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Soil Fertility
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- Example of soil testing help fertilizer recommendations in Tibet
In 1980’s, a soil survey conducted in Tibet revealed that almost all the farmland soils were deficient in N and P but sufficient in K. Since then, only N and P have been considered in the fertilizer recommendations for crop production.
- Spatial variability and estimation accuracy of soil properties at different sampling intensities
Spatial variability of soil properties was studied, and their corresponding estimation accuracy was compared at three sampling intensities. Spatial structure of soil properties change with their variety at different sampling intensities, soil pH, NH4+―N, P and S were best fitted with various semi-variation models respectively, soil OM, Mg and S could be simulated by the same model. The fitting degree of models, effective range and spatial dependence of variation were not absolutely corresponding with sampling intensities. Soil properties with significant model-fitting degree were estimated, the result showed that estimation accuracy of soil OM and S enhanced as sampling intensity increased, however, it was not the case for soil NH4+―N and Ca.
- Effect of Rain Intensity and Different Farming Practices on Nutrient Losses from a Purple Soil
Agricultural non-point source pollution has put tremendous pressure on environment and thus drawn attention globally. Though numerous studies have been conducted on nutrient losses from farmlands, the information regarding effect of farming practice on soil nutrient losses from purple soils on the sloping farmlands is rare. Therefore, this study was aimed to explore the effect of rain intensity and farming practices on N and P losses from sloping lands. The experiment was designed as a completely randomized block design and equipped with artificial rain system and simulated runoff blocks. Results revealed that the surface runoff was positively correlated with rain intensity, while the underground runoff was negatively correlated with the total runoff. At a given rain intensity, amounts of both surface runoff and soil eroded were the biggest for the flat cultivation treatment. Soil erosion and surface runoff were reduced remarkably with contour cultivation under a small to medium rain intensity, but the effect was weakened as rain intensity increased to heavy rains. The carrier transporting soil P out of the field was found to be sediments and thus, the amount of P lost was closely related to rain intensity. Under the small to medium rain intensity, soil N was mainly moved out of field by runoff, especially for the underground runoff. To control loss of soil N that is responsible for non-point source pollution, underground runoff should be controlled first. To control loss of soil P, another non-point source pollutant, however, soil erosion should be minimized with any possible means. Soil erosion and surface runoff can be effectively controlled by contour cultivation under a small to medium rain intensity, so does loss of soil P. As the underground runoff was increased by contour cultivation, N loss from the soil was increased, particularly when fertilizer application is carried out just before a rain or during a rain, imposing greater risk to environment pollution.
- Southwest China's Acid Uplands Hold Great Potential
Southwest China has about 9.2 million ha of acid arable uplands, comprising half of the arable lands (18 million ha) in the provinces of Sichuan, Chongqing, Yunnan and Guizhou. Infertility of the acid uplands is a major constraint to production. These soils exhibit a wide range of nutrient deficiencies such as P, K, Ca, Mg, B and Mo. Application of aglime along with balanced fertilization could significantly improve crop yields by 20% - 30% and proved to be effective against vegetable diseases grown on the Chengdu plain and Chongqing. The PPI/PPIC China Program's Chengdu Office estimates that average annual rates of 120-180 kg N, 90 kg P2O5 and 90-150 kg K2O/ha will be required to maintain maximum economic yields in these soils. This technique can be applicable to large areas of acid soils in southwest China including Sichuan, Chongqing, Yunnan and Guizhou providing a potential for increased use of P and K in combination with liming.
The picture below shows the effect of ag-lime on corn growth on an acidic soil in Mingshan county, Sichuan province (3 rows of limed corn on the left and the unlimed 3 rows on the right).
Phosphorus Remains a Nutrient Limiting Factor for Crop Production in Southwest China
Although mineral phosphate fertilizers have been used in China for over 40 years, recent research shows that P is still a major nutrient limiting factor in soils for crop production in Southwestern China. According to soil test data, about 70-90% of soil samples from grain growing fields were deficient in soil available P. In soils were vegetable were grown, however, the number of soil samples deficient in available P was much less, ranging from 9-21% (only Sichuan and Chongqing were sampled). It is known that farmers apply heavy doses of N and P fertilizers, and also some K, to their vegetable fields to assure a higher income. (Note: in the picture, P0 and P7.5 denote amounts of P2O5 applied per mu, which is equivalent to 0 and 112.5 kg P2O5/ha)
A field experiment of mineral phosphate fertilizer on corn was conducted in a P deficient purple soil with available P content of 8.1 mg/kg in Jianyang county, Sichuan province in 2001. Results showed that applied P significantly increased corn growth (as seen in the above figure and documented by corn yield (Table 1)). According to the 2nd National Soil Survey, this soil is representative of 2.06 million ha of farm land in Sichuan and Chongqing. In these areas, farmers normally apply only 60-75 kg P2O5/ha (some apply even less). If all the farmers increase their P2O5 application to 112 kg/ha, the increased phosphorus need would range between 97,000 - 136,000 t of P2O5 for this soil type.
Table 1. Effect of P application on corn yield in Jianyang county, Sichuan province in 2001.
Amount of P2O5 applied (kg/ha) | Corn yield (kg/ha) | Yield increase (%) |
0 | 5235 | - |
37.5 | 5850 | 11.7 |
75.0 | 6300 | 20.3 |
112.5 | 6810 | 30.1 |
150.0 | 6750 | 28.9 |
- Balanced Fertilizer Use and Ag-lime Boosts Vegetable Yield and Quality
In the vegetable growing areas in Southwestern China, a long time reliance on heavy dressings of N fertilizers has caused cases of severe imbalance for other plant nutrients such as K, Ca, Mg, B, and Mo in the soil. Besides this nutrient imbalance, increased soil acidity is another problem resulting from long-term over use of N fertilizers.
Recent research conducted in the Southwest region shows that balanced fertilizer use in combination with application of Ag-lime can overcome these problems (dolomite in both Ca and Mg deficient soils...and calcite for Ca deficient soils). This integrated technology significantly improved vegetable yields, quality, and shelf-life at market. For example, in field trials and demonstrations, vegetable yields usually increase 20 to 80% and market shelf-life by 3 to 5 days if balanced fertilizer technology was adopted.
The picture below (taken in Peng City, Sichuan Province), shows cauliflower which received balanced fertilizer application including ag-lime (on the left side) and farmers' practice (on the right side). In this specific trial, the integrated fertilizer technology increased cauliflower yield by over 31% compared to the farmers' practice.--
- Feeding corn with potash to maintain high yield
In a 3-year fixed field trial, it is observed that corn yields increase with an increase in K application (fig. 1). About 150 kg K2O/ha can produce the highest corn yield from 5.6 to 7.1 t/ha in 2002-2004. Soil testing shows that with this application rate, soil available K is also maintained above the critical level of K deficiency (data not shown here). Below this rate, soil available K is in serious deficit, reducing soil fertility.
Fig. 1 Relationship between corn yield and potash application in
the monitored village in Guizhou, China in 2002-2004. (blue diamonds
-2002; yellow triangles-2003; pink square-2004)
Fig. 2 Relationship between corn yield and phosphate application
in the monitored village in Guizhou, China in 2002-2004. (blue
diamonds -2002; yellow triangles-2003; pink square-2004)
Corn yields did not respond to the applied P in the 3-year period of field experiment (Fig. 2). This is attributed to its adequate soil reserves at the beginning of the experiment. After three years without P application, the soil available P2O5 was still above the critical level.
Based on the results, the potash recommendations for corn grown on this soil was 150 kg K2O/ha. The situation for P on this soil is unusual, since P is the major limiting factor for corn and other crops in acid soils in Guizhou where P is needed for high yield of corn and other crops. According to other experiments conducted in the province, the recommended rate of P2O5 is 90-120 kg/ha. The results of this experiment, however, does substantiate that P application is not needed if the soil P is built up.
- Low soil pH depressed pineapple growth at its early stages
Poor growth of pineapple at its early stages was found recently to be related to low pH values at 4 to 5 at top soil layer in Hainan province. The low pH may be induced by long term use of high rates of nitrogen fertilizers on the course textured soils. The local collaborators claimed that the pineapple usually grow poorly or is stunted with appearance of brown-red stripes along the leaf veins and old leaves burned at its seedling stages after transplanting (refers to fig. 1 and fig. 2). This situation gets improved as pineapple roots penetrate to the deeper soil layers and finally turns to normal at flowing stage (refers to Fig. 3). This finding is very helpful to local farmers to solve this widespreading problem by using ag-lime or other basic materials.
 
Fig. 1 Pineapple grown strongly acid soil Fig. 2 Close-up of the high acidity suffered pineapple
Fig. 3 Normal growth of at later stage
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