Fate of Manure Nitrogen Applied for Grass Silage Production

 

Final Report submitted by Washington State University

Livestock Nutrient Management Program

July 2009

 

Purpose:

Characterize the effect of management factors such as re-seeding of cropland as well as timing and amount of manure and irrigation water application on crop uptake of nitrogen, soil nitrate-N concentration, nitrate+nitrite-N concentration in shallow ground water underlying the field, and the relationships between these matrices.

 

Overall Description of the Study

 

In 2004, there was an interest by the Whatcom Conservation District and the Department of Ecology’s Bellingham Field Office to do a study that quantitatively measured management practices on a grass field where dairy manure was applied annually and relate these practices to shallow groundwater nitrate+nitrite-nitrogen (N) concentrations. The location of the field was in an area where the depth to groundwater was relatively shallow (ranged from 0.5 to 11 feet depending on seasonal variation), and the soil type was known to be one where nitrate-nitrogen would leach (poorly graded sand with silt and loam).

 

 A contractor for the Department of Ecology’s (Ecology) Environmental Assessment Program (EAP) installed 6 shallow groundwater wells (13 feet deep) and 1 deep groundwater well (38 feet deep).   The EAP sampled these wells every 4 to 6 weeks from 2004 to 2008. The Washington State University (WSU) Livestock Nutrient Management Program collected grass, manure, soil, and irrigation water samples throughout the 4-year period. Weather data was also collected during this time frame.

 

The intent of the study was to measure surface activity and monitor groundwater parameters to assess the effectiveness of recently adopted Dairy Nutrient Management Plans in protecting the quality of the Sumas-Blaine Aquifer at a typical dairy. Therefore, there was relatively little instruction by WSU or Ecology on what management practices to adopt or use throughout the study. The only area of management that was modified due to the data that was collected from the study was the irrigation schedule. It appeared in 2005 (the first full year of the study) that the grass field went dormant in the summer months. Soil moisture and nitrate-N concentrations were low, and grass growth slowed. After the first year, at our suggestion, the dairy farmer intentionally tried to apply more irrigation water earlier in the growing season to prevent grass dormancy.

 

Management Practices

Each year the management practices on the field were different. Prior to the start of the study in 2004, the field was re-seeded from grass back into grass in the spring using conventional tilling practices (subsoiling, rotatilling, plowing, disking, seedbed preparation, cultimulching, and planting).

 

Data collection started in the fall of 2004.  Grass was harvested 4 times and manure was applied 3 times (Tables 1 and 2).  In 2005, grass was harvested 4 times (Table 1). The intent was to harvest a 5th cutting in the fall, however the weather did not permit.  There was approximately 1.5 tons/acre of grass (on dry matter basis; estimate made in December 2005) remaining in the field through the winter months.  Manure was applied 5 times in 2005 (Table 2). Irrigation water was applied 2 times from the beginning of August through the middle of September (Table 3).

 

In 2006, grass was harvested 5 times and manure was applied 3 times (Tables 1 and 2). No manure was put on the field in early spring (March) because of the large amount of grass remaining in the field through the winter. Commercial fertilizer was applied on 5/25/06 because no manure was available (Table 4). Irrigation water was applied 2 times in 2006 (Table 3).

 

 In 2007, grass was harvested 5 times and manure was applied 4 times (Tables 1 and 2). Commercial fertilizer was applied on 6/26/07 because no manure was available (Table 4).  Irrigation water was applied 3 times (Table 3).

 

In 2008, grass was harvested 5 times and manure was applied 5 times (Tables 1 and 2). Irrigation water was applied 2 times (Table 3).

 

Table 1. Grass harvest dates from 2004 through 2008.

Year

Grass Harvest Dates

2004

4/28/04

7/19/04

8/16/04

10/7/04

 

2005

4/28/05

6/12/05

7/17/05

8/25/05

 

2006

4/21/06

5/25/06

7/5/06

8/15/06

9/27/06

2007

5/6/07

6/14/07

7/30/07

8/28/07

10/10/07

2008

5/9/08

6/16/08

7/21/08

9/2/08

10/21/08

 

Table 2. Manure application dates from 2004 through 2008.

Year

Manure Application Dates

2004

3/18/04

4/30/04

7/14/04

 

 

2005

2/18/05

5/13/05

6/27/05

8/9/05

8/31/05

2006

None

4/27/06

7/11/06

10/7/06

 

2007

3/14/07

5/18/07

8/6/07

9/7/07

 

2008

3/10/08

5/20/08

6/23/08

7/31/08

9/13/08

 

 

 

 

 

 

 

Table 3. Irrigation water sampling dates from 2005 through 2008.

Year

Irrigation Water Sample Dates

2005

8/17/05

9/7/05

 

2006

7/22/06

8/22/06

 

2007

7/17/07

8/23/07

9/12/07

2008

7/8/08

8/16/08

 

 

Table 4. Commercial fertilizer

dates from 2006 and 2007.

Year

Commercial Fertilizer Dates

2006

5/25/06

2007

6/26/07

 

Manure was primarily applied using an aerator (also referred to as subsurface deposition  or SSD).  In the summer, the dairy farm does not have enough manure to apply after the second cutting.  If possible, the neighboring dairy will apply manure using an injector (this happened in 2005 and 2008). On the years when manure was not available from the neighboring dairy, commercial fertilizer was added (2006 and 2007).

 

The following questions were forwarded to the WSU Nutrient Management Program from Nora Mena at the Washington State Department of Agriculture in February of 2009.  Data from the study was used to answer the questions. In some cases there was no information available.

 

 

*     What level of irrigation/rain water will affect nitrate movement through the root zone- first foot, second, etc.?

 

*     The soil samples that were collected for this grant were taken only at the 1-foot level.  There was no measurement of root zone or second foot soil nitrate-N concentrations. One-foot soil samples were taken weekly throughout the fall (August through November), and analyzed for moisture level and nitrate-N concentration.  Precipitation was recorded daily.  There were times in the fall when the amount of precipitation was high over a relatively short period of time (1 to 2 weeks).  A fairly rapid decrease in 1-foot soil nitrate-N concentrations occurred at the time of high precipitation.  This was followed by elevated groundwater nitrate+nitrite-N concentrations in the following winter months in 2006 and 2008.  Below are some graphs highlighting this information:


 

*     In 2005, soil nitrate-N concentrations went from 22 ppm (10/25/05) to 12 ppm (11/1/05) to 6 ppm (11/10/05) over the 2-week period (figure 1).  Soil moisture went from 36 to 43 to 46% over the same time period (increased 10 percentage units (figure 1). Between 10/25/05 and 11/1/05 there was 2.2 inches of precipitation, and between 11/1/05 and 11/10/05 there was also 2.2 inches of precipitation (total = 4.4 inches of rain over 2 week period).  Mean groundwater nitrate+nitrite-N concentrations continued to decrease through the fall and winter despite relatively high rainfall over a 2-week period (September = 20 mg/L and by March 2006 = 13 mg/L (figure 1). 

 


 

*     In 2006, soil nitrate-N concentrations went from 31 ppm (11/1/06) to 16 ppm (11/15/06) over a 2-week period (figure 2).  Soil moisture went from 31 to 34% over the same time period (increased 3 percentage units; figure 2) indicating movement of nitrate below one foot.  Between 11/1/06 and 11/15/06 there was 8 inches of precipitation.  Mean groundwater nitrate+nitrite-N concentrations increased from 9 mg/L in the fall to14 mg/L in the winter (figure 2).    

 


 

*     In 2007, soil nitrate-N concentrations went from 19 ppm (10/16/07) to 12 ppm (10/30/07) over a 2-week period (figure 3). Soil moisture went from 36 to 39% over the same time period (increased 3 percentage units; figure 3). Between 10/16/07 and 10/30/07 there was 3 inches of precipitation. Mean monthly groundwater nitrate+nitrite-N concentrations did not vary much throughout the fall and winter (October – 8 mg/L through Feb – 9 mg/L).   

 


 

*     In 2008, soil nitrate-N concentrations went from 30 ppm (10/31/08) to 10 ppm (11/7/08) over a 1-week period (figure 4).  Soil moisture went from 37 to 51% over the same time period (figure 4). Between 10/31/08 and 11/7/08 there was 5 inches of precipitation.  The manure application rate (715 lb/acre/year of total N; figure 5) was high compared to nitrogen removal by the grass (393 lb/acre/year of nitrogen; figure 5).  Fall soil nitrate-N concentrations (average of September and October – 29 ppm) were higher than in previous years, and mean monthly groundwater nitrate+nitrite-N concentrations increased from the fall into the winter (October – 5 mg/L to March - 13 mg/L; figure 4).  

 


*     The amount of grass nitrogen harvested was greatest in 2006 and 2007 (430 and 458 lbs of nitrogen/acre, respectively; figure 5). The application of manure total N in 2006 and 2007 (363 and 386 lbs/acre, respectively) was about half of that applied in 2005 and 2008 (642 and 715 lbs of manure total N/acre; figure 5). In fact, the amount of grass nitrogen harvested in 2006 and 2007 was greater than the amount of manure total N applied (figure 5).

 

*     In general, during the fall, when there was a high amount of precipitation over a relatively short period of time, soil moisture increased and soil nitrate-N concentrations decreased. Decreasing depth to water following fall precipitation events indicates movement of soil pore-water through the unsaturated zone to the water table. As the water moved vertically through the soil profile, nitrate-N appears to move from the 1-foot level with the soil pore-water to the water table.

 

*     In 2008, the concentration of nitrate-N in the 1-foot soil sample tended to be greater during the fall (ranged from 10 to 41 ppm; figure 4) than the soil nitrate-N concentrations in 2005 (ranged from 5.5 to 22 ppm; figure 1); 2006 (ranged from 14 to 31 ppm; figure 2), and 2007 (ranged from 10 to 25 ppm; figure 3).

 

*     Mineralization activity after application, how soon, how much, what conditions?

*     This information was not collected during this study. There is a possibility that some of this information may become available in another study that is being conducted by Dr. Joe Harrison and the Washington State University Livestock Nutrient Management Program.

 

*     What information is important for nutrient planners to consider when developing recommendations for whole farm nutrient management?

*     Comparison of NLOS model predictions and observed concentrations of nitrogen in soil. This was completed by conference call and ADOBE Connect in April 2009.

 

*     What did we learn regarding good manure management for grass fields that have been re-seeded?

*     Information about manure management practices that would be ideal in a year when there was re-seeding of a grass field was not collected during this study.

 

*     In 2008, the amount of manure total N applied (715 lbs total N/acre) exceeded the amount of grass nitrogen harvested (393 lbs/acre) by almost double (figure 5). Average fall soil nitrate-N concentrations (average of September and October soil samples) in 2008 were higher (29 ppm) compared to average fall soil nitrate-N concentrations in 2006 (21 ppm) and 2007 (16 ppm) when manure total N applied was similar to grass total nitrogen harvested (figure 21). These results suggest that, in grass fields that have received manure for many years, the amount of manure total N applied to the field can be similar to the total amount of grass N harvested that year without compromising quantity or quality of the grass stand. In 2006 and 2007, when total manure N applied was similar to grass N harvested, the quantity (grass yield; figures 6 through 9) and quality (measured as crude protein; data not shown) of the grass harvested equaled or exceeded the quantity and quality of grass N harvested when approximately double the amount of manure total N was applied than grass N harvested (year 2008; figure 5).

 


 


 


 


*     Other factors besides the nitrogen supplied to the grass crop effect grass yield. Moisture level in the soil as well as available heat units appear to have affected grass yield at different times throughout the study.

 

*     Grass yields (tons of dry matter/acre) were lower in 2008 (figure 9) than in 2006 and 2007 (figures 7 and 8) despite the fact that the amount of manure total nitrogen applied was almost twice as much as grass nitrogen harvested in 2008 (figure 5). The dairy farmer had also applied irrigation water earlier in the growing season compared to previous years in an attempt to keep soil moisture levels higher (soil moisture remained at 25% or greater during the driest part of the growing season) and prevent grass from slowing in growth due to lower soil moisture content during the summer months. The grass stand in 2008 was 4 years old, and there was a high concentration of clover in the stand. These factors may have contributed to the lower grass yield in 2008. However, it appears that the air temperature in 2008 was noticeably lower than in previous years, and this would affect yield.

 

*     Growing degree units (GDU) are a measure of thermal time by calculating the daily accumulation of heat. There are different equations available for calculating GDU. Three methods were used in this study and will be reported below.

 

*     The first method used to calculate GDU for corn crops is written below.

         GDU = (maximum temperature + minimum temperature)/2 – 50° F

Daily maximums greater than 86° F are set equal to 86.

Daily minimums less than 50° F are set equal to 50.

*     At 50° F it is assumed that corn growth is 0. As temperature increases, the growth rate increases.

*     The optimum temperature for crop growth is considered 86° F.

 

*     The cumulative grass yield (7.2 tons/acre) was highest in 2007 and lowest in 2008 (5.9 tons/acre; figures 8 and 9). The cumulative GDU values through October were 2,344 and 1,648 in 2007 and 2008, respectively (figure 10). This is a difference of 696 GDU (daily accumulation of heat units) between the 2 years. The greater heat units in 2007 aided in greater grass yields.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GDU = (maximum temperature + minimum temperature/2 – 50º F
 

 


*     There was a 42% reduction in GDU through October in 2008 compared to 2007. Grass yield was reduced by 22% in 2008 compared to 2007.

 

*     The cumulative GDU through October was plotted against the cumulative grass yield for the years 2005 through 2008 (figure 11). Cumulative GDU through October explained ~79% of the variation in grass yield (figure 11).

 


 


*     In 2005, the weather conditions did not allow for the final cutting of grass to be harvested. Therefore, in December 2005, measurements were collected to determine the approximate quantity of grass remaining in the field. Below is a graph including the remaining grass in the field for the fall/winter 2005. Cumulative GDU through December explained ~64% of the variation in grass growth (figure 12).

GDU = (maximum temperature + minimum temperature/2 – 50º F

 
 
 


 


*     Grass growth starts prior to 50° F in the Pacific Northwest. The exact time at which grass growth begins is not well documented. Therefore, 2 equations were used to calculate GDU using a grass growth model.

 

1)     The second method for calculating GDU is from a British Columbia Publication – Determining range readiness and growing degree-days (GDDs) – Rangeland Health Brochure 11 (Fraser, 2006).

*     GDU's start to accumulate after pasture is snow free, and cannot begin before March 1. There must be 5 consecutive days when the daily average temp exceeds 32° F before GDU's begin to accumulate (referred to as "start up")

*     GDU = (maximum temperature + minimum temperature)/2 – 32° F

*     If GDU is negative it is not included in the data set (no growth occurred)

 

*    
Figure 13 is a graph plotting cumulative GDU (°F) using the Fraser (2006) equation referred to above:

 

 


*     The cumulative GDU through October was plotted against cumulative grass yield for the years 2005 through 2008 (figure 14). Cumulative GDU through October explained ~66% of the variation in grass yield (figure 14).

 


 


The third method for calculating GDU is from the publication titled ‘N rate and timing relationships with tissue N concentration and seed yield in perennial ryegrass’ (Griffith and Thomson, 1996).

*     GDU's start to accumulate January 1. The base temperature for temperate grass is 32° F.

*     GDU = (maximum temperature + minimum temperature)/2 – 32° F

*     If GDU is negative it is not included in the data set (no growth occurred)

 

*     Figure 15 is a graph plotting cumulative GDU (°F) using the Griffith and Thomson (1996) equation referred to above:

 


 


*     The cumulative GDU through October was plotted against cumulative grass yield for the years 2005 through 2008 (figure 16). Cumulative GDU through October explained ~66% of the variation in grass yield (figure 16).

 


 

 


*     Three methods were used to estimate growing degree units. All of the methods had a fairly strong relationship (at least 64% of the variation in yield was explained by thermal heat units) with grass yield. This suggests that thermal heat units strongly influence grass growth. The more heat units the higher the yield.

 

*     Soil Moisture has also been shown to influence grass growth in this study

 

*     In 2005, there was 1.2 inches of precipitation between 6/29/05 and 7/17/05 (figure 17).  However, between 7/17/05 and 8/11/05 there was only about 0.2 inches of precipitation (figure 17).  During this time period, soil moisture levels dipped below 20%, and were very low at the 7/28/05 (14%) and 8/5/05 (13%) soil sampling dates (figure 17). Soil nitrate-N concentrations were also very low (5 to 6 ppm) during the 7/28/05 and 8/5/05 soil sampling dates (figure 17). The grass had slowed in growth and manure was applied 3 weeks and 3 days after the July cutting. The addition of manure as well as irrigation water during mid August increased both soil moisture and nitrate-N concentrations (figure 17).

 


 


*     In later years of the study the dairy farmer applied irrigation water earlier in the growing season (started in July instead of August).  In 2007, irrigation water was applied around the week of 7/17/07 for the first time followed by 2 more irrigation events during the remainder of the growing season.  During July and August, soil moisture levels remained at 20% or higher, and soil nitrate-N levels remained between 18 and 20 ppm, also (figure 18). The time between the July and August cutting was reduced by 1 week and 4 days from 2005 to 2007, however grass yield (0.88 and 0.86 tons/acre) and nitrogen removal (61 and 62 lbs N/acre) were similar in 2005 and 2007, respectively.

 

*     These results suggest that applying irrigation water earlier in the growing season (in this study it was July instead of August) can increase soil moisture content which will reduce the likelihood of grass becoming dormant during the driest part of the year. This can increase the yield of grass harvested, and hence increase the amount of nitrogen removed over a growing season.

 

*     Summary of nitrate+nitrite-N concentrations in wells over 4 year period and relationship to surface activity and conditions.

 

*     Conventional tilling (subsoiling, rotatilling, plowing, seedbed preparation, cultimulching) of the soil and re-seeding back to grass resulted in elevated soil nitrate-N and groundwater nitrate+nitrite-N concentrations in the fall following re-seeding. This study also documented elevated groundwater nitrate+nitrite-N concentrations in the 2nd fall after conventional tilling (figures 19 and 20).

 


 


 

*     Results from this study coupled with the fact that the dairy farmer planned to re-seed this test field in 2009 led to the opportunity to do a study comparing the effects of re-seeding grass using conventional tilling practices to minimum tilling practices on soil nitrate-N and groundwater nitrate+nitrite-N concentrations. This study is in the initial phases and will continue for the next 2 years.

 


*     In 2005, there didn’t appear to be movement of nitrate-N into the groundwater related to times of heavy rainfall in the fall.  Mean groundwater nitrate+nitrite-N concentrations (average groundwater nitrate+nitrite-N concentrations in mg/L were: Sept = 20, Oct = 19, Nov = 19, Dec = 17; figure 21) continued to decrease during the winter despite relatively high manure total N application (642 lb/acre; figure 5). However, in 2008, following another year of high manure total N application (715 lb/acre) and the highest average fall soil nitrate-N value observed (29 ppm), mean groundwater nitrate+nitrite-N concentrations increased from 6 to 11 mg/L from November to December (figure 21). Fall groundwater nitrate+nitrite-N concentrations (mg/L) were greater in 2005 than in 2006 through 2008 (figure 21). The elevated levels of nitrate+nitrite-N in the groundwater in 2005 compared to following years may have been a residual effect of the release of nitrate-N in the soil due to conventional tilling and re-seeding in the spring of 2004.

 

*     In 2006, the amount of grass nitrogen harvested (430 lbs N/acre) was actually greater than the amount of total manure N applied (363 lbs N/acre) over the growing season (figure 5). However, approximately 90 lb of manure total N/acre was applied on 10/7/06 after the final cutting (on 9/27/06).  Soil nitrate-N from the final manure application apparently leached into the groundwater during the following winter. The mean groundwater nitrate+nitrite-N concentration increased from 7 mg/L in November 2006 to 15 mg/L in January 2007 (figure 21).

 

*     In 2007, soil nitrate-N concentrations were low compared to the other years. The average soil nitrate-N concentration for September and October was 16 ppm, whereas average soil nitrate-N concentrations for September and October were 29, 20, 21, and 29 ppm for 2004, 2005, 2006, and 2008, respectively (figure 21). Mean groundwater nitrate+nitrite-N concentrations remained below the 10 mg/L drinking water standard from May 2007 through November 2008.  Some of the reasons for the lower soil nitrate-N and groundwater nitrate+nitrite-N concentrations in 2007 may be:

*     It had been 3 years since re-seeding the grass field using conventional tillage methods,

*     The amount of manure total N applied for the previous 2 growing seasons (2006 and 2007) was less than the amount of grass N harvested and about half of that applied in 2005 and 2008,

*     No manure was applied after the final grass harvest on 10/10/07,

*     Denitrification due to low oxygen in some of the wells removed nitrate that would have been there.

 

*     Describe methods used in the study (needed to ensure appropriate translation into use for planning and management activities)

*     How was organic N mineralization from the same year applications, previous year applications, and soil organic matter accounted for? 

*     Are the assumptions researchers used about appropriate N application rates the same assumptions used in local dairies Nutrient Management Plans?

*     The intent was not to recommend the ‘appropriate N application rate’, therefore, we made no assumptions as to how organic N mineralization from the same year applications, previous year applications, or soil organic matter were accounted for. The data presented in this report and other material (such as fact sheets, field day presentations, or excel files in conference calls) is actual information that was recorded and measured.

*     The intent of the study was to document the activities that took place on the research field such as the timing, amount, and method of manure application.  Other activities that were documented included the time and amount of grass harvested, the time and amount of irrigation water applied, and the fact that conventional tilling of the field occurred prior to the start of the study in 2004. Other data that was collected during the study by either WSU or the Department of Ecology consisted of weather data, grass yield and nitrogen content, manure nutrient content, soil nitrate-N data, irrigation water nitrogen content, and groundwater nutrient content.

*     In regard to the comment ‘need to ensure appropriate translation into the use for planning and management activities’, we used a worksheet developed to estimate plant-available nitrogen (Oregon State University Extension Bulletin EM 8954-E, January 2008) as a method to approximate the amount of plant-available nitrogen that was present each year of the study. 

 

Table 5. Data from this study was entered into a worksheet that estimates plant-available nitrogen (PAN) from manure (Oregon State University Extension Bulletin EM 8954-E, January 2008).

Year

PAN from manure NH4-N (lbs/acre)

PAN from this year’s manure organic-N (lbs/acre)

PAN from residual manure organic N (lbs/acre)

Total manure PAN (lbs/acre)

2005

211

96

33*

341

2006

76

92

56*

224

2007

85

99

65*

249

2008

185

154

76

415

*The PAN from residual organic N (lbs/acre) prior to 2004 was estimated based on 2004 estimates because earlier data was not available.

 

*     In 2006 (May) and 2007 (June), there was 1 application of commercial fertilizer applied late spring and early summer, when no manure was available.

 

Table 6. Calculations for plant-available nitrogen from commercial fertilizer (communication with Dr. Dan Sullivan, Oregon State University in April 2009).

Year

PAN from commercial  NH4-N fertilizer application (lbs/acre)

Crop N removal from this years PAN application (lbs/acre)*

Unaccounted for PAN from commercial fertilizer (stored in soil, stored below ground in plant, or lost via gas loss or leaching; lbs/acre)**

Residual N mineralized from commercial N application (lbs/acre)

2006

30

18

12

<1

2007

48

29

19

<1

* Above-ground crop nitrogen removal efficiency for perennial grass is 60%.

** Remainder of nitrogen not recovered in above-ground forage (40% of PAN) is stored in soil organic matter, roots, or lost.

 

*     In 2006 and 2007, PAN application from commercial ammonium fertilizer should be added to total PAN from manure to estimate the total amount of PAN available from manure and commercial fertilizer.

*     Total amount of PAN available from manure and commercial fertilizer (lbs/acre)

·       2006 = 224 + 30 = ~254

·       2007 = 249 + 48 = ~297

 

 

 

 

 

 

 

Table 7. Comparison between measured manure and commercial fertilizer applications and calculations from the plant-available N worksheet (Oregon State University Extension Bulletin EM 8954-E, January 2008).

Year

Manure + Commercial Fertilizer Ammonium-N (lbs/acre)*

measured

Manure + Commercial Fertilizer Ammonium-N (lbs/acre)**

 

Nitrogen Mineralized from Soil OM (lbs/acre)***

calculated

Sum of Measured Manure NH4-N, Commercial Fertilizer N, and N Mineralized from Soil OM (lbs/acre)

Total Manure + Commercial PAN (lbs/acre)

worksheet

Difference between PAN and Measured Manure and Commercial Fertilizer Ammonia + Estimated Mineralize N from Soil (lbs/acre)

2005

411

226

144

555 (370)^

341

214 (29)^^

2006

172

108

140

312 (248)

254

70 (-6)

2007

192

127

168

360 (295)

297

82 (-2)

2008

316

174

148

464 (322)

415

49 (-93)

Accum 2005 - 2008

1091

635

600

1690 (1235)

1307

383 (-72)

*Manure + commercial fertilizer ammonium-N was not adjusted for volatilization losses in these calculations.

**The assumption was made that approximately 45% of the manure ammonium-N was volatilized.

***Estimated soil OM = For every 1% Soil OM there is 20 lbs N available per acre per year for crops (Cogger et al., 2001 and Sullivan et al., 2000).

^The values in parenthesis have been adjusted for manure ammonia volatilization losses (column labeled ‘Manure + Commercial Fertilizer Ammonium-N (lbs/acre)’ + column labeled ‘Nitrogen Mineralized from Soil OM (lbs/acre)’).

^^ The values in parenthesis have been adjusted for manure ammonia volatilization losses (column labeled ‘Sum of Measured Manure NH4-N, Commercial Fertilizer N, and N Mineralized from Soil OM (lbs/acre)’ - column labeled ‘Total Manure + Commercial PAN (lbs/acre)

worksheet’).

 

*     Results from Table 7 indicate that there is similarity (less than 9% difference) between the measured amount of manure ammonium nitrogen adjusted for volatilization losses + commercial fertilizer nitrogen + estimated nitrogen mineralized from the soil and plant available nitrogen estimates from worksheet in 3 of the 4 years.

 

 

 

 

 

 

 

 

 

Table 8. Measured crop nitrogen removal and plant available nitrogen from manure and commercial fertilizer.

Date

Crop Nitrogen Removal (lbs/acre) measured*

Total Manure + Commercial PAN (lbs/acre)

worksheet

Difference between measured crop nitrogen removal and estimated crop nitrogen removal from PAN**

2005

440^

341

99

2006

430

254

176

2007

458

297

161

2008

393

415

22

*Crop nitrogen removal was measured by harvesting grass in 2-ft by 2-ft squares in 10 locations throughout a 22-acre field. Dry matter yield was estimated from the grass harvested in the 2-ft by 2-ft squares. The grass from these squares was sub-sampled and sent to a lab for crude protein and nitrate analyses. Dry matter yield was multiplied by the nitrogen content (estimated from crude protein content) in the grass samples to estimate nitrogen removal by the crop.

**The difference between measured crop nitrogen removal and plant-available nitrogen from manure and commercial fertilizer is partially the nitrogen that is released from soil OM. We would estimate that nitrate-nitrogen released from soil OM annually would be approximately 145 to 165 ppm.

^338 lbs/acre crop N harvested and removed from field + 102 lbs/acre of crop nitrogen remaining in field because the last cutting was unable to be harvested.

 

*     In 2005 and 2008 manure plus commercial fertilizer ammonium nitrogen applied was approximately double the amount that was applied in 2006 and 2007. In 2005 and 2008 (99 and 22 lbs/acre, respectively), the difference between measured crop nitrogen removal and plant available nitrogen from manure and commercial fertilizer was less than in 2006 and 2007 (176 and 161 lbs/acre, respectively; Table 8).

 

*     The equations in the worksheet used to calculate plant available nitrogen from manure and commercial fertilizer do not account for nitrate-nitrogen that will become available during the growing season from soil OM. Therefore, the difference between measured crop nitrogen removal and plant available nitrogen from manure and commercial fertilizer would be an estimate of the amount of nitrate-nitrogen that is released from soil OM. The difference between measured crop nitrogen removal and plant available nitrogen from manure and commercial fertilizer in 2005 and 2008 (99 lbs/acre in 2005 and 22 lbs/acre in 2008; Table 8) was less than the amount of nitrate-nitrogen that would be available from the soil OM annually (approximately 145 to 165 ppm). This is an indication that more manure ammonium nitrogen was applied in 2005 and 2008 than the crop actually needed for growth throughout the year because there is a high probability that more nitrate-nitrogen was release from soil OM than the 99 and 22 lbs/acre that was calculated in Table 8. This indicates that the crop did not remove all of the nitrogen that was available over the growing season.

 

*     Explanation of how manure application rates were determined.  For example:

*     Who calibrated the equipment, how and when?

·       Custom operators did all of the manure applications to the field. The custom operator that was doing manure application at each event was not recorded. However, I know of 2 custom operators that did manure applications (Northwest Liquid Transport and Edaleen Dairy).  I believe Pacific Pumping may have done some of the manure applications in the first 2 years of the study.

·       Who calibrated the equipment, how and when was not recorded during this study.   

 

*     Who ran the equipment making the applications?

·       Employees who worked for Northwest Liquid Transport, Edaleen Dairy, and Pacific Pumping drove the tractor that applied manure to the field.

 

*     Who collected the manure tests for each application, how and when?

·       Lynn VanWieringen with WSU Livestock Nutrient Management Program collected the manure sample as it was coming out of the manure application equipment at each manure application event. Lynn would walk out to the manure application equipment while manure was being applied to the test field and fill a 5-gallon bucket with manure.  The manure in the bucket would be stirred vigorously and a sample would be taken to measure the ammonia N content with an Agros Meter. As soon as that sample was analyzed, the remaining manure in the 5-gallon bucket would be stirred vigorously and manure would be placed in nalgene containers. The manure samples would be placed in a freezer within a half- hour of being acquired.

 

*     Who determined the rate and method of manure application?

·       The dairy farmer

 

*     Who recorded the actual amount of manure applied?

·       The custom operators had a flow meter on the pump or in the tractor that was monitored while manure was applied to the field. Typically Lynn would ask the dairy farmer how much he intended to put on, and then would ask the tractor driver how much was being put on while the sample was being collected. However, prior to any amount being entered in the spreadsheet, the dairy farmer would calculate the actual amount of manure that went onto the field from the bill that the custom operator sent. This system is not as precise as if this was a ‘controlled research study’ where the researcher actually applied and measured manure application rates. However, because there is a cost associated with manure application, the amount that was actually applied to the field was agreed upon by both the custom operator and dairy farmer. If the custom outfit said that more was applied than actually was the dairy farmer would get upset for paying too much money and too high of an application rate, and if the custom operator said less was applied than actual was they would receive less money.

 

*     How did the researchers and the farm operator communicate information regarding soil and manure tests and application time and rates?

*     The dairy farmer and Lynn would talk on the phone, in person, or by e-mail. Many times the dairy farmer left a message on the phone answering machine as to when manure would be applied or when grass would be harvested. All data was sent to the dairy farmer prior to each conference call related to the study. At different times during phone conversations the data would be discussed.

*     Barb Carey from the Department of Ecology would e-mail the dairy farmer about when she would be coming up to do groundwater sampling. Barb and the dairy farmer would visit at times while she was sampling.

 

Implications

 

*     Conventional tilling of the soil (subsoiling, rotatilling plowing, seedbed preparation, and cultimulching) probably caused the greatest increase in soil nitrate-N and groundwater nitrate+nitrite-N concentrations in this study. The average groundwater nitrate+nitrite-N concentration during the fall following conventional tilling (November 2004 through January 2005) was ~27 mg/L. The average groundwater nitrate+nitrite-N concentration the second fall after conventional tilling (November 2005 through January 2006) was ~17 mg/L.

 

*     The accumulative amount of manure total N applied over a growing season likewise had a major impact on soil nitrate-N and groundwater nitrate+nitrite-N concentrations. In 2008, when approximately double the amount of manure total N was applied that of grass N harvested, soil nitrate-N and groundwater nitrate+nitrite-N concentrations increased in the fall and winter, respectively. In November 2008, the average groundwater nitrate+nitrite-N concentration was 6 mg/L, and increased to 11 mg/L in December 2008.  This level is only slightly higher than the drinking water standard of 10 mg/L. However, denitrification associated with low dissolved oxygen concentrations lowered nitrate-N concentrations in some wells.

 

*     Timing of manure total N applied can impact soil nitrate and groundwater nitrate+nitrite-N concentrations. In 2006, the amount of grass nitrogen harvested was greater than the amount of manure total N applied. Therefore, the assumption could be made that soil nitrate-N and groundwater nitrate+nitrite-N concentrations should have remained relatively low throughout the fall and winter months, respectively. However, 90 lbs/acre of manure total N applied in October after the last cutting of grass probably lead to elevated groundwater nitrate+nitrite-N concentrations during the winter (November 2006 – 7 mg/L, December 2006 - 13 mg/L, and January 2007 – 15 mg/L).

 

*     Grass yield, and hence the amount of nitrogen removed, can be impacted by weather conditions.

*     In 2005, the grass growth slowed when soil moisture levels dipped below 20%.  Irrigating earlier in the growing season during subsequent years (July instead of August) prevented soil moisture levels from dipping below 20%.  In some years, this reduced the time between cuttings by over 1 week during the summer months.

*     Air temperature can impact grass growth.  In 2008, the quantity of grass harvested was lower than previous years.  A measure of daily accumulation of heat (GDU) indicated approximately 696 less GDU (42%) in 2008 (the coolest year of the study) than in 2007 (the warmest year of the study).  It appeared that lower thermal heat over time impacted grass yields in 2008.

 

References

 

Cogger, C.G., A.I. Bary, S.C. Fransen, and D. Sullivan. 2001. Seven years of biosolids versus inorganic nitrogen applications to tall fescue. J. Environ. Qual. 30:2188-2194.

 

Fraser, D.A. 2006. Determining range readiness and growing degree-days (GDDs). B.C. Min. For. Range, Range Br., Kamloops, B.C. Rangeland Health Brochure 11.

 

Griffith S. M. and T. W. Thomson. 1996. N Rate and timing relationships with tissue N concentration and seed yield in perennial ryegrass. Seed Production Research at Oregon State University.

 

Sullivan, D. M. 2008. Estimating Plant-available Nitrogen from Manure. Oregon State University Extension Bulletin EM 8954-E.

 

Sullivan, D. M., C.G. Cogger, A.I. Bary, and S.C. Fransen. 2000. Timing of dairy manure applications to perennial grass on well drained and poorly drained soils. J. Soil Water Conserv. 55:147-152.