what's been applied to the field in years past will offer insight into what may already be in the ground or what nutrients may no longer be present. Water Consider what kind of water has been applied to the field. Does irrigation water contain dissolved nutrients such as nitrogen (N), sulfur (S), or chloride (Cl)? If so, it should be counted as input. What's around you? Consider water sources that could run into your field. Is there a manufacturing facility nearby? What makes up these water sources can impact how you plant. See also Fertilizer Nutrient management Sustainable agriculture References Agriculture Agricultural soil science Sustainable agriculture