Conventional flooding irrigation causes an overuse of nitrogen fertilizer and low nitrogen use efficiency in intensively used solar greenhouse vegetable production

In China, fertilizer nitrogen input is three to five times greater than vegetables require during typical intensively managed solar greenhouse vegetable production, causing a large loss of nitrogen (N) and contaminating groundwater. Excessive N input may result from flooding irrigation, a conventional practice of Chinese vegetable growers. To test this hypothesis a six-season field experiment was carried out, examining two production models (conventional flooding irrigation with over-fertilization and drip irrigation with optimizing fertilization) with and without straw application. Tomato yield, nitrate residues, nitrate leaching, nitrogen and water use efficiency, apparent nitrogen loss, and the soil organic carbon content were measured. Compared to conventional flooding irrigation model, tomato yield was increased by 9% with drip irrigation model, while the inter-annual variation of yield decreased significantly. Nitrate leaching and apparent nitrogen loss also diminished substantially. Fertilizer N and water inputs were reduced by 78% and 43%, respectively, demonstrating an improvement in water and nitrogen use efficiency with drip irrigation. Straw application had a marginal effect on both systems. Soil organic carbon slightly increased during the six growing seasons while soil nitrate leaching decreased. These results demonstrate that without the improvement of irrigation systems, it will be hard sustaining an intensively used solar greenhouse vegetable production system.