A compost is considered mature (i.e., finished) when the energy and nutrient containing materials have been combined into a stable organic mass. The composting process results in a dark-brown material in which the initial constituents are no longer recognizable and further degradation is not noticeable. The length of time needed to achieve finished compost will vary with many factors and can take anywhere from a couple of weeks to over a year.

Making sure that a compost is finished before adding it the soil is very important. Application of an unfinished, carbonaceous compost could affect plant growth adversely since the compost may have its own demand for nutrients as the breakdown to maturity continues in the soil. In addition, immature composts made from nitrogen-rich feedstocks are often high in ammonium which can be toxic to plant growth. Because of the risks with use of immature composts, farmers would be wise to allow a period of at least a week between application of any compost to land and planting or seeding of crops.

Compost as a nutrient source. Finished compost is a dilute fertilizer, typically having an analysis of about (1-1-1 N-P₂O₅-K₂O), but this varies with regard to the original materials that were incorporated into the pile and how they were composted. In general, the nitrogen content of composts will vary according to the source material and how it is composted. If nitrogen-rich feedstock is used, nitrogen becomes less available as the compost matures because the composting process stabilizes nitrogen. However, nitrogen slowly becomes more available when using a carbonaceous material. Nitrogen in the form of ammonium (NH⁴) or nitrate (NO³) is readily available for plant absorption. However, these constituents are low in composts. A finished compost has little ammonium, as it is oxidized to nitrate during composting and curing or it may be lost to the air during turning. Nitrate can be leached or consumed by the organisms doing the composting. If a compost is to be used in a greenhouse mix, it is especially important that it be low in ammonium because this compound is toxic to plants at high levels.

The majority of the nitrogen in finished compost (usually over 90%) has been incorporated into organic compounds that are resistant to decomposition. Rough estimates are that only 10% to 30% of the nitrogen in these organic compounds will become available in one growing season. Some of the remaining nitrogen will become available in subsequent years and at much slower rates than in the first year.

Carbon to Nitrogen Ratio. A material having 30 times as much carbon as nitrogen, for example, is said to have a Carbon to Nitrogen Ratio (C:N) of 30:1. This C:N plays a crucial role in the availability of nitrogen in any organic material added to the soil. If the C:N is much above 30:1 microorganisms will immobilize (i.e., consume and make unavailable for plant uptake) soil nitrogen. The average C:N for composts sampled on farms in 1996 was 16.9, which represents the C:N that one would expect from a mature compost. However, some of the composts sampled had C:Ns above 30:1, with one at 41:1, which would cause immobilization of nitrogen, particularly if added in large amounts to the soil.

Phosphorus. Similar to nitrogen, much of the phosphorus in finished compost is not readily available for plant uptake since it is incorporated in organic matter. Furthermore, not all of the phosphorus released from compost is available for crop uptake, because some of the phosphorus released from organic matter by microbial and chemical action is quickly made unavailable by binding with other elements in the soil. This also happens with much of the phosphorous added from fertilizer.

Some studies where plants have been grown with compost as the sole source of fertility added have shown phosphorus deficiency more readily than nitrogen or potassium deficiencies. Generally, farmers should consider that compost is too low in phosphorus to consider use of compost in short-term fertilization of crops and should provide an additional source of phosphorus to ensure adequate crop nutrition. In the long run, however, repeated compost applications can increase levels of available phosphorus in the soil. For example, addition of 1” of compost containing 1% P₂O₅ will add 750 lb of this nutrient per acre.

Potassium. Potassium in finished compost is much more available for plant uptake than nitrogen and phosphorus since potassium is not incorporated into organic matter. However, much of the potassium can be leached from the compost since it is water soluble. In one study, potassium levels were reduced by 25% when a finished compost was left uncovered in the open over a winter.

Soluble Salts. In general, soluble salts are not a concern from additions of composts to field soil. However, soluble salts can be a serious problem when using a compost in greenhouse mixes. Incorporation of 40 tons/acre of compost in the top 6” of field soil would be a ratio of 50 parts soil to one part of compost. Compost used in the preparation of greenhouse media will make up a much greater percentage of the whole mix and therefore will have a greater influence on all aspects of fertility, including soluble salts. There have been studies that have shown that compost used in greenhouse media can create problems with high soluble salt concentrations. Some of the composts tested had soluble salt levels that could cause toxicity in greenhouse mixes. It is important to have composts tested for salt levels prior to using them in greenhouse mixes.

Compost and pH. The pH of finished compost is usually slightly alkaline. In general, composts will not raise soil pH to undesirably alkaline levels because of the low total alkalinity of composts. However, caution should be taken if the compost has been “stabilized” with the addition of lime (thus increasing the total alkalinity) or with heavy applications to certain crops such as potatoes, for which the soil pH should be about 5.3. Heavy applications cause increases in soil pH that might last for a growing season.

Heavy Metals and Trace Elements. The danger of heavy metals in some composts has received much attention. At one time, some heavy metals in some composts were high enough to be toxic to plants (copper, nickel, zinc) or of concern to human health (cadmium). There have been documented cases where elements such as boron have been raised to toxic levels with repeated applications of compost. These composts with high metals or boron were made from materials with high concentrations of these elements. Governmental regulations control the materials that may be used in composts for applications to farm land. None of these toxicity problems are likely to occur with compost that has been made from farm manures or crop residues or with the commercially available composts of today.

Have Compost Analyzed. Some soil test labs (see list of labs) will test compost. The analysis will help you evaluate the maturity of a compost and amounts of available nutrients present. Check to be sure the lab analyzes compost before submitting samples.

Take Soil Test After Applying Compost. A good way to evaluate the effect of compost in the fertility of a soil is to obtain a soil test after applying a compost. The soil test measures available plant nutrients, soil pH, and heavy metal accumulation in the soil. Check with your soil testing laboratory to see if they perform an analysis for heavy metals.

REDUCED TILLAGE

The excessive tillage that occurs on most vegetable farms (plowing, harrowing, cultipacking, bedding, cultivating) has many unintended consequences for soils and the environment. Some of the problems associated with excessive tillage include: loss of organic matter and beneficial soil organisms, increased soil erosion and pesticide runoff, reduced soil fertility, loss of soil structure and porosity, compaction, surface crusting, formation of plow pans, reduced root growth, poor drainage, and reduced water holding capacity during droughts. Results from a recent survey of 55 vegetable farms in Connecticut found that almost 90% of conventionally-tilled vegetable farms had plow pans, compared with 33% for reduced-till operations, while the latter group had almost twice as much organic matter in their soils.

Tillage is also expensive and consumes a lot of energy. Reduced-tillage systems can often reduce fuel usage and field preparation time by over 66% when compared with conventional tillage systems. These systems usually provide equal or better yields than conventional tillage and may provide many other benefits as well.

Reducing the amount of tillage that takes place or swapping to some form of conservation tillage can help reverse the problems associated with excess tillage and begin to restore the health of a soil. There are many ways to reduce tillage on your farm, from simply swapping from moldboard plows and disc-harrows to using spaders or subsoilers which cause fewer problems, to implementing strip-till, zone-till, ridge-till, no-till or permanent-bed systems. Most reduced-till systems are used in conjunction with cover crops or organic mulches to protect the soil surface at all times, help increase organic matter over time, or to help control weeds. Other examples of ways to reduce tillage include: using chisel plow shanks, subsoilers or zone-tillers to loosen soil before preparing raised-beds instead of a plow and harrow; the use of summer cover crops, such as buckwheat, after an early cash crop, as a substitute for repeated harrowing to control weeds; rotary mowing crop residues instead of disking; switching to tillage radishes or other deep-rooted cover crops to help break up plow pans: and switching to a no-till drill to plant cover crops, instead of passing a light harrow to assure good seed-to-soil contact for emergence.

Deep zone-tillage, also known as vertical-tillage, is one of the more promising and versatile methods of reduced tillage for vegetables in our climate and can help vegetable farmers reverse the ill effects of years of excessive tillage on their soils. Deep zone-tillage is similar to no-till in that it relies on the residue of a cover crop to protect the soil surface and help improve soil health over time. Unlike no-till, which relies on a heavy blanket of plant residue in the planting row to protect the soil, and inadvertently delays crop growth in Northern climates, deep zone tillage uses a 5-inch-wide tilled strip to simultaneously break up plow pans, prepare a seedbed and warm the soil. The cover crop must be dead before preparing the seedbed. Planting and fertilizing can often be done in the same pass, further reducing fuel, machine hours, labor costs, fertilizer rates, and soil compaction. Soil drainage can be improved immediately and continues to improve each year.

Machines used for deep zone-tillage usually consist of a lead coulter to cut through the killed-cover crop residue, followed by a deep shank or subsoiler to break up the plow-pan, and finally a pair of fluted coulters and a rolling basket to prepare a narrow seedbed and help break up soil clods. The deep shank is mounted onto a hinged frame which allows the shank to rise out of the ground when it encounters large rocks or ledge, while spring resets push the shank back into position after passing over the obstacle. Crop roots grow deep through the slit made by the shank rather than just spreading out in the top few inches of soil above the plow pan. Additional coulters or (finger-like) residue managers are mounted on the planter in front of the planting shoe to remove excess cover crop residue and stones to provide a finished seed bed.

The soil surface between the crop rows retains the heavy surface residue from the dead cover crop. The 5-inch-wide tilled strip is slightly raised, warms faster than residue-covered soils or flat surfaces, and does not allow water to build up enough speed to erode a slope. Roots and surface residue from the cover crop in the untilled area between crop rows does not break down as fast as when the soil is tilled/aerated, so organic matter tends to rise slowly over time. With the return of organic matter, comes the return of beneficial organisms, better soil structure and a healthier, more productive soil.

No-till planters have double-disk openers and closing wheels to create and close the seed furrow in a thick cover crop residue. These planters rely on down-pressure springs and/or extra weight to assure that the seed furrow can be created, especially in a dry or compacted soil. If the accumulated crop residue is too thick or unevenly distributed the planters may also have residue managers to move some of the debris before planting. No-till planting can be used for late-planted vegetables in New England, after the soil has warmed under the cover crop residue. It works well for pumpkins and winter squash or summer plantings of sweet corn or other vegetables. When transitioning from conventional to no-till, yields have been know to decline slightly for a few years before recovering as the soil characteristics improve. No-till is very fuel efficient.

Strip-tillage, sometimes referred to as shallow zone-tillage, is similar to deep zone tillage without the subsoiling shank to break up the plow pan. The machine has a large front coulter to cut through the residue, followed by two opposing coulters and a rolling basket to prepare and smooth a narrow seedbed through the surface residue. Because the machine lacks a deep shank, this system does not have the ability to improve drainage immediately, and it may take several years for the soil health attributes and drainage to improve. However, on farms without a plow pan this system can provide most of the benefits of deep zone tillage and uses less fuel.

Ridge tillage is a reduced tillage system where the crop is grown on top of permanent ridges. The old crop residue and the top of the ridge is scrapped away or flattened before or as the new crop is planted and then the ridge is restored to full height during the final cultivation. Usually two cultivations are required to help control weeds, loosen the soil and re-construct the ridges. As with many reduced-till systems, specialized equipment is required for planting, cultivating and possibly harvesting. Ridge tillage helps conserve moisture, lower inputs, and provide a warmer and dryer soil environment for seeds.

Permanent bed systems help limit soil compaction and maintain soil structure. Equipment and foot traffic is limited to paths or tracks between the beds. Some permanent beds are raised structures while others are not. There are many different ways to construct permanent beds. One simple method is to use a spader to till the soil and provide a rotation between cover crops and cash crops to provide organic matter, nutrients, weed suppression and a great soil environment for healthy crops. Mulch is often used with permanent raised beds to add organic matter and suppress weeds