Soil salinity
Greenhouse vegetable cultivation often requires a greater degree of management and larger input of nutrients and irrigation. However, over-fertilization and over-irrigation for vegetable cultivation resulted in nutrient accumulation in soil and led to soil salinity [8, 9]. Salinity reduces phosphate uptake and accumulation in crops grown in soils primarily by reducing phosphate availability. Salinity can directly affect nutrient uptake, such as Na+ reducing K+ uptake or by Cl- reducing NO3- uptake. Salinity can also cause a combination of complex interactions that affect plant metabolism, susceptibility to injury or internal nutrient requirement. Salinity has been described as the 'AIDS of the soil' and its influence is spreading throughout society where crop production has been seriously affected and caused economic hardship.
Continuous cropping
As the development of specialized vegetable production, continuous cropping is inevitable in greenhouses. A lot of vegetable such as tomato (Lycopersicum esculentum), pepper (Capsicum frutescens), eggplants (Solanum melongena), and cucumber have frequently suffered continuous cropping obstacle [10]. At the same time, poorly differentiated plant mass getting into the soil under continuous cropping negatively affects soil organism communities [11]. This negative action leads to the change in metabolism of microbes from the primary to the secondary [12]. Continuous cropping obstacle has became a main problem for sustainable production of vegetable, for example, serious plant diseases and fall of yield, which intimidated facility vegetables production sustainable development, especially in North China [5, 13–17].
Soil acidification
A number of agricultural practices have expanded the areas of acidification soils. The main causal factor is the growth of plants that use large amounts of basic ions (e.g. legumes); particularly when fertilizers that leaves acidic residues (such as Superphosphate) are used.
Nutrition accumulation
At present, fertilizer application rates in intensive agricultural systems have increased dramatically in recent years, especially in greenhouse vegetable production systems [18]. These high fertilizer inputs and the extremely low crop recoveries of fertilizer nutrients lead to marked deterioration in soil and groundwater quality and the systems are clearly unsustainable [19]. Soil chemical and biological properties in greenhouse vegetable production may change dramatically after several years of continually high inputs of fertilizers and irrigation water and planting of shallow rooting vegetable crops compared with open field cereal production systems. Soil OM, alkalihydrolyzable N, and available P and K have been observed to accumulate significantly in vegetable greenhouses [5]. High concentrations of P and imbalances of N, P and K often occur in the intensively managed soils. High fertilizer application rates may lead to increasing salinity in the surface soils of the plastic film greenhouses in which vegetables are grown [20].
Compaction
Some researcher found that bulk density was higher in greenhouse soils than uncovered soil. In recent years, there has been increasing interests in intensive vegetable cultivation, this caused the soil compacted. Compaction of soils causes a reduction in soil pore space. This reduces the rate at which water can infiltrate and drain through the soil. It also reduces the available space for oxygen in the plant root zones. For this reason, some of the major consequences of compaction are poor drainage, poor aeration, and hard pan surfaces which cause runoff. Repeated cultivation of some soils leads to a breakdown of soil structure and this also increases the likelihood of compaction.
Chemical residue
Although not as large a problem as some of the other types of soil degradation, the presence of chemical residues can be quite a problem on a local scale. These residues derive almost entirely from long term accumulation after repeated use of pesticides, etc., or of use of pesticides or other chemicals with long residual effects. Some problems that result from chemical residues include toxic effects on crop species and contamination of workers, livestock and adjacent streams.
The studies on the soil degradation of greenhouse soil and its affection mechanism on vegetables are highly important for us to maintain high land capacity. For a sustainable management of soil in the greenhouse, it is urgent to improve the fertilizer and irrigation management for vegetable production, especially for the winter season under greenhouse conditions. Excessive nitrogen application can be effectively avoided by site-specific fertilizer application based on soil and plant analysis.
Prevention from soil degradation in greenhouse