Use of municipal compost in potato rotation
J. A. MacLeod1, J. B. Sanderson1 , B. Douglas2 and R. Henry3
1Crops and Livestock Research Centre,
Agriculture and Agri-Food Canada,
Charlottetown
2P.E.I. Agriculture & Forestry,
Charlottetown, P.B.I.
3R. Henry & Associates,
Breadalbane, P.E.I.
Compost was made from source separated municipal waste with or without disposable diapers included in the compostable waste stream. The composts were applied prior to barley in a barley- red clover-potato rotation on a Charlottetown fine sandy loam soil. A control which did not receive compost was included in randomized complete block experiments with four replications at each of seven locations. Nutrient levels in the compost were determined by sampling lots as delivered to each location prior to and during the spreading operation. Nutrient levels in compost are presented in Table 1.
The analysis of barley tissue sampled at the "boot stage" showed higher levels of the plant nutrients P, K, Ca, Mg, Zn and S in barley grown with "diaper" compared to "standard" compost (Table 2). Only P, Na, Cu and Zn levels were higher in barley grown with "standard" compost than barley grown without compost. Application of "standard" and "diaper" compost decreased barley yields by 18% and 11%, respectively, when averaged over all locations. At four locations there were no significant yield responses to either compost. At three locations "standard" compost significantly decreased yields and at only one of those three locations "diaper" compost significantly decreased yields.
Yields of forage averaged over all locations were 25%higher
for the plots which received compost than forage yields on the check plots.
The "standard" and "diaper" composts produced similar forage yields. Composts
increased the concentrations of the major nutrients N, P and K in the forage
and concentrations of P and K were higher in the forage which received
the "diaper" compost than forage which received the "standard" compost
(Table 3). This is consistent with the higher levels of P and K in the
"diaper" compost.
Concentrations of Ca, Mg and B were not significantly affected by compost application. This reflects the low concentrations of these elements in compost relative to concentrations present in unamended soils. Concentrations of Cu, S and Zn were higher in forages where compost had been applied and were similar for the two types of compost. Concentrations of these elements, even from the compost amended plots are in the low portion of the range considered sufficient for red clover (Table 4). This indicates that although the compost Cu levels were approaching the maximum permissible in 'Class A' compost, continued application is unlikely to be detrimental to forages.
At the time of writing analysis of potato yield data is incomplete. Data from one location shows similar potato yield benefits from the two types of compost. Potato yield benefits appear to be lower than yield increases previously obtained with compost made from agricultural wastes.
Apparent limited yield response reinforces the concept that the Agriculture Industry will only be able to bear a portion of the cost of municipal waste disposal through value of compost in commercial crop production. More detailed analysis required to ensure that heavy metal levels in the potato tubers remain within acceptable ranges.
