Injecting potash 5-7" deep in the row can put a charge in ridge-till and no-till corn yields, says Iowa State University (ISU) soil scientist Antonio Mallarino.
Ridge-till yields soared by 8 bu/acre with deep-banded potash compared to other methods of placement. No-till corn yields climbed 4-5 bu/acre.
Mallarino began comparing three methods of placement for both phosphorus and potassium: fall broadcast, fall deep banding and spring banding through the planter.
Neither broadcast potassium (K) nor starter fertilizer had been effective on ridge-till corn. Also, K-deficiency symptoms have shown up under all tillage systems when spring soils have been dry. This was especially evident in some areas last spring.
The research involved both corn and soybeans. No-till and ridge-till crops were planted in 30” rows where the deep banding took place.
Banded phosphorus (P) almost always increased early corn growth in no-till and ridge-till, Mallarino found. But P placement seldom increased yield for either corn or beans in any of the three tillage systems. The differences were small for K-banded soybeans, too. The two band placements often did not differ.
It was a different story for corn deep-banded with K. Corn yields were up 4-5 bu/acre in no-till and 8 bu/acre in ridge-till compared to broadcast or planter-banded K. K rates ranged from 35 to 140 lbs K2O/acre.
“It's likely that the response to deep-banded K is greater when late spring-early summer rainfall is below normal,” Mallarino explains.
“Under normal conditions, corn grown in no-till or ridge-till draws a high percentage of nutrients from near the soil surface because of the higher nutrient levels present there. However, when surface soil layers become drier, root development increases in deeper portions of the soil profile.”
This seems to be more of a factor with potassium than with phosphorus.
Deep banding fertilizer for no-till corn, in effect, becomes strip-till. Many trials have shown a yield advantage for strip-till over conventional no-till. That advantage has been largely attributed to soil that's warmer in the strips. It approaches the soil temperature of conventionally tilled ground.
Mallarino's research indicates that deep-banded K may also be a factor in higher strip-till corn yields.
University of Minnesota (U of M) research has also shown a major advantage for banding P and K in ridge-till and no-till systems. George Rehm, U of M soil scientist, placed the nutrients 3-4" deep. No starter is needed when this is done.
“We suggest a rate of 40-50 lbs of potash per acre for corn after soybeans even though soil test values for potassium are in the medium or high categories,” Rehm says. “It should be 60-80 lbs when potassium is in the low category.”
Double those rates if the banded fertilizer is to be applied only once in two years for a corn-soybean rotation.