Risks of continous maize planting explained

Experienced farmers everywhere have learned that maize is best not planted two seasons in a row on the same piece of land. For soil fertility and crop yield reasons, it is best rotated with a legume crop.

Yet continous maize planting is a reality in some places, even when the farmers know the effect on the soil and on yields. Some of the reasons are declining access to arable land and population pressures. Continous planting is also frequently seen in urban agriculture, where the maize is often planted on public land on which the farmers have a different attitude to that towards their own private land.

The security of the crop on this type of land is sometimes tenous. It is not unheard of for municipal authorities to slash them down before harvest for one reason or another. Theft of crops grown on public land can be high. Use of a piece of land in this scenario can often shift from one person to another, as they are often occupied without any rental arrangements with the owning authority.

For all these reasons those who farm this kind of land assume an attitude of gambling to their
activities : they try to get as much out of the land while putting as little as possible into it because of all the risks involved. While some may use fertilizers, few are willing to use time-consuming organic fertility management regimes. And yet getting good yields with continous cropping of maize requires even more careful management practices than does rotational cropping.

Peter Thomison, a maize specialist with the Ohio State University Extension Service in the state of Ohio, USA and Robert Mullen, nutrient management and soil fertility specialist
with OSU Extension, recently gave very clear advice on the topic during a recent crop field day in their home state.

Thomison said he and other agronomists never recommend planting maize in the same field two years in a row. They always recommend a rotation with legumes. Farmers who choose to plant maize-after-maize should take into consideration possible problems with crop residue and
stand establishment and a need for increased nitrogen, along with the possibility of disease, weed and insect damage.

Thomison and Mullen have researched the risks involved in maize-after-maize. Mullen said there was an average of a 7 percent increase in production of rotational over other systems, and in some circumstances significantly higher.

Although much research has been conducted, Thomison said the benefits of the rotation system still are largely unexplained. Yields increase in rotation studies even after limiting factors appear to have been controlled in continuous cropping. There appear to be holistic benefits to the rotation system that are not yet fully understood.

Rotated maize is better able to tolerate stress such as drought than continuous maize, and usually has a better root system to take in water and nitrogen. When choosing to plant maize-after-maize, Thomison said tilling land works better than zero or minimum tillage systems because it better removes the residue from the previous crop.

"Zero-tillage continuous maize is not an attractive option," Mullen said.

Residues can contribute to lower yields because they can carry disease from the previous year; can keep soils cooler and wetter during and after planting, as well as during harvest; and can decrease the efficiency of herbicides.

In addition, Thomison said input costs will increase because more nitrogen is needed, along with pesticides and insecticides to deal with the increased pests.