Soil Fertility and Nutrient Cycling in Grazed Systems Miguel L. Cabrera Crop & Soil Sciences University of Georgia

Topics Cycling of N, P, and K in pastures Nutrient distribution Soil sampling Soil pH and liming Fertilizing with urea fertilizers Water quality

Nitrogen Required in large amounts Bermudagrass: lb N/acre/year Fescue: up to 215 lb N/acre/year

Microbial N 50 lb N Plant 50 lb N 100 lb N Soil Org N 30 lb N Inorg N 20 lb N

1100 lb N fertilizer 50 lb N Microbial N Plan t 50 lb N Removal with Hay Soil Org N 20 lb N Soil Inorg.N 30 lb N Fate of Fertilizer N in Hayed Grasslands

TreatmentManagement Organic N accumulation lb N/acre/year HayedMonthly cuts to 2 inches 51 (23%) Franzluebbers and Stuedemann (2009) Organic N accumulation rate in upper 12 inches of soil during 12 years of haying or grazing with a yearly application of 220 lb N/acre as NH 4 NO 3.

Microbial 50 lb N Plant 50 lb N 100 lb N 40 lb N 15 lb N NH 3 + N 2 O 5 lb N NO lb N Org N 30 lb N Inorg N 20 lb N Org N 15 lb N

1100 lb N fertilizer 50 lb N Microbial N Plan t 50 lb N Animal Intake 40 lb N Feces+Urine Soil Org N 15 lb N NH 3 + N 2 O 5 lb N NO 3 Leaching 20 lb N5 lb N Soil Inorg.N 30 lb N 15 lb N 10 lb N Animal body Fate of Fertilizer N in a Grazed Grassland

TreatmentManagement Organic N accumulation lb N/acre/year HayedMonthly cuts to 2 inches51 (23%) High Grazing Pressure Maintained at 1300 lb/acre92 (42%) Low Grazing Pressure Maintained at 2600 lb/acre122 (56%) Franzluebbers and Stuedemann (2009) Organic N accumulation rate in upper 12 inches of soil during 12 years of haying or grazing with a yearly application of 220 lb N/acre as NH 4 NO 3.

TreatmentManagement Organic N Accumulation lb N/acre/year HayedMonthly cuts to 2 inches78 (34%) High Grazing Pressure Maintained at 1300 lb/acre174 (76%) Low Grazing Pressure Maintained at 2600 lb/acre182 (79%) Franzluebbers and Stuedemann (2009) Organic N accumulation rate in upper 12 inches of soil during 12 years of haying or grazing with a yearly applications of 230 lb N/acre as broiler litter.

Farm 1Farm 2Farm 1Farm kg N yr % of Total N input N input Mineral Fertilizer 60,39533, Grain Feed11,95943, Maize Silage1, Hay3,0115, Total Inputs76,58983, N output Milk12,06614, N 2 O emission2,032N/A2.7N/A NH 3 volatilization 4,0673, NO 3 Leached2054, Total Outputs18,37017, N remaining58,21965,

Take-home Message for N Hayed Systems: 20 to 35% of applied N builds up soil organic N Grazed Systems: 40 to 75% of applied N builds up soil organic N

Phosphorus Required in lower amounts than N Bermudagrass: 25 to 75 lb P/acre/year Fescue: 10 to 15 lb P/acre/year

Soil 80 lb P Plant 20 lb P 100 lb P

1100 lb P fertilizer 80 lb P 20 lb P Soil P Plan t 20 lb P Removal with Hay Org + Inorg P 80 lb P Fate of Fertilizer P in Hayed Grasslands

Soil 80 lb P Plant 20 lb P 100 lb P 16 lb P

1100 lb P fertilizer 80 lb P 20 lb P Soil P Plan t 20 lb P Animal Intake 16 lb P Feces+Urine Soil Org+Inorg P 80 lb P 4 lb P Animal body Fate of Fertilizer P in a Grazed Grassland

Take-home Message for P Hayed Systems: 80% of applied P builds soil P Grazed Systems: 95% of applied P builds up soil P

Potassium Required in similar amounts as N Bermudagrass: up to 480 lb K 2 O/acre/year Fescue: up to 250 lb K 2 O/acre/year

Soil 10 lb K Plant 90 lb K 100 lb K

1100 lb K fertilizer 10 lb K 90 lb K Soil K Plan t 90 lb P Removal with Hay Inorg K 10 lb K Fate of Fertilizer K in Hayed Grasslands

Soil 10 lb K Plant 90 lb K 100 lb K 80 lb K

1100 lb K fertilizer 10 lb K 90 lb K Soil K Plan t 90 lb K Animal Intake 80 lb K Feces+Urine Soil Inorg K 10 lb K Animal body Fate of Fertilizer K in a Grazed Grassland

Take-home Message for P Hayed Systems: 10% of applied K builds up soil K Grazed Systems: 90% of applied K builds up soil K

Topics Cycling of N, P, and K in pastures Nutrient distribution Soil sampling Soil pH and liming Fertilizing with urea fertilizers Water quality

0.90 lb N Average N, P, and K Returned in Feces and Urine (lb nutrient/cow/day) 0.45 lb urine 0.45 lb feces lb N/a lb N/a 0.40 lb K 0.3 lb urine 0.10 lb feces lb K/a lb K/a 0.15 lb P 0.02 lb0.13 lb urine lb P/a feces lb P/a Nutrient Distribution in Pastures

66 x 40 feet 2 round bales fed 6.5 cows/acre for 4 months lb inorg. N/acre in upper 6 inches Jungnitsch (2008)

Temperature-Humidity Index Franklin et al. (2009)

Pasture-based dairy in western Virginia.

Manure Distribution

Rotation Frequency Years to Get 1 Pile/sq. yard Continuous27 14 day8 4 day4 – 5 2 day2

Improving Nutrient distribution Rotational grazing in small square paddocks Short grazing periods Trough in each paddock Minerals away from troughs and shade Alternating feeding locations Feeding locations in low fertility zones

Topics Cycling of N, P, and K in pastures Nutrient distribution Soil sampling Soil pH and liming Fertilizing with urea fertilizers Water quality

Auger, probe, spade. Discard organic duff. Sample to 4 inches. Collect samples in clean, plastic container. Mix, remove debris, subsample if necessary. Soil Sampling

Sampling is Critical A soil test is no better than the soil sample submitted for analysis. Sampling error is the most common source of error in soil test results. The goal of soil sampling is to obtain a representative sample for each paddock.

Sample Individual Paddocks Courtesy: Univ. of Missouri Extension

Field Average Sampling One Core Random Composite Sample One average Soil Test level Take random samples for each 10 acres. Avoid areas near shade, troughs, trails.

Topics Cycling of N, P, and K in pastures Nutrient distribution Soil sampling Soil pH and liming Fertilizing with urea fertilizers Water quality

Soil pH and Liming Sources of soil acidity Measuring soil pH Problems in acid soils

Sources of Soil Acidity Acids in Precipitation H 2 O + CO 2   H 2 CO 3  H + + HCO H 2 SO 4 and HNO 3 - Rainfall pH < 4.3 in many industrial areas

Man-Made Causes of Acid Rain Exhaust from cars, trucks, and buses Power plants that burn coal Pollution from industry

Sources of Soil Acidity Nitrogen Transformations Nitrification: NH 4 + NO H + Ammonium Nitrate Hydrogen Ions Ammonia Volatilization: NH 4 + NH 3 + H + Ammonium Ammonia Hydrogen Ion

Measuring Soil pH Salts: decrease soil pH (negatively charged soils) Water0.01 M CaCl 2

January July December Fertilizer and manure application, average Georgia soil ΔpH average = 0.6 pH w pH CaCl2 Measuring soil pH

The UGA method for measuring pH avoids the seasonal variation in pH caused by differences in the soil’s salt content. Equivalent water pH = pH in 0.01 M CaCl

Problems in Acid Soils Miller et al. (2003) Critical pH = 4.85 Equivalent Water pH = 5.45

Applications of lime every 3 to 4 years are needed in Southeastern soils to maintain appropriate chemical balances in the soil.

Nutrient Availability as Affected by pH

Topics Cycling of N, P, and K in pastures Nutrient distribution Soil sampling Soil pH and liming Fertilizing with urea fertilizers Water quality

Fertilizing with Urea Fertilizers Source: H. Vroomen -TFI, and AAPFCO

Ammonia Losses in Spring 2006

Ammonia Losses in Spring 2005 Days after application NH 3 loss (% of applied N) Nitamin® UAN Urea Soil water content (g g -1 ) Rainfall (mm) Rainfall Soil water content

Ammonia volatilization losses under field conditions Fertilizer Ammonia loss (% of applied N) Fall 2004 Urea UAN Nitamin® 19 a* 6 b Spring a 13 a 14 a Within a column, values followed by the same letter are not significantly different according to Fisher’s LSD at p=0.05 Fall 2005Spring a 33 b 34 b 24 a 18 a

Hornbeck et al (2010)

Topics Cycling of N, P, and K in pastures Nutrient distribution Soil sampling Soil pH and liming Fertilizing with urea fertilizers Water quality

Water Quality Avoid applications between Nov and March Provide off-stream water (troughs) Restrict access to riparian areas Provide stream crossings

Avoid applications between November and March

Stream Crossing

Before After

Thomas et al. (2000 ) Differences in phosphorus and E.coli between stream in crossing and control stream before and after installation of stream crossing.

SUMMARY Grazing animals return 80-90% of N, P, and K Nutrient distribution can be improved by: Rotational grazing (small paddocks) Water troughs Feed and salt locations Proper soil sampling is critical Soil pH should be maintained by liming Losses of ammonia from urea can be reduced by 0.5 inches of rain or irrigation Water quality can be improved by: Avoiding applications from Nov-Mar Providing water troughs Limiting access to riparian areas