Fig. 4: Spatial distributions of the rice nutrient balance ratio from 2009 to 2019 in SW China.

The maps show the spatial distributions of the rice nitrogen nutrient balance ratio (NBRN) in 2009 (a) and 2019 (b), the spatial distributions of the rice phosphorus nutrient balance ratio (NBRP) in 2009 (c) and 2019 (d), and the spatial distributions of the rice potassium nutrient balance ratio (NBRK) in 2009 (e) and 2019 (f). Nutrient balance ratios greater than zero represent excessive fertilizer inputs, ratios equal to zero represent balanced fertilizer inputs, and ratios less than zero represent insufficient fertilizer inputs. The color bands denote various nutrient balance ratio classes. The box of the violin plot denotes the interquartile range with the median value shown as a bold line, the whiskers of the violin plot indicate the 1.5 interquartile range, and the outer border of the violin plot denotes the data distribution. The symbol t denotes the value obtained from the t-test, with the asterisk (*) indicating that the mean difference between 2009 and 2019 is statistically significant at the 0.05 confidence level.