Nitrogen Loss Potential at Pagel s Ponderosa Dairy

Transcription

1 Understanding Nutrient & Sediment Loss at Pagel s Ponderosa Dairy - 9 Summer 21 Nitrogen Loss Potential at Pagel s Ponderosa Dairy Eric Cooley, Dennis Frame and Aaron Wunderlin UW Extension/Discovery Farms Nitrogen is one of the macronutrients required to produce a crop. The dynamics of the nitrogen cycle allows nitrogen to take many forms: as a component of organic matter; as a volatilized gas; and it can exist in a variety of ionic forms in the soil, with nitrate and ammonium among the most common. The excessive loss of nitrogen in the nitrate form can cause issues in groundwater, because of the potential for a number of health concerns for humans and animals. In salt water systems, nitrate is usually the limiting nutrient for algae growth. Algal blooms can cause death to aquatic life such as in the hypoxic zone in the Gulf of Mexico. This fact sheet focuses on nitrogen loss in surface runoff and tile line flow at Pagel s Ponderosa Dairy (PPD) and the factors affecting observed nitrogen loss. Surface and tile water monitoring Surface runoff and tile line flow was monitored year-round at PPD in three basins managed entirely by PPD. Surface runoff monitoring began in field year 24 at three locations (P1, P2, & P3) and tile line flow monitoring began in 25 in two basins (P4 & P5). Research ended at the end of field year 28 for all basins except for P2, which ended in 26 because it was non-typical in terms of fields in this region. Roughly one month of surface runoff and two months of tile line flow monitoring were missed due to the installation of equipment (missing data is annotated by an asterisk in graphs). The monitored surface area of P1/P4 was 2.5 acres, P2 was 22.1 acres, and P3/ P5 was 13.2 acres (Figure 1). Total nitrogen loss recorded in these areas was divided by the basin size to calculate pounds of nitrogen loss per acre, so the data would be comparable. Nitrogen loss in each of these basins was then averaged to produce a total average nitrogen loss, also referenced in this fact sheet. To be consistent, the data presented in this report is based on our definition of a field year, which is the 12-month period from October 1 through September 3. The field year always represents the calendar year in which it ends, which means that the field year ending September 3, 27, is the 27 field year (FY27). Figure 1. Surface runoff and tile flow monitoring Cropping was alfalfa in 24 for all basins and corn silage for the remaining field years in all basins (Table 1). Field Year Basin P1/P4 P2 P3/P5 P1/P4 P2 P3/P5 P1/P4 P2 P3/P5 P1/P4 P3/P5 P1/P4 P3/P5 Crop Alfalfa Alfalfa Alfalfa Corn Corn Corn Corn Corn Corn Corn Corn Corn Corn silage silage silage silage silage silage silage silage silage silage Table 1. Cropping in monitored basins

2 Precipitation and flow trends The general precipitation trends for the study period were at or below the 3-year average of 3.3 inches for Kewaunee County for all but field year 24 (Figure 2). Analysis of the annual flow for each basin in figure 2 shows that over the five year study period, both basins had very similar runoff patterns. From a surface runoff perspective, P3 had higher runoff as compared to P1 in all years. From a tile flow standpoint, slightly higher annual flow was observed at P4 in FY5 and FY7; however P5 was slightly higher in FY6 and FY8. Figure 2. Monthly average surface and tile flow over a 5-year period Precipitation & flow, in Inches Precipitation and Basin Flow Frozen Precipitation Non-frozen Precipitation Surface Runoff Tile Flow 3-Yr Precipitation (3.3 inches) P1/P4 P3/P5 P1/P4 P3/P5 P1/P4 P3/P5 P1/P4 P3/P5 P1/P4 P3/P5 FY24* FY25* FY26 FY27 FY28 Surface nitrogen loss The total average nitrogen loss for all surface basins was 13 lbs/acre/year. Analysis of data collected at PPD shows variation in total nitrogen loss. The relatively low surface nitrogen loss in FY4, even though considerable runoff occurred, is likely due to the protective cover of the alfalfa crop growing in the field in all three basins (Figures 2, 3 & Table 1). Alfalfa protects the soil surface and utilizes soil nitrogen. Surface nitrogen loss in FY5 were low in basins P2 and P3, but were higher in P1 (Figure 3). In FY5, the crop had switched from alfalfa to corn in all three basins (Table 1). The nitrogen loss at P1 is likely the result of sand-laden manure that was applied just prior to freezing. A few loads of sand-laden manure were applied between 11/2/4 to 1/19/5. The ground froze on 12/13/4 and snow cover occurred on 12/2/4. The sand-laden manure had a very low nutrient content (2-2-2) and was applied at approximately 1 ton/acre (nitrogen appli cation of 2 lbs/acre). It is believed that the snow cover enhanced the runoff which resulted in an increased loss of nitrogen. Our hypothesis is that the surface application of sand-laden manure on frozen ground increased nitrogen loss by 3 to 4 times when compared to the loss at P2 and P3. Field year 26 had more surface nitrogen loss than FY5 in two basins (Figure 3). Heavy rains caused considerable surface runoff and nitrogen loss in mid and late May. Protective cover from the emerging corn crop was minimal as the corn was recently planted in all three basins. The rains were so extreme that the prolonged saturated conditions killed a majority of the crop; and corn was replanted in all basins in early June. Excessive runoff volume was determined to be the main factor causing the nitrogen loss in all basins. For example, nitrogen loss in P3 was the highest because of higher relative surface runoff (PPD-4). Surface nitrogen loss at P1 and P3 was lower in FY7 than FY6, and loss at P1 was lower than P3 (Figure 3) Surface Nitrogen Loss by Basin Site P2 removed Not sampled P1 P2 P3 FY24 frozen ground FY24 non-frozen ground FY25 frozen ground FY25 non-frozen ground FY26 frozen ground FY26 non-frozen ground FY27 frozen ground FY27 non-frozen ground FY28 frozen ground FY28 non-frozen ground Figure 3. Surface runoff nitrogen loss in each basin by field year Liquid manure was injected at P1 on 1/9/6; whereas, sand-laden manure was surface applied to the majority of P3 on 1/23/7. This late surface application was requested by the Discovery Farms Program to determine the effect of surface applications on frozen ground. The intent of the late surface application was to apply manure on frozen ground without snow cover, but a storm established snow cover before the application was made. The surface application on frozen, snow-covered ground likely contributed to the increased nitrogen loss in basin P3. Overall, surface nitrogen loss in FY8 was slightly higher than the 4-year average (Figure 3). Although tillage and manure applications were different, total nitrogen losses were similar among the two basins. Basin P1 had V-type deep chisel plowing performed in the fall followed by a liquid manure injection. Most of P3 had sand-laden manure surface applied and disked in the fall. The higher than average surface runoff volume may have been a factor in the higher nitrogen loss in both basins. It should be noted that total nitrogen applications in P3 were approximately half compared to nitrogen applications in P1.

3 Tile nitrogen loss The total average nitrogen loss for all tile basins during the monitoring period was 62 lbs/acre/year. Analysis of yearly basin flow shows a large variation in nitrogen loss. The major contributing factors for nitrogen loss in tile appear to be flow volume and nutrient application rate. The comparison of the annual tile flow (orange bars in Figure 2) to the total nitrogen loss for each corresponding basin and year in figure 4 shows that in years with high flow volumes (FY6 and FY8), nitrogen loss in tile was higher than years with lower flows. The comparison of nitrogen application rates between basins shows some correlation to tile nitrogen loss. In the four years of monitoring, basin P4 always had higher rates of nitrogen applied compared to P5; and nitrogen losses were always higher at P4. The application rate was only slightly higher in P4 during FY5 and FY6, but nitrogen applications were substantially higher in basin P4 as compared to P5 during FY7 and FY8. These higher application rates in FY7 and FY8 also resulted in higher nitrogen loss between the two basins. Yield (lbs/acres) P4 Tile Nitrogen Loss by Basin Figure 4. Tile drainage nitrogen loss in each basin by field year P5 FY25 frozen ground FY25 non-frozen ground FY26 frozen ground FY26 non-frozen ground FY27 frozen ground FY27 non-frozen ground FY28 frozen ground FY28 non-frozen ground Frozen versus non-frozen ground Of all nitrogen lost through surface runoff, 57% came during frozen ground and 43% during non-frozen (Figure 5). Similarly, of all nitrogen lost via tile flow, 52% came during frozen ground and 48% during non-frozen (Figure 6). Unlike surface sediment and phosphorus loss in these basins, surface runoff nitrogen loss was more prevalent during the frozen ground period. Fertilizer or manure applications on snow-covered ground may have created a higher potential for surface nitrogen loss during the frozen ground period because the snow prevented contact between the nutrient and the soil. 5-yr Basin Average: Surface Nitrogen Loss Nitrogen loss in tile came from both flow through the soil profile - and preferential flow paths. It is believed that preferential flow paths through the soil can carry nitrogen to tile lines even under frozen conditions. This theory is based on the speciation of nitrogen and similar water chemistry to surface water during frozen ground. Flow through the soil profile was theorized to occur based on low concentration precipitation events that were consistent over long time periods. These conditions were most often observed during non-frozen ground conditions. 4-yr Basin Average: Tile Nitrogen Loss 43% 57% Frozen ground Non-frozen ground 48% 52% Frozen ground Non-frozen ground Figure 5. Surface nitrogen loss averaged over 5 years Figure 6. Tile nitrogen loss averaged over 4 years

4 Timing of surface nitrogen loss The full years of surface water data were analyzed for the three surface water basins to determine when nitrogen loss was most likely to occur. Unlike surface sediment and phosphorus loss which were predominant in May, the dominant month for surface nitrogen loss is March (Figure 7). The comparison of total surface nitrogen loss to surface runoff is a near perfect match with the amount of runoff similar to the amount of total nitrogen lost from the basins. Although the speciation of nitrogen varied distinctly during the frozen versus non-frozen period, the total surface nitrogen loss seems to be dominantly controlled by volume of surface runoff Total Nitrogen Loss by Month Total Nitrogen Runoff Depth Figure 7. Average surface nitrogen loss by month for FY25 - FY Runoff (inches) Surface versus tile comparison To assess the relative loss of nitrogen in tile drained landscapes, the total tile nitrogen losses (P4 & P5) were compared against surface losses (P1 & P3). As seen in figure 8, tile nitrogen losses account for 82% of the total losses. Although some nitrogen is lost from the surface, tile losses are the dominant delivery pathway in these agricultural landscapes. One main factor influencing potential nitrogen loss is tile flow volume. Restricting tile flow in Wisconsin s sloped landscapes can produce blowouts upstream of the restricting device due to head pressure in the tile system. The second factor influencing nitrogen loss is the nitrogen application rate. The implementation of nutrient management plans that credit all sources of nitrogen can significantly reduce the risk of nitrogen loss in tile flow. Management practices which reduce tile nitrogen loss (constructed wetlands) are expensive and can take large amounts of land out of production. 4-yr Basin Average: Total Nitrogen Loss Tile: 62 lbs/acre/year average 82% 18% Surface Tile Surface: 13 lbs/acre/year average Figure 8. 4-year average nitrogen loss in surface & tile Basin comparison Over the four years of surface and tile data collection, higher nitrogen losses were always found at P1/P4 (Figure 9). Although surface loss varied, tile loss at P4 was always higher than P5; making total losses higher each year. The reasons include flow (FY5 & FY7) and nutrient application rates (FY7 & FY8). FY26 had lower flow and only a slightly higher nitrogen application rate at P1/P4 compared to P3/P5, and slightly higher losses were observed. The reason for this could not be determined by agronomic and field observation data Total Nitrogen Loss by Basin Surface Tile Figure 9. Total nitrogen loss by basin in surface and tile P1/P4 P3/P5 P1/P4 P3/P5 P1/P4 P3/P5 P1/P4 P3/P5 FY25 FY26 FY27 FY28

5 Nitrogen speciation An important aspect of understanding the potential for nitrogen loss from agricultural farming systems is the form that nitrogen takes 12. as it leaves the field. A species comparison of surface and tile nitrogen losses can be found in 1. figure 1. Because of the small fraction of nitrogen in the ammonium and organic nitrogen form, Total 8. Kjeldahl Nitrogen (TKN) was graphed. TKN is 6. the summation of both ammonium and organic nitrogen. The amount of organic nitrogen and 4. ammonium present in surface runoff is important because of the different forms nitrogen takes as it 2. interacts with soil, air, and water. Organic nitrogen is present in manure and as plant residues decay.. During the warmer months of the year, bacteria in the soil convert organic nitrogen to ammonium and, subsequently, ammonium into nitrate. Both of these forms of nitrogen (ammonium and nitrate) are usable by growing plants. Generally, high levels of organic nitrogen or ammonium in surface runoff were only observed under two sets of circumstances: if there is a short window of time between manure application and a surface runoff event, or from a runoff event following a manure application to frozen fields. As indicated in figure 1, TKN can be a substantial portion of nitrogen loss in surface flow, but is usually a smaller fraction in tile. FY5 showed high loss of TKN in both surface and tile. The majority of the loss in 25 occurred on frozen ground when sand-laden manure was applied on ice crusted soil. The ice crust was so developed that a majority of the alfalfa crop was lost. It is believed that a large portion of the nutrients were lost because of an extreme rain fall event that fell on the ice-crusted soil. Based on soil properties, it was expected that nitrogen loss in the nitrate form would be most dominant in tile. Soils have a negative electrical charge, and the nitrate ion also has a negative charge. Because like charges repel, the nitrate ion is not easily retained in soil and can move to the lower depths where the tile resides. 4-yr Basin Average: Surface nitrogen species loss Basin Average Nitrogen Species Loss TKN Nitrate S T S T S T S T FY25 FY26 FY27 FY28 S - Surface T - Tile Figure 1. Basin average nitrogen loss in surface & tile In contrast, ammonium is a positively charged ion. Because opposite charges attract, ammonium is usually held by the soil and does not move through the soil. Ammonium loss almost exclusively occurred from surface and tile flow during frozen ground conditions. Ice and snow can prevent sufficient contact of ammonium with the soil, causing potential loss. It is hypothesized that preferential flow through frozen soils caused delivery of ammonium to the tile; because ammonium should be removed as it flows through the soil profile. It should be noted that the loss of ammonium from both surface and tile occurred mainly during frozen ground. Fish are more sensitive to ammonia during cold water conditions, and the management of ammonium loss during frozen ground conditions is critical to prevent fish kills. Surface nitrogen loss in the organic form was observed to occur mainly following either nutrient applications on frozen, snow-covered ground or when large amounts of soil loss occurred. Tile nitrogen loss in the organic form was observed during the same periods. It is believed that preferential flow paths supplied the main transport pathway of organic nitrogen to tile. 4-yr Basin Average: Tile nitrogen species loss 45% 18% 37% Nitrate Ammonium Organic N 93% Nitrate Ammonium Organic N Figure 11. Form of average surface nitrogen loss 5% 2% Figure 12. Form of average tile nitrogen loss

6 Conclusion Average nitrogen loss for all surface basins during the monitoring period was 13 pound/acre/year with large variations in nitrogen loss between basins and years. Surface runoff, in combination with cropping and timing of nutrient applications, were believed to be contributing factors to the variance in loss. Average nitrogen loss for all tile basins during the monitoring period was 62 pound/acre/year with large variations in nitrogen loss between basins and years. Total yearly nitrogen loss was closely related to yearly flow trends and nutrient application timing which are believed to be the major contributing factors for nitrogen loss in tile. Approximately 57% of all surface nitrogen lost during the monitoring period for all basins came from frozen ground and the remaining 43% from non-frozen ground. Approximately 52% of all tile nitrogen lost during the monitoring period for all basins came from frozen ground and the remaining 48% from non-frozen ground. During the frozen ground period, nitrogen loss in the form of ammonium and organic nitrogen were comparatively higher than non-frozen ground for both surface and tile. March was the most dominant month for surface nitrogen loss, with considerable losses also noted from January through June. Comparing the total surface nitrogen loss to runoff, there is a near perfect match with the amount of runoff equating to the amount of total nitrogen lost from the basins. Tile drainage nitrogen loss (82% of total) from fields was higher than surface nitrogen loss (18% of total). Although nitrogen loss in the nitrate form was the highest in both surface and tile, nitrate was by far the most dominant in tile. Nitrogen loss in the ammonium form occurred during frozen ground conditions on the surface and, almost exclusively, occurred in tile during the frozen ground condition. Nitrogen loss in the organic form was observed to occur mainly during nutrient applications on frozen, snow-covered ground or when large amounts of soil loss occurred on both surface and tile drainage. In tile drainage, it appears that the majority of nitrogen in nitrate form is being delivered by flow through the soil profile, where as delivery of nitrogen in the ammonium and organic form is occurring through preferential flow paths. The data presented in this article were provided by the U.S. Geological Survey as part of a cooperative agreement with the UW-Discovery Farms Program. This material is based upon work supported in part by the National Institute of Food and Agriculture (NIFA), U.S. Department of Agriculture, Federal Administration Extension Projects, under Agreement No This fact sheet is part 9 of a 13 part series and can be found along with the rest of the fact sheets on the web at: or by calling the UW-Discovery Farms Office at by the Board of Regents of the University of Wisconsin System. University of Wisconsin-Extension is an EEO/Affirmative Action employer and provides equal opportunities in employment and programming, including Title IX and ADA requirements. Publications are available in alternative formats upon request.