Factors leading to excessive nitrogen fertilization on apple in the Loess Plateau

Objectives Excessive nitrogen fertilization in apple production is common in the Loess Plateau area of China. Investigating the main influence factors is helpful to guild scientifically efficient orchard fertilization, improve the nitrogen use efficiency, guarantee the development of apple industry sustainably, and promote the realization of fertilizer zero growth goals.

Methods Orchard investigation and soil sampling in the typical apple production areas of the Loess Plateau were used for this study. Indices relating to apple production, purchase price, nitrogen fertilizer rate, production management and technology in 2012–2013 and orchard soil organic matter contents in 2013–2014 were calculated. We analyzed the effect of nitrogen fertilizer rates on apple production and fruit size (purchase price) respectively, the effect of orchard soil organic matter content on nitrogen fertilizer rates, and the grower’s technology adoption and difference of PFP_N under different technologies from apple market, orchard soil quality and adoption of supporting technologies respectively.

Results The median and mean nitrogen fertilizer rates in tested area were 921 kg/hm² and (1032 ± 32) kg/hm², respectively, and the overuse proportion was more than 90%. The median and mean orchard soil organic matter contents were 9.8 g/kg and (10.2 ± 0.3) g/kg, which were far lower than the national standard of high quality organic matter content of the orchard (> 15 g/kg). The increased nitrogen fertilizer application did not affect apple yields significantly, but increased the fruit sizes significantly, which was closely related with the price of apple. With the reduction of orchard soil organic matter content, the nitrogen fertilizer rates were on the rise but not significant (the reason was that organic matter in orchard was generally low and the difference between blocks was very small). The adoption rates of the extended technologies were quite different, and the technology of enhancing efficiency but minimizing nitrogen input was the least adopted among the technologies. The effect of the enhancing efficiency but minimizing nitrogen input technology was different among the growers using the technology, and the rate was very low in using the technology in a right way.

Conclusions Preference of big fruits in the apple market, lower soil fertility in apple orchard and limited extension of saving nitrogen techniques were the main reasons for the excessive nitrogen input. Therefore, establishing a good apple quality evaluation system, accelerating the work of orchard soil fertility improvement, and strengthening the extension of enhanced efficiency nitrogen management technologies should be considered in the future.