Effect of continuous cropping on Soil

Due to the subject to restrictions and producers of cultivated land quantity and climatic conditions of high economic benefit pursuit, vegetable production in China widespread problem of excessive application of chemical fertilizer, highly intensive production, high multiple crop index, single species of vegetable cultivation, years of continuous cropping and soil physical and chemical properties of evil.

One, the problem of continuous cropping, the soil physical and chemical properties.
Vegetable growth process. On the one hand, the root system of the soil from the uptake of water and nutrients, but also to the soil to secrete a proton, ion and organic matter and other root exudates. Under the condition of continuous cropping, the accumulation of toxic substances in root exudates caused the root damage seriously, in addition to the number of microbial populations, the population has a certain impact on the microbial metabolism, growth and development, so that the root exudates increased, and in turn, the soil enzyme activity, resulting in a variety of vegetable crops.
The changes of vegetable continuous cropping and soil microorganism.
Bacteria in soil are the most bacteria, followed by actinomycetes. The number of fungi in the end. The relative numbers of three major types of microorganisms in the soil have not changed much. The longer the soil continuous cropping years, the higher the total microbial content. However, the total content of microbial biomass was not positive correlated with the content of soil pathogenic bacteria, and the key of the disease occurred light or heavy. With the increase of continuous cropping years, the soil bacteria increased, the species and quantity of fungi decreased. But the species and quantity of harmful fungi increased, and the content of actinomycetes decreased with the increase of continuous cropping years. This change of soil microbial structure, so that the growth and development of vegetables, quality and so on. The research showed that the root vigor of tomato was significantly different from the continuous cropping years. The quality of Tomato in 2 years and 4 years was not significantly different, but the quality of tomato was significantly lower than that of continuous cropping for 8 years. With the increase of continuous cropping years, the quality of vegetables decreased year by year.
Two. The changes of the continuous cropping and soil enzyme activity
Soil enzyme is an important indicator of soil biological activity. They are involved in the biological cycle of various elements, the decomposition of organic matter, the formation of humus, etc.. Soil enzyme activity is a sign of soil metabolic activity, and it is closely related to the abundance and activity of soil enzymes and microorganisms. The level of soil enzyme activity can reflect the transformation of soil nutrients (especially nitrogen and phosphorus). Soil enzyme activity distribution and the soil ripening degree, soil physical and chemical properties, organic matter, and soil curing degree, soil physical and chemical properties and organic matter and associated with the soil of continuous cropping.
Soil enzyme, including extracellular and intracellular, extracellular enzyme is soil macromolecular organic matter (such as cellulose, hemicellulose and lignin) in the degradation process required. The intracellular enzyme is a small molecule (such as amino acids, sugars) essential substances in the degradation process.
The transformation of soil urease directly involved in the transformation of N organic compounds in soil. Moreover, the effect of urease is very special, it can only be hydrolyzed urea ammonia. Urease activity increased with the increase of urea application. However, the activity of urease in soil is too high, and it can easily lead to the loss of ammonia volatilization. Therefore, the soil should be rational use of nitrogen fertilizer, control the urease activity, reduce nitrogen loss and environmental pollution, the conversion of enzymes can not be directly absorbed by the plant to the decomposition of sucrose into glucose and fructose, so that the soil biological activity. High conversion enzyme activity, indicating that soil biological activity, soil fertility of the soil in good condition; catalase can destroy soil biochemical reaction of hydrogen peroxide, alleviate the harm of plant; continuous cropping years increasing, soil phosphatase, soil protease, sucrase, soil cellulose enzyme activity has increased, and they and soil organic matter content were positively related. So. Adding organic fertilizer in the garden can improve the activity of soil enzymes. Increase the life of the garden soil.
Three, vegetable crops of the sense of self poisoning.
The action of a chemical plant is a favorable or unfavorable effect of the metabolism of plants or microorganisms on the environment of other plants and microorganisms. If the plant released from the chemical sensing material to the same stubble or under the same family or the growth of the plant to inhibit the growth, the role of this is known as the self - toxic effect. It is a growth inhibition that occurs in the species. The research showed that: the root exudates and stubble of pea, tomato, cucumber, watermelon and melon were separated from the root exudates and the residual stubble, which influenced the plant growth by affecting the cell membrane permeability, enzyme activity, ion absorption and photosynthesis.
Major control measures of vegetable continuous cropping obstacles: between different crop rotation, intercropping, the number of pathogenic bacteria in soil can be significantly lower. Application of ecological organic fertilizer to change the composition of soil microorganism. Use of natural rainfall leaching to remove salt, reduce the accumulation of salt in the soil surface. Water should be poured into the soil, the soil surface accumulation of salt dilution, for root absorption. The use of infection resistant varieties and grafting technology can overcome the pathogen. Based on some beneficial bacteria to soil specific pathogen produce harmful substances or through competition for nutrients and space and other ways to reduce the infection of pathogenic bacteria and the number of roots, thereby reducing disease. Some of the microbial fertilizer could antagonize some pathogenic microorganisms and inhibit the effect of disease.
It can be seen that the soil continuous cropping obstacle caused by harmful microorganisms can be effectively reduced by effective agricultural cultivation system and cultivation technology.