The Effects of Different Organic Apple Production Systems on Seasonal Variation of Soil Properties and Foliar Nutrient Concentration

The Effects of Different Organic Apple Production Systems on Seasonal Variation of Soil Properties and Foliar Nutrient Concentration

Summary

A certified organic apple orchard was established to study the interaction of ground cover management strategies and nutrient sources on orchard performance in the southern region of the US. Trees received one of four ground cover management treatments as an under canopy mulch: 1) urban green compost (GC), 2) refuse wood chips (WC), 3) shredded commercial paper (SP), and 4) mow-and-blow vegetation (MB). Across all ground covers, one of three nutrient source treatments was applied: A) control – the ground cover treatment provides nutrients (NF), b) composted poultry litter (PL), C) a commercial pelletized, poultry-based product (CF). For this presentation, significant main effects of treatments and interaction effects were presented. WC and GC treated trees had greater soil [NO3], [P], [K], and [Mg] at 0-10 cm depth. Soil [K] was also greater at 10-30 cm depth but there were no treatment effects for other nutrients. WC+CF treated trees had the highest foliar [N], whereas MB+NF had the lowest foliar [N]. Overall, the WC and GC treated tress exhibited trends for increased foliar [N] and [P] along with specific leaf weight compared to MB and SP regardless of nutrient source. Foliar [Mg] was affected by nutrient source but not ground cover treatment. Trees treated with WC and nutrients provided by CF were the tallest and had the longest average shoot length after one growing season.

Objectives/Performance Targets

Orchard nutrition and fertilizer recommendations are based upon nutrient content in the soil and foliar. However, there is little information about nitrogen availability in organic apple orchards due to the complicated biological diversity of the soil. Also, the limited study of organic orchard nutrition has been done in the arid Pacific Northwest or the colder Northeast region with little or no research in the lower-Midwest or Southern Regions. To address these questions, seasonal soil and foliar nutrient concentrations, soil properties, weed density, and tree performance were observed to three fertilizers with four groundcover managements in the southern region of the US.

Accomplishments/Milestones

1. Soil Nutrition and Properties
A. Soil Nutrition
GC treated trees had greater soil [NO3] at 0-10 cm depth from May to October and would provide more available nutrients around root zones. GC materials had a 16.1 value of C/N ratio that organic N in GC is well mineralized by soil microbial community. The different fertilizers did not affect soil [NO3] at 0-10 and 10-30 cm depths except June. Soil [NO3] and [NH4] were decreased during growing season at both depths. This decreased inorganic N was opposite results that we previously examined in the small organic orchard where we did not irrigate at. The inorganic N in soil may be leached into the deep soil because rain was frequently happened during summer. Therefore, electric conductivity that is proportioned to the salt concentrations was decreased, and soil pH was increased during growing season. The soil pH ranged between 6.4-7.2 at 0-10 cm and 6.1-7.2 at 10-30 cm depth during growing season. WC and GC treated trees had greater soil [K] and [Mg] at both depth. Soil [Ca] was increased during growing season at both depths. The most micronutrients had not significantly differences among the treatments during growing season.
The organic matter did not have any significant differences among the treatments during growing season but at 10-30 cm depth in October. Soil solution [NO3] in 30 cm depth was very varied among the treatments, and statistic analysis could not be preceded. The solution was rapidly decreased with collection dates because the available water in the soil may stay around the installed lysimeter resulting in dilution effects of the nitrate concentrations with time. Nonetheless, the WC and GC treated trees had greater the solution [NO3] during sampling dates.
B. Soil Properties
Double-ring infiltrometer was used for measuring infiltration rate per each tree (the middle area of between data and guard tree) in November. The GC treated soils were the slowest infiltration rate, whereas the WC and MB were the faster infiltration rate. WC may have more active biodiversity in the soil. MB treated soil had a lot of roots under ground resulting in more pore space in the soil where the water molecules can be rapidly filled into. On the other hands, the GC treated soil had a slower infiltration rate that we did not expected even though there were no statistics differences among the treatments. MB treated soil showed the smallest soil bulk density because there were more weed roots or grasses roots under the ground resulting in distributing more space. There also existed a couple of small holes under the SP treated soil, which also contribute to smaller soil bulk density. The soil water content {((fresh soils-dried soil)/fresh soil)*100} had the greater at GC and SP plots.

2. Tree Performance
A. Leaf Nutrition
WC+CF treated trees had the highest foliar [N], whereas MB+NF had the lowest foliar [N] in August. Overall, the WC and GC treated tress exhibited trends for increased foliar [N] and [K] compared to MB and SP regardless of nutrient source, which was the same trend that WC and GC had a higher soil [N] and [K]. WB and SP had greater foliar [P], and GC had lower foliar [P], which may indicate negative interaction with [N]. GC treated trees received the lowest foliar [Ca] even though no significant differences were found among the treatments for the [Ca]. This was the opposite trends of [K] except WC since [K] is known to antagonize [Ca] uptake. Foliar [P] and [Mg] were affected by nutrient source but not ground cover treatments. Foliar macro nutrients at all mulch plots regardless of nutrient sources had optimal levels, but the [Mg] had lower values than recommended ranges (0.35-0.5 %), especially SP with 0.24 % in leaf. Sheredded paper contained lower [Mg] compared to the other mulch materials and would provide lower soil [Mg].
SP treated trees had the highest foliar [Mn], even though SP treated soil pH was even higher than optimal soil pH value for tree growth at 10-30 cm soil depth. Foliar [Zn] ranged 16 to 23 ppm of deficient levels at all mulch plots (35-50 ppm of recommended levels).
The GC treated trees had the greatest specific leaf weight, an indicator of leaf thickness, compared to the other mulch plots regardless of nutrient source. Even though the total chlorophyll content did not show any significant differences among the treatments, GC and WC treated trees had higher chlorophyll contents.
B. Tree Performance
The trees fertilized with WC and CF had the highest tree height increment and greatest new shoot extensions after one growing season. WC and GC treated trees had the fastest incremental increase for tree height, new shoot extension, and annual trunk cross sectional area compared to SP and MB mulch plots regardless of the fertilizers. Shoot extension was directly related with annual trunk cross sectional area, which was 0.8041 of R2 value. Although the WC materials did not release nutrient elements well, small particles of wood chips would provide some nutrient sources into the soils. Also, very little weed invasion around trees grown under WC in June may provide more available nutrients to the trees compared to GC mulch plots that had more weed density. The vegetation management was more affect to the leaf N concentration than nitrogen fertilization rate, and early weed control is critical for young apple tree growth (Neilsen et al., 1984). WC+NF treated trees had the greatest root volume, whereas MB+PL had the lowest root volume. The WC and GC treated trees showed trends for greater root volume compared to MB and SP.

3. Weed Density, Japanese Damage, and Soil Water Potential
SP and WC had lower ranged 20% and 40 % of weed density, respectively in June. MB and GC ranged around 80% of weed density. Again, WC did not have any significant differences soil [NO3] compared to MB and SP in 10-30 cm depth, but WC had the greatest foliar [N] and better tree performance. This may be partly caused by weed competition for nutrients and water availability in young apple trees, especially in early growing season. Although the GC and MB had similar weed density, the weed volume was different. The compost mulch plot with high weed density and weed volume can be a habitat for larva, although it provided a good nutrient pool for tree growth. The relationship of shoot growth or leaf thickness (SLW) and JB damage was vague.
Irrigation was installed and supplied when soil tension meter was indicating slightly dry condition from May to August. So, soil water tension was similar value among the treatments during the growing season.

Impacts and Contributions/Outcomes

This research was one year experiment with young vegetative apple trees. Therefore, the long-term research is required for understanding nutrients released, soil and foliar nutrient relationships, and tree performances in the future.