Orchard floor management for improved tree growth and soil health in organic peach systems

Jennifer R. Reeve, Plants, Soils, and Climate, Utah State University, Logan, UT, Catherine M. Culumber, University of California, Diane G. Alston, Corey V. Ransom and Brent L. Black, Utah State University

Background/Question/Methods: Successful management of organic fruit trees requires the development of agroecological strategies for managing tree growth, soil health, nutrient supply, and pest pressure. To determine the best approach for establishing and managing peach trees (Prunus persica L.) organically in climates characterized by hot dry summers and cold winters such as the Intermountain West, seven organic and three integrated and conventional treatment combinations were established in two first leaf orchards at the USU Kaysville Research Farm, Utah, in 2008. Treatments consisted of different tree-row and alleyway mulch and fertilizer combinations that varied in residue quality and quantity. Organic orchard treatments were straw mulch with a grass alleyway, straw mulch and a Birdsfoot trefoil (Lotus corniculatus) alleyway, living mulch (low-growing shallow rooted allysum, Lobularia maritima) with grass alleyway, living mulch and legume alleyway, woven plastic mulch with a grass alleyway, and tillage with grass alleyway. Treatments assigned to the integrated orchard were conventional fertilizer plus herbicide, compost plus herbicide, conventional fertilizer with paper mulch and reduced herbicide, compost with paper mulch and organic herbicide. All alleyways in the integrated orchard were planted to grass. In organic treatments, paunch manure compost was applied as needed. Compost was supplemented with a feather meal 13-0-0 fertilizer starting in year three to avoid over application of phosphorus (P) and potassium (K). Conventional treatments received a similar rate of N applied as 16-16-16 and urea.
Results/Conclusions: Organic orchard tree growth was initially slowed by living and straw mulches present in the tree-row. By 2011, 4th leaf trees were largest in treatments with legume alleyways, despite considerable tree-row weed/living mulch pressure. This was attributed to reduced competition between tree roots and legumes, increased N acquisition and improved soil health. In the integrated orchard trees were larger in the compost plus conventional herbicide compared to conventional fertilizer and herbicide treatment. Paper mulch depressed tree growth in combination with both compost and conventional N sources, but more so in combination with compost and organic herbicide where weed control was moderate. Pest pressure increased in treatments that provided greater ground cover, however, increased pest pressure did not result in greater crop damage. Weed pressure not a lack of N was determined to limit organic tree growth in this study. A legume alleyway may alleviate the need for intensive weed control when establishing organic peach orchards. However greater vigilance is required when managing an increased risk of arthropod pests.