Fertilizer management for conservation tillage
Farmer interest in conservation tillage for crop production is expanding. Research has shown that use of one or more conservation tillage systems will work on most soils in Minnesota. The system, to be successful and profitable, must be modified to fit soil texture. There is no “one size fits all” conservation tillage system. Each system (no-till, strip-till, ridge,till) has unique advantages and the preference among crop producers varies across the state.
A conversion from full width to conservation tillage requires some changes in use of traditional management practices. This is especially true with fertilizer use. Therefore, a description of fertilizer management practices that should be used in conservation tillage systems will be summarized in the paragraphs that follow.
NITROGEN USE: Results of research conducted to date lead to the conclusion that there is no need to change rate of applied fertilizer N when there is a switch from full width to conservation tillage systems. The current concept that addresses rate of applied N that is used throughout the Corn Belt is appropriate for both full width and conservation tillage production systems.
Timing of the fertilizer N is flexible in both tillage systems. Growers usually develop a preference for time of N application. Best Management Practices (BMP’s) that pertain to N timing have been developed for several region of Minnesota when corn is planted with full width tillage. These BMP’s are also appropriate for corn planted in conservation tillage systems.
However, special consideration should be given to placement. Results of various research trials conducted across the Corn Belt lead to the conclusion that fertilizer N should be placed below the crop residue—not in contact with residue on the soil surface. Efficiency of N use by corn is reduced substantially if fertilizer N remains in contact with crop residue.
There is no indication that source of N should be changed if there is a switch to conservation tillage. All N sources are equal if applied so that loss of N is minimized. This statement is appropriate for both full width and conservation tillage systems.
PHOSPHATE APPLICATION: Research and grower experiences have produced the same conclusion. Placement of phosphate fertilizer in a band is one of the keys to profitable production from a conservation tillage planting systems in Minnesota. There are several options for the location of the band. Placement of fertilizer to the side of and below seed level at time of planting works for all soil textures. Except for sandy soils (loamy sand, sandy loam), phosphate fertilizer can be placed in contact with the seed (pop-up) and this has become a very popular practice.
Rates of phosphate needed in a band are not different from rates used for banded application in full width tillage. If the soil test for phosphorus is in the very low range, the rate of banded phosphate suggested increases fro 30 to 60 lb./acre as the desired yield increases from 100 to 200+ bu./acre. The suggested rate increases from 20 to 45 lb./acre for the same yield range if the soil test for phosphorus is defined as low. When the phosphorus soil test is in the medium range, suggested rates for the same desired yields increase fro 20 to 35 lb./acre. When the phosphorus test is high, the rate of 10-15 lb. phosphate per acre is suggested for all desired yields.
POTASH USE: The concept for the use of potash is different. The banded application near the seed is still highly recommended. Compared to full width tillage systems, however, rates should change. When soil test values for potassium are less than 160 ppm, a rate of 80 lb. potash per acre is suggested. This should be adequate for two years of production in a corn/soybean rotation. When corn follows corn, the rate of 80 lb. potash per acre should be applied before each corn crop.
ZINC: As with full width tillage systems, base application of zinc on results of a soil test. Application of zinc is most effective if applied in a band at planting.
SOIL TESTING IS STILL IMPORTANT: The previous paragraphs provide a justification for the importance of soil testing in conservation tillage systems. Rates of phosphate, potash, and zinc used in a band vary as the relaative levels of these nutrients in the soil change. There are many questions about the procedure that should be used for the collection of soil samples. Current information suggests that the soil cores should be collected to a depth of 6 to 8 inches at a distance of 6 inches away from the row. This procedure provides the best indicator of nutrients available to the corn crop in conservation tillage systems.
The changes described in the previous paragraphs are important when there is a switch from full width to conservation tillage systems. There will probably be others as more information is collected from various research trials.