Nitrogen footprint and nitrogen use efficiency of greenhouse tomato production in North China

The greenhouse vegetable industry represents 20% of the total vegetable production area in China, yet produces 35% of output and 60% of economic value. However, the nitrogen (N) fertilizer input is estimated to exceed crop requirements by a factor of 5 to 6, leading to concern about environmental harm. This study compares greenhouse tomato production under conventional and recommended farming practices in the important production district of Shouguang in Shandong Province. Nitrogen footprint (NF) and nitrogen use efficiency (NUE) were used as measures of farming performance over the period 1998 to 2016. Conventional farming practices were found to have changed greatly. Tomato yields almost doubled, total fertilizer inputs increased by 117% and there was a major shift from inorganic to organic N inputs. Greenhouse buildings were also progressively modernized, as earlier wood, bamboo and cob constructions were replaced by brick and later steel-frame constructions. The total NF of tomato produced under conventional practice ranged from 5.1 to 7.7 g kg(-1) between 1998 and 2016. Although the NF from farming operations had decreased over time, the NF associated with greenhouse construction had increased steeply. The NF associated with the production of farming inputs made a relatively minor contribution. In comparison, the NF of tomato grown under recommended practice was around 75% lower. The nutrient use efficiency (NUE), including apparent recovery efficiency (ARE) and partial factor productivity (PFP) under conventional practices ranged from 2.6% to 5.7% and 48.3-84.7 kg kg(-1), whereas the corresponding values were as high as 33% and 221-240.7 kg kg(-1) with recommended practice. Taken together, these results indicate enormous potential for improved fertilizer management in greenhouse tomato production. However, compared to other regions or countries, there exist great space to improving the NUE, and then reducing the NE Additionally, they also point to a need for greater consideration of the environmental impacts associated with greenhouse construction. A priority is to understand the barriers associated with adoption of recommended practices. There may be a role for policies to incentivize improved environmental performance. Further education and training of vegetable industry workers may also be helpful. (C) 2018 Elsevier Ltd. All rights reserved.