NEPC2011 Meeting Index

Lloyd Owens spoke next. His presentation was Pasture Management Strategies to Minimize Nutrient Losses in Surface Runoff and Subsurface Flow. Lloyd introduced his talk by saying, “With the ever increasing public concern about our environment and the desire of agricultural producers to be environmentally responsible, environmental impacts of livestock in pastoral systems is receiving increased focus.” The objectives of his research are to study multiple pasture management systems with different levels of nitrogen fertilization to determine sediment and nutrient losses in surface runoff, and nutrient losses in subsurface flow.

Three general pasture systems are being studied:

A. Continuous, unimproved grazing

1. Cattle with access to stream

2. Cattle fenced away from stream

B. Rotational, “medium-fertility” pasture system

1. Weekly rotation in summer

2. Wintered in one paddock

3. Different N levels and N sources

C. Rotational, “high-fertility” pasture system

1. Weekly rotation in summer

2. Rotated in winter

3. N fertilizer; then grass-legume mixture

Studies on sediment loss from pastures were short to long term. With continuous, unimproved grazing management, these were the lengths of time each scenario was studied:

  1. Cattle with access to stream

    • No grazing (3 years) April 1974 – March 1977

    • Summer-only grazing (3 years) April 1977 – March 1980

    • All-year grazing (7 years) April 1980 – March 1987

  2. Cattle fenced away from stream

    • All-year grazing (6 years) April 1987 – March 1993

    • Vacant periods (16 years) April 1993 – March 2009 (Cattle removed from mid-Feb through April)

Sediment loss on the continuously grazed unimproved pasture ranged from 0.2 ton per acre when left ungrazed for 3 years to just under 1.2 tons per acre when grazed year-around. Summer-only grazing and all-year grazing with cattle fenced away from stream had the same soil loss of 0.6 ton per acre. Cattle removed during the late winter - early spring thaw period and also fenced away from the stream showed a soil loss of only 0.3 ton per acre. Not only does this reduce soil loss, but it is also good to allow the grass in the pasture to green-up without the stress of grazing brought to bear right away.

Looking at sediment loss on the treatments for the rotational, “medium-fertility” pasture system, 3 management scenarios/periods were studied:

  1. Summer rotation/winter feeding in one paddock only (sacrifice area).(Period 1 — 12 years)

    • Nov 1974 – Oct 1986
  2. Summer rotation only (Period 2 — 3 years)

    • Nov 1986 – Oct 1989
  3. No grazing; hay was made (Period 3 — 5 years)

    • Nov 1989 – Oct 1994

Summer rotation pasture with winter feeding had the highest soil losses of all 3 scenarios. This is to be expected as the winter feeding caused a lot of soil surface to be exposed to sheet and rill erosion due livestock traffic while the soils were wet or thawing in the sacrifice area (apt term when on sloping ground). Soil losses ranged from yearly soil losses of less than 0.1 ton per acre to a high of 2.5 tons per acre from exposed soil in 1982, most soil lost during the dormant season. Summer-only rotational pasture had minor yearly soil losses of less than 0.1 ton per acre. Hayed pasture had virtually no soil loss.

Rotational, “high-fertility” pasture system had minimal sediment loss and this included winter rotation-al occupancy. Well-fertilized grass being rotationally grazed formed an excellent ground cover.

Surface runoff nutrient loss and pasture systems data were looked at next. With the continuous, unimproved grazing management with the stream fenced off or not, nitrogen and phosphorus levels in the water were very low simply because availability of nutrients were not there except from voided feces and urine from the grazing animals. The weighted concentration levels of nitrate-N and soluble-P seen under the various scenarios described above were between 0.1 ppm (most often) to 0.3 ppm for N and between 0.01 ppm (most often) and 0.03 ppm for P in storm flows. It appears fencing off the cattle from the stream was not worth the trouble, especially since it became a haven for multiflora rose. In the case of P, the highest weighted concentration came from ungrazed pasture. Grass tea leachate from runoff water running through a grass thatch. Base flow levels of nitrate-N varied a bit more between treatments but were still very low for all.

For the rotational, “medium-fertility” pasture system, these were the treatments:

  • N fertilizer at 50 lbs/Ac annually (5 years)

    – May 1974-Apr 1979

  • N fertilizer at 150 lbs/Ac annually (11 years)

    – May 1979-Apr 1990

  • Rotational grazing vs Haying with 0 N/Ac (7 years)

    – May 1990-Apr 1997

  • NH4NO3 vs (NH4)2SO4 as N source – 100 lbs/Ac (4 years)

    – May 2001-Apr 2005

  • Continuous grazing vs management intensive grazing – urea as N source – 100 lbs/Ac (4 years)

    – May 2005-Apr 2009

Total N loss from the medium fertility pasture system never exceeded 16 pounds per acre per year for all the years studied. Most years the loss was less than 2 pounds per acre. Nitrate-N was a small part of the total N lost from the system. The range in nitrate-N concentrations detected in surface runoff is wide and largely reflects the timing of runoff event with when the pasture was fertilized with N. Run-off P losses were significant in this system.

The rotational, “high-fertility” pasture system received these treatments:

  • 200 lbs N/Ac annually (5 years) —- May 1975 – Apr 1980

    • Summer rotational grazing – orchardgrass

    • Winter rotational grazing/feeding – tall fescue

  • 0 lbs N/Ac (19 years) —- May 1980 – Apr 1999

    • legumes interseeded into grass
  • 200 lbs N/Ac; hay made in summer areas (4 years)

  • 50 lbs N/Ac in winter grazing areas (4 years)

    • May 1999 – Apr 2003
  • 200 lbs N/Ac with summer grazing (6 years)

    • May 2003 – Apr 2009

(Winter grazing areas removed from pasture study – 2005)

Nitrate losses were higher in the high fertility pasture system as one might expect, but for the most part nitrate losses were below 10 ppm for most runoff events. Runoff N was highest within 10 days of N fertilizer being applied. Legumes interseeded in the grass without N fertilizer had the lowest nitrate losses on all treatments. The highest loss of total N from the high fertility pasture system was less than 32 pounds per acre and occurred in only one year. Most years had total N losses of less than 10 pounds per acre. Again, nitrate-N made up a small portion of the total N lost.

Runoff P levels were slightly lower than P runoff levels found in the medium fertility pasture system. However, treatments are not easily compared. The additional N fertilizer produced a better pasture sod so less P is likely to be lost to runoff. Soluble-P losses in surface runoff for “medium-fertility” and “high-fertility” systems were:

  • Most of the soluble-P is loss in surface runoff.

  • Strong correlation between amount of soluble-P lost and the amount of runoff.

  • Highest concentrations were in events that occurred soon after P fertilizer application.

The third issue looked at was subsurface nutrient loss and pasture systems. For the continuous, unimproved pasture systems nitrate-N and soluble-P concentrations are low in the base flow (ground-water (spring) flow only) of a pasture stream.

For the rotational, “medium-fertility” pasture system soluble-P concentrations are very low, usually less than 0.10 ppm in base flow. The winter feeding area of that system had nitrate-N concentrations above 10 ppm in the base flow and this took awhile to dissipate below 10 ppm after the winter feeding was discontinued as the manure mineralized and was lost to groundwater by leaching.

Subsurface losses of nitrate-N occurred mostly during the dormant season - \~75% of the yearly losses. This loss spikes in March and April and is high also in November and December before freeze-up.

For the rotational, “high-fertility” pasture system, soluble-P concentrations are very low, usually less than 0.10 ppm in the base flow. Summertime losses of nitrate-N to groundwater were less than 10 ppm. Winter time losses of nitrate-N to groundwater were often near 10 ppm most years, spiking to 18 ppm in 1980. Towards the end of the experiment on this system, both winter and summer nitrate-N concentrations in the groundwater were at their lowest for the entire time the experiment ran.

Conclusions and recommendations are:

I. Soil Loss

A. Pasture systems that are not overgrazed, either unimproved or improved, will be within soil loss tolerance limits.

B. Pasture systems are good systems for controlling soil loss and sediment entering streams, ponds, reservoirs, etc.

C. Practices that will help reduce or prevent the potential for soil loss are:

1. Fencing livestock away from streams, and
2. Using limited rotation of a herd during winter feeding as contrasted with constant occupancy in a small pasture (sacrifice area).

II. Surface Runoff

A. The most likely times for high NO3-N concentrations to occur in runoff are within a few days following N fertilizer application.

B. Therefore, fertilizer applications should not be made on saturated soils and/or when runoff is likely to occur within the next runoff event.

C. P fertilizer should be applied to pastures only in response to soil tests indicating a need.

D. Unimproved pastures, if not overgrazed, usually have better surface runoff water quality than ungrazed wooded areas.

III. Subsurface Flow

A. In fertilized pastures, much more N will be lost in the groundwater than surface runoff.

B. It can take several years to see the full impact of surface management practices on ground- water quality.

C. Nitrogen application levels should not exceed 100 pounds per acre annually taking into account manure, purchased fertilizer, and legume contributions (also hay that has been brought in for feed).

D. Another strategy is to use legumes as the primary source of N for pastures with N fertilization restricted to strategic applications to overcome summer slump or to stockpile in the autumn.

The bottom line is that these results show that grazing systems on medium textured soils, when well-managed, are among the best in main stream agriculture from a water quality and soil erosion standpoint.