Mineral mass balances reveal the phenology of evergreen and deciduous tree crops' nutrient uptake

Recent economic, environmental, and regulative concerns force farmers to precise their fertilization practices. Yet, a critical knowledge gap concerning the temporal variability in perennials' nutritional requirements renders most fertilization applications inefficient. While mass balance studies could illustrate the dynamics of crops' mineral uptake, their association to field conditions remains a challenge. Hence, we constructed an empirical framework to convert data from lysimeter studies to applicable farming information. We fitted quadratic equations to the correlations between irrigation and drainage mineral concentrations of three perennial crops-almond, avocado, and pomegranate. Then, we derived the optimal irrigation mineral composition by the interpolation point of the nitrogen, phosphorus, and potassium curves. We also matched polynomials to the relations between leaf mineral concentrations and fertilization compositions and established mineral diagnostic references for each sampling period. Repeated measures of the crops' response curves illustrated a temporal variability in their nutrient uptake, highlighting that the evergreen avocado extracts nutrients throughout winter, early blooming almond extracts nutrients in spring, and late fruiting pomegranates obtain minerals throughout summer. Moreover, the deciduous almond and pomegranate require extensive summer fertilization for the following spring's bloom. Recurrent leaf diagnosis exhibited that almond leave's optimal nitrogen concentrations drop by midsummer. Optimal phosphorus concentrations in avocado and pomegranates doubled during summer, as did the optimal potassium concentration in pomegranates' leaves. Accordingly, we established an empirical approach to process data from lysimeter studies and constructed specific fertigation assays for almond, avocado, and pomegranate trees.

Automated summary

Farmers need to adjust fertilization practices based on the nutritional requirements of crops, but there is a lack of knowledge regarding the temporal variability of nutrient requirements for perennial crops. By constructing an empirical framework and conducting research, we can provide practical and applicable fertilization information and methods for farmers.