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Compost Trials in Newly Planted Orchards

Program Contact: Tianna DuPont, Tree Fruit Extension Specialist
(509) 663-8181 •

yngorchCompost Trials in Newly Planted Orchards, 1995-1997

Report by: Tim Smith, WSU Extension

Use of compost is a hot new topic in agriculture. There are an ever-increasing number of cities, stockyards and chicken ranchers touting their products to the tree fruit industry, as well as any other high value per acre crop.

Below I have reported the most up-to-date results of a number of in-orchard compost trials we have placed in North Central Washington. But first:

Composts—what are they?

These commercially sold, organic waste, soil amendment products come from a number of waste reduction programs in cities and farms around the region. It is not acceptable anymore to dump organic, compostible waste into a landfill. You now have a range of products available, some are “composts” in name only, so beware. “Composts” are generally produced from organic materials, such as livestock manure, sewage solids, wood chips, livestock bedding, tree leaves, and lawn clippings.

Despite the variability in the original substances going into the compost mix, and the complexity of the composting process, most composters are putting out a relatively consistent product. Compost “brands” vary because producers are working with different waste products and recipes, so you should ask for recent test results. Important variables include nutrient content, salt index, moisture content and percentage of non-compostable substances (soil).

Nutrients: Nutrient content is often quite low, often only 1-2 percent by weight. Since nutrient content is low, and organic carbon (undecomposed plant matter) is often quite high, most composts should be considered soil amendments, not fertilizers. They have potential for improving some aspects of soil quality when used at high rates over the short term, but do not work well as traditional, (quickly available) plant nutrient sources. Nutrient release will occur slowly as the compost is further broken down by soil organisms, often over a two or three year period. Slow nutrient release is often thought to be an advantage with some crops, but must be approached with care in young fruit orchards. If you wish to use composts as a nutrient source, they must be incorporated into the soil, and relatively high rates must be applied yearly. Waiting for a crop response will try the patience of most growers. Composts may maintain an orchard that is presently in good nutrient balance, but may not be suitable for correcting deficiencies.

Dried poultry waste has more actual plant nutrient content per unit of weight than most other composted products. However, the major nutrients are generally in the 4-7 percent (of dry weight) range, and the product is often far from being “finished” compost.

Salts: You should run a test on each new batch to be sure it isn’t too salty. Products with a salt index of 4 or less doesn’t seem to hurt trees when used moderately, even when placed in the root zone or piled at the base of the tree. However, most composts have a salt index higher than 4.

Some “salts” are the fertilizer components, such as N, P, K, Zn, etc., and are beneficial, if provided to the tree in diluted form. Other salts may be sodium or chloride, and are generally considered harmful to plants. So, to avoid tree damage, you must mix composts well with soil, and use modest rates. Trees planted into too-salty soil will be slow to break buds, and will grow slowly, if at all, early in the season. Those that survive often put on a burst of growth from mid-season to Fall, if excessive salts were leached away from the roots.

As the salt index of the compost increases, you must lower your rate per acre or per tree. Young trees are especially sensitive to salts from any source, including conventional fertilizers.

Moisture: There is a variable amount of water in compost. It often has 50-60 percent water by weight, even when the product seems fairly dry. It is the dry matter in the compost that is important, so you should do a moisture test, and pay by the adjusted dry ton.

(Simple moisture test: weigh out 10 pounds of delivered product. Spread it on the kitchen table to air dry. No, wait a minute- maybe that would complicate things around the house. Spread the product on paper in a dry, well ventilated shed. Weigh the dried product. Divide the end weight by the starting weight, then multiply by 100. This gives you a rough percentage dry weight. To do this properly, you would have to dry the product in the oven, but I doubt you could get away with that, either.)

Other Qualities: While the sellers of various composts will sing praises of their source vs. other composts, I doubt that we need to argue the biological merits of compost from one city or farm vs. another. Some producers claim their product protects crops from soil pathogens. Evidence of disease control is usually based on greenhouse pot tests, using high rates of compost on plants other than fruit trees. The disease control often involves pathogens that are not specific to common orchard problems. We should stay skeptical on these disease control claims until we see better work done on the subject. So far, my compost trials show no economically significant control of replant disease.

Claims of improved soil moisture holding capacity are weakly supported by research. One major effect of compost application comes from the usually-positive effect of a mulch. A 3-6 inch deep mulch, using many different products (not sawdust!), often leads to a tree growth response, especially on “weak” sandy soils.

Some of the non-greenhouse plant tests were done using very high rates of compost. For instance, one source tested their product by mixing in a 6 inch deep layer mixed into a garden soil. Agriculturally speaking, this is about the equivalent of 100-120 tons of compost per acre, which would cost, for some products, from $4000 to $7500 / acre, plus application costs. Obviously, the use of low-input composts at high rates would be a better economic choice on home gardens than farmland. Most of people’s positive compost experience comes from home garden use, which is great, but the observed garden benefits are not directly transferable to farms. Most farmers that use organic wastes from livestock apply 10 to 20 tons per acre, amounts that do give crop response, but far more product than we can economically use with commercial compost.


If you are a fruit grower, you should ask compost advocates and sellers about orchard results, developed through tests, not testimonials. Benefits are difficult to measure, therefore, proper tests are not often carried out. Tests that give valid results are difficult to set up, time consuming, and expensive. Because of this expense, they are rarely done properly. Tree growth differences of less than 25 percent are difficult to “eyeball” because young tree growth is quite variable. If you can “see” growth differences, the growth has probably been increased by 40-50%, an effect which is rare with any product, other than soil fumigants.

Opinion, for what it’s worth: There are no regulations encouraging the compost seller to use only information developed through careful, well designed tests. While most composters are as honest as the rest of us, and strongly believe that they are selling a good, useful product, some appear to be selling you a product full of “hopes and feelings”. Compost use is a “good” behavior, beneficial to the soil, the environment, and people who need to dispose of organic waste products. You will have difficulty proving their claims wrong (or right.) The evidence of compost benefit is often taken from one or two duplicated magazine articles describing tests run by unheard-of people at obscure research centers, claiming major benefits to annual plants. You can be sure that the article you are now reading will not be hand-out material. Keep an open, but slightly skeptical, mind. Low rates of compost can cost $100 to $200 an acre. Low rates are not likely to do your orchard measurable good. Applying the rates reported as beneficial in some tests could cost you thousands of dollars per acre, and be much more labor intensive than you can do in larger scale plantings. The investment you make on any product should return at least a small profit, and be neutral or beneficial to the environment.


“BIOSOLIDS”: Biosolids are the slightly-processed or semi-processed solids that settle out of city sewage. These products have been spread (one time per field) on Eastern Washington wheat land during the fallow season, often with very good subsequent wheat growth and production. All concerned, farmer and producers, are very pleased with the results. There is enough wheat land in Eastern Washington to take care of the disposal of this beneficial product for hundreds of years. As with most “composts” these have quite a highly variable water content,depending on the source. Biosolids can vary in qualities and physical characteristics as it is delivered. Some has been dried, ground and screened to improve its handling characteristics. As this biosolid industry has evolved, some local biosolids managers have better refined their product, which greatly improves its appearance, somewhat “de-smells” it, and greatly reduces potential heavy metal content. However, the “point source” that the original organic matter came from is objectionable to many of the more sensitive public, if they bother to think about it.

As of this moment in American history, public attitudes about the use of even “composted” human waste on fresh fruit or vegetable production lands should prevent anyone in the fruit industry from using it. This stuff is too close to the source, if you know what I mean. Packinghouses specifically forbid the use of sewage biosolids in the production of fruit, not because of real safety issues, but because of the image problem. We don’t want to get into the position of having to have signs above the fruit section at the local store, assuring the public that human waste is not hazardous, and these apples are just fine if washed carefully. ( Just be sure to wash your hands before handling other food items ). Really,…….. trust us on this one. There are plenty of other places that we can put biosolids to beneficial use, we don’t need them on orchards.

MUNICIPAL COMPOST is a mixture of leaves, chipped tree limbs, yard waste, and (sometimes, but rarely) “biosolids” from various cities, composted into an earthy, well mixed organic amendment that any home gardener would be happy to use on their garden. This product has become available because many cities decided to recycle yard and park waste, rather than throw the stuff into the dump at great cost. Of course, these cities would like to turn this waste into gold, so are selling it to anyone willing to buy. There is some small amount of nutrient in the compost, but most of the value is in the organic matter, which can act as a nutrient buffer and improve the soil structure for a year or two after application.

COMPOSTED CHICKEN LITTER is also called DPW- for “Dried Poultry Waste.” It is the stuff used to cover the floors of the vast chicken coops of Western Washington and Oregon. It is composed of lots of wood chips and chicken “droppings”, (and a few decomposed chickens) aged and scratched around under the biddies feet for a few months or so, until the chickens can’t stand it anymore, then piled and turned until it is well composted. This stuff is hot. There is quite a bit of nitrogen, phosphorus and zinc in the product (the ammonia in some batches almost brings tears to your eyes) . While you can safely use lots of unsalty municipal compost in the orchard, you must be careful with DPW rates. Too much at once can burn the trees. Some so-called chicken “compost” is actually chicken litter, uncomposted, complete with feathers and chicken parts.

We get some pretty impressive grower testimonials about the positive effects of chicken litter. I hear that it improves the growth of trees struggling to survive on shallow, poor soil zones, especially in the strange soils near Chelan and Manson. This positive effect has been limited to a few very specific situations, and has not been duplicated under more normal orchard soil conditions. In general, DPW treatments tend to show the most benefits on the worst soils. If your orchard has some bald spots where trees grow poorly, it’s worth a look. Just go easy on the rate per tree. A 5 gallon bucketful per tree applied all at one time can burn and kill the tree.


I really had high hopes that we would be able to measure benefits from the use of composts on fruit trees. It would have been just be so peachy if we could have used a waste product to get better tree growth on some difficult replant sites. Soil fumigation has proven very vital and effective, but we still can’t get the kind of consistent tree growth seen on “virgin” sites. I hoped that fumigation and compost combined would do the trick. Unfortunately, I have not been able to get results in orchard trials that lead me to believe that economic rates and application methods will pay off for the grower. Below are the results of a number of trials we have placed in commercial orchards:


After some interesting trial results in 1994, I increased efforts in 1995 and 1996. I placed either municipal compost or chicken litter on apples or pears in four different replant sites Spring, 1995, with follow-up applications in 1996. and 1997 In 1996, Co-worker Guy Witney, (an experienced compost spreader), and I set up a large compost trial in newly planted apples to demonstrate the effect of surface application of different rates of various products. These trials alternated the treatments randomly in the orchard and involved up to 110 treated vs. untreated trees each, so we gave the products a good chance to work (or not). We are measuring vegetative growth of the tree for the first two or three years after planting.


In August 1996 and 1997, leaf analysis for N, P, K, S, B, Fe, Ca, Mg, and Zn did not show us any differences in leaf nutrient content between the various treatments in these trials, despite intensive (and costly) sampling.


NOTE: Calculating the increase in the cross sectional area of the trunk is a very accurate way to measure a trees’ vegetative growth. The “Percent Growth” mentioned below is calculated by determining the trees’ present cross sectional area, then dividing that by the cross sectional area of the tree measured at the time it was planted, then deducting 100 . A 100% growth indicates that the tree trunk has twice the cross section area that it had when it was planted.

Municipal compost (Kent and Seattle, Washington) on apple:

TREATMENT 1st Season 1st Season 2nd Year Fruit/Tree
NO Compost 136% Trunk Growth 17.3 inches leader growth 10.7
4 Tons Compost / Acre 135% 15.1 8.4
8 Tons Compost / Acre 134% 16.7 10.2

There was no statistical difference between any of these treatments. Pay no attention to the very minor numerical differences, there was no treatment effect. With the normal variation we see in tree growth, it was odd to see all the tree growth and fruit yields average out this close.

Chicken litter compost was mixed into the planting hole soil Spring 1995, then to soil surface in Spring, 1996:


No Compost 79% 280% 616% 22.5
1.5 pounds / tree 91% 283% 698% 30
3.0 pounds / tree 76% 260% 695% 19

There was no statistical difference between any of these treatments. Pay no attention to the minor numerical differences, they doesn’t mean anything.

Mixed into the planting hole, Spring 1995 , soil surface applied Spring, 1996:


NO COMPOST 180 Percent 688% 1445% 7.6 lbs./ tree
3 POUNDS / YEAR 194% 695% 1566% 4.4 lbs. / tree

NOTE that the growth of the trees remained the same for the first two seasons, then began to be different in the third year. Also note that the untreated trees yielded more in the third season, which explains why they grew less than the treated ones.

Note: the “rate per acre” referrs to the rate applied to a band 6 feet wide down the tree row. The first application was applied soon after planting and lightly incorporated, the second application was made to the soil surface, and not incorporated. There are four blocks of 10 trees treated for each product- the “middle” 8 trees are measured in each block, for a total of 32 trees per treatment.


GROWTH % 1996 GROWTH % 1997 YIELD 1998 lb./tree
UNTREATED 82 315 19.39 pounds
MUNICIPAL 2.5 T 73 271 20.40
MUNICIPAL 5 TON 73 295 19.46
CHICKEN LIT. 1 T 73 294 17.00
CHICK.LITTER 2 T 67 254 17.39
BOVINE 2.5 TON 80 294 19.53
BOVINE 5 TON 72 246 19.24
HUMIC ACID 1000 LBS / YEAR 63 250 18.20
WOOD ASH 900 LBS. YEAR 1 79 290 16.95
COMPOST MIX 78 266 16.21
AVERAGES 74 278 18.38

There were some minor numerical differences between treatments relative to trunk growth, but we should probably wait before making any suggestions that these treatments did anything at all. Especially since the untreated trees grew slightly better than those we treated.

1997 LEAF ANALYSIS DATA- August Leaf Sample (same 320 tree test as above).


UNTREATED 2.17 0.18 1.84 1.46 0.24
MUNICIPAL 2.5 T 2.18 0.18 1.70 1.44 0.24
MUNICIPAL 5 TON 2.24 0.18 1.80 1.44 0.25
CHICKEN LIT. 1 T 2.23 0.18 1.81 1.41 0.25
CHICK.LITTER 2 T 2.09 0.17 1.73 1.37 0.22
BOVINE 2.5 TON 2.08 0.17 1.94 1.38 0.23
BOVINE 5 TON 2.11 0.17 1.68 1.40 0.21
HUMIC ACID 1000 LBS / YEAR 2.14 0.18 1.83 1.50 0.23
WOOD ASH 900 LBS. YEAR 1 2.24 0.17 1.84 1.51 0.26
AVERAGES 2.16 0.18 1.80 1.43 0.24

The most impressive aspect of the leaf analysis is the lack of real differences amoung the treatments. We also tested for levels of zinc, boron, copper, iron and manganese, with similar lack of differences.