Compost micronutrient availability in crop production

Compost can provide the following essential micronutrients in an available form: boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) (Diacono and Montemurro, 2010). While micronutrient crop requirements are in small quantities when compared to macronutrients, they are essential to plant growth and development, and many soils are low on these elements. The micronutrient content of compost varies widely depending on the feedstocks, soil and environmental conditions.

Effects of compost heavy metal content in crop production

Heavy metals are toxic and persistent pollutants that may be present in feedstock materials for compost and are used as soil amendments (Ozores-Hampton et al., 2005b). Toxic metals may accumulate in the soil (Sterrett et al., 1982; Yuran and Harrison, 1986) or are uptaken by the plant and accumulate in the edible plant parts, where they pose a potential threat to consumers (Shiralipour et al., 1992). Metals that pose the greatest threat to human health are Cd, Cu, Pb, Ni and Zn (Chaney, 1993). Presently, biosolids and biosolids mixed with either YTW or MSW are regulated at the federal level under the Clean Water Act Section 503 (USEPA, 1994, 1995). The Clean Water Act Section 503 classified the quality of two biosolids based on the nine regulated pollutant elements concentration limit; the pollutant ceiling concentration and pollutant concentration; and two loading rates-based limit, cumulative pollutant loading rates (CPLR) and annual pollutant loading rates (APLR) (USEPA 1994,1995). Eighteen states have regulations in place that are more restrictive than Section 503 (Goldstein, 2000). Evaluation of potential food-chain transfer of Cd, Cu, Pb, Ni and Zn in compost shows that consumption for 70 years of 60% of garden food, produced on pH 5.5 soils and amended with 446 tons/acre of compost, would be safe (Chaney, 1994). Biosolids or compost made from waste materials that do not meet EPA 503 standards for pollutant concentration should not be applied to horticultural land (Ozores-Hampton and Peach, 2002). Therefore, repeated, long-term applications of compost made from waste materials with pollutant content below maximum acceptable levels under state and federal regulations should be suitable for vegetable production (Ozores-Hampton et al., 1994a,b; Ozores-Hampton et al., 1997).

Accumulation of soluble salts and compost application in crop production

The electrical conductivity of some compost can raise a concern with repeated applications over a long period of time. Furthermore, high compost rates can proportionally increase EC soil concentrations. High EC concentration can inhibit germination of direct seeded crops and growth and development in sensitive species. Normally, EC will decline over time due to crop removal and leaching by rainfall. However, in desert areas where rainfall is limited, EC accumulation due to high compost in EC and/or with high application rates needs to be considered annually. Some of the EC in animal manures is from the nutrient salts, such as K, Ca and Mg. However, compost high in sodium is not desirable in crop production.

Using compost in a fertility program in crop production

The fertility program for conventional and organic fruit orchards, vegetable and ornamental production can be divided into two major parts: an organic-amendment-based program and supplemental fertility program consisting of inorganic or organic fertilizer such as ammonium nitrate, urea and potassium sulfate, plus micronutrients to supply the plant nutrients requirements.

Those using composts must practice sound soil fertility management to prevent nutrient imbalances and associated health risks, as well as surface-water and groundwater contamination. Matching compost supplied nutrients to vegetable nutrient requirements should be the goal of a conventional vegetable fertility program (Ozores-Hampton et al., 2011). Overfertilization will be inefficient and expensive, which may contribute to nutrient runoff, groundwater pollution, soil toxicity, pest and disease susceptibility, excessive production of foliage and reduced vegetable quality and yields. Similarly, under-fertilization can reduce vegetable yield and/or quality.

Table 3.1 provides an analysis of compost suitable for fruit orchards, vegetable and ornamental production. Since actual nutrient content varies considerably between compost sources, a representative product sample should be sent to a laboratory for analysis of moisture and nutrient content such as total N, phosphate (P2O5), potash (K2O), calcium (Ca), magnesium (Mg) and micronutrients. Additionally for compost, nitrate-N (NO3-N) and ammonium-N (NH4-N) is recommended. Accurate compost analysis requires that a representative sample be submitted, so several subsamples should be collected and combined for analysis.

For successful integration of compost into conventional vegetable fertility programs, we recommend the construction of an N-P-K crop massbalance where the fertility inputs and net release of N will be quantified and vegetable crop N-P2O5-K2O requirement will be taken into consideration. Calculating N availability from compost can be complex since N must be transformed by soil microorganisms before it can be utilized by the vegetable crop as NO3-N. An example of a tomato fertility program for Florida is provided as a guide in Table 3.1.

The first step in building the tomato fertility program is to determine the tomato crop nutrient requirements by taking a soil sample for analysis of N-P-K and micronutrients. These results can be compared to the local crop recommendations for N-P2O5-K2O. This information can be found in a local state or regional "vegetable production handbook" or by contacting a local extension faculty. Then, the identification of locally available compost. Once the compost was located and identified, determine the nutrient content and N, P and K availability from laboratory analysis or from other sources such as given in Table 3.2. The microbial activity involved in the N cycles, which is accelerated by high temperatures and slowed down with low temperatures, needs to be considered and N release rate adjusted as need. Then, the next step will

Table 3.2 Nitrogen (N), phosphorus (P) and potassium (K) concentrations and N mineralization rates of compost for vegetable crop production

Organic feedstocks2

N

P ------(%) -

K

Rate of N release (%/year)

Biosolids

3-6

2-3

0.10-0.15

3.0-20

Brewery waste solids

1.3-1.8

0.02

0.13-0.18

5.0-10

Dairy manure

1.2-1.5

0.3

0.9

6.0-15

Feedlot manure

1.9-2.2

0.3-1.2

0.6-3.2

3.0-15

Fruit and vegetable waste

1.39

0.26

1.19

10

Gin trash

1.2-3.8

0.2

1.2

10

Horse manure

0.5

0.2

0.4

10

Food waste

1.1-1.8

0.03-0.09

0.35-0.45

2.0-12

Municipal solid waste

2.3

1.11

0.64

3.0-10

Mushroom substrate

2.5

1.3

0.9

10

Olive mill waste

3.5

0.17

2.3

20

Poultry manure

1.3-5

3.0

2.0

20

Yard waste

1.0-1.2

0.2-0.3

0.2-1.4

2.0-10

Altieri and Esposito, 2010; Ahmad et al., 2008; Aram and Rangarajan, 2005; Bellows, 2003; Chellemi and Lazarovits, 2002; Diver et al., 1999; Drinkwater, 2007; Gaskell, 2009; Gaskell and Smith 2006, 2007; Gaskell and Klauer, 2004; Hartz and Johnstone, 2006; Hartz et al., 2000; Kuepper and Everett 2004; Prasad, 2009a,b; Pressman, 2009; Sooby et al., 2007; Rosen and Bierman, 2005; VanTine and Verlinden, 2003; Zhang and Li, 2003.

be the calculation of compost application rates to supply recommended amounts of N, P2O5 and K2O to the tomato crop so that yield estimates are realized (Tables 3.2 and 3.3). To calculate the correct application rate of compost, multiply by availability factors (70%—80% for P and 80%-90% for K) to obtain the amount of P and K that will be available to vegetables from the application of compost. Then, multiply the total P by 2.29 and K by 1.2 to obtain P2O5 and K2O (Table 3.3). The advantage of using compost rather than raw manure will be that, although P can be over-applied with compost, the improvement in soil structure with the compost OM application will increase water infiltration and reduce runoff, thereby decreasing the total P transported over the land surface to potentially pollute surface water (Spargo et al., 2006). Finally, determine whether application of inorganic commercial fertilizer is needed. Once a fertility program is established, a unit cost per nutrient can be calculated. The cost per unit of nutrients can be calculated by multiplying the nutrient fertilizer unit cost by the organic amendment available nutrient content and then by selecting the most cost-effective one to be applied to the tomato crop.

Table 3.3 Florida nutrient mass budget for conventional tomato production2

Material inputs

Application rate (lb/acre DW)t

Nrate (lb/acre)

N mineralization rate (%)

Total (lb/ acre NO,)

Total (lb/acre

P2O.5)*

Total (lb/ acre K2O)X

Yard waste compost at 4.0 ton/ acre (40% moisture and 1% N, 0.2% P and 0.8% K with 70% P and 80% K availability)

6,725

67.2

10

6.7

21.5

43.0

Inorg

anic fertilizer application

Ammonium nitrate”

568.5

193.3

-

-

Triple phosphate

170.7

-

78.5

-

Potassium sulfate

105.6

-

-

57.0

Total

-

-

200

100

100

2 Tomato (Solarium lycopersicum) nutrient requirements based on 200 lb/acre of nitrogen (N), 100 lb/acre phosphoric acid (P2O5) and potassium oxide (K2O) with a medium soil test levels of P and K, respectively (Olson et al., 2010).

y DW = dry weight; NO, = nitrate.

* P x 2.2910 = P2O„ K x 1.2047 = K2O.

w Ammonium nitrate (34% N); triple phosphate (46% P2O5); potassium sulfate (54% K2O).

Chapter 3: Fertility program using compost

Environmental monitoring has shown elevated NO3-N or P concentration to be widespread in both surface and groundwater, often occurring in regions with concentrated horticultural production systems. Compost applications have many positive effects on the soil and agricultural production system. Routine applications often result in increased soil bulk density, AWHC, improved soil structure, increased soil carbon content, additional macro and micronutrients, buffered pH, reduced soluble salts, increased CEC and increased biological activity and diversity (microbial biomass). Also, compost use can improve water quality in high production areas by improving the soil and decreasing the use of highly soluble synthetic inorganic fertilizers. However, a fertility program using compost requires the understanding of the contribution of nutrients such as N, over time, P, К and other micronutrients that are present in most compost sources. Higher compost application rates for soil conditioning may produce excessive nutrient buildup in the soil and nutrient loss to the environment if the compost program is not carefully planned. In dry climates with low opportunity for nutrient loss due to leaching, high compost application rates can produce excessive salt and P and К soil accumulation that can interfere with plant growth, nutrient uptake or cause a deficiency of other nutrients. The first step in building a conventional fertility program will be to take a soil sample and send it to a soil laboratory for a nutrient analysis. These results should be compared to the local crop recommendations. Second, select the compost based on local availability. Then, determine the nutrients available from the compost and use synthetic inorganic fertilizer sources to satisfy the crop nutrient requirements not supplied from the compost source.

World populations are exploding, and the ever increasing need for more food supplies is driving more land area into intensive agricultural production. In parallel, global waste production is increasing, and therefore connecting waste streams to horticulture production throughout compost utilization can increase crop production without impacting the environment.

 
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