Towards ecologically-based fertilizer recommendations that improve soil quality in high-density apple orchards

Towards ecologically-based fertilizer recommendations that improve soil quality in high-density apple orchards

Summary

The purpose of this project is to create sustainable soil fertility management practices for Mid-Atlantic and Southern apple growers by integrating the use of carbon-based soil amendments, such as compost and mulch, into new high-density orchard systems, thereby lessening the use of synthetic fertilizers. During the past year, we recruited a doctoral student (Cody Kiefer) and have established study sites at Virginia Tech’s Alson H. Smith, Jr. Agricultural Research and Extension Center (AREC), and at the orchards of two grower cooperators (Silver Creek Orchards and Catoctin Mountain Orchard). Preliminary data from the first year is presented within this report.

Objectives/Performance Targets

Objective 1: Survey commercial apple growers in the Mid-Atlantic region to identify the fertilizer formulations, quantities, and application frequencies most commonly employed.

• The goal of the survey is to better understand current fertilizer practices in order to better effect change in grower behavior.

Objective 2: Use an interdisciplinary approach to examine the benefits of utilizing carbon-based soil amendments in commercial apple orchard systems so that we can investigate the interaction between soil nutrient source and orchard productivity. Our project will investigate microbial community composition, biomass, and soil biological activity in the soil, particularly in the rhizosphere (the soil-root interface). The research will occur on replicated plots located in three separate regional apple orchards.

• Our research will utilize a research farm trial comparing synthetic fertilizers (calcium nitrate), chicken litter compost, municipal yard waste compost, and treatments that integrate synthetic fertilizers with composts when applied to newly planted high-density apple trees.
• We will also develop additional replicated on-farm trials with two cooperating growers.

• Among the three farm sites outlined in this objective, this research project will span over 200 miles and put growers throughout the Mid-Atlantic in close proximity to the test sites, which will encourage faster adoption of the most effective treatments.

Objective 3: Educate stakeholders in orchard nutrition management. Develop printed and web-based outreach materials to support educational activities.

Accomplishments/Milestones

In April and May 2014, apple trees were planted at the three research locations. The treatment rates (pounds of nitrogen per acre) were identical at each location (Table 1). However, the mulch and compost were sourced locally and varied at each site.
 

Table 1. Treatment rates and site maps.

*Fertilizer rate 40 t/ha/year N, then 20 t/ha/year N in subsequent years.

**Maps depict the experimental design. The number corresponds to the treatment; the letter corresponds to the replicated block.

Experimental Design and Statistical Analysis

A split plot completely randomized design with four four-tree replications for each treatment was used for at each location. The main plots are mulch versus no mulch. The four subplots are the fertilizer inputs: compost, calcium nitrate, both compost and calcium nitrate (CaNO₃), and an unfertilized control. There is an untreated buffer tree between each subsplot and two untreated buffer trees between main plots. Mulch applied at 1m widths, 10cm depth and large-aggregate material sourced locally for each site.

Response variables to be measured:

• Tree growth by trunk cross-sectional area on an annual basis
• Leaf nutrient status
• Soil nutrient status
• Terminal shoot growth and branching
• Fruit yields and quality (in year two, if there is fruit, but more likely not until year three)
• Microbial biomass and community structure

Milestones

• Tree planting dates:
  • 14 May 2014 at AREC
  • 8-10 May 2014 at Catoctin
  • Apr 2014 at Silver Creek
• Treatments applied:
  • 18 Jul 2014 at AREC
  • 22 Jul 2014 at Catoctin
  • 26 Aug 2014 at Silver Creek
• Fall soil samples dates:
  • 23 Oct 2014 at AREC
  • 24 Oct 2014 at Catoctin
  • 16 Oct 2014 at Silver Creek
• Leaf sample dates:
  • 13 Sep 2014 at AREC
  • 6 Sep 2014 at Catoctin
  • 12 Sep 2014 at Silver Creek
• A second application of CaNO₃ occurred during leaf sample dates.

Preliminary Data:

Trunk cross-sectional area (TCSA) was measured in June 2014 for baseline data and again, after tree growth had subsided, in October 2014. Baseline measurements were not different among the treatments at the Winchester and Thurmont sites for either date (Tables 2 and 3, respectively). At the Tyro site, the mulch + compost treatment trees had greater TCSA than the no mulch + CaNO₃ treatment during the June measurement and the no mulch + control treatment during the October measurement (Table 4). Otherwise, there were no differences among treatments.

Soil tests performed in June 2014, prior to the treatment applications indicated uniformity in soil nutrition across the experiments at the Winchester and Tyro sites (Tables 5 and 7, respectively). The Thurmont site revealed higher iron content in the mulch + CaNO₃ treatment than all of the non-mulch treatments and the mulch + control treatment (Table 6). By Fall 2014 sampling, differences were evident among treatments. At the AREC site, phosphorus was higher in the mulch + compost treatment than either CaNO₃ treatment and the mulch + control treatment (Table 8). Also, potassium and magnesium was also higher in this treatment than the no mulch + CaNO₃ treatment. The CaNO₃ treatments at the Thurmont site had lower magnesium content than compost and control treatments at the October sampling date (Table 9). High phosphorus levels at the Thurmont site are likely due to the grower’s previous compost applications. At the Tyro site, the no mulch + compost treatment had greater magnesium and zinc than the no mulch + CaNO₃ treatment (Table 10). There were no biologically significant differences in the leaf mineral content at any of the sites (data not shown). These preliminary data show initial benefits to use of compost at these three orchard sites.

Impacts and Contributions/Outcomes

Study sites have already been a source of discussion and demonstration for the public and commercial apple growers in the Mid-Atlantic region. During an open house at the AREC on 16 Aug 2014, Mr. Kiefer gave two presentations on his project to nearly 85 people. Many of these individuals were very interested to learn about the emphasis on sustainability that is included in this project. On 10 Sep 2014, a group of nearly 50 growers and associated industry personal toured the AREC research site to learn about the first year’s results.

As this project progresses, the project’s results will be used to better inform apple growers’ fertilizer practices. We will do this through conducting an in-service extension training on soil biology and management for Cooperative Extension personnel in the Mid-Atlantic region in the final year of the project. Tree-fruit consultants and representatives from regional fertilizer dealers will also be invited to attend the session. The in-service workshop will be held as part of the annual Virginia Cooperative Extension In-Service training in Blacksburg, and/or as a session at the Alson H. Smith, Jr. AREC. Funds for in-service training are made available through Virginia Cooperative Extension on an annual basis. 

Results from this project will be used in the tree-fruit extension program to provide valuable information about high-density apple systems in the Mid-Atlantic. When sufficient data has been collected, Mr. Kiefer and Drs. Peck and Williams will publish numbered extension bulletins so the information can be widely disseminated in print and electronic formats. We will also publish our results in a mix of horticulture and soil science themed peer-reviewed scientific journals, such as HortScience, Horticulture Research, Applied Soil Ecology, and Soil Biology and Biochemistry.

Collaborators: