Your root zone determines the level of a field's productivity. Managing what happens to the biologic teamwork between soil, nutrients and roots offers a prime opportunity to farm even more efficiently.
Improving soil organic matter content through high residue is the most profitable way to manage this area, according to a seven-year University of Illinois (U of I) study.
U of I researchers Emerson Nafziger, Bhupinder Farmaha and Fabian Fernandez examined 35 field trials across five states. They compared deep-banded phosphorus (P) and potassium (K) to strip-till and no-till broadcasting P and K.
Their findings pinpointed the most important variable for higher yields -- soil surface residue -- which trumps both levels and placement of P and K. Fernandez, who is now with the University of Minnesota's Department of Soil, Water and Climate as a nutrient-management and water-quality specialist, calls the combination of roots, soil and nutrients the "million-dollar trio" and stressed this is where farmers should focus to increase profits.
The researchers used their results to develop the following "profit pointers" to be used as management guidelines:
-- Deep-banding P and K does not save money or fertilizer. Nutrient placement doesn't affect soybean and corn roots' efficiency. "Most roots lie within 2 inches of the soil surface, where the greatest P and K uptake occurs," Fernandez explained.
Whether P and K were broadcast or banded in no-till and strip-till systems, there was no corn yield difference because of the placement. The same held true for soybean yields. The potential advantage with deep banding can happen in soils where P and K become fixed in the soil, or where soil-test levels are very low, conditions that didn't exist in this study.
-- Environmental concerns about soil P runoff are a good reason to deep-band P. "Banding P binds it to soil particles in the soil profile, so it's unlikely to move," said Sadorus, Illinois, farmer Steve Stierwalt. He's deep-banded P for seven years but has not found a yield benefit. He's also familiar with the Illinois research as president of the Association of Illinois Soil and Water Districts.
-- Nutrient placement (broadcast versus banding) has little to do with where roots absorb P and K. Roots did not increase in banded P and K zones. The yield response to P and K was the same regardless of nutrient placement.
-- Strip-till improves root environment for nutrient and water uptake. Strip-till delivered a 15-bushel-per-acre corn yield boost (9%) over no-till. It had 9% higher soil organic matter than no-tilled soils in the Illinois studies. This resulted in higher yields (and crop residue), which increased soil organic matter compared to no-till systems.
-- Strip-till's higher soil organic matter creates more stable soil aggregates and water-infiltration rate. Strip-till had 23 to 24% greater P and K uptake than no-till treatments regardless of nutrient placement. Its lower soil bulk density translates to easier root penetration. The crop uses resources to build yields instead of larger roots to try to compensate for no-till's less-favorable conditions, Fernandez said.
-- Strip-till systems (deep-banded) also increased soybean yields compared to no-till (broadcast and deep-banded). This is likely from improved soil conditions, including greater water content.
-- Strip-till boosts absorption. Corn roots in strip-till systems absorbed P and K more efficiently than in no-till systems, measured as uptake amount per root surface area.
-- Roots "cost" a plant a lot of energy. Strip-till's higher soil organic matter levels enable plants to capture nutrients more efficiently with smaller roots, the research documented.
-- No-till has a more stressful root environment than strip-till. This costs the plant more energy to develop and maintain more roots to capture water and nutrients.
-- Size matters. No-till system corn and soybean roots were larger, but strip-till roots were more efficient.
-- Adequate P and K levels are more important than fertilizer placement (banding versus broadcast). Nutrient placement (broadcast versus deep-banded) did not produce longer roots or root density. Applying more P and/or K did not produce longer roots or root density, and banding doesn't reduce required rates. Deep-banding P and K results in high soil nutrient levels in the row (where the fertilizer is applied) and low levels between rows.
-- Long-term and short-term impacts. Corn absorbs P throughout the growing season. Corn absorbs all the K it needs early in the growing season (by R2), with most of that during stages V12 through R2.
-- Competitive advantage. Strip-tilled soybeans had improved nutrient uptake and 20% greater surface soil water content during seed fill compared to no-till in both deep-banded and broadcast P and K.
-- Soil moisture and planting. Soil moisture storage was similar between no-till and strip-till except early in the season, where moisture in the strip-till row was lower. Having slightly drier conditions in the strip-till row can help improve planting operations and germination as soils warm up faster.
DON'T TAKE SHORTCUTS WHEN SOIL-SAMPLING:
The greatest source of soil-test inaccuracy often results from how the sample was collected. Keep these pointers in mind to improve the odds of the most accurate tests:
-- Where P and K are banded, take two to three cores away for each core taken in the fertilizer band.
-- It's better to take fewer samples made of more cores than more samples made of fewer cores. â€¨
-- Make a composite sample of 10 to 20 cores in a bucket, and mix thoroughly. â€¨
-- Place approximately 2 cups of soil in a labeled sample bag. â€¨
-- Mark sample locations using GPS so you compare the same locations each time.
"Crop residue's a big deal as we try to keep P on the farm where we want it," said Steve Stierwalt, a Champaign County, Illinois, farmer. That's why he's strip-tilled for 25 years. "Strip-till residue absorbs falling raindrops' energy and keeps soil from breaking away."
He strip-tills because it allows him to "plant earlier than my full-tillage neighbors in cold, wet springs," he said. "The black strip warms up quickly and is higher than surrounding ground, so it drains well.
"Banding does not increase yields, but we still have to keep P in place," he explained, adding strip-till residue holds the soil and limits the possibility broadcast P leaves with eroding soil.
"The challenge," Stierwalt said, "is how to convince farmers to till less. Research shows that most of them don't think they have an erosion and nutrient-loss problem."
One solution could be freshening fall ammonia strips in spring instead of cultivating them, suggested Dan Schaefer, director of nutrient stewardship for the Illinois Fertilizer and Chemical Association.
"Farmers don't have to run a spring field cultivator; they can just plant on those strips," he said. Schaefer is planning a related demonstration project.
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