Managing plant-available N for organic sweet corn Dan M. Sullivan Oregon State University Crop & Soil Science PNW Vegetable Association, Nov 18, 2010
Today Keys to fertility management in intensive vegetable production systems
Nutrient management guide Sweet corn, western Oregon, Pub # EM9010-E. Oct 2010. Integrates conventional and organic management Available at: extension.oregonstate.edu/catalog/ Dan.Sullivan@oregonstate.edu
Section on organic management starts on page 12 in Sweet corn, western Oregon nutrient management Guide, OSU EM Pub #9010-E Available at: extension.oregonstate.edu/catalog/ Dan.Sullivan@oregonstate.edu
Organic Summary for sweet corn (p. 12 in Sweet corn, western Oregon, Pub # EM9010-E) Lime to maintain ph between 5.8 and 6.2 Other nutrients: Monitor via soil testing, add when soil test indicates need Avoid buildup of excess P in soil by limiting manure or compost application Nitrogen: fine tune each year using past experience Use winter legume cover crops to provide plantavailable N from sustainable source
Organic nitrogen management for sweet corn 1. Sweet corn under conventional management (no organic inputs) requires 100 to 150 lb N fertilizer per acre 2. Transition to organic: supply 100 to 150 lb PAN from preplant winter cover crops + organic fertilizers. 3. Determine preplant N application: rate and source using OSU Organic Fertilizer Calculator. 4. Monitor success of N management each year. Options: 1. Mid-season soil nitrate test ( PSNT; corn 12 inches high) 2. Zero N plot 5. Gradually reduce N inputs in successive years as you gain confidence
Response to N fertilizer Conventional experiment station trials, corn following fallow (no organic inputs) 15 12 Mid-season nitrate-n in soil: 10 ppm Yield t/a 9 6 3 0 1992 1993 1994 2002 2003 2002 WA 2003 WA 0 50 100 150 200 250 N Rate, lb/a From: Aurora, OR and Puyallup, WA. In: OSU sweet corn nutrient mgmt guide
Keys to sustainable management Sustainable management provides enough N for the crop maintains soil quality
Use soil tests ph lime requirement Phosphorus (P), Potassium (K) Tell you about health of soil in terms of supplying many nutrients Valid for all farming systems
Farm 9 Farm 10 Farm 11 Farm 8 Soil ph Farm 5 Farm 6 Farm 7 Farm 4 Farm 3 Farm 2 Farm 1 7.0 6.5 6.0 5.5 5.0 Ospud project farms, 2006 Soil ph
Soil test P and K Farm 1 Farm 2 Farm 3 Farm 4 Farm 5 Farm 6 Farm 7 Farm 8 Farm 9 Farm 10 Farm 11 Farm 1 Farm 2 Farm 3 Farm 4 Farm 5 Farm 6 Farm 7 Farm 8 Farm 9 Farm 10 Farm 11 200 160 120 80 40 0 800 600 400 200 0 Phosphorus (P) Potassium (K) Ospud project farms, 2006 Soil test K (ppm) Soil test P (Bray P1)
Irrigation water nitrate-n (lb N per acre-ft) Farm 1 Farm 2 Farm 3 Farm 4 Farm 5 Farm 7 Farm 8 Farm 9 Farm 10 Farm 11 50 40 30 20 10 0 Ospud project farms, 2006 Irrigation water nitrate-n (lb/acre-ft)
Organic matter inputs are magical Provide all 16 plant-essential nutrients Common prescription for correcting macro/micronutrient deficiencies: add OM Food for soil life When OM inputs > OM decomposition, soil fertility increases
Organic matter stability rapid decomposition and nutrient release sugar, protein hemicellulose cellulose Green leafy plant material Animal manure, crop residue (straw) Compost CO 2 lignin Humus very slow decomposition ( stable ) Adapted from: SARE Handboook 4, Building Soils for Better Crops, Fig 8.1
New soil organic matter is most active Can bring a soil back to life via consistent organic matter additions Takes 3 to 5 years of increased organic matter addition to reach new equilibrium value for a particular cropping system
Denitrification N 2 or N 2 O N Cycle Ammonia NH 3 Nitrate NO3 - Plant Uptake Ammonium NH 4 + Leaching Organic Nitrogen
Soil Nitrate-N (ppm) Soil Nitrate-N (ppm) 20 15 10 5 120 100 80 60 40 20 MF new organic farm 0 5/1 6/1 7/1 8/1 9/1 WUG established organic farm with annual organic soil amendment 0 5/1 6/1 7/1 8/1 9/1 Fallow Phacelia Vetch Rye Vetch Vetch 3 to 5+ yr amendment history may have bigger impact on soil N mineralization rate than what was done this year Andrews and Sullivan, 2009 (unpublished)
Legumes: key to providing enough N for rotation Half of legume N converts to plant-available N rapidly (30 days) Other half of legume N contributes to longterm fertility Legume N converted to nitrate-n by soil biology Nitrate-N from legumes or any other source subject to leaching loss
Above-ground N in winter cover crop Garrett and Luna, 2007 Lewis Brown farm
Cover crop effect on nitrate-n Lab incubation in moist silt loam soil (72 o F) Garrett thesis, 2009
Fertilizer N equivalency of winter vetch cover crop for summer organic broccoli Vetch winter cover Winter Fallow Broccoli yield (ton/acre) 7 6 5 4 3 2 0 100 200 300 Feather meal N rate (lb total N per acre) Vetch winter cover crop = 100 lb feather meal N/ac Garrett and Luna, 2007 Lewis Brown farm
Cereals recycle N. Cereal crop residues may temporarily immobilize N. oats, wheat, rye, barley, sorghum-sudan Recycle N within cropping systems Can be used to trap N that would otherwise be lost by leaching (fall rains in western OR) For significant fall N uptake, seed by Oct 1 Cereals do not provide significant amount of additional PAN for next crop May cause short-term tie-up of plant available N (for 3 to 6 weeks after incorporation in spring)
Winter cereal cover crop captured N, preventing it from leaching Six year leaching study (passive lysimeter) N leached in winter following sweet corn Fertilizer N rate for sweet corn No winter cover crop Cover crop b (lb/a) Leachate nitrate-n concentration (mg/l or ppm) 0 6 3 50 8 5 200 15 9 Annual nitrate-n loss via leaching (lb/a) 0 20 12 50 28 22 200 60 35 Average for 6 sweet corn crop years. Willamette silt loam soil, Aurora, OR. Adapted from: Feaga et al. (2010). Soil Sci. Soc. Am. J. 74:186 195.
The greener the crop residue, the more N is mineralized following the crop Higher N concentration in leaves than in stems Legumes: 2.5 %N (mature) to 5% N (young) Non-legume: 1% N (mature) to 3% N (young)
PAN from cover crop residue (lab incubation in soil at 22 o C) Plant available Plant-available N from N decomposition (PAN), % (% of total N applied) 80 60 40 20 0-20 -40-60 after 10 weeks after 4 weeks 0 1 2 3 4 Breakeven crop residue N% (4 wk) below 2% = immobilization (negative PAN) above 2% = mineralization (positive PAN) Nitrogen concentration in cover crop residue (%) From: Datta, Sullivan and Andrews, unpublished, 2010
OSU Calculator: Estimates PAN release from organic fertilizer and cover crops http://smallfarms.oregonstate.edu/calculator
Crops use most N during rapid vegetative growth Seedling, early growth (low N demand) Rapid vegetative growth (high) Reproductive growth (no N demand) Specialty organic fertilizers applied preplant do reasonable job of supplying N when it is needed (rapid vegetative growth)
Sweet corn growth (biomass/day) and plant N uptake (lb/acre/day) Peachey and Hart, 2009. In: OSU sweet corn nutrient mgmt guide
PNW 513. Available online: OSU Extension and Experiment Station Publications.
Sweet corn: Midseason nitrate-n test From Gale, 2005. In: OSU sweet corn nutrient mgmt guide.
Soil nitrate-n vs. table beet yield Table beet yield (Mg/ha) 40 35 30 25 20 15 10 5 MF Farm 2009 5 10 15 20 25 30 Fallow Fallow + feather meal Phacelia Vetch (PV) PV + feather meal Rye Vetch (RV) RV + feather meal Vetch (V) V + feather meal Soil nitrate-n (mg/kg) on May 18, 2009 Andrews, Poole and Sullivan, 2009. unpublished
Leave a zero N plot in your field to see impact of current season N inputs You might be surprised at how much N is being provided by soil reserves In-season soil nitrate testing also valuable monitoring information
Zero N experiment across six organic farms: whole potato plant N uptake Crop Nitrogen Uptake (lb/acre) 250 crop N uptake = 2 lb N per acre per day 200 150 100 50 0 20 40 60 80 100 120 140 Days after planting shows crop response to mineralized N with no current season N fertilization or N min from winter cover crop From: Sullivan et al., OSU Extension EM8949-E (2008)
Sustainable Management Keys 1. Get and use basic soil tests 2. Organic inputs are magical 3. New organic matter is most active 4. Legumes: key to providing enough N for rotation 5. Cereals recycle N. Cereal crop residues may temporarily immobilize N 6. The greener the crop residue, the more N is mineralized 7. Crops use most N during rapid vegetative growth 8. Leave a zero N plot in your field to see impact of current season N inputs
Dan M. Sullivan Oregon State University Crop & Soil Science Dan.Sullivan@oregonstate.edu