The Agricultural Value of compost
The following is taken from a recent United Kingdom Report titled “COMPOST USE IN AGRICULTURE CONSOLIDATED REPORT”, EB NATIONWIDE LTD AND THE BRITISH POTATO COUNCIL.
Artificial fertilisers are valued 0.34, 0.33 and 0.20 per kilogram for nitrogen, phosphate and potash, respectively (The Farm Management Handbook 2003/04, UK).
Magnesium and sulphur also have a value but are often incorporated in fertilisers and liming materials as a consequence of manufacture or source materials. With UK compost containing approximately 8.1 kg total nitrogen, 3.3 kg total phosphate and 6.6 kg total potash per tonne of moist product, the total nutrient content of compost is worth over 5 per tonne but, as much of the nitrogen is in slow release form, is worth 2.50 to the crop after application (75/ha at 30 t/ha compost application).
 Many benefits from organic matter in compost are long term and are found from repeated applications building up soil organic matter and hence fertility. Assigning an economic value to organic matter is currently difficult but with the possible adoption of carbon credit systems within agriculture in the future the importance of this value looks to increase.
Certainly this project has identified a buffering effect of the compost on soil pH levels. Compost can raise soil pH when it is low and stabilize it when it is at or above neutral. This can counteract the effect of inorganic fertilisers, which tend to lower soil pH over time. If the buffering effect of a typical 30t/ha application of compost is equated to that of a 2t /ha application of agricultural lime, this will equate to a saving of in the region of 33/ha (16.50/t lime delivered and spread excluding VAT).
The work carried out on the soils from the plots where compost was applied has shown that water holding capacity can be improved in light textured soils equivalent to 12.5 mm irrigation water /ha. Irrigation has an annual capital charge of 250 to 500 per hectare and water/labour charges of 1.20 to 1.60 per mm of water applied per hectare (The Farm Management Handbook 2003/04). Water can be saved through improving the retention of rainfall and irrigation within the root zone, and reducing surface runoff by increasing infiltration rates. At an average cost of 72 per hectare per 25 mm application, 30t compost applied per hectare (over time and for a number of irrigated crops to build up soil effects) is worth 2.40 per tonne of compost. If two out of eight 25 mm irrigations could be cut through efficiencies, then 144/ha could be saved giving the compost a value of 4.80 per tonne.
The spreading of compost can be accomplished very effectively with rear discharge muck spreading equipment. A spreader can hold 10 tonnes and take 3 minutes to load and another 3 minutes to spread. Turnaround time depends on the distance from the loading area to the field but can be as short as 10 minutes. However, a typical daily rate of application would be 200 t/day. With labour, the cost of a loader and the tractor plus spreader hire charges, the application cost per tonne of compost works out at 1.85/t, or 55.50/ha based on 30 t/ha applied. This cost is offset by the liming value and the reduced costs for the spreading of artificial fertilisers.
Haulage costs are the principal limiting factor on assigning a delivered and spread cost to compost. Due to the low bulk density of compost generally a lorry load will be equivalent to 16 tonnes. The haulage distance will limit whether the farmer is able to collect and spread compost or whether contractors will need to be employed. Using farm haulage equipment may be cheaper due to fuel price differentials and because existing equipment can be used during quiet times.
However, farm haulage may still cost 4/t depending on distance (120/ha at 30 t/ha)
Contracting costs need to be assigned according to an individual site. For guidance at an application rate of up to 35t/ha a spreading cost of 3.50/t and haulage of 6.25/t giving an overall cost of 9.75/t (excluding VAT) might be quoted. From our research lower costs of delivery and spreading have been quoted but again this is dependent on proximity of the source of compost to the land to which it will be applied.
Overall, the value of applying good quality compost to farmland is in the long term improvement of soil and land as an asset. The value of the compost as a fertilizer (75/ha), its liming qualities (33/ha) and for soil improvement effects giving water savings through reduced irrigations (144/ha) is partially offset by the cost of haulage (120/ha) and spreading (55.50/ha). Depending on the crops being grown, soil type and the circumstances around a given farm, this gives a net value of compost, applied at 30 t/ha, of 2.55/t assuming farm equipment is used for haulage and spreading rather than contractors. Further value may be ascribed to compost from yield improvements according to the crop being grown.
(The Web Master would be extremely grateful to anyone who is sufficiently expert in Indian agricultural economics and is willing to spend some time converting the above figures into equivalent Indian fertiliser prices, and other costs.)
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