A second important point is to consider all potential nitrogen sources for a crop. A third management practice is timing nitrogen fertilizer application. The last point to consider is the placement of nitrogen fertilizers or organic nitrogen sources such as sludge and manure. Any management practice that results in more of the applied nitrogen being taken up by the crop decreases the potential for nitrate contamination of groundwater. Proper placement near the plant roots may increase the plants' nitrogen uptake efficiency.
Many farmers overlook the nutrient value of their livestock manure and poultry litter.
Both are very high in nutrient value and should be considered and subtracted from calculations of fertilizer needs. Manure and litter can reduce fertilizer costs and still provide enough nitrogen for crops, while leaving little nitrate to leach into the groundwater. Application practices also affect nitrate leaching into the groundwater. For instance, if the manure is applied sooner than the crop can use it, a large portion of the nitrate can be lost by leaching. Nitrogen sources should always be applied as near as possible to the time of most rapid plant growth.