Box 3. Box 3 Uses and misuses of manure

Soluble minerals are not used on organic farms. Although crude rock phosphate may be allowed, potassium chloride is banned; sylvanite, another form of potassium chloride, may be permitted. The main alternative mineral source for crop nutrients is animal or green manure. Manure treatment used on any mixed farm improves soil quality, but conventional crop rotation seems equally effective². Manure breakdown cannot be synchronized with crop canopy growth, as is desirable, but continues throughout the growing season. Ploughing in of legume crops (a necessary part of the organic method to build soil fertility) and continued manure breakdown leads to nitrate leaching into aquifers and waterways at identical rates to conventional farms¹. Degradation of organic material from manure in the soil produces significant amounts of nitrous oxide and methane, the most potent greenhouse gases. Manure is variable in composition, yielding unpredictable nutrition for crop growth: there is only a poor relationship between available nitrogen for crop growth and organic content of soil. Organic regulations recommend hay for animal feeding, but hay-fed animals infected with Escherichia coli O157 incubate this dangerous organism longer than 'conventional' animals fed with grain²⁶.