Spectral Vegetation Indexes Applied to Nitrogen Sufficiency Index: A Strategy With Potential to Increase Nitrogen Use Efficiency on Tomato Crop

Abstract

The tomato crop is one of the most demanding of nitrogen fertilizers. This element on soil has an elevated mobility that can represent danger to the environment and reduces its efficiency. Therefore, the purpose of this study was to evaluate the methodology for recommending nitrogen fertilizer for tutored tomatoes with a variable rate based on nitrogen sufficiency index. The treatments consisted of a reference plot and five treatments with the nitrogen sufficiency index calculated on spectral indexes NDVI, GNDVI, MCARI, PSSRa and the SPAD value. The productivity was evaluated considering the fruits size and viability. The descriptors of quality, color, soluble solids, total acidity, titratable acidity and flavor were also evaluated. All the indexes evaluated decreased significantly with the applied nitrogen during the cycle, the only exception being MCARI, which resulted in a similar nitrogen quantity to the reference. The NDVI, GNDVI, PSSRa and SPAD value indexes presented a total applied nitrogen decrease varying from 25.2% to 43.8%, neither reducing significantly the productivity nor the fruits quality. The marketable fruits productivity varied from 2332.9 to 2773.8 g.plant-1 among treatments. Only the NDVI and the SPAD value presented significant improvements on the partial factor of nitrogen productivity, among the applied treatments.

Monitoring Plant Status and Fertilization Strategy through Multispectral Images

“…Their study used the NDVI index as a predictor parameter and the correlation between the vegetation index and the yield were of 0.67 and 0.71 in two different regions of Spain. Another study conducted by [52] showed the possibility to use vegetation indices to improve the use of nitrogen fertilization in tomatoes cultivated in protected environment. Applying the spectral sensors ASD Field Spec HandHeld 2, and the Minolta SPAD 502, the authors compared the spectral response of tomato plants in the reference plot and with lower levels of nitrogen fertilization.…”

“…The use of NDVI and the SPAD measurements as a nitrogen level parameter allowed to reduce significantly the use of nitrogen fertilization maintaining the same yield levels and fruit quality compared to the reference plot [52]. On the other hand, during three years of field trials with different levels of nitrogen fertilization [53] evaluated vegetation indices of tomato plots through the use of a multispectral radiometer (MSR-87, Cropscan Inc., Rochesters, MA, USA).…”