Animal manure Some animal manures from conventional farming practices could be contaminated with hormones, antibiotics, pesticides, disease organisms, heavy metals, and other undesirable substances. Because of this animal manures must come from organic sources. Manure testing is available through commercial labs and is recommended in situations where there is any doubt about the purity of manures. Manure testing is required by the European Union. Dairy and beef cow, horse, sheep, swine, and poultry manure can be spread directly on land and incorporated. The amount of nitrogen in manure sources from different animals can vary by a factor of 3 or 4. The amount of nitrogen in the fresh manure that ends up available to the plant is also very …show more content…
Crops grown to add nutrients to the soil are called green manures and are usually sown in late summer or autumn. Some plant species are selected as green manures or cover crops, because of efficient, deep root systems that bring nutrients up to the soil surface, others because they are hardy or more tolerant of nutrient, moisture or environmental stresses. The most important green manures are plants that together with bacteria are able to capture nitrogen from the atmosphere and make it available to plants. Examples of green manures are Trifolium repens (white clover) and Trifolium incarnatum (Crimson clover). Green manures can also be used to cover bare patches of soil in the spaces between crops, or during intervals between one crop and the next. Fast-growing mustard sown before mid-September can be incorporated in October, for example, or the frosted remains left as mulch. Other benefits of green manures include protection of the soil surface from compaction by rain and shelter for beneficial insects such as ground beetles. (www.rhs.org.uk, 2015) The effect of green manures or cover crops on rodent populations or rodent damage to trees must be taken into consideration. (Biernbaum, 1994)