In the spring of 2000, two peach blocks were set up as a trial for mulch of community collected leaf organic matter (OM) to improve orchard soils. Specifically, we compared the use of leaves to no leaves applied, and we compared the use of supplementary nitrogen to offset the nitrogen needs of decomposing OM. Finally, we compared incorporating leaves into soils where new trees were being planted or applying leaves only to the soil surface. Tree growth, nutrient status, and fruit quality were determined. Information about composting and the benefits of soil OM were relayed to growers who readily adopted the practice as a measure to improve soil fertility, increase tree growth, and improve yields.
Encourage the use of a community solid waste for a beneficial agricultural practice.
Extend the productive lifespan of peach orchards (lifespan declines 40% for second planting)
Reduce/replace input of chemical fertilizers
Demonstrate the use of leaf organic matter for improving the soil quality of young peach orchards
Determine the best application strategy for using leaf organic matter on young peach orchards regarding tree growth, survival, and productivity
Determine if the addition of calcium and nitrogen to the soil from leaf organic matter affects peach fruit quality and postharvest storage life
The project began in the fall of 1999 when 6 acres of plots were identified and mapped out. Two plantings were used. The first was a four year old block of ‘Jersey Queen’ peaches and the second planting was made up of ‘Sugar Giant’ trees to be planted when treatments were initiated. Each plot was 6.7 m x 29.3 m (22 ft. x 96 ft.) and contained 6 trees. Within the Jersey Queen block, 40 plots of 6 healthy trees were identified. Of the 6 trees in the plots, the two end trees would serve as guard trees and the interior 4 trees were data trees. The Sugar Giant block was designed to include 60 plots, each plot had six trees. Individual plots for leaf mulch applications included the area under the trees extending to the middle of the drive row on either side of the data and guard trees. Studies have shown that the root zone is almost entirely limited to the area under the trees in the sod and vegetation free zone. Peach trees usually do not grow roots under sod due to the strong competition from grass roots.
Leaves were applied at the onset of the study, February and March of 2000. In the case of the bearing trees, leaves were applied with a side delivery mulch spreader, and, where the new trees were to be planted, leaves were spread using a rear delivery manure spreader. Plots received leaves to a depth of approximately 15 centimeters, which on an area basis is approximately 45Mg ha-1 (18T / acre). Data was collected from the plots from 2000 until the end of the 2002 growing season.
Treatments applied: In the established Jersey Queen orchard there were 4 treatments in a split plot design with the main treatments being leaves verses no leaves and supplemental nitrogen vs. no supplemental nitrogen. Supplemental nitrogen applications were introduced to improve the carbon to nitrogen ratio where leaves were added. The treatments in the Jersey Queen block were 1) no leaves with no nitrogen (CO), 2) no leaves with added nitrogen (CN), 3) leaf application with no nitrogen (LO), and 4) leaf application with added nitrogen (LN). Nitrogen treatments were applied in 2000 and 2001 at a rate of 5.2 lbs of calcium nitrate per plot or 14 oz. per tree.
In the new orchard where the new Sugar Giant trees were planted, two additional treatments were included. We split that treatment where the leaves were applied and incorporated half of those plots into the soil while the other plots remained on the surface. Incorporation of leaves prior to the next tillage season is a New Jersey state requirement for leaf application. Since the regulations were written with annual field crops in mind, and not perennial tree fruit crops, we included the incorporation treatment to understand the benefits or problems of the tillage requirement on a perennial crop. All of the treatments in the established trees were surface applied and not incorporated. The first four treatments in the new Sugar Giant orchard were the same as the Jersey Queen block; 1) no leaves and no nitrogen, 2) no leaves and added nitrogen, 3) leaf application, 4) leaf application and added nitrogen. Then two additional treatments were added; 5) Incorporated leaves with no nitrogen (LIO), and 6) incorporated leaves with added nitrogen (LIN).
Trunk cross sectional area (TCSA) was determined at inception in 2000, and following each growing season when the trees were dormant. TCSA is a measure of tree size and correlates well with yield for peach trees.
Soil moisture samples were extracted from each plot during the growing season when there had been no precipitation for at least 10 days prior. Five sets of data were used in analyzing the soil moisture data. Samples were first weighed fresh and then again following oven drying at 105 degrees C for 72 hours to assess the percentage of moisture in the soil.
Nutrient analysis Initial soil samples were taken in late 1999 from quadrants of each of the orchard blocks. In 2000 and 2001, soil samples from each plot were taken and analyzed for standard nutrients and organic matter content.
Leaf tissue, in addition to soil analysis, was analyzed from each plot. Leaf tissue nutrition is considered a more accurate indicator of plant nutrition than soil analysis since nutrients are disproportionately taken up into the plant. Also, fruit tissue samples were analyzed from 40 plots of the bearing JQ block.
Fruit tissue nutrients, in particular calcium, are indicators of fruit quality. Flesh of ripening fruit was sampled from each of the 40 plots in the established JQ block. Calcium plays a key role in cell wall integrity and therefore strongly influences fruit flesh quality. In a previous experiment, calcium had increased in leaf tissue samples of field crop plants supplemented with leaf mulch. Because of this, careful attention was given to determine the mulch effect on leaf and fruit tissue calcium content. Flesh samples were immediately frozen until lyophilized prior to tissue nutrient analysis.
Fruit postharvest quality was assessed in 2002. Fruit samples at harvest were divided into three equal samples of 15 fruit each. Each 15 fruit sample were balanced to received fruit of the same range of maturity as visually determined by ground color. One sample was evaluated at harvest, and then after 7 and 14 days of postharvest storage at 0-1 °C. Fruit were measured for diameter and flesh firmness was determined. With a small piece of the skin removed at opposite sides of the peach at right angles to the suture line flesh firmness was determined by inserting a McCormick Fruit Pressure Tester (Yakima, Wash.) equipped with a 7.9 mm stone fruit tip (Kader and Mitchell, 1989).
Trunk cross sectional area (TCSA).
The most important finding of the study was the significant TCSA increase due to leaf mulch. The established Jersey Queen trees began the study with no significant differences but by the end of the first season (2000), trees with mulch and trees with nitrogen were clearly larger than the control trees that had no mulch and no nitrogen added. Nitrogen as well as leaf mulch increased TCSA. In each sample from 2001 through 2003, the treatments followed the same pattern of growth increase. In 2000, mulched trees were 10% larger and the gains increased by 2002 to 13% larger tree trunk cross sectional area. CO (control with no added nitrogen) was smallest, CN and LO were similar, and LN had the greatest growth. Previous work showed that trunk size directly correlated with yield in peaches. So the larger trees have a correspondingly larger yield. Fruit samples were used for nutrient analysis, however yield was not determined.
Weather played a significant part in tree growth and the interaction of mulch with tree growth. The established 4-year-old trees began the experiment with a more extensive root system, whereas the newly planted Sugar Giant trees had a very small root system. During the summer of 2000, rainfall occurred frequently. Rainfall for the months of June through August of 2000 was 15.65 inches compared to only 12.00 and 10.33 for 2001 and 2002 respectively. Frequency of the 2000 precipitation kept soil moisture high. NOAA ranked the 2000 summer precipitation 86th wettest of the past 108 recorded years.
Soil that was covered with mulch retained more moisture than exposed soils and it appears that the mulch limited aeration of the soil. The lack of oxygen restricted root growth and the trees with leaves were stunted in growth. The data showed that the reduction in growth between the mulched and unmulched plots reduced tree size throughout the length of the study signifying the importance of obtaining optimal growth during the first season. Nitrogen treatments mitigated the damage and provided growth comparable to the controls but not better than the controls. A method for mitigating the lack of soil aeration during wet seasons
We observed that the method of leaf application can mitigate the problems we encountered with soil oxygen. Leaves that were distributed using a rear delivery mulch spreader was both faster, and delivered leaves in a pattern where there was more leaves delivered in the drive row and application rate diminished at you reach the center of the tree row. With the center of the tree row with few leaves allows air to pass freely into the soil thereby reducing the stress that we saw in the Sugar Giant trees. In fact, the rear delivery mulch spreader was the choice machine of the grower who initiated discussions leading to this project.
Both leaf mulch and supplemental nitrogen increased tree growth gains compared to control trees. However, growth of newly planted Sugar Giant trees with leaf mulch did not increase when the growing season was particularly wet as it was during 2000. Merwin at Cornell showed that heavy mulch cover in combination with a particularly wet growing season can reduce soil aeration and therefore reduce root growth. In this study, the year 2000 was particularly wet and trees that did not have large established root systems were most impacted. Soils with significant organic matter components develop good soil tilth. Good tilth in turn increases aeration of heavy soils by the development of aggregate particles that provide additional soil space for air.
Mulch helps maintain soil moisture by reducing vegetation, increasing organic matter, which binds water, and physically shielding the soil from direct sunlight and drying winds. Sampling for soil moisture requires a 10-day rain free period prior to sampling to allow gravitation to remove water above field capacity. In 2000, opportunities to sample soil were limited due to the frequent rain events. Mulched plots in 2000 retained 36% more soil moisture than unmulched plots. In 2001, second season for the mulch, moisture retention of mulched plots was 21% above unmulched plots. Weathering of mulch reduced the retention of moisture in the soil to 13% more, however this was no longer statistically different from the controls. Clearly, mulch provided significant moisture benefits to crop plants that strongly influence growth and yields.
Soil nutrient statistical analysis samples showed more differences due to the year of sampling than due to treatment effects. Soil samples were obtained below the mulch layer and therefore may not have documented the bulk of nutrients added from the addition of leaves. the most notable nutrient to increase due to organic mulch was potassium. In 2001, there was reported to be 44 pounds more potassium per acre in plots where leaves were applied compared to plots without leaves. Base saturation of magnesium dropped about 5% in plots with leaves applied compared to control plots.
It is very possible that nutrients from the leaf mulch did not pass into the soil matrix from the litter layer. The litter layer was NOT included in soil sampling for nutrients or for soil moisture. It is also possible that variability in the samples obscured benefits.
Leaf Tissue Nutrients
Leaf nutrient analysis discerned an effect of the supplemental nitrogen treatments; nitrogen was higher where nitrogen was applied, but only where no leaves were applied to the soil. However, the supplemental nitrogen had no effect on leaf nitrogen content where leaf applications occurred. Leaf application treatments did significantly increase leaf boron content in both plantings consistently. One other interesting thing was that leaf copper content was reduced due to the leaf applications, but only in the newly planted Sugar Giant trees. The copper was not affected by the nitrogen applications and was not significantly affected by leaf application in the established Jersey Queen trees.
Fruit tissue nutrients
Year of sample was the strongest variable in fruit nutrients, P, K, Ca, Mn, Cu, B, and Na all were significantly affected by year. Only K, B, and Al were significantly affected by treatments. Boron was the most affected where the leaf mulch treatment increased the B content an average of 25.3% over the two years. The leaf mulch increased K by 10 to 12% during the two sample years. Aluminum appears to be enhanced somewhat more by the nitrogen applications than by leaf mulch although some increase was seen from those treatments as well. It was disappointing to see that the calcium did not show statistical gains from the leaf mulch but the lack of proof was probably due to variability rather than lack of gains since the 2002 sample means indicated numeric improvements.
Fruit postharvest quality
Fruit flesh firmness is the best indicator of postharvest storage life of peaches. Fruit in this study ranged only from 13.4 to 14.0 on the day of harvest. There were no significant differences between sets of sample at any of the three sample times. It was a concern that trees with mulch would have softer fruit since excess nitrogen that could come from uncontrolled decomposition of OM could provide nitrogen in detrimental amounts. Fortunately it was determined that there was no injury or, loss of firmness resulting from the leaf applications. Means of extreme sets ranged by only 7% and considering variability, this was not sufficient to detect differences. Loss of fruit firmness did not occur over 14 days of storage averaging less than one half of one percent for the worst treatment.
Impacts of Results/Outcomes
Organic mulch has been considered the best ground cover for orchards by many of our older pomology textbooks but has not been used due to cost and availability. Not only is the practice an excellent horticultural practice, but also serves the dual role in the community of providing a terminal destination for street collected leaves, which can accumulate, into larger piles. Utilization of this community waste is a boon to sustaining soil quality in areas that benefit from increased soil OM.
Field days and several speaking engagements provided opportunities to discuss the benefits of using community collected leaves to improve orchard soils. Growers representing twenty five to thirty five percent of New Jersey peach acreage now have a better idea why OM is good for the soil and either have used leaves to improve their soils or now consider using leaf OM on their orchards.
Soil moisture benefits was the most significant soil improvement measured in this study. Over the three years following leaf applications, measured soil moisture was increased 36%, 21%, and 13%, respectively, over plots without leaf applications. Soil moisture benefits are most likely the major factor contributing to increased tree growth in the leaf mulched plots. Although it was not quantified for this study, tree size is correlated to yield, so that means that the soil moisture benefits would have direct bearing on tree size and yield.
In looking at the annual benefits to the water holding capacity of mulched plots, we observed a steady annual decrease in soil moisture retention. Since we saw that the residue of the initial leaf application diminished due to leaf decomposition, it was concluded that reapplication of the leaves annually would benefit to water holding capacity. The single application of leaf mulch was not sustaining throughout the study.
Tree growth, as measured by trunk cross sectional area (TCSA), increased significantly due to leaf mulch treatments and nitrogen applications. Growth is the most important benefit in the culture of stone fruit. In our research, TCSA correlated to mass of harvested fruit. Basically, larger trees produce more fruit. In peach orchards, tree vigor is critical to produce new flower buds for fruit production. In this trial, both leaf mulch and supplemental nitrogen increased tree size that affects yield. ‘Jersey Queen’ trees increased 10 to 13 % more than control trees during this study as a result of leaf mulch and nitrogen.
Leaf tissue analysis of nutrients detected increased tissue nitrogen resulting from the soil nitrogen treatments. However, on treatments with leaf mulch applications, nitrogen was not statistically different from the untreated trees. Leaf mulch and OM limited nitrogen available to the tree roots. One reason for that was the fact that decaying plant matter needs nitrogen as a building block for microbial activity and extracts nitrogen during decomposition. The second factor was that leaf mulch and OM have a higher affinity to bind soil nutrients than mineral components of the soil. This higher affinity releases less nitrogen into the soil matrix at any one time and acts to buffer the availability of nutrients for more sustained growth.
In addition to the effects of nitrogen on plant tissue nutrient content, the leaf mulch treatments increased plant tissue boron content significantly. Late in the season, mulched trees were visibly greener with denser foliage. Boron is vital for establishing fruit set and growth but no other nutrients increased due to the leaf mulch project. It is possible that the leaf surface area of the trees increased and since we only measured the concentration of leaf nutrients, it is feasible that we would have detected other differences had we quantified the total leaf mass rather than by concentration as is traditionally done.
Postharvest fruit quality was tested to determine if there was a benefit or detriment to leaf mulch. Trees fertilized with excess nitrogen can suffer from two types of ailments. One is a decrease in winter hardiness if trees are grow actively late in the fall and the wood does not hardened off sufficiently for winter. Tree mortality was not observed from winter injury as could have been expected if late season release of nutrients delayed hardening of tissue. The second ailment commonly attributed to excess nitrogen is greener, softer fruit. Postharvest storage results indicate that nitrogen release did not detract from fruit quality. Fruit were neither improved nor damaged by the steady release of nutrients from the decomposing leaves.
Growers using leaves to mulch orchard soils have done so while not adding supplemental fertilizers. A strong benefit to utilizing leaf mulch is that OM is composed of old plant and generally breakdown into nutrients in the proper proportions of new trees and plants. The application of 15cm thick layer of leaves supply 400 lbs of N and 640 lbs of Ca in a useable form along with a leaf content of: 1.0% N, 0.1% P, 0,38% K, 1.6% Ca, 0.2% Mg, and 0.11% S. The match is perfect and environmentally sustainable for both the communities that have the solid waste situation and the grower who receives the benefit of improved soils and sustained nutrient release.
The economic impact of leaf mulch includes both costs and benefits. Time is required to administer the shipping and handling of leaves to the farm, and documenting requirements of the state. Labor is critically important for spreading leaves during the dormant season and the loads frequently include quantities of trash. Labor must be provided to collect the trash from the fields. Another cost incurred is the space involved in receiving leaves and preparing the OM to be spread at your farm
On the plus side is the savings of not needing to purchase fertilizers for the orchards. Another benefit would be tipping fees paid by the community that needs to dispose of leaf waste. Tipping fees typically run from $2 to $4 per cubic yard of leaves delivered and is necessary to supplement the cost of handling and spreading. The most obvious benefits are the increased yields produced by the orchards and the increased lifespan that individual orchards my have as a result of improved soil quality. It is our goal to have orchards be sustaining and a major factor to sustaining orchards is maintaining soil quality, fertility and productivity.
Growers representing 25 to 35 percent of New Jersey peach acreage now have a better idea why OM is good for the soil and either have used leaves to improve their soils or now consider using leaf OM on their orchards.
Support was strong for this project by growers interested in making use of leaf mulch in their operations. Assistance was desired in making leaf applications easier particularly from a regulatory perspective. In anticipation of a second project, growers were eager to volunteer to initiate studies on their farms and offered to begin prior to funding. Growers seem to be generally aware of the benefits, but appreciate reassurance and data on performance as well as observations of replicated studies. Not only do growers learn, but researchers also learn from observing practices of growers and can assist in spreading knowledge of technique, perspective, and important contacts.