Use of Interseeding Grass Technology to Reduce Nitrate Concentration in New Seeding Grass Silage

Final Report for FW03-317

Project Type: Professional + Producer
Funds awarded in 2003: $6,000.00
Projected End Date: 12/31/2006
Region: Western
State: Washington
Principal Investigator:
Dr. Joe Harrison
Washington State University
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Project Information



Approximately 115 acres of Harry Faber’s dairy is planted in grass and ensiled. The grass is usually harvested for silage every 30 days throughout the growing season. Currently, the grass is reseeded every five to seven years because it is a priority to grow high quality forage on the dairy, and grass yields and quality tend to deteriorate over time in an established stand. Reseeding grass helps to maintain high production levels in the dairy herd and reduce the amount of feed imported onto the farm as purchased commodity feeds and alfalfa hay.

New seeding grass has a potential to be high in nitrates. This is primarily due tilling the soil, which causes mineralization of N (conversion of organic N to nitrate N) in the soil. Though this is not toxic to plants, it can lead to both health and production problems in the dairy herd.

This project evaluated an alternative practice to conventional tilling that consists of planting new seeding grass in a no-till and minimum-till situation. By using a no-till method of preparing the soil for grass planting, the amount of nitrate N accumulation in the plant should be reduced because the ground will not be tilled. Our goal was to determine if planting grass seed into a no-till sod will improve quality and maintain high yields in the grass stand, thereby minimizing the need to reseed using a conventional-till method at five- to seven-year intervals.


1) The quality data (chemical analysis of crude protein, nitrate-N, and fiber) from the no-till grass plot were compared to the quality data collected on the conventional-till grass plot in 2004 and industry standards of grass quality.
2) Yield estimates of the no-till grass will be compared to yield estimates collected on the conventional-till grass stand in 2004.
3) Manure application rates and soil nitrate levels will be monitored to evaluate the effects of no-till on the environment (potential for reduced nitrate content in the soil due to reduced tillage of the ground).
4) An economic analysis will also be conducted on no-till vs. conventional-till.


The project design consisted of two plots, a no-till and a conventional-till. The grass present on both plots was sprayed with herbicide on March 31, 2004, and reseeded with a 50:50 blend of orchardgrass:fescue on April 8, 2004. The tilled plot was rotatilled, plowed and cultipacked on April 6 and 7, 2004. No tilling was done to the no-till plot prior to planting on April 8, 2004. There was approximately one week between the herbicide application and reseeding.

Manure was applied at the same rate to both plots five times in 2004—four times with an aerator and once with a tanker. Grass was harvested four times for silage throughout the growing season (every 30 to 33 days). Soil samples were collected at the time of harvest for each cutting.

Over the entire growing season, there was approximately a 12% increase in grass dry matter harvested from the till plot versus the no-till plot. However, the amount of grass harvest (DM basis) at forth cutting was greater for the no-till plot. Crude protein concentrations tended to be lower for the till plot during the first three cuttings (range 7 to 10%); however, nitrogen harvested was greater for the till plot due to the increased dry matter yields. Nitrate concentrations in the grass were lower for the till plot during the first three cuttings (cutting 1 – 14% lower, cutting 2 – 49% lower, cutting 3 – 104% lower). This was contrary to what was expected. We anticipated that nitrate concentrations in the grass and soil would be higher in the till plot due to mineralization that would occur because of tilling. At this time, the reason for this finding is unknown.

The nitrate concentration in grass correlated to the crude protein concentration in the grass. As the crude protein content in the grass increased, the nitrate concentration in the grass increased. This strong relationship may partially explain the lower nitrate concentration in grass on the tilled plot versus the no-till plot. The tilled plot had lower crude protein concentrations in the grass, which led to lower nitrate concentration.

Fiber concentration in the grass was higher for the no-till treatment at first cutting, and was similar between plots for cuttings two through four. This may have been because of the grass matter that was still present in the plot from the previous year. Although there was a greater concentration of fiber in the no-till plot for first cutting, the digestibility of the fiber was greater than the till plot. Differences in fiber digestibility between the two grass plots diminished at later cuttings. Therefore, it appears that crude protein concentrations tended to be greater for the no-till plot, and fiber concentrations were similar between the plots for the majority of the cuttings. This suggests that the quality of the forage is not compromised by using the no-till method to reseed grass forage.

There was little difference in soil nitrate concentrations between the till and no-till plots. The results from this study indicate that the no-till method of seeding grass will not reduce soil nitrate concentrations compared to a conventional-till method.

An economic analysis was done to evaluate the differences in cost between a conventional-till method and no-till method used to reseed grass. The tilled plot yielded 0.58 tons of grass dry matter per acre more than the no-till plot over the entire growing season. However, it costs approximately $19/ton of grass DM more with the conventional method. The increased yielding grass did not offset the cost of the conventional-till method.

These results suggest that grass of similar quality can be grown on a Barnhardt gravelly loam soil using a no-till method to reseed grass versus a conventional-till method. However, it is important to monitor crude protein levels in the new seeding grass for either no-till or conventional-till practices. High nitrate concentrations in feedstuffs can cause health and production problems for dairy cattle grass DM yields will be lower during the first growing season after replanting using the no-till method versus the conventional-till method of reseeding grass. The difference in grass DM yield is great at the beginning of the harvest season, and tends to even out by the end. The economic analysis suggests that the increase grass DM yield for the conventional-till plot did not offset the increased cost associated with the conventional-till method versus the no-till method. It cost approximately $12 more per ton of grass DM to reseed the grass using the conventional-till method versus the no-till method.


The results from this study were presented at a field day at Harry Faber’s farm on May 12, 2005. There were five posters and two fact sheets presented at the field day.

There will be three newsletter articles published in the WSU Dairy Newsletter. The first of the three articles was published in the June edition of the WSU Dairy Newsletter, titled “Conventional Tilling versus No Tilling to Reseed Grass: I. Is it an option for you? Grass yield and Nitrogen Dynamics.” The remaining two articles will be published in the next two editions of the WSU Dairy Newsletter.


Eleven people attended the field day. Two people requested additional information about the no-till vs. conventional-till study. The Whatcom Conservation District has discussed the possibility of publishing information from this study in a newsletter article.


Responses from attendees of the field day were positive. Some producers who attended the field day asked questions about what types of soil the no-till technology would work in, what the yield differences were and what the economic impacts of using the no-till technology versus the conventional-till technology to reseed grass were.


We aren’t sure why the conventional-till plot didn’t have high soil nitrate values as anticipated; one soil scientist suggested it may be due to the fact that the plots had inputs of manure and soil organic matter mineralization that far exceeded what the crop could use. This caused soil nitrate concentrations to be too high in general, and one may not see the spike in soil nitrate concentrations due to tilling. He suggested that manure not be added to soil that had greater than 30 ppm at establishment to demonstrate differences in soil nitrate concentration due to tilling.


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  • Becky VanWeerdhuizen
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Participation Summary

Research Outcomes

No research outcomes
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.