Soil Fertility and Forage Availability Travis Harper Agronomy Specialist University of Missouri Extension
Outline Introduction Soil Testing Fertilizer Application Saving Money on Fertilizer
Introduction Forage management begins and ends with soil Soil provides: Support for the plant Aeration Water Nutrients
Plant Nutrient Requirements Macronutrients Nitrogen Phosphorus Potassium Sulfur Calcium Magnesium Micronutrients Iron Zinc Manganese Copper Boron Chloride Molybdenum Cobalt Selenium Sodium Silicon Nickel Vanadium
Nitrogen Primary component of a plant s growth processes In other words, it s what makes plants grow Almost always the most limiting nutrient in forage production
Phosphorus Extremely important nutrient Root growth and development Seed production Fruit production
Potassium The most important function of potassium is the osmotic pull that draws water into a plant s roots
Calcium Cell structure Uptake of nitrate Cell growth Soils are rarely deficient if limed
Magnesium Constituent of chlorophyll Chlorosis is a common deficiency symptom Grass tetany Magnesium sulfate Dolomitic limestone
Boron Nodule formation in legumes Soybean Alfalfa
Soil ph and Liming Extreme ph affects nutrient availability ph less than 5.0 causes aluminum toxicity ph less than 4.5 causes hydrogen toxicity ph for grasses needs to be at least 5.0 For many legumes, the minimum is 5.5 or higher Liming is the most important thing you can do for your soil
ph and Nutrient Availability
Outline Introduction Soil Testing Fertilizer Application Saving Money on Fertilizer
How do we know? Natural indicators Only way to know for sure is to test your soil
Proper Soil Testing 20 acres or less In MIG, each paddock separately Avoid trees, water and feeding areas Stay away from roads
Proper Soil Testing Take 15-20 samples in a random pattern Sampling depth is 6 inches Best to use a soil probe or auger Discard organic material from top of sample Mix samples in a PLASTIC bucket Remove 1 pint to send to the lab Improper soil sampling is a waste of time and money!
Soil test data from one core is highly variable Soil test P (Bray-I, lbs./acre) 200 180 160 140 120 100 80 60 40 20 0 Mean: 44 STD: 48 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 Core number
Accuracy can be increased by dividing fields based on known variability Soil test P (Bray-I, lbs./acre) 200 180 160 140 120 100 80 60 40 20 0 4 8 11 14 19 22 25 28 31 36 40 45 48 51 54 57 60 63 3 16 38 Overall Mean: 44, STD: 48 Old manure piles Pasture Pasture mean: 20, STD: 17 Feeding area mean: 114, STD: 52 Core number Feeding areas
Outline Introduction Soil Testing Fertilizer Application Saving Money on Fertilizer
Nitrogen Forms Plants uptake nitrogen in the form of either nitrate (NO 3 ) or ammonium (NH 4 ) Urea is converted to ammonium and carbonate ions Carbonate ions cause an increase in ph At high ph, ammonium is converted to ammonia (as much as 30% lost in 3 days) Agrotain delays this reaction from happening for up to 2 weeks
Nitrogen Sources Fertilizer Source Yield (tons per acre) Ammonium Nitrate 4.5 Urea 4.6 Ammonium Sulfate 5.3 Urea treated with Agrotain 4.8 Kallenbach, 2005
Nitrogen Application In grazing systems you may not need nitrogen fertilizer! Nitrogen also comes from organic matter, legumes, atmosphere If these sources provide adequate forage growth/distribution, additional nitrogen input may be unnecessary
Forage Availability Why do you raise cattle? How do you make more money? What is your biggest cost in raising cattle? What is the cheapest way to feed cattle? What forage provides the most grazing?
Nitrogen for Tall Fescue Unfertilized Forage Yield Herd feed requirement April June August October
Nitrogen for Tall Fescue Hay Traditional spring fertilization for Hay: - apply nitrogen in mid March - maximizes natural growth curve Forage Yield Herd feed requirement April June August October
Nitrogen for Tall Fescue Pasture Spring fertilization for Pasture: - apply nitrogen in early May - extends spring forage into July - less response, higher potential value Forage Yield Herd feed requirement April June August October
Nitrogen for Tall Fescue Pasture Forage Yield Herd forage demand Fall fertilization for Pasture: - apply nitrogen in mid August - increases and extends fall forage - less response, higher potential value April June August October
Outline Introduction Soil Testing Fertilizer Application Saving Money on Fertilizer
Soil Fertility Poor soil fertility is often the cause of poor yields, thin stands, legume failure, and plays a major role in weed pressure Applying needed lime, phosphorus, and potassium is critical You should follow recommendations on soil test
Fertilizer is Just Too Expensive New Seeding: Lime Phosphorus Potassium Nitrogen Established Seeding: Lime Nitrogen Potassium Phosphorus Better to use the Bucket principle
Bucket Principle
Alternative Fertilizer Sources Poultry Litter Ton of litter contains 63 lbs N, 55 lbs P 2 0 5, and 47 lbs K 2 0 70-75 dollars worth of fertilizer Nitrogen is 10% inorganic, 90% organic Organic portion becomes available over time Distributes nitrogen more evenly over growing season
Poultry Litter Inorganic portion can be lost to volatilization, same as urea A portion of the rest can be lost to leaching Only about 50% of nitrogen is ever plantavailable Typical application rate is 2 tons/a Excessive phosphorus is an issue
Your Own Cattle 1400 lb cow 0.63 lbs of nitrogen per day 126 lbs per year 0.298 lbs of phosphate per day 60 lbs per year 0.487 lbs of potash per day 97 lbs per year Based on 200 grazing days per year
Your Own Cattle
N 2 Fixation in Mixed Stands Species N 2 Fixed (lb./a) Ndff Year 1 Older (%) Alfalfa 70 80 120 180 60 94 Birdsfoot trefoil 30 60 80 150 40 94 Red clover 10 90 40 330 40 96 White clover 1-100 20 300 37 100 (Ledgard and Steele, 1992; West and Mallarino, 1996)
Nitrogen or Legumes?
Legumes Stands with greater than 30% legumes need no nitrogen fertilizer Legumes must be inoculated prior to first seeding Legumes require higher soil fertility than grasses Legumes work very well in MIG systems 99% of pasture herbicides kill legumes
Questions? Test Your Soil!