Foliar nutrient concentrations of three economically important tree species in an alley-cropping system

Authors: O'Brien, Peter; THOMAS, ANDREW - University Of Missouri; Sauer, Thomas; Brauer, David

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2020
Publication Date: 6/24/2020
Citation: O'Brien, P.L., Thomas, A.L., Sauer, T.J., Brauer, D.K. 2020. Foliar nutrient concentrations of three economically important tree species in an alley-cropping system. Journal of Plant Nutrition. 43(17):2557-2568. https://doi.org/10.1080/01904167.2020.1783303.
DOI: https://doi.org/10.1080/01904167.2020.1783303

Interpretive Summary: Alley-cropping is an agroforestry practice where tree rows are planted at wide spacings to allow for crop or livestock production in the alleyways. By pairing economically important tree species with crop production, these systems have the potential to diversify outputs and improve resource use efficiency. However, little guidance on nutrient management in alley-cropping systems is available. This lack of information is partially due to the numerous and diverse circumstances that the practice can be implemented, and it is complicated by the need to provide nutrients to both trees and a crop understory. While soil nutrient levels are a good guide for crop management plans, they may not provide a good indicator of tree nutrient status because trees access a larger volume of the soil profile (i.e., space and depth). Thus, nutrient contents in leaf tissue (i.e., foliar nutrient concentrations) are often used to guide management plans for trees. However, goals for tree growth in alley-cropping systems are not the same as those in fruit and nut production orchards, so management plans in production orchards may not be suitable for guiding nutrient management. To address this knowledge gap, we monitored foliar nutrient concentrations in three economically important tree species in an alley-cropping system for nine years. In all three species – red oak, pecan, and black walnut – we found that leaf tissue concentrations of Mg and Ca increased over time, while N, K, S, Fe, and Na decreased. Leaf nutrient levels in red oak and pecan were much more similar to each other than to black walnut. Additionally, foliar nutrient concentrations were the same when fertilized with either poultry litter or synthetic N fertilizer. Overall, the foliar nutrient levels were slightly lower than values reported from fruit and nut production orchards, but these results do not necessarily indicate that these trees are nutrient deficient. Rather, these differences likely represent the different goals of alley-cropping systems, where trees provide other services than fruit or lumber production, such as reducing animal stress, increasing forage production, improving nutrient and water use efficiency, and contributing to long-term soil health. Our study highlights the importance of understanding production goals when creating nutrient management plans in integrated systems. Land managers, agronomists, and other researchers will find these results useful in understanding tree nutrient status and guiding nutrient management strategies in alley-cropping systems in the future.

Technical Abstract: Alley-cropping systems that pair economically important tree species with crop production in alleyways have the potential to diversify outputs and improve resource use efficiency. However, management practices are more complex because trees and crops have different nutrient requirements and access different depths in the soil profile. Foliar nutrient concentrations are often used to determine fertility plans for fruit and nut production orchards, but these recommendations may not be appropriate in integrated tree and crop production systems. This research describes foliar nutrient concentrations in three different tree species, red oak (Quercus rubra L.), pecan [Carya illinoinensis (Wangenh.) K. Koch], and black walnut (Juglans nigra L.), at an alley-cropping site in northwest Arkansas, USA from 2004 – 2012. Foliar nutrient concentrations did not differ in trees fertilized by poultry litter when compared to those receiving synthetic N fertilizer. Concentrations of nutrients changed over time in all three species, with Mg and Ca increasing and N, K, S, Fe, and Na decreasing as trees aged. A principal components analysis indicated that leaf nutrient levels in red oak and pecan were much more similar to each other than to black walnut. Some of the foliar nutrient concentrations identified in this study were inconsistent with sufficiency ranges reported in fruit and nut production orchards. However, given the multiple aims of an alley-cropping system, these inconsistencies may not represent deficiencies in available nutrients for these tree species.