Prediction of soil nutrient content via pXRF spectrometry and its spatial variation in a highly variable tropical area

• Published in: Precision agriculture Vol. 23; no. 1; pp. 18 - 34
• Main Authors: Pelegrino, Marcelo Henrique Procópio, Silva, Sérgio Henrique Godinho, de Faria, Álvaro José Gomes, Mancini, Marcelo, Teixeira, Anita Fernanda dos Santos, Chakraborty, Somsubhra, Weindorf, David C., Guilherme, Luiz Roberto Guimarães, Curi, Nilton
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-02-2022; Springer Nature B.V
• Subjects: Agriculture; Atmospheric Sciences; Biomedical and Life Sciences; Calcium; Calcium ions; Chemistry and Earth Sciences; Computer Science; Cost analysis; Decision making; Life Sciences; Nutrient content; Physics; Polynomials; Potassium; Precision farming; Prediction models; Regression analysis; Regression models; Remote Sensing/Photogrammetry; Scientific imaging; Sensors; Soil analysis; Soil chemistry; Soil fertility; Soil investigations; Soil nutrients; Soil properties; Soil Science & Conservation; Spatial variations; Spectrometry; Spectroscopy; Statistics for Engineering; Tropical environments; Tropical soils; X-ray fluorescence; Proximal sensor; Random forest; Regression analysis; Soil fertility spatial prediction; Digital soil mapping
• ISSN: 1385-2256; 1573-1618
• DOI: 10.1007/s11119-021-09825-8

Precision agriculture provides detailed information on the spatial variability of soil properties, including nutrient content, allowing for local-specific decision making. Recently, proximal sensors have been used to accurately predict soil properties, contributing to reduce costs of conventional wet-chemistry analyses for soil characterization. However, further investigations on this approach in tropical soils are needed. This work aimed to use portable X-ray fluorescence (pXRF) spectrometry data for prediction of exchangeable Ca
2+
and available K
+
and P contents in soils of a highly heterogeneous tropical area and evaluating its practical applications. 90 samples from soil A horizon were collected in a regular grid design, and analyzed through pXRF and for nutrient contents. Such data were split into modeling (63 samples) and validation (27 samples) datasets. Linear regression (LR), polynomial regression (PR), power regression (PwR) and stepwise multiple linear regression (SMLR) were tested for predictions. The models were used to spatially represent nutrient contents across the area and to compare the practical effects of varying regression models. PXRF elemental data provided reliable predictions of exchangeable Ca
2+
and available P via SMLR and PwR, respectively, reaching root mean square errors (RMSE) of 5.66 cmol
c
dm
−3
for Ca
2+
and 9.13 mg dm
−3
for P. Available K
+
predictions were not successful. Different models yielded contrasting maps showing the classes of soil fertility across the area, drawing attention to the importance of testing multiple prediction models and using the best one for precision agriculture. Fusion of data from different proximal sensors may enhance available K
+
predictions.