*Article* **Long-Term Fertilizer Reduction in Greenhouse Tomato-Cucumber Rotation System to Assess N Utilization, Leaching, and Cost Efficiency**

**Yucong Geng 1,†, Muhammad Amjad Bashir 1,2,† , Ying Zhao <sup>3</sup> , Jianhang Luo <sup>3</sup> , Xiaotong Liu <sup>3</sup> , Feng Li <sup>4</sup> , Hongyuan Wang <sup>1</sup> , Qurat-Ul-Ain Raza <sup>5</sup> , Abdur Rehim 2,5, Xuejun Zhang 3,\* and Hongbin Liu <sup>1</sup>**


**Abstract:** Technology-oriented approaches to reduce chemical fertilization in agroecosystems without influencing the vegetable yield is a proficient method for sustainable agriculture and environmental safety. However, short-term studies are not capable to indicate the effects of various inputs in a long run; therefore, a six-year experiment was conducted in Ningxia, China. The experimental units were: no fertilizer control (CK: 0 kg N ha−<sup>1</sup> ), chicken manure (M: organic N 362 kg ha−<sup>1</sup> ), reduced chemical fertilizer (RCF: chemical N 992 kg ha−<sup>1</sup> + organic N 362 kg ha−<sup>1</sup> ), and conventional fertilizer (CF: chemical N 1515 kg ha−<sup>1</sup> + organic N 362 kg ha−<sup>1</sup> ). The study aimed to assess the effects of reduced fertilization on yield, nitrogen (N) use efficiency (NUE), N leaching, and the economic benefits. The results achieved herein indicate that RCF has significantly improved the NUE, reduced N leaching (23.7%), and improved the N economic benefit (NEB, 41.8%) as compared to the CF. Based on yield, net benefit, and NUE conditions, the optimum N application range was 634–821 kg N ha−<sup>1</sup> for tomato and 556–778 kg N ha−<sup>1</sup> for cucumber. The study concluded that reduced chemical application of N is an important factor to control environmental pollution and improve fertilizer use efficiency. Further experiments are suggested to examine the optimum N rate provision from chemical fertilizer and its ratio with organic fertilization.

**Keywords:** vegetable yield; nitrogen use efficiency; nutrient leaching; leaching-to-input ratio; nitrogen fertilizer economic benefit
