Effect of different rotation systems on media nutrient and enzyme activityin solar greenhouse tomato rhizosphere

The development of eco-agriculture and sustainable agriculture has been followed by the rapid development of greenhouse tomato in organic media culture. This has sustained a year-after-year increase in land area under greenhouse tomato production. However, the conventional planting and production allows persistent reuse of the same medium for cost reduction, which has led to heavy disease and insects infestation. This has deteriorated the plant physical and chemical characteristics with decreasing yield output and fruit quality. These production challenges have constituted a major bottleneck restricting sustainable development of greenhouse tomato in organic media culture. This paper studied the changes in biological and physicochemical characteristics in rhizosphere media under three crop rotation systems - normal cropping, alternate cropping and continuous cropping. The effects of the different crop rotation systems on enzyme activity, organic matter content and main nutrients in rhizosphere media of tomato under solar greenhouse were analyzed. The study laid relevant scientific reference for the sustainable development of greenhouse tomato in organic media culture. The results showed that the activities of protease, phosphatase, urease and catalase decreased in organic media culture under continuous cropping of tomato. Also the contents of organic matter, nitrogen, ammonium nitrogen, available nitrogen, total phosphorus, available phosphorus, total potassium and available potassium decreased. Normal cropping conditions had little effect on enzyme activity, organic matter content and major nutrients contents. Chemical properties were closely related with biological properties in organic media under normal cropping, alternate cropping and continuous cropping. This resulted in changes in micro-ecological environment, and further changes in plant growth, disease and insects intestatins, yield and fruit quality of tomato. Protease, phosphatase, urease and catalase activities were significantly correlated with organic matter and main nutrients contents. Among the four enzymes, urease activity had the strongest correlation with organic matter and main nutrients contents. This suggested that urease activity was the main factor influencing the media fertility. Plasticity indexes of available potassium, available phosphorus, total potassium and catalase was higher than other indexes in all the treatments. Under different crop rotation systems, plasticity index of new media was largest, followed by that for alternate cropping system and then continuous cropping system. The result suggested that enzyme activity well correlated with organic matter and main nutrients contents in greenhouse tomato rhizosphere media under different crop rotation systems. Also enzyme activity, organic matter and main nutrients contents were important elements of media material cycle. It was therefore possible to use enzyme activity in characterizing organic matter and nutrient state which reflected the intensity and direction of various biological activities in media. Enzyme activity, organic matter and main nutrients contents decreased after continuous cropping, tomato nutrient source reduced and inhibited tomato plant growth. However, enzyme activity and main nutrients of media culture were less affected under normal cropping treatment. It suggested that continuous cropping media culture was not suitable for tomato growth. Biological and physicochemical characters of normal cropping media and new media were very similar. The normal cropping system was adaptable to the growth and development of solar greenhouse tomato.