Corn & The Environment

Corn & Soil Fertility

Soil nutrients, particularly potassium, phosphates, and nitrogen - the latter in the form of either nitrate or ammonium - are needed for corn growth and development. The fertility needs of corn tend to be higher, when expressed on per-hectare basis, than those of other crops. When adjusted to reflect differences in average crop yields, however, fertility needs for corn are similar to, or lower than for other grain species (See table below.) Note, however, the zero nitrogen requirement for soybeans which is a legume crop.

Plant nutrient needs can be supplied by a reduction in soil nutrient levels and organic matter breakdown - processes sometimes called "soil mining" - or by the application of organic or inorganic fertilizers. Organic fertilizer materials (for example, manure, compost, "sludge" from municipal waste treatment, and crop residues) must be broken down by soil micro-organisms to produce inorganic fertilizer ions - the same ones supplied by commercial "inorganic" fertilizers - before they can be taken up by plant roots.

With legume crops such as soybeans and alfalfa, nitrogen fertilizer needs are supplied by nitrogen-fixing bacteria which live in root nodules and which convert atmospheric nitrogen to organic compounds subsequently used by plants. This does not occur for corn and most other crop species.

If nutrients are available in excess of plant needs, the result can be the contamination of subsurface water, especially with mobile nutrients such as nitrate. However, if insufficient fertility is available, the result is lower rates of organic matter production by the crop and lower yields.

Soil testing

Soil testing can be used to predict, with good accuracy, fertilizer application needs in the case of potassium and phosphate. Techniques have been recently introduced which should permit similar accuracy with soil nitrate-nitrogen tests (see Ontario Ministry of Agriculture, Food and Rural Affairs, Publication 296, Field Crop Recommendations), although further research on soil nitrate-nitrogen testing is still required.

Nitrates in ground water may represent one of the largest environmental problems associated with agriculture (Ontario Farm Environmental Coalition, 1992). High soil nitrate levels can result from the use of manure or synthetic fertilizers, or from the vigorous growth of high- nitrogen-fixing legumes such as alfalfa. The challenge is to develop and perfect techniques which will enable farmers to meet the fertility needs of crop plants while reducing the risk of ground water contamination.

Crop rotations

The increased use of crop rotations in which corn follows perennial legumes crops, such as alfalfa and red clover, provides a means of using the high nitrogen-fixing ability of the latter to supply part or all of the nitrogen fertility needs of the corn crop.

Research in Ontario has shown that, while all corn varieties (indeed, all crop species) produce lower yields when insufficient fertility is available, higher yields are obtained with newer, rather than older, corn hybrids under conditions of low soil fertility, because newer hybrids use nitrogen more efficiently (Tollenaar et al., 1993).