Soil Sampling & N Management Nick Andrews (503) 678 1264 x 149 Nick.andrews@oregonstate.edu
Soil Sampling For Home Gardens & Small Acreages (EC 628) Test soil every 2 3 years in the spring or summer for ph and immobile nutrients. Test soil nitrate N at least twice/year for a few years in vegetables (before main growth and at end of season) Each soil sample should represent one soil type or management area Sampling technique is critical 1 cup of soil represents all the soil in the field. Lab grinds the sample and tests a few grams. 1 ac foot 4,000,000 lbs
Management Units Soil type Crops Management history
Reference areas for diverse farms (WSU Pub EM050 E) E) Reference area
Soil Sampling For Home Gardens & Small Acreages (OSU Pub EC 628) 15 20 soil cores per area Break up clods, remove organic material, mix samples in clean bucket & submit ~1 cup to a lab store cold or dried.
Sample Depth (OSU Pub EM 9104) Nitrate N (NO 3 N) moves down with water: sample to 12 Immobile nutrients: phosphorus (P), potassium (K), calcium (Ca), Magnesium (Mg), Zinc (Zn) and lime Conventional tillage mixes immobile nutrients: sample to 6 8 Vegetables, conventionally tilled cereals, recently established tblihd perennials No till: consider stratified sampling: 0 2 and 2 6 Established perennials (orchards, berries, pastures) & long term no till annuals
Stratified Sampling for Immobile Nutrients & ph (OSU Pub 9104) Is field tilled at least once every 3 years? Yes use conventional 6 8 depth If no, has fertilizer been top dressed for more than 2 3 years? No use conventional 6 8 depth Yes consider stratified sampling at 0 2 & 2 6 for ph, P, K and other immobile nutrients
Stratified Sampling for Immobile Nutrients & ph (OSU Pub 9104) Insert probe to 6 8 Analyze 0 2 and 2 6 samples separately Compare 0 2 results with fertilizer guides
Tissue Testing in orchards and berries 1. Tree fruits, nuts and berries store nutrients in the plant soil testing alone is useful lbut insufficient. 2. Sample most recent fully expanded ddleaves in late lt summer (late July mid August). After period of rapid growth, before senescence. 3. Refer to sufficiency levels in University nutrient management guides. 4. Tissue testing accounts for non fertilizer N.
Nitrogen Sources Soil organic matter Cover crops and crop residues Compost and other soil amendments Irrigation water Fertilizers Little o organic N sources must decompose to mineral N (e.g. nitrate N) to become plant available (PAN)
N Cycle Denitrification Ammonia N 2 or N 2 O NH 3 Nitrate NO3 - Plant Uptake Ammonium NH 4 + Leaching Organic Nitrogen Courtesy of Dan Sullivan OSU Crop & Soil Science
Low N = Immobilization ~2% total N High N = Mineralization Mineral N is converted to Organic N Organic N is converted to Mineral N Soil microbes have ~2-4% total N
Organic Fertilizer Labels: guaranteed analysis N P K 3 2 2 Total N Available Available phosphate potash NOT 2 (K O) available N (P 2O 5 ) 2
Cover Crops Reduce erosion Protect soil structure Increase organic matter Reduce weed pressure Nectar and pollen for beneficial i insects Grow your own N Supply N w/o supplying P Scavenge residual N
OSU Organic Fertilizer & Cover Crop Calculator
Cover Crop Sampling
Submit sample to lab Total percent N Percent dry matter
OSU Calculator Equations PAN estimate (% of fertilizer N) 100 VK equation cover crop 80 60 Cover crop Incubation (70d) 70 d 40 28 d 20 0-20 0 1 2 3 4 5 Organic input N (% dry wt) "Stable" Compost
Soil Organic Matter: Seasonal Nitrate N (NO 3 N) Levels 20-40 ppm 0-5 ppm Jan Apr Jul Oct Jan
Types of Soil Organic Matter Pool Biologically Active Size/Age (years) Small 1-5 Functions Meat: nutrient mineralization, macro- aggregation, disease suppression Protected Intermediate Bones: soil structure, 5-30 porosity, water relations Stable Large Micro-aggregation, g CEC, 50-10,000 fate of compounds, color
Cumulative available N from an organic source Year 1 = available N 2 + 3 + + 4 + + + 5 + + + + Courtesy of Dan Sullivan OSU Crop & Soil Science
Organic equilibrium Organic matter & soil C accumulate over time Soil fertilizer (e.g. N mineralization) increases over time MAINTENANCE PHASE SOIL BUILDING PHASE 2-4 years or more
Putting it all together Gaskell et al. (2007). Soil Fertility Management for Organic Crops. UC Davis 7249.
University Nutrient Management Guides
N credits for organic vegetables
N requirements of vegetables Gaskell et al. (2007). Soil Fertility Management for Organic Crops. UC Davis 7249.
Pasture N Applications (OSU Pub FG 63) Based on moisture and T sum 200 (0 C base) temperature DD = (Daily max + Daily min) 2 that regulate plant growth
EM 8677 Useful analyses (W. OR) Organic matter ph (acidity) & SMP buffer (Shoemaker- McLean-Pratt ) NO 3 (nitrate): use 12 deep samples P (phosphorous) Weak Bray K (potassium) Ca (calcium) Mg (magnesium) B (boron) & Zn (zinc)
Soil Testing & Interpretation: Soil Testing & N Management Nick Andrews (503) 678 1264 x 149 Nick.andrews@oregonstate.edu