Compost 



EVALUATING QUALITY 



Dr. George Estes 



Composting represents the most rapidly ex 

 panding and environmentally sound strategy 

 to handle solid organic wastes. In composting, 

 micro-organisms convert organic materials into 

 soil-like material of potential value as a plant-growth 

 medium. At the commercial level, it involves a pre- 

 cisely controlled decomposition with careful attention to 

 inputs and to such composting conditions as moisture, 

 oxygen, and temperature. 



Our consumptive society generates about 200 mil- 

 lion tons of waste annually. Only three options exist 

 for its disposal: incineration, landfilling, and 

 landspreading/horticultural use. Since over bO percent 

 of the total waste stream is organic 

 material, composting — reducing 

 odor, variability, and particle size — 

 can turn this mix into a homog- 

 enous material for horticultural use. 

 Because so much of the waste 

 stream is a potentially good nutri- 

 ent resource and feedstock, com- 

 posting can reduce waste disposal 

 costs for municipalities and fertil- 

 izer/media costs for horticulturists. 



Unfortunately, performance stan- 

 dards do not exist to evaluate com- 

 post "quality." The information which 

 accompanies a compost purchase is 

 often very limited or totally absent. 

 If assay data is present, it is often 

 meaningless. Furthermore, produc- 

 tion of a uniform product is often 

 difficult due to such factors as vari- 

 able inputs (leaves, manure, biosolids, 

 wood ash, brush etc.), the process 

 (windrow, in-vessel, static pile), or 

 the location of the operation. Confi- 

 dence in the product is essential for 

 acceptance by the highly sophisticated horticultural in- 

 dustry: greenhouse production cannot be jeopardized 

 by use of a growing medium having unknown proper- 

 ties. 



Finished compost is usually dark brown or black and 

 resembles commercial potting soil, although it may be 

 much coarser. However, laboratory analysis must be 

 conducted on a compost sample to test whether the 

 product will be suitable for your intended use. 



Any reliable producer of compost should provide 



analytical information to permit evaluation of the prod- 

 uct to make sure of its proper usage within your grow- 

 ing system. Specific values will govern whether the 

 compost can be used directly as a growing medium, as 

 a mulch, as a soil amendment, or as a component of a 

 potting mix. Two laboratory measurements — soluble 

 salts and ammonia (NH^-N) levels — are priorities in de- 

 termining suitability as a growth media: if either mea- 

 surement tests high and plants are placed into the pure 

 compost, devastating results can occur. Secondarily, 

 tests for pH, C:N, and available nutrients offer valuable 

 information on quality; the C:N ratio refers to the bal- 

 ance between total N (nitrogen) and total C (carbon). 



This is important because it affects nitrogen (N) avail- 

 ability. The inputs to the process supply carbon as the 

 energy source and nitrogen for protein synthesis for the 

 micro-organisms and commonly have a C:N ratio of 

 about 35:1. The finished compost usually has a C:N ra- 

 tio of about 15-20:1 after experiencing a weight reduc- 

 tion of over 50 percent during the composting pro- 

 cess. 



Finally, tests for total nutrient content, organic-N 

 concentration, and even trace metal content provide 



APRIL & IM AY 



