Nitrogen Management Based on Visible/Near Infrared Spectroscopy in Pear Orchards

Jie Wang,Xiaojun Shi,Yangchun Xu,Caixia Dong

doi:10.3390/rs13050927

Abstract

The timely estimation of nitrogen (N) requirements is essential for managing N fertilizer application in pear orchards. Visible/near infrared spectroscopy is a non-destructive and effective technique for real-time assessment of leaf N concentration, but its utility for decisions about fertilizer application in the pear orchards remains to be determined. In this study, we used leaf spectroscopy to determine leaf N concentration, used this value to calculate the amounts of N required for supplementary fertilization, and then evaluated the effects of the application. Over the two-year study, Cuiguan pear trees were treated with N at the following rates: 0 (N0), 100 (N1), 200 (N2), 300 (N3), and 400 (N4) g N per tree, regarded as five “controlled” N application rates. Another four “regulatory” treatments (Nr1-4) were fertilized as the “controlled” N application rates the first year, then given adjusted N application by topdressing as calculated using the N concentrations inferred from visible/near infrared spectroscopy data the second year. A model (R2 = 0.82) was established the first year to relate leaf spectra and N concentration using a partial least squares regression with full bands (350–2500 nm). The amount of N in the topdressing for the supplemental treatments was determined using the predicted leaf N concentration and the topdressing calculation method adapted from the N balance formula. Results showed that adjusted N applications of the Nr1 and Nr2 increased yield by 26% and 23%, respectively, over the controlled treatments N1 and N2. Although treatments Nr3 and Nr4 did not increase yield significantly over N3 and N4, the partial factor productivity of nitrogen in Nr4 was higher than the N4. The transverse diameter of fruit from Nr1 trees was significantly higher than from N1 trees, while the longitudinal diameter of fruit from Nr1, Nr2, and Nr3 trees was significantly higher than from N1, N2 and N3 trees, suggesting that fruit longitudinal growth and single-fruit weight is stimulated by adjusted N applications. However, the soluble solids in fruit from trees receiving adjusted N were not significantly greater than in fruit from non-supplemented trees. In conclusion, our results illustrate that regulatory N management contributes to fruit yield and quality especially in the nitrogen deficiency condition and improves the nitrogen use efficiency in nitrogen surplus. The N prediction model established using the nondestructive visible/near infrared spectroscopy is convenient and economical.

Highlights

Pears (Pyrus L.) are cultivated throughout the world, China is the leading producer of Asian pears [1], one of the most common fruits cultivated in both North andSouth China [2]
The results show that the low leaf nitrogen leaf nitrogen concentrations were determined for trees receiving the controlled and re concentrations conferred by the insufficient basal fertilizer treatments can be increased latory treatments
Non-destructive monitoring of leaf nitrogen concentration, as well as the corresponding ability to precisely manage N application, is likely to be essential for improving pear production

Summary

Introduction

Pears (Pyrus L.) are cultivated throughout the world, China is the leading producer of Asian pears [1], one of the most common fruits cultivated in both North andSouth China [2]. Pears (Pyrus L.) are cultivated throughout the world, China is the leading producer of Asian pears [1], one of the most common fruits cultivated in both North and. N is an important fertilizer input in pear cultivation, and optimizing its application in pear orchards is important for Remote Sens. Conventional fertilizer application practices in China overuse N and phosphorus, which leads to soil acidification, salinization, and impaired water quality [4]. Pears in Europe receive 40–50 kg·N·ha−1 to maintain good fruit quality and production; amounts higher than 160 kg·N·ha−1 are rarely applied [6]. Excessive N application often results in the stimulation of shoot growth and leads to the production of fruits with undesirably high N concentrations, making them more prone to post-harvest physiological and pathological disorders [7,8]. Management practices that produce high yielding crops without wasted N are needed to achieve sustainable agriculture in China [12,13]

Methods

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Discussion

Conclusion