Corn/soybean fertilization programs
By David G. Hallauer
Meadowlark District Extension Agent, crops and soils/horticulture
In this space a couple of weeks ago, we discussed soil fertility and soil testing for crops and forages in general terms. If you recall, I noted in that column that recent research supported application of fertilization prior to planting both corn and soybean in our corn/soybean rotations, rather than doubling up on one crop to feed the other as has been common in the past.
For starters, if you are applying fertilizer to your corn to feed the subsequent soybean crop, you aren't necessarily hurting yourself--if soil test levels are in the non-responsive range (15 to 20 ppm phosphorous (P) if using the Mehlich 3 that the K-State Soil Testing Lab uses). If you get below that 15 ppm P, however, in to a responsive range, research from Franklin County in 2008 and from Republic County from 2006-2009 would definitely support application of P to both crops. In the Franklin County research, soybeans grown without any P yielded 31 bushels per acre when soil test levels were very low. When 100 pounds/acre of 7-21-7 was applied 2x2 at planting, the yield increased six bushels per acre (four was considered significant).
At the Republic County site (a rotation study with 10 ppm P), three years of data shows similar results. Without P added, soybeans yielded 51 bushels per acre. Soybeans grown on residual fertilizer applied to corn at 20, 40, and 80 pounds P2O5 to feed the soybeans yielded even better: 54, 55, and 57 bushels/acre respectively (all significantly different than the 0 P treatment). When 80 pounds of P2O5 was applied to corn PLUS 40 pounds directly to the soybean crop, yield was 61 bushels per acre, again a significant difference (2009 data pending).
Bottom line: If your soil test is in the responsive range, apply at least a nutrient sufficiency rate each year. Another option would be to add additional P2O5 to build soil test levels to 20 ppm, at which time you could maintain that level with applications every two years.
Garden soil management
It's difficult to emphasize enough the positive benefits of organic matter in soils. Soil tilth, nutrient cycling, and water infiltration all increase with good organic matters. For gardeners, fall is usually a great time to add organic matter for its benefits next year.
Doing so might be difficult this year, however. The two things that tend to restrict organic matter additions in the fall are frozen soils and moisture. And while frozen soils aren't a problem, moisture right now is!
Tillage in wet soils destroys structure and results in clods that are slow to break down. We can also create 'tillage' layers that prevent root growth. That said, be careful about trying to work in organic matter or get old residue worked in to the soil this fall. Until soils dry out a little (we don't want them too dry or too wet), hold off on tillage. Organic matter can also be worked in during the spring, though it's usually as wet or wetter then.
When soil conditions are right to allow tillage, a 2-inch deep layer of organic matter (leaves, etc...) is adequate to aid most soils. Five to 6 inches should be the maximum addition at any one time. Shredding the material before application encourages faster and more complete decomposition due to increased surface area.