The profitability of high-density apple (Malus ×domestica Borkh.) orchards depends on rapidly establishing tree biomass and then obtaining high fruit yields as soon as possible after planting. Apple growers will often apply mineral nitrogen (N) fertilizers such as calcium nitrate [Ca(NO3)2], ammonium nitrate (NH4NO3), and urea [CO(NH2)2], to promote vegetative growth. The effects of N fertilizer timing and concentration on vegetative growth, leaf N concentration, and fruit quality in established high-density orchards in arid regions have been well documented (Dong et al., 2005a; Klein et al., 1989; Neilsen and Neilsen, 2002; Neilsen et al., 2009). However, there is a lack of research-based recommendations for appropriate fertilizer formulation, timing, and application methods to use for young apple orchards in the Mid-Atlantic region of the United States (this includes the states of Delaware, Maryland, New Jersey, New York, North Carolina, Pennsylvania, Virginia, and West Virginia). In addition, there have been few studies describing the effects of carbon-based fertilizers, such as compost, on apple tree growth and productivity in newly planted high-density orchards in this region.
Furthermore, mineral N fertilizers may lead to negative environmental impacts. For example, ground applications of mineral N fertilizers in orchards have been observed to increase N leaching in orchard systems (Dong et al., 2005b; Merwin et al., 1996). This is of growing concern in watersheds, such as the Chesapeake Bay, where agricultural N has become an environmental pollutant. In an effort to reduce N pollution, the Environmental Protection Agency has enacted Total Maximum Daily Load limits on the amount of N that may enter the Chesapeake Bay Watershed (United States Environmental Protection Agency, 2010). Because of these regulations, detailed nutrient management plans are now needed for animal and agronomic productions systems within Chesapeake Bay watershed. It is possible that horticultural crop production systems may need to develop similar nutrient management plans in the future. Given these challenges, it is important to develop fertilizer application approaches and materials that can reduce environmental N loss from apple orchards.
One approach to improving soil fertility and reducing N loss is to use carbon-based amendments, such as composts. In apple orchards, compost applications have been shown to improved edaphic properties, including soil OM, microbial biomass carbon (C), microbial respiration, and soil mineral nutrition in fine- and coarse-textured soils (Forge et al., 2013; Neilsen et al., 2014; Rumberger et al., 2004; Sas-Paszt et al., 2014; Yao et al., 2006). For example, Kramer et al. (2006) observed that compost amended soils had 42% greater OM and 35 and 57% greater microbial biomass C and N, respectively, than soil fertilized with mineral N fertilizer. In addition, compost applications in coarse soil increased apple leaf N by 5%, K by 4%, Mn by 13%, and Zn by 5% compared with an unfertilized control (Sas-Paszt et al., 2014). However, compost applications do not appear to affect the vegetative growth or fruit yield or quality independent of soil texture (Forge et al., 2013; Neilsen et al., 2014; Rumberger et al., 2004; Sas-Paszt et al., 2014; Yao et al., 2006). In contrast to the results observed in apple orchards, Baldi et al. (2010) found that when compost was tilled into fine textured soil to a depth of 25 cm in a 7-year-old peach orchard, fruit yield increased by 38% in the first year, as did soil quality measures such as, OM, soil mineral nutrition, and microbial biomass C compared with the unfertilized control.
It appears that the contrasting results are contingent on soil texture, plant species, and the specific feedstock used to produce the compost. Composts made exclusively from plant material, such as yard wastes, have a higher C:N ratio than manure-based composts. Amending soil with a high C:N ratio compost will initially immobilize N, then mineralize N slowly but for a longer period of time than manure-based composts (Hartz et al., 2000). Therefore, it is necessary to determine how compost produced from different feedstocks, such as chicken litter and yard waste, may affect tree growth and productivity in an orchard.
Using an integrated compost–mineral fertilizer strategy may provide trees with N when it is most needed, while also conferring the benefits of compost mentioned previously. In an apple orchard with coarse textured soils, integrated compost–mineral fertilizer applications resulted in 33% more soil OM and 55% less NO3− leaching than soil fertilized with mineral fertilizer [Ca(NO3)2] (Kramer et al., 2006). However, integrated compost–mineral fertilizer applications did not increase soil microbial biomass C and N or potentially mineralizable N compared with the mineral fertilizer treatment. In other horticultural cropping systems, integrated fertilization approaches have been used to increase crop yields while improving soil quality. For example, parsley plants that were fertilized with the integrated treatment, compost and NH4NO3, had 69% more biomass than an unfertilized control, whereas plants that received compost alone increased biomass by 18% compared with an unfertilized control (Mylavarapu and Zinati, 2009). In this study, the integrated treatments also increased soil total C and N, microbial biomass C, and microbial respiration similarly to the compost amendments. Similar results have also been documented for broccoli and tomatoes planted in coarse-textured soils (Hernández et al., 2014; Stamatiadis et al., 1999). Thus, integrated compost–mineral fertilizer applications may be an approach to reduce environmental N loss while providing trees with sufficient N and enhancing soil quality.
Fertigation, a method which dispenses soluble fertilizers through irrigation lines, is another strategy that may reduce the negative environmental impacts from mineral fertilizer applications. Studies in arid apple producing regions with coarse soil, such as Israel and British Columbia, CAN, have demonstrated that fertigation can improve fruit quality and yield, tree growth, and leaf N concentration (Dong et al., 2005b; Klein et al., 1989; Neilsen et al., 2009). In a pot culture study, fertigating trees with N increased shoot growth by ≈58% and 82% compared with foliar N applications and the unfertilized control, respectively, and increased fruit yield by 28%, and fruit size by 22% compared with the unfertilized control (Dong et al., 2005a, 2005b). Similar results were observed in temperate regions with fertile, fine-textured clay soils, where N fertigation increased fruit yield by 25%, flower bud formation by 40%, and shoot growth by 85% in established apple orchards compared with broadcast fertilizer use (Kipp, 1992). Results from this study suggest that fertigation may improve apple tree yield and shoot growth in the fine-textured soils of the Mid-Atlantic.
The objectives of our study were to evaluate the effects of fertilizers, including ground applied Ca(NO3)2, compost, integrated compost-Ca(NO3)2, and fertigation with Ca(NO3)2, on tree growth and productivity and soil fertility in a newly planted apple orchard. We hypothesized that the integrated applications of composts and Ca(NO3)2 would supply apple trees with sufficient nitrogen to maintain adequate growth and productivity while also improving soil quality.
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