Study On The Effect Of Straw Returning And Chemical Potash Fertilizer Application In Promoting The Capacity Of Supplying Potassium In Farmland Soil

Potassium is one of the most important quality elements for plant. Its natural abundance and biological effectiveness in soil play a crucial role on normal growth and development of plant, yield formation, nutritional quality of agricultural products and so on. However, in originally potassium-rich soil on Guanzhong plain, potassium in soil is hard to make ends meet over the years due to the little or no potash fertilizer input. Increasing of input of potash fertilizer is the most direct and effective method in supplying and ease the imbalance of potassium imbalance. But for a long time the local farmers did not have the habit to apply potash fertilizer for the originally potassium-rich soil and the expensive price of potash fertilizer. To provide theoretical support for reasonable utilization of potassium-rich agricultural wastes and maintain the sustainability of the potassium in soil, we evaluated the effect of straw returning universally implemented measure in Shaanxi province recent years on potassium supplement and potassium fractions in the soil compared with chemical fertilizer input. Main results were as follows:1. To evaluated the effect of straw returning on forms and spatial distribution(stratification) of potassium in agricultural soil in winter wheat-summer maize rotation system on Guanzhong Plain. Results showed each component of soil readily available K was significantly increased in 0~5 cm soil layer in the grianfield soil after 13 years of straw incorporation. However, readily available K was seriously depleted at 5~15 cm and 15~30 cm soil layer compared to the vineyard soil. Stratification ratios of readily available K and its components in grainfield soil were observed higher than in vineyard soil. Compared withvineyard soil, the content of non-exchangeable K in grainfield soil was decreased obviously. The contents of mineral K and total K in grainfield soil were observed close to vineyard soil. Readily available K was observed correlated with its components, non exchangeable K and total K significantly or extremely significantly, but not significant correlation with mineral K in grainfield soil. However readily available K were observed significantly correlated with its components and non-exchangeable K, but no significant correlation with mineral K and total K. Therefore, straw incorporation was preferable to maintain the significant correlation between available components with total content of soil Kand coordinate the contents and spatial distribution of soil K in different forms, but no significant effect on the content and spatial distribution of soil mineral K and total K.2. To provide theoretical basis for the applicability of “extraction method of available potassium(K) using cool nitric acid” by evaluating K fractions and their relationships in K-enriched calcareous soil in northwest China. Results showed that large variability of each K fractions in surface soil and variable coefficients varied between 1.9% and 33.8%. No significant differences were found between different straw-returning modes. The content of K extracted by cool nitric acid was 1.43 and 0.30 times that of readily and slowly available K,respectively. Also, highly significantly positive correlation was found between K content extracted by cool nitric acid and readily available K in soils(r=0.82). Meanwhile, the results of principal component analysis showed K extracted by cool nitric acid was in the first principal component with readily available K, where both had high loading. Additionally, the results of path coefficient analysis showed soil K extracted by cold nitric acid was composed by non-specifically adsorptive K, specifically adsorptive K and non-exchangeable K, and it was mainly contributed by exchangeable K, which similar with readily available K in soil.Therefore, extraction method of available K using cool nitric acid could be used as a reliable method to measure the level of available K content in K-enriched calcareous soil.Exchangeable K could be the main supplier to available K in soil.3. To study the releasing of straw potassium and fertilizer potassium after incorporated into soil, as well as the dynamics of the potassium in different fractions in the soil. Results showed that soil available components of potassium, containing water soluble potassium,non-specifically absorptive potassium, specifically absorptive potassium and slowly available potassium, were all significantly increased by straw incorporation and potash fertilizer input,and increased with the increasing net potassium input as well. The effect of potash fertilizer was better than crop straw in increasing available components of soil potassium while the net potassium input almost equal with each other. Releasing and fixation of exogenous potassium in soil could be synchronously done in a short time, and potassium from crop straw was more likely to be fixed in the soil than from potash potassium. On the other hand, structural potassium trended to decrease after exogenous potassium input. The input of exogenous potassium could promote the activation of soil potassium relatively, and potassium from fertilizer was better than crop straw.The main conclusions based on the above experimental research can be made:(1) Straw returning can play a positive role in improving fertility of soil potassium, but not in the short run.(2) Available potassium trends to accumulate in the topsoil under long-term straw returning. To promote the root potassium nutrition, appropriately deep ploughing is necessary.(3) Exogenous potassium no matter from straw or fertilizer cannot completely transform into readily available potassium after input in the soil. Potassium from straw is more likely to be fixed than from chemical fertilizer.