizer and manure solely or compost will result in nitrate accumulation. Cultivation and plow systems also can affect the process of nitrate accumulating and leaching. Down flows due to irrigation or precipitation are the necessary condition and carrier for transference and leaching of accumulated nitrate in soil. Great pores are the main channels for down flows. These factors always work corporately. Mathematical model, which has been developed quickly and used widely, may be a good method to study and predict nitrate leaching in farming land.

[A long-term field trial on fertilization and on use of recycled nutrients in farming systems III. Recycling rate of P and N through a composting cycle and recoveries of P and N in organic manure].

The results from a nine years experiment indicated that the average loss rate of N and P contained in harvest products through a feeding-composting cycle was about 30%. Under high yield conditions, the amount of recycled N and P from 60% of harvested products and through a composting cycle in a farming system were about 55-70 kg.hm-2 and 9-11 kg.hm-2, respectively, equivalent to 37%-47% of N and 36%-44% of P from fertilizers applied every year to the system.

[Changes of crop yield and soil fertility under long-term application of fertilizer and recycled nutrients in manure on a black soil III. Soil nutrient budget].

The nutrient budget of fertilization models under different treatments was calculated using data from a field experiment over the period of 1985-1999. The results indicated that application of nitrogen fertilizer accelerated a large deficit of soil phosphorus, and the use of nitrogen and phosphorus accelerated the deficit of potassium. The experimental data demonstrated the appearance of a large area of soil deficit of phosphorus from 1970s and of potassium from 1980s in China. Nutrient recycled in farming system improved soil nutrient budget, but could not meet the nutrient requirements from high-yield crops. The use of recycled nutrients with an appropriate use of fertilizers according to the soil fertility could produce higher crop yields, balance soil nutrient budget, and not cause surplus nutrients to emit into environment.

[A long-term field trial on fertilization and on use of recycled nutrients in farming systems IV. Soil fertility changes].

The fertility changes of soil under different fertilization treatments of a twelve years field trial indicated that the application of compost recycled in a farming system with appropriate amount of fertilizer applied to balance the soil nutrient budget, could not only produce higher crop yields and less surplus of nutrients into environment, but also improved soil fertility with significant increase of soil organic carbon and nitrogen in cultivated layer. However, maintaine higher soil available phosphorus, it was not sufficient just to balance the budget of soil phosphorus, and more phosphorus fertilizer application was needed.

[Stable mechanisms of soil aggregate and effects of human activities].

Soil aggregate is the basic unit of soil structure. Its formation is a natural process but influenced severely by human activities, including land utilization, tillage disturbance, manure application, and cropping system. The improvement of soil structure is decided not only by total amount of organic C inputed into soil, but also by the composition and characteristic of organic matter. Owing to the different composition and characteristic of organic matter, there are different mechanisms for the stability of micro- and macro-aggregates.

[Mechanisms of organic cementing soil aggregate formation and its theoretical models].

Soil aggregate is the basic unit of soil structure, and its formation and stabilization has direct effect on soil fertility and crop growth. For black soil with high content of organic matter, organic cementing substance is an important factor in forming soil aggregates. Based on the recent researches on organic cementing agents, this paper was focused on the nature of organic cementing substances, the effect of soil organisms and plant roots in forming soil aggregates, and the theoretical models and stable mechanisms of soil aggregate formation.

[Effect of different fertilization system on soil nutrient budget].

A long-term experiment was carried out on a damp palm soil about ten years under the condition of nutrient recycling and reutilization. The quantity of crop nutrients transferred from the system, and the nutrient budget of N, P and K in soil were studied. The results of a ten-year field experiment indicated that the use of nutrients recycled in the farming systems with appropriate amount of fertilizers applied according to the soil nutrient supplying ability could not only produce high crop yield, but also balance the soil nutrient budget, so that, there were no significant surplus of nutrients (mainly inorganic nitrogen) which might emit or leach out of soil into environment.