Approaches for Establishing Organic Stone-fruit Orchards in Utah and the Intermountain West

Adequate nutrient supply and weed control is critical for the successful establishment of fruit trees. A lack of available N and inadequate weed control is of particular concern in organic tree fruit establishment, especially when a short growing season and shallow alkaline soils limit natural fertility and use of nitrogen fixing winter cover crops, as is the case in the Intermountain West. In order to determine the best approach for establishing peach trees (Prunus persica L.) organically in the Intermountain West, six organic and four integrated and conventional treatment combinations were established in two first leaf orchards at the Kaysville Research Farm, Utah, in 2008. Treatments in the certified organic orchard were: 1) straw mulch with compost and a grass alley way; 2) straw mulch, compost and a legume alleyway; 3) living mulch (low-growing shallow rooted sweet alyssum, Lobularia maritime L.), compost and grass alley way; 4) living mulch, compost and a legume alley way; 5) woven plastic mulch, compost and a grass alley way; and 6) tillage, compost and a grass alley way. Paunch manure compost was applied at a baseline rate of 90 g total N per tree and adjusted up or down based on tree growth. Treatments in the integrated orchard were: 1) conventional fertilizer (N–P–K 90 g N per tree) plus herbicide; 2) compost (90 g total N per tree) plus herbicide; 3) N–P–K with paper mulch and reduced herbicide;and  4) compost with paper mulch and organic herbicide. All treatments in the integrated orchard were planted with grass alley ways. In the organic orchard, tree growth was initially slowed in combination with both living and non-living mulches. By the end of 2011 trees were largest in legume alley way treatments, despite considerable tree row weed pressure, suggesting N limitation. However, in the integrated orchard trees were largest in the compost herbicide treatment indicating that weed control, not lack of nitrogen was likely limiting growth. Paper mulch depressed tree growth in combination with both N sources, but more so in combination with compost and organic herbicide were weed control was moderate,  than with N–P–K and conventional herbicide. Tree growth in organic treatments matched tree growth in the conventional control when good weed control was achieved. A legume alley way may help alleviate the need for intensive weed control when establishing organic peach orchards.