When used in a responsible manner, the addition of nutrients in the form of fertilizers can increase crop production in years of favourable growing conditions, improve a farm's chances of economic survival by reducing losses in years of unfavourable growing conditions, and maintain or improve the quality of soils. Fertile soils that have a good natural store of plant nutrients can produce high crop yields on their own, and fertilization will generally be minimal. Applying the correct amount of fertilizer is important. By applying too little fertilizer, a soil may be 'mined' of its plant nutrients, and crop yields may become progressively lower over the years. This is a sign of soil degradation .
Soil testing can determine the nutrient needs of a soil and the right amount of fertilizer to apply.
Over-fertilization wastes fertilizer resources and money, and the surplus plant nutrients may overload the soil and cause environmental harm by contaminating surface and groundwater and the atmosphere. Manitoba, Nova Scotia, and Newfoundland use fertilizers on the largest proportion of cultivated land. On an area basis, Saskatchewan reported using fertilizer on the lowest percent of cultivated land. This is probably because of the high proportion of total production which comes from fallow land where additional fertilizers are often not applied, the high risk of drought and the consequent risks of not obtaining positive returns, and the high cost of fertilizers compared to the current market value of wheat. Although a large share of Canada's soil nutrient needs could be supplied by manure, limited supply and problems with distribution and lack of consistency of quality mitigate against its widespread use, except in certain regions of eastern Canada.