USE OF ORGANIC APPLICATIONS TO INCREASE PRODUCTIVITY OF HIGH DENSITY APPLE ORCHARDS

Minimizing use of agrochemicals in fruit growing is a goal of integrated fruit production (IFP). Recently, a range of locally available organic materials have been advocated for possible orchard use. Over the past decade, a series of randomized, replicated field trials were established in grower and research orchards in British Columbia to test the effectiveness of these materials when applied to the surface as mulches or mixed to 30 cm depth as soil amendments. Mulch application most consistently affected tree growth, as indicated in a long term field trial where cumulative yield after 5 crop years was increased by surface application of shredded paper, alfalfa and biosolid mulches. Soil nutrient status and soil biological activity were altered by surface mulching and at another site trees were buffered against moisture stress. Initial growth stimulation from mulching was not sustained at a site where excessive irrigation reduced N availability. Rotovation of a biosolid-amendment to 0.3 m depth prior to planting improved the P-nutrition and initial growth of apple. Amendment treatment did not always affect apple tree performance. Effects were not observed at sites with strong fertigation regimes or fertile soils or when sites had overriding growth limitations unaffected by treatment (e.g. replant disease, K deficiency). INTRODUCTION In the semi-arid, irrigated fruit growing regions of the Pacific Northwest of North America, there are economic factors inducing greater intensification of fruit production, as typified by high density orchards of new apple cultivars on dwarfing rootstocks (Hampson et al., 2002). At the same time, environmental concerns are creating a trend towards minimizing the impact of these production systems on the environment by adoption of integrated fruit production (IFP) techniques (Intl. Soc. Hort. Sci., 1990). Increased use of organic materials as soil amendments or surface mulches have been advocated (Merwin et al., 1995) as compatible with IFP since fertilizer and herbicide inputs can be reduced. Their use may be particularly valuable on coarse-textured soils with limited nutrient and water holding capacity (Neilsen et al., 1998). Little information is available concerning the effects of mulches and amendments on apple tree performance and soil quality in typical modern orchards in semi-arid regions. A series of field trials were established in British Columbia orchards to determine the effect of a range of organic materials used as mulches or amendments on growth, yield and nutrition of apple trees and alteration of orchard soil properties. MATERIALS AND METHODS All randomized and replicated field trials were established in high density apple orchards on dwarfing rootstocks (Table 1). Treatments involved either surface application of organic materials (mulching) or amendment of the surface soil by incorporation of the organic materials to 0.3 m depth. The check treatment at each site was the industry standard herbicide strip, usually 1-2 m wide. Fertilization and irrigation practices followed standard commercial production practices for the region (Brit. Col. Ministr. of Agr.& Food, 1998). Experimental designs were randomized complete blocks. Standard annual measurements were made of tree vigor, yield and leaf nutrition as previously Proc. XXVI IHC – Sustainability of Horticultural Systems Eds. L. Bertschinger and J.D. Anderson Acta Hort. 638, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 348 described (Neilsen et al., 2002). At site 1, soil protozoa and Pratylenchus penetrans populations were identified by methods previously described (Forge et al., 2002). Soil C was determined by combustion analysis (LECO Corp., St. Joseph, MI, USA) and soil P by inductively coupled argon plasma spectrophotometry after extraction in 0.25M HOAC + 0.015M NH4F (Van Lierop, 1988). The organic materials used in the experiments exhibited a range of nutrient contents and chemical properties (Table 2). Analysis of variance was performed on all plant and soil data to elucidate treatment effects using the general linear model of SAS Institute Inc. Means were separated using Duncan’s multiple range test. RESULTS AND DISCUSSION Mulch Experiments At site 1, after six growing seasons there was a large variation in size of apple trees, as indicated by differences in average trunk cross-sectional area (TCSA) among various mulch treatments (trts) (Fig. 1). Largest trees were associated with various combinations of shredded paper mulch (trts 3, 4 and 5) with TCSA more than 50% larger than check trees. Smallest trees were consistently observed for the check trees and for trees grown with 2 applications of 45 t ha of Greater Vancouver Regional District (GVRD) biosolids. Cumulative yield, 1995-1999, was higher for all trts relative to the check . The greatest cumulative yield (80% greater than check) was measured for trees grown with shredded paper mulch (trt 3). Despite having similar size, trees with trt 2 (GVRD-biosolids only) exceeded cumulative yield of check trees. Soil properties in the 15 cm below the mulch were altered by surface mulching. For example, soil C was increased relative to check treatments beneath all but the black plastic mulch (trt 6, Fig. 2). Application of biosolids (trts 1, 4 and 5) increased extractable soil P relative to the standard check treatment. A stimulation of biological activity after biosolids application was indicated by a relative increase in protozoa numbers for trts 1 and 4 (Fig. 3). Also noteworthy was a decrease in population of the root-feeding nematode, Pratylenchus penetrans, associated with replant disorders, beneath mulches containing alfalfa (trt 2) or shredded paper combinations (trts 3, 4 and 5). At site 2 (Table 1), first year TCSA increment and numbers of fruit in second year were significantly increased by 3 of 4 mulch treatments (Table 3) but effects faded by third year. Leaf N concentrations were generally low at this site and likely limited growth. Application of Ogogrow increased leaf N in the first year but only when co-applied with Newstech spray-on-mulch in second year. Frequent large applications of irrigation water with rates not adjusted to individual plots are applied in this block since the coarsetextured soils are prone to water stress. Under these conditions it is difficult to maintain sufficient N in the root zone even after the application of N-mineralizing mulches. Adjustments in irrigation may be required to maximize the benefits of mulching. Mulch and Amendment Experiments Growth of ‘Gala’ apple trees at site 3 (Table 1) was not strongly influenced by either mulch or amendment treatments (Fig. 4). An exception was trees mulched with Riverside wood waste after application of 45 t ha of Envirowaste (trt 5) and trees amended twice with Envirowaste (trt 4) which had greater vigor (larger TCSA) than trees receiving the amendment alone (trt 1). The grower co-operator fertigated with both N and P daily from April early June each year. At site 4 (Table 1), growth and initial yield of ‘Gala’ apple trees in the first 2 growing seasons was unaffected by any soil management treatment (Fig. 5). In the third growing season, an irrigation treatment was created in which selected trees received 50% of atmometer-scheduled irrigation which was otherwise applied in this plot. Fruit size was reduced on average by 5% in this water stress treatment. This reduction in fruit size was not observed for trees growing in mulched or amended plots. All trees received a