Working the ground improves mineralization Tilling the soil costs more money than no-till. But recent research indicates that a little tillage increases nitrogen efficiency at lower N rates. With soaring N prices, that could be important this spring.
This research also is important because some environmental groups, concerned about water quality, are calling for reduced N use by farmers.
University of Illinois research assistant Jeff Wessel compared six N rates (0, 40, 80, 120, 160 and 200 lbs/acre) under three tillage systems. The systems were no-till, strip-till (10" bands tilled in the fall) and mulch-till (fall chiseling followed by one pass in the spring with a disk or field cultivator).
"There is evidence in the scientific literature that suggests tillage influences corn fertilizer N requirements," Wessel explains. "In fact, the extension services in Minnesota, Missouri and Kentucky advise corn growers to reduce fertilizer N usage when tillage is used, relative to zero-till. We wanted to determine the impact of different tillage systems on corn fertilizer N requirements under our conditions."
The testing, done over three years in eight environments, showed that at low N rates - 0-80 lbs/acre - yields increased significantly as tillage increased. For instance, with no nitrogen fertilizer applied, mulch-till yielded 132 bu/acre, strip-till went 124 bu/acre and no-till yielded 108 bu/acre.
At higher N rates - 120-200 lbs/acre - yields were statistically similar for all three systems. However, at the higher rates, no-till always posted the highest numerical yield. For example, at 160 lbs N/acre, yield was 204 bu/acre for no-till, 201 bu/acre for mulch-till and 200 bu/acre for strip-till (see table).
The optimum economic N rate for no-till was 200 lbs/acre, while 160 lbs/acre was the optimum rate for mulch-till and strip-till.
"Where nitrogen was not limiting yield, the zero-till outperformed the other two systems because of greater water availability," Wessel points out.
"The higher yields with mulch-till and strip-till at N rates of 0-80 lbs/acre are due to greater mineralization of soil N," he explains. "In unfertilized corn, mulch-till increases the soil N supply by 23 lbs/acre more than does zero-till. Strip-till increases soil N by 16 lbs/acre, compared to zero-till."
Why is mineralization greater as tillage increases?
The reduced surface residue on tilled ground means a higher soil temperature. That warmer, drier soil environment speeds microbial activity, which increases mineralization, Wessel explains.
Interestingly, his research shows that tilling one-third of the soil (strip-till) results in an increase in mineralization over no-till that's roughly two-thirds of the increase seen with full-width mulch tillage (16 vs. 23 lbs).
"This probably means a little tillage goes a long way in terms of N mineralization," Wessel says.