Contamination concerns by the horticulture market

A major concern in the horticulture market is compost quality (Ozores-Hampton, 2017). Even though many compost applications in the horticulture market are annual, the collective results of yearly applications can be permanent. This raises more concerns than most other markets because the horticulture market is linked to the food chain. Horticulture soils produce edible products for humans or animals consumption. Permanent contamination of farm soils with inert, heavy metals or other undesirable compounds may render the land unproductive in the future and raises all kinds of concern for liabilities. The United States simply cannot afford to use poor quality compost products on prime farmlands.

High-quality composts will only improve prime farmland when they are applied.

The source of potential contamination and the frequency are important to the public. The horticulture industry believes that composts with biosolids should be more carefully monitored than YW because of the potential for heavy metal or disease contamination (Goldstein and Steuteville, 1993; Jones, 1992). The fear of the unknown is often what guides public perceptions.

In a survey of California farmers, the highest concern rated among respondents was physical or chemical contamination (Grobe and Buchanan, 1993). A trial marketing program in Ohio, linking farmers with sawdust from a cabinet maker, failed because of the small pieces of formica residuals in the sawdust. Since the formica was white and was readily distinguishable, many farmers refused to set up trial loads to be used as soil amendment. Those involved in the survey identified the formica contamination as a major barrier to establishing a soil amendment program with the available sawdust.

The leading method to ensure that the potential danger for contamination is reduced is to compost only source-separated materials. Table 12.2 shows in column D the lowest of all in heavy metals due to separating the materials at the source. Although many of the long-term effects of regular compost applications with contaminants are not yet known, there is a logical relationship between cause and effect. There is current research indicating that chemical removal can be achieved at integrating compost into the operation, either as a perimeter measure or by tilling it in (Faucette et al., 2009).

Environmental benefits associated with composts applications

The simple task of playing "what if" before decisions are made can save all of us a lot of time and effort. For the part of life requiring change, the decision to change will result in things getting either better or worse. If we get positive results, we are encouraged to like change. If we get negative results, we are discouraged. By playing the "if-then" game ahead of time, we can better prepare ourselves for anticipated outcomes (Diacono and Montemurro, 2010).

1. Water holding capacity: mineral soils receiving 10-15 tons/acre of compost can generally be expected to increase in water holding capacity by 5%-10% (McConnell et al., 1993). This is obviously dependent upon initial soil conditions. Tester (1990) observed that up to twice as much water was available in a single application of compost 5 years later. The study was performed on sandy soils which respond favorably to water retention properties of compost.

Table 12.2 Heavy metal concentrations in municipal solid waste (MSW)-derived compost

Metal

Processing method (mg/kg dry weight)

A

B

C

D

Zinc

1,700

800

520

230

Lead

800

700

420

160

Copper

600

270

100

50

Chromium

180

70

40

30

Nickel

110

35

25

10

Cadmium

7

2.5

1.8

1.0

A. Mixed household wastes are composted without preparation. The process takes approximately 12 months. After composting, the product is screened and inerts are removed.

B. The collected household wastes are separated into two fractions. The material contains most of the easily degradable organic material. Between 2!4 and 5 months are needed for this composting process.

C. The collected wastes are shredded and then processed, resulting in a fraction to be composted. This fraction is free of most inerts, such as glass and plastics.

D. Wastes are separated at the source. The organic components are collected separately at households. All necessary steps are taken to ensure that components containing heavy metals do not enter the organic components.

Source: U. S. Environmental Protection Agency, 1994,1995.

  • 2. pH: an application rate of 10-20 tons/acre of a slightly alkaline compost usually increases pH by 0.5-1.0 in acid soils. While the pH interaction is often confusing, there is a time factor for reactions to occur that is somewhat immeasurable due to the variables involved, including moisture, temperature and soil type. Each individual soil should be tested prior to compost applications to determine the impact of the pH component in the total management plan.
  • 3. Cation exchange capacity (CEC): the ability of a soil to hold nutrients for plant. It is a magnetic force which holds the nutrients. Similar to water holding capacity increases discussed earlier, CEC increases from compost applications of sandy soils are significant (McConnell et al, 1993). In fact, the increased CEC means less fertilizer leaching and greater nutrient availability to crops. This combination needs to be analyzed for each crop grown in each type of soil. Organic matter is a leading reason many soils have higher CECs, unless the clay content is high, and so understanding the correlation between CEC and OM additions is important to manage many growing systems. Table 12.3 identifies a direct positive relationship with increasing

Table 12.3 Effect of organic matter (OM) percent on cation exchange capacity (CEC)

pH

OM (%)

1

2

3

4

5

6

5

0.8

1.6

CEC (meq/100 g soil)

2.5 3.4 4.2

5.0

6

1.8

3.6

5.4

7.2

9.0

10.7

7

2.8

5.5

8.3

11

13.8

16.5

Source:

Magdoff

and

Weil,

2004,

calculated

by

equation.

OM and CEC values. Keep in mind that the further to the right of the table, the less dependent we are on fertilizer and other chemical nutrient inputs (Magdoff and Weil, 2004).

Therefore, these companies have no incentive to help the compost industry move further to the right. Marketing compost to horticulture will eventually affect sales in other markets (such as pesticides and fertilizers), probably negatively. If chemical companies do promote compost applications, they may be jeopardizing future sales. When other businesses are affected by compost applications, do not expect them to just stand there and watch their market slowly disappear. The relationships between chemical companies producing fertilizers and compost facilities really should be synergistic, not competitive. The higher CEC of compost will hold nutrients more tightly in the soil, reducing amounts of leachable compounds. Fertilizer will therefore be more effective, and fertilizer companies should receive less negative press from non-point source pollution concerns. Studies in fertilizer and compost interactions should be carefully analyzed. An important thought to consider when reviewing this research is: what is the agenda (motive) of the entity funding the research? If the funder is a compost facility, they want to sell all their product at as high a price as possible. If the funder is a fertilizer facility, they too want to maximize sales and profitability. From either source, research must be read with a suspecting eye and conclusions drawn based on a neutral point of view. It is often too easy to make data appear to be more significant than it is.

Beware of the promises made by some companies. It is not possible for miracle cures to occur from compost applications to soils. For instance, one leading national company reported increased profitability from compost applications even though yields were not as good as with conventional fertilizer program. Also, they reported that OM in the soils increased from 1.2% to 2.5% from the application of 2-3.5 tons/acre of compost. That was some compost! A 3.5-ton application of compost testing 70% OM would yield: 3.5 tons x 80% dry matter x 70% OM = 1.96 tons/ acre of OM. Accordingly, 1.96 tons/acre of OM/2 million lb of soil = less than 0.001 increase in total OM of the parent soil.

4. Nitrogen availability: for some composts, within 1 year after application of 30 tons/acre of compost, about 150-200 lb on N is available (Kidder and O'Connor, 1993). The residual N content of compost applications is often another variable that depends on native soil type and climate. Table 12.4 shows typical release rates for temperate climates with adequate rainfall to drive chemical reactions, providing microflora ideal conditions.

Most farms, to rectify soil losses from erosion, land apply most of their animal manures. However, many of the animal manures currently being applied may contribute to non-point source pollution because they are more easily eroded and leached than products which are composted prior to application. Composted animal manures and farm wastes may help reduce non-point source pollution by converting nutrients into less leachable forms. By composting the animal manures prior to application, nutrients are locked up and rely on microorganisms to become available (Maynard, 1994). Figure 12.1 shows how the N release curve is similar to that of what plants require in order to maximize yield and, however, compared to a urea fertilizer, leach less which is more environmentally friendly (Tyler, 1996).

Evidence that compost can help reduce contamination of groundwater after fertilization is intensifying in the horticulture production. About 50% of the drinking water in the United States is supplied by groundwater, and when NO3 reaches levels of 10 ppm or higher, danger exists. Nitrate leaching occurs after application of commercial fertilizers or non-com-posted animal manures (Maynard, 1994). For farms disposing of animal manure during cold weather, further regulations may restrict raw manure

Table 12.4 Total percent (%) availability of nitrogen (N) per year for three consecutive yearly compost applications containing 1% N

Application number

Year

1

2

3

4

5

1

25%

10%

10%

5%

5%

2

-

25%

10%

10%

5%

3

-

-

25%

10%

10%

Cumulative total

25%

35%

45%

25%

20%

Source: Tyler, 1994.

Total organic nitrogen (N) mineralization for temperate climates. Source

Figure 12.1 Total organic nitrogen (N) mineralization for temperate climates. Source: Tyler, 1996.

applications on water-saturated or frozen soil because of runoff potential into local rivers and lakes (Quaife, 1993). Anyone who has applied animal manure to sloped, frozen land just prior to a heavy rainfall knows the potential danger of contaminating nearby watersheds. Ironically, composted animal manures do not pose as great a danger, and so they offer great flexibility for proper farm animal manure disposal and increased window of time for applications. Maynard (1994) found that applications of 0.5 and 1 inches of composts each year for 3 successive years resulted in a slight increased NO3 concentration in groundwater. Although all treatments of compost plots remained below 10 ppm NO3 in groundwater, plots with commercial fertilizer nearly reached 15 ppm (Maynard, 1994). This suggests that a cumulative effect of fertility from composts is first released and then becomes leachable in the soil profile. Since the maximum concentrations in the compost-treated plots was just under 10 ppm, Maynard's (1994) study suggests three yearly applications may be the limit for compost applications based on NO3 measurements alone. It has also been demonstrated that more mature composts have a higher concentration of organic N in relation to total N. Similarly, Tyler (1994) also suggests that the third year is the time when additive effects from yearly compost applications may become excessive (Tyler, 1994). These additive effects of available N levels in soils, provided by compost applications, are shown in Table 12.4.

For farmers under pressure from regulations affecting non-point source pollution, compost applications may produce significant dividends. The focus is simply shifted from economics associated with production to economics associated with insurance and potential liability from pollution. With normal fertility and animal manure management programs, depending on the soil and rainfall, much of the fertilizer and nutrients applied can leach into the groundwater (Diacono and Montemurro, 2010). Compost applications may help reduce this leaching and therefore potential contamination of surface wells (Grobe and Buchanan, 1993). Future direct land application standards for animal manure may be based on P limitations, especially in areas where P have been elevated in the ecosystems (Ozores-Hampton, 2017). Since farmers have traditionally applied nutrients based mainly on N requirements, regulations based on P requirements will be challenging to meet because of traditional production practices. Table 12.5 is a good example of how application rates of animal manure may differ for the land required, depending on whether N or P is used for application guidelines. The comparison of how much land it takes to apply animal manure to a corn crop, in an agronomically correct, based on both N and P requirements. These are rules only, and application rates may vary widely according to crop rotation, yields, animal manure and soil tests (Cubbage, 1994).

The number of acres needed for animal manure applications on a 500-cow dairy if P is used as the limiting factor, 746 acres are needed for continuous corn compared to 218 acres if N is used as the limiting factor. The additional acreage required, almost three times the amount required for traditional N limitations, is a challenge for any farmer to meet overnight. Therefore, if the P standard becomes accepted in all states (and it is already well on its way), farmers will have more incentive than ever to compost the animal manure to avoid purchasing additional land for animal manure application.

The Pennsylvania (USA) Nutrient Management Act was passed in 1993 in farm nutrient management. Large animal operations must develop a plan for animal manure (nutrients), and if residual animal manure is identified, the plan must state plans for use (Riggle, 1994). Many farms

Table 12.5 Comparison of land base needed for animal manure applications based on nitrogen (N) and phosphorous (P)

Number of cows

N (lbs)

P2O5 (lbs)

Acres required for continuous corn

Acres required for corn after and soybeans

N

p2o5

N

P2O5

50

3,277

3,358

22

75

30

75

100

6,554

6,716

44

149

60

149

200

13,107

13,432

87

298

119

298

500

32,768

33,580

218

746

298

746

1,000

65,536

67,160

437

1,492

596

1,492

Source: Cubbage, 1994.

have chosen composting as a method to reduce leaching and make animal manure more valuable to crops (Riggle, 1994). When animal manure is stockpiled to reduce the non-point source pollution concern and applied only when good weather prevails, it can lose up to 50% of initial N values, reducing the agronomic value to the farmer (Logsdon, 1993b). However, composting the animal manure prior to application would reduce losses of nutrients and decrease or prevent leaching.

5. Phosphorous: this is a major concern in non-point source pollution issues. State officials in Florida cited P from dairy pasture runoff as the cause of increased algae blooms in Lake Okeechobee, FL (Cubbage, 1994). This led to further regulations and the adoption of an animal manure application standard based on P content. Phosphorous in dairy manures can range from 6 to 28 lb per 1,000 gal of animal manure, which means farmers may not be able to apply as much manure to their lands as they have in the past (Rynk, 1994; Cubbage, 1994). The implications are that farmers need more land just to comply with new P guidelines. Since animal manures are high in moisture content and their nutrients easily leached, it makes sense for these "wastes" to be composted first. Composting will alter the state of many of the nutrients, making it more difficult for them to leach. More importantly, when compost is applied, it is in a drier form that is less prone to runoff during heavy rains.

In the Great Lakes region, there is more concern with P than other areas due to many issues associated with surface waters (Cubbage, 1994). Excess P is extremely stimulating to aquatic plant life, often growing up to 500 lb of OM per lb of P (Cubbage, 1994). There is a misconception about how P enters surface waters. Unlike N, which is mobile in certain forms and can leach readily through soil profiles, P is not as mobile. Phosphorous tends to stay attached to soil particles and move with these particles into runoff entering lakes and streams (Cubbage, 1994; Gagnon et al., 2012). Another real benefit of using compost on farms and from composting animal manures will be to help reduce soil erosion and in turn reduce P pollution.

 
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