Higher crop prices may have producers looking to expand acres. Some producers are taking old pasture or hay fields and putting them into crop production. It seems pretty simple: spray burn down herbicide, no-till plant herbicide-resistant beans and then spray again. But this doesn’t deal with some of the other issues that may occur on these fields. Most forage fields are in grasses because they are not suitable for crops: shallow topsoil, gravelly or sandy texture, eroding slopes. If topsoil is lost it can take hundreds of years to replace. Fields may also have compaction issues due to grazing or haying.
Many fields converted this way show severe nutritional problems, especially potash deficiency. Severe potash deficiency will show up as yellowing on the edges of lower leaves. Many of the hay fields have not been adequately fertilized for the amount of nutrients removed. Three tons of fescue hay removes 100 pounds of potash and 27 pounds of phosphate. The nutrients in pastures will be rearranged so the potash and phosphate will be high near the water and shade areas and reduced in the rest of the field.
If producers decide to go ahead and convert from grass, the following steps increase your chances for a good crop yield:
1. Take a soil test and apply lime and fertilizer according to the soil test before planting. Lime should be applied six months to one year before planting. A good pH is needed to for the nitrogen-producing nodules. University of Missouri soil tests recommend the amount of potash and phosphate needed to replace what is removed by the crop plus one-eighth of what is needed to build it up to a good level. So applications are not a one-time event but need to be made yearly.
2. Use the soil probe to monitor for compaction problems. Compacted soil will restrict roots and compound the fertility problems. Fields might benefit from deep ripping or mulch tillage under the row but this will increase erosion. Many fields do not have enough soil depth to use a ripper.
3. Inoculate beans prior to planting. Soybeans need to produce rhyzobium bacteria nodules to make nitrogen for the plant. Organic matter from the decaying sod will provide some nitrogen the first year but inoculating will allow the plant to provide its own nitrogen.
Producers are encouraged to contact their local MU Extension agronomy field specialists if they have specific questions about converting fields to row crops.