Orchard floor management practicies for improving soil quality and optimizing nitrogen uptake efficiency

Final Report for SW00-016

Project Type: Research and Education
Funds awarded in 2000: $130,330.00
Projected End Date: 12/31/2004
Matching Non-Federal Funds: $45,120.00
Region: Western
State: Oregon
Principal Investigator:
Anita Azarenko
OSU - Dept. of Horticulture
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Project Information

Abstract:

Orchardists have identified orchard floor management as critical for the success of alternative orchard floor management systems (AOFMS). This project investigated soil quality and N uptake, utilization, and distribution in a range of AOFMS. Soil nutrients, physical properties, and community structure were used to evaluate soil quality under different soil amendments (compost, bark mulch, or mowed clippings) and weed control practices (herbicide or cultivation). Trees were labeled with 15N to determine how AOFMS influenced fertilizer uptake and utilization. In general, compost had the greatest effect on soil quality and resulted in the least efficient uptake of fertilizer.

Project Objectives:

1. Evaluate the effect of alternative orchard floor management systems on soil quality with emphasis on soil biological characteristics.
2. Determine if the AOFMS can alter the uptake efficiency of fertilizer N, its distribution, and recycling within the tree.
3. Determine feasibility of AOFMS in commercial orchards (by considering the effect on pest populations, tree growth, yield, and fruit quality)
4. Perform cost and return analyses for different AOFMS.
5. Communicate the research findings at Integrated Fruit Production workshops, grower meetings, annual professional meetings, and via grower, scientific, and web-based publications.

Introduction:

A grower-driven Integrated Fruit Production (IFP) Program is being implemented in the fruit growing district of Hood River, OR. It considers production, environmental, and economic issues in an orchard system framework. As part of this program, orchardists, field representatives, extension, and research faculty identified components of the orchard system that need better understanding and improvements. Orchardists suggested alternative orchard floor management systems (AOFMS) to address major concerns in orchard systems, such as improving soil fertility and pest management and controlling soil erosion, surface runoff of pesticides, and compaction. Orchardists identified within tree row management as critical for the success of AOFMS.

The movement of fertilizer-derived nitrates in the groundwater is a major concern in orchards. The percentage of N from applied fertilizer that is removed from the field by the crop is lowest in fruit trees, <20% (11). The highest soil nitrate concentrations have been discovered below the root zones of orchards (10). Over application of nitrogen in orchard systems has been a common practice (7, 12). However, no economic incentive exists to manage N because fertilizer costs represent a small proportion of expenses. More recently, an awareness of the direct and indirect consequences of over fertilization with N on fruit quality and maturity, tree growth, and productivity is developing. Based on these concerns, grower input, and a review of the current practices in annual and perennial cropping systems of IFP and organic producers, we evaluated soil quality and N uptake, utilization, and distribution in a range of AOFMS. Criteria for tree row management systems defined by the orchardists included: reduce surface runoff, enhance soil fertility, not compete for nutrients and water, provide weed control, not interfere with irrigation strategies, not host voles and gophers, not harbor insect pests and diseases, and be economical. Soil physical characteristics include bulk density and infiltration rate. Organic alleyway management can improve both of these physical properties (4). Soil chemical quality characteristics include organic matter content, nutrient availability, and pH. Soil management can be used to alter soil organic matter content, total N, and available P and K (6, 8). Nutrient management practices in organic orchards, such as applying mown clippings to the alleyway, enhance nutrient transfer and increase nutrient availability (4). In addition to the criteria listed above, orchardists are interested in how soil biota can be manipulated to optimize nutrient availability. Relatively little is known about the effect of management practices on the soil community in perennial systems. Changes in biological parameters are often indicators of change in soil quality (5). Microbes are responsible for the decomposition of organic inputs and conversion of nutrients into forms available to plants. Soil management can alter the soil community in annual and perennial systems (3, 9). Soil organisms are responsible for cycling nutrients in the soil. Soil community enrichment has been correlated with leaf phosphorous content (3). Changes in soil biodiversity have also been associated with nitrogen mineralization and availability (1). This project aimed to evaluate soil physical, chemical, and biological quality as well as N uptake, utilization, and distribution in a range of alternative orchard floor management systems (AOFMS).
1. De Ruiter, P.C., J.A.Van Veen, J.C. Moore, L. Brussard, and H.W. Hunt. 1993. Calculation of nitrogen mineralization in soil food webs. Plant Soil. 157: 263-273.
2. Ferris, H, Bongers, T, de Goede, RGM, 2001. A framework for soil food web diagnostics: extension of the nematode faunal analysis concept. Appl Soil Ecol 18, 13-29.
3. Forge, T.A., E. Hogue, G. Neilsen, and D. Neilsen. 2003. Effects of organic mulches on soil microfauna in the root zone of apple: implications for nutrient fluxes and functional diversity of the soil food web. Appl. Soil Ecol. 22: 39-54.
4. Goh, K.M., D.R. Pearson, and M.J. Daly. 2001. Effects of apple orchard production systems on some important soil physical, chemical and biological quality parameters. Biol. Agric. Hortic. 18:269-292.
5. Kennedy, A.C. and R.I. Papendick. 1995. Microbial characteristics of soil quality. J. Soil Water Cons. 50:243-248.
6. Merwin, I.A. and W.C. Stiles. 1994. Orchard groundcover management impacts on apple tree growth and yield, and nutrient availability and uptake. J. Amer. Soc. Hort. Sci. 119:209-215.
7. Merwin, I.A., J.A. Ray, T.S. Steenhuis, and J. Boll. 1996. Groundcover management systems influence fungicide and nitrate-N concentrations in leachate and runoff from a New York apple orchard. J. Amer. Soc. Hort. Sci. 121:249-257.
8. Munro, T.L., H.F. Cook, and H.C. Lee. 2002. Sustainability indicators used to compare properties of organic and conventionally managed topsoils. Biol. Agric. Hortic. 20:201-214.
9. Neher, D.A. 1999. Nematode communities in organically and conventionally managed agricultural soils. J. Nematol. 31: 142-154.
10. Nightingale, H.I. 1972. Nitrates in soil and groundwater beneath irrigated and fertilized crops. Soil Sci. 114:300-331.
11. Sanchez, E., H. Khemira, D. Sugar, and T.L. Righetti. 1995. Nitrogen management in orchards. p. 327-380. P. Bacon (ed). Nitrogen Fertilization in the Environment. Marcel Dekker, Inc. New York, NY.
12. Weinbaum, S.A., R.S. Johnson and T.M. DeJong. 1992. Causes and consequences of over fertilization in orchards. HortTechnology 2:112-121.

Research

Materials and methods:

Detailed soil quality analysis and 15N labeling studies were performed at OSU’s Lewis Brown Research Farm in Corvallis, OR and the MCAREC farm in Hood River, OR. Tree rows were treated either with a conventional herbicide or tillage with an in-row cultivator. Within each row, soil amendments were applied representing a range of C:N ratios. The amendments used were bark mulch, compost, and mowed vetch/barley clippings (cut in the alleyway and blown into the tree row. In addition, the feasibility of tillage alone and in combination with amendments was evaluated at 2 commercial organic orchards.

Research plots at the Corvallis site (LB) consisted of 7-year-old ‘Fuji’ trees on dwarfing M26 rootstock planted on a 1.7m x 4.3m spacing. Each plot contained 5 trees. The Hood River site (HR) consited of alternating rows of 3-year-old ‘Red Delicious’ on M7EMLA rootstock and ‘Granny Smith’ trees on M26EMLA rootstock. Tree spacing was 1.5m x 5.5m. HR plots contained 4 trees. Treatments at both sites were replicated 3 times in a split-plot design with herbicide vs. cultivation as the main effect and amendment as the sub-plot effect.

Under objective 1.
In 2001, soil samples were collected and bacterial and fungal biomass was determined in each AOFMS treatment. In 2002 and 2003, soil community analysis was conducted using nematode populations as an indicator (3). At LB, soil respiration readings were taken from March through October of 2003 as an indicator of mineralization. Soil organic matter, nutrient content, and pH were analyzed before the trial began and in 2002 and 2003. Bulk density and infiltration rates were determined each year using the soil quality kit.

Under objective 2
Fertilizer N was applied at bud-break each year. A rate of 22.5 kg/ha was used at HR and 45 kg/ha at LB based on tree age and vigor and soil and leaf N levels. Labeled urea was applied to single, different trees within each plot for the 3 years of the trial. Enriched (15NH4)2SO4 was used in 2001 and depleted (15NH4)2SO4 in 2002 and 2003. Components of the labeled trees were sampled during each growing season and at harvest in 2003 the trees were destructively harvested and split into components: fruit, spurs, leaves, 1st year growth, old growth, and roots. Component samples were used to determine how much of the N was derived from fertilizer, how the fertilizer N was distributed in the tree, and if uptake and distribution were changed by AOFMS over time.

Under objective 3
Cooperating farmers were interviewed to determine the feasibility of whether the investigated soil management practices could be incorporated in their orchards. Tree growth was determined by measuring trunk circumference and calculating area each fall. Yields were weighed each year. In 2001, fruit from HR was processed on a fruit processing line. Weed assessments were done visually. Traps were set at LB to determine if rodent pests were increased by soil amendment.

Research results and discussion:

Objective 1 – Chemical Characteristics – Herbicide and cultivation treatments had little effect on soil quality. Soil amendments did affect chemical quality. Compost generally caused the greatest change in soil nutrient content. The total amount of N (7.3 ppm NO3- and 1.7 ppm NH4 at LB) and P (76 ppm at LB) was greatest in soil under compost amendment. The change in P from before application to 2003 was highest in compost treated plots. Bark mulch also increased N and P at HR. Compost amendment also significantly increased the pH of the soil (a change of 1 pH at LB).
Compost amended soils contained more organic matter than soils under other treatments (3.8% at HR and 4.9% at LB compared to 2.2% and 3.6% respectively in unamended soil). At LB, the infiltration was fastest under compost. However, the differences were not significant. At HR, infiltration was slowest under compost and fastest under bark mulch, although differences were again not significant. Bulk density was lowest in compost amended soils at both LB and HR. In soil moisture measurements taken every 2 weeks at LB during the summer of 2003, soil moisture under compost and bark mulch was not significantly different from the unamended and mow and blow plots. Early in the season, soil temperatures under compost and bark mulch amendments were lower than in the control and mow and blow plots. As the season progressed, these differenced disappeared.
Microbial activity and mineralization as indicated by soil respiration was not affected by herbicide vs. cultivation treatments except immediately following mow and blow application of fresh green vetch/barley cover crop. Activity was highest in compost amended plots, followed by bark mulch. Except immediately following amendment, respiration rates in mow and blow plots were not significantly different from the control.
Soil nematode analysis was used as an indicator of soil community structure, enrichment, and diversity. In 2002, when amendments were 2 years old, compost had the greatest effect on the soil population. At both sites compost amended soils had the highest number of total nematodes, bacterivores, and fungivores. The number of nematodes in the CP (colonizer-persister) 1 ranking was also highest in compost amended soils, indicating enrichment of the soil environment. In 2003, after the application of a fresh layer of compost and bark mulch, the differences among the treatments were diminished. In both years, herbicide and cultivation had little effect on the soil population. Despite differences between treatments, when data are presented graphically on a faunal profile plot as suggested by Ferris et al. (3), all treatments fall in the B or C quadrats. The B quadrat represents N-enriched soil with low disturbance levels and a maturing soil community. The C quadrat represents similar soil with less enrichment. These soil types are both hypothesized to be appropriate for perennial crop production.
It appears that soil amendments can improve soil quality. Additions of organic matter improve physical characteristics. Nutrient availability is also increased. It is not clear if changes in soil chemistry are due to the chemical content of the amendment or to increased size and activity of the soil microbe populations remobilizing nutrients.

Objective 2 – Trees in the compost plots were the least efficient at taking up N from fertilizer. The % N derived from fertilizer (NDFF) was lowest in compost treated plots for all plant parts and all years of 15N application. With compost amendment the activity of soil microbes was increased. Mineralization by soil microbes may have remobilized soil nutrients, increasing the availability of N from sources other than fertilizer in these plots and decreasing the amount of N from fertilizer taken up by the trees.
Uptake efficiency of trees in bark mulch plots was low in trees labeled with 15N in 2003 but the uptake efficiency and NDFF in 2002 labeled trees was similar to the mow and blow treatment. Bark mulch has a high C:N ratio. This may lead to the immobilization of N applied as fertilizer and its slow remobilization over time. While less NDFF was utilized by the trees in bark mulch plots in the first year after application, slowly available 15N remobilized by soil microbes may be taken up by the tree, increasing uptake efficiency a year after 15N application.
The uptake efficiency and NDFF of 2003 labeled trees in mow and blow plots was higher than the control, but this difference is not consistent across plant parts. While the older wood, roots, and spurs of mow and blow treated trees had lower NDFF than the control, the fruit, current year’s wood, and leaves had higher NDFF than the control. With fewer nutrients available from the soil and less microbial activity than in compost and bark mulch amended plots, trees in mow and blow plots relied more on N provided as fertilizer. Rapidly growing and reproductive tissues are strong sinks for N, thus more NDFF is distributed to these tissues.

Objective 3 – The grower cooperator who continued treatments through the end of the project reported that soil amendments layered under the trees caused problems with scion rooting. Care had to be taken to keep amendments away from the base of the trees. He also reported uneven and delayed ripening in amended plots. Despite these problems, this grower has incorporated compost into his management practices to improve soil quality.
At LB, there were no significant differences in tree growth due to treatments. At HR, the trunk cross sectional area of trees in compost plots was significantly higher than in other plots (21.7 cm3 in compost plots, 18.1 cm3 in control plots). In herbicide/compost and herbicide/bark mulch treatments, root growth is increased by a flush of fine roots growing in the amendment layer. There does not appear to be a compensating decrease in root growth lower in the profile in these plots. Yield differences among treatments were not seen. At LB, trees had a strong biennial bearing habit and at HR trees were young and their yields variable. No differences were seen in the quality of the fruit from HR.
Weeds were best controlled by herbicide and by bark mulch and compost. There are few rodent pests at either site, and they were not increased by soil management practices.

Research conclusions:

It is surprising that there was little difference between herbicide use and cultivation. This outcome allows us to reassure organic and sustainable growers that cultivation practices in perennial systems do not appear to decrease soil quality. This may be due to the limited number of times cultivation is necessary in an orchard, especially if there is some tolerance for weeds. Herbicides, applied only a few times a year, again with some tolerance for weeds, do not appear to decrease the soil microbial populations.
The use of soil amendments to improve soil quality may be a valuable management tool for orchardists. The problem of scion rooting should be avoided by leaving a bare area around the base of trees. Further research should be done to determine how amendments can be used to make nutrients available at times of high tree demand. Although it did not have much effect on soil quality, mow and blow applications of fresh green plant material may provide a rapid burst of nutrient availability. Slowly available nutrients from bark mulch may be useful in controlling nutrition in newly planted orchards. Compost improves soil quality and microbial activity. It could be used as a source of nutrients and organic matter in the orchard system.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Updates and results of this project have been presented at multiple meetings. Presentations at extension meetings and tours often include discussions of soil quality and hands-on demonstrations of soil quality measurement methods.

2001
March – IFP Soil quality workshop, Mosier, OR – soil quality presentation and demonstration
June – Lewis Brown Farm, Tree fruit field tour, Corvallis, OR – tour of research plots International Horticulture Society Field Tour, Corvallis, OR – tour of research plots
July – Pear growers talk and demonstration of Rinieri cultivator, Corvallis, OR
August – Hood River, MCAREC field day – soil quality presentation

2002
July – Hood River, MCAREC field day – soil quality presentation and demonstration
November – NW Organic Research Symposium, Yakima, WA – poster – Apple research review, Hood River, OR – poster

2003
May – Extension farm tour, Salem, OR – tour of grower/cooperator plots – Organic Tree Fruit Production Conference, Denver, CO – research presentation
July – Hood River, MCAREC field day – soil quality talk and demonstration

2004
February – Hood River winter fruit production meeting – presentation of research
June – Extension Service Stone Fruit Tour, Corvallis, OR – soil quality and biology discussion
July – ASHS annual meeting, Austin, TX – research presentation

Project Outcomes

Project outcomes:

In a mature apple orchard managed conventionally, we can expect approximately 50 bins/Ac yield at $150 a bin. The gross per acre is $7500. For an organic system, yield is projected to be 40 bins/Ac at $225 a bin, for a gross return of $9000 per acre. The inputs for management systems vary in cost, especially initial start-up costs for purchasing equipment. Conventional systems maintaining a weed free tree row with herbicides and using no soil amendments would cost the grower $50/Ac to manage. If compost is used as an amendment and tree rows are cultivated to manage weeds, the cost is $18,340/Ac. This total includes the purchase of an in-row cultivator and row mulcher. If bark mulch is substituted for compost, the total is $18,190.

Farmer Adoption

Despite problems he reported with the compost amendment, one of our cooperating farmers has included compost amendments in his orchard management practices. It is too early to assess farmer adoption on a large scale, but orchardists have expressed interest in soil amendments as tools for weed and nutrient management, especially in organic systems.

Recommendations:

Areas needing additional study

Additional research needs to be conducted to determine how altering the soil community structure affects nutrient availability and turnover. How organic or low-input soil management practices can be used to control and time nutrient availability is also an area that needs further investigation. In addition, investigations are needed to determine if soil community structure can be used as an indicator for soil quality and function. Research in other perennial systems to expand the application of these findings should also be conducted.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.