# Presentation: 622558

## Iowa CREP Meeting/TourOctober 15, 2007

**Why off-field practices/buffers? **
- Jim Baker, IDALS (professor emeritus, Dept. Agric. and Biosystems Eng. Iowa State University)

## Upper Mississippi River Sub-basin Workshop(Illinois, Iowa, Minnesota, Missouri, and Wisconsin; plus Indiana and Ohio15 science panels comprised of 75 nutrient/water quality researchers)

## Importance of hydrology/land-use:

- Emerging science suggests that current nutrient impairment problems are not mainly due to mismanagement of fertilizers and manures, but more to historic changes in land use and _**hydrology**_ that came with the conversion of prairie and wetlands to cropland.

## Schematic showing modes of transport and importance of rate and route of infiltration water

## Current understanding:

- In tile-drained landscapes:
- N losses greater
- Carrier, subsurface drainage water
- Dominated by NO3 form
- Occur with sustained flows
- Usually in spring at time with little ET/nutrient uptake
- In “rolling” landscapes with good surface drainage:
- P losses greater
- Carriers, runoff water and sediment
- Usually dominated by P in sediment
- Occur with “flashy” rainfall-runoff events
- Year around, worse in spring with less vegetative cover

- Past projections of simple “win-win” or even “low-hanging fruit” situations were seemingly overly optimistic, particularly with respect to rate (and timing) of nitrogen additions, and what was perceived as wide-spread use of excess, or insurance, nutrients.

## N mgt. potential:

- Potential for reducing NO3-N leaching losses with N mgt. is highly dependent on where we are in terms of current rate and timing practices.
- In Iowa, e.g., recommended rate for corn after soybeans is 100 to 150 lb N/acre.
- In 2005, based on fertilizer N sales, 142 lb N/acre was applied to corn.
- How much additional manure N was applied can only be estimated.
- Based on leaching data, reducing the N rate from 150 to 125 lb/acre would reduce losses about 15%.
- Based on Minnesota timing data, Iowa which applies about 25-30% of its N fertilizer in the fall, might reduce leaching losses about 4% if no N was applied in the fall.

## Potential relative reductions in nitrate leaching in Corn Belt for specific corn/soybean mgt. changes

| PRACTICE | CHANGE | REL. REDUCT. |
| --- | --- | --- |
| N rate on corn | 150 reduced to
   125 lb/ac | **** |
| timing | no fall N-fertilizer
   applications | ** |
| cropping

buffer strips
 | switch to perennials

1-5% of area                       | ******************

- |
| tillage | plow to long-term,
   continuous no-till | ** |
| wetlands | 1-5% of area | ********** |

## There are land-use and off-site changes that do offer large potential reductions in nutrient losses, i.e. a “new landscape vision” (e.g., new crop rotations in association with carefully designed and sited wetlands and buffers)

## One additional issue is that of soil quality/sustainability (and like “global warming,” there is not agreement about the degree, importance, and solution of this issue)

- _N rate/mass balance example for corn-soybeans:_
- For corn following soybeans, Iowa recommendation for N is 100 to 150 lb/acre.
- For corn, N inputs minus outputs is already negative at a fertilizer/manure rate of 150 lb/acre.
- For soybean, N removed in grain is about twice that fixed as a legume so mass balance is negative.
- Loss of organic matter to make up for deficit N not only reduces soil quality, but also water quality (lower infiltration rate and water holding capacity have several ramifications).

## General Conclusions

- Sufficiently high soil nutrient levels are necessary for good crop growth; thus some loss is inevitable.
- Historic changes in land-use and hydrology have resulted in productive agriculture, but are also mainly responsible for nutrient impairment problems.
- N and P transport and losses are affected quite differently by surface and sub-surface landscape drainage processes.
- Some improvement in in-field nutrient management is possible, but off-site practices also are needed, using targeted/site-specific designs.
- There are no easy answers, and care must be taken to avoid promoting the wrong practices.
- Improvements will be incremental, and variability in weather can dominate both short- and long-term outcomes.
- Management impacts on soil quality/sustainability bears further consideration.
- A new landscape vision has considerable potential (but an approach that likely will require public funding).
- Current and evolving resource problems continue to create demand for new solutions that only additional research can provide.

## “We have an opportunity/obligation to create a coordinated, integrated initiative that builds on research and addresses compelling needs”Wendy Wintersteen, Dean, College of Agriculture and Life Sciences, ISUApril 12, 2006