Increasing Agricultural Complexity: An Approach for Integration of Trees in Cropped Landscapes

Temperate agricultural practices that lower external inputs, increase potential for carbon (C) storage, and augment system resilience, particularly through agrodiversity, remain crucial to productive landscapes. Agroforestry systems, the combination of trees and crops, achieve such shifts in agricultural management, predominantly when positive interspecific interactions are optimized. Although early growth competition between tree-crop systems has been well documented, little work has developed effective techniques to minimize residual antagonism with agroforestry systems. To mitigate such competition, we used a model tree-crop system to test the effectiveness of nutrient spiking the tree component [Pinus strobus L. (white pine)] on reducing belowground competition with the crop component [Zea mays L. (corn)]. Nutrient spiking is widely used in monoculture plantation systems, but no work has redirected this technique to multispecies agroforestry systems. We hypothesized that the internal accumulation and retention of nutrients associated with nutrient spiked pine seedlings will lower stress on native soil resources after out-planting, permitting increased nutrient availability for crop growth. Two levels of nutrient spiking [untreated (S0) and spiked (S1)] of white pine were intercropped with corn, as well as monoculture controls for each species, under greenhouse conditions. After 2 months, root biomass response of corn and pine was significantly higher (19% and 52% respectively as compared to monoculture growth) in the nutrient spiking treatment. Nutritionally, nitrogen (N), phosphorus (P) and potassium (K) significantly increased in pine tissue with pre-transplant spiking. This presumably reduced stress on native soil nutrients and resulted in the steady or increased N, P, and K uptake in corn shoot tissue (increases of 19%, 0%, 49% respectively) intercropped with spiked pine in comparison to corn in monoculture. Our findings contribute a preliminary examination of pretransplant nutrient spiking practices to reduce resource stress and mitigate nutritional competition during early crop growth in an agroforestry context. Such specialized practices may be useful in order to promote integration of trees in cropped landscapes for the eventual benefits of nutrient and hydrological regulation as well as increased productivity and C storage capacity.