Differences in Soil and Tree Responses to Organic Orchard Fertilizer and Ground Cover Management.

Despite increased demand, organic production in the Southern U.S. has been limited. Apple producers have identified the need for research with organic fertilizers and for effective management of ground covers to provide adequate tree nutrition. To assist producers transitioning from conventional to more sustainable and organic fruit production in the South, a 1.15-ha organic research orchard was established in 2005 in Fayetteville, AR. The objective of this study was to determine whether the interactions of organic nutrient sources and ground cover management improve soil biological activity and nutrient availability in concert or in competition with tree growth and nutrient uptake. The study was established as a replicated complete block design fully guarded with treatments applied annually prior to bud break, including four ground covers, compost (C), wood chips (W), shredded paper (P) and mow-and-blow (M), and three nutrient sources, a control with only ground cover supplying nutrients, composted poultry litter, and a poultry litter based organic commercial fertilizer. Soils were sampled at the 0-10 and 10-30 cm depths in the spring before and after treatment applications. Microbial biomass and enzyme activities appeared to benefit from M in the surface 10 cm, while dissolved soil-extractable and soil-solution N pools frequently were greatest under C at depths to 30 cm. Fertilizer applications did result in some increases in dissolved organic N pools in the surface 0-10 cm. While foliar N was similar and at a sufficient level in C, M, and W, but not P, tree growth and canopy development in C and W were significantly greater than in M, followed by P. Results show that management practices affect soil health differently than tree growth. The effects on soil health may not be completely manifest in the trees for several years as the system stabilizes and trees achieve their final size.