부산대학교 도서관

Nitrogen (N) and water deficiency jointly limit apple production in semiarid apple-producing regions worldwide. A 4-year field experiment (2017–2020) was conducted on China's Loess Plateau to systematically identify the responses of apple yields, fruit quality, and the dynamics of soil water and NO 3 −-N in 6-m soil profiles to different N (i.e., urea) application rates of 0, 300, 450, 600, 750, and 900 kg N ha−1. The results showed that apple yield averaged 30.02 t ha−1, with remarkable interannual fluctuations, although its differences between N rates were not statistically significant during 2017–2020. Similar responses were recorded for fruit quality indices, except that N-fertilization significantly increased total soluble solids compared with the non-N treatment. Interestingly, soil moisture differed considerably between N rates within the 100–300 cm depth, showing increasing soil moisture with increasing N rates, while an opposite trend was observed at 500–600 cm. The calculated minimum N rates achieving the balanced and maximum soil water storage within the 6-m profile (SWS 6 m) were 244 and 323 kg ha 1, respectively. Distinctive responses of NO 3 −-N to N rates were observed at 100–300 cm depth, whereas equivalent NO 3 −-N concentrations between N rates were recorded across the 520–600 cm depth. The minimum N rates achieving the balanced and maximum residual soil NO 3 −-N within the 6-m profile (RSN 6 m) were 412 and 509 kg N ha 1, respectively. Notably, SWS significantly linearly increased as a function of RSN across the 6-m soil profile, implying the capacity of N fertilizer to facilitate soil moisture. Collectively, N fertilization slightly affected apple yield and fruit quality but significantly altered soil moisture and NO 3 −-N within the 6-m soil profile. An N application rate of 412 kg ha 1 was recommended to support apple production and maintain balanced SWS 6 m and RSN 6 m for rainfed apple orchards on China's Loess Plateau. [Display omitted] • Apple yield and fruit quality differed slightly among different N application rates. • N-fertilization potentially increases the SWS 6 m and WUE in apple production systems. • 412 kg N ha 1 is recommended to maintain balanced SWS 6 m and RSN 6 m simultaneously. • 516 kg N ha 1 is identified as the upper limit for N rate in rain-fed apple orchards. • Farmers′ rampant use of N fertilizer is imperiling apple production in China. [ABSTRACT FROM AUTHOR]