Much of the nitrogen from the manure spread during cold weather, on soil that contains moisture, is held in the soil and is available in the spring. 25 to 50% of the organic nitrogen converts to nitrogen that is readily available to the growing crop if manure is spread in March or April. Agitating manure in storage before spreading it will improve nutrient uniformity, though it is still important to test the manure and spread it uniformly on the fields, especially if it is sand-laden manure. Sand-laden manure that is stored in a pit varies significantly in consistency and nutrient composition from the beginning to the end of emptying so 3 manure tests should be taken. Straw-packed manure also has less nutrient value than liquid manure so should be tested.
The different sources of nitrogen make no difference to their uptake in crops. Crops cannot tell the difference between fertilizer, livestock manure or green manure cover crops. It also makes no difference if it is the first time manure is put on a field or not, it still will have equal nutrient values. Spreading on the same field over three years, on the other hand, can result in a significant amount of nitrogen being “slow released”. After the third year, manure that was spread two or three seasons earlier will still be releasing nitrogen. It is therefore important to test the soil for how much nitrogen is available.