THE CHALLENGE OF PREDICTING NITROGEN AVAILABILITY FROM SOILS Indiana CCA Conference December 19, 218 Steve Culman Assistant Professor of Soil Fertility School of Environment and Natural Resources Ohio State University culman.2@osu.edu, soilfertility.osu.edu
N Trials in Same Field 1 years (CS rotation) 5 6 7 8 9 Grain Yield (bu/ac) 21 211 212 213 214 Fertilizer N Rate (lb N/Ac)
N Trials in Same Field 1 years (CS rotation) 5 6 7 8 9 116 bu/a 17 bu/a 143 bu/a 84 bu/a 139 bu/a Grain Yield (bu/ac) 21 211 212 213 214 77 bu/a 98 bu/a 113 bu/a 11 bu/a 116 bu/a Fertilizer N Rate (lb N/Ac) Yield of Zero N: 77-143 bu/a (66 bu)
N Trials in Same Field 1 years (CS rotation) 5 6 7 8 9 116 bu/a 17 bu/a 143 bu/a 84 bu/a 139 bu/a Grain Yield (bu/ac) 166 #N 137 #N 116 #N 187 #N 132 #N 21 211 212 213 214 76 bu/a 98 bu/a 113 bu/a 11 bu/a 116 bu/a #N #N 99 #N 179 #N 27 #N Fertilizer N Rate (lb N/Ac) Yield of Zero N: 77-143 bu/a (66 bu) Agronomically Optimum N Rate: 99 #N (151 #N)
N Trials in Same Field 1 years (CS rotation) 5 6 7 8 9 Grain Yield (bu/ac) 21 211 212 213 214 Fertilizer N Rate (lb N/Ac) Yield of Zero N: 77-143 bu/a (66 bu) 77-149 bu/a (73 bu) Agronomically Optimum N Rate: 99 #N (151 #N) 67 #N (183 #N)
Yield at N è optimal N rate (Is there a relationship?) If N yields are high, then optimal N rates will be.? Grain Yield at Zero N (bu/ac) 13 11 9 Grain Yield at Zero N (bu/ac) For all Ohio corn rate trials Agronmic Optimum N Rate (lb N/Ac) Agronmic Optimum N Rate (lb N/Ac)
Reduction in Yields of Unfertilized Corn Without fertilizer N, corn yields in productive soils average about 7 percent of optimum yield in a soybean-corn rotation. (short-term) Joern and Sawyer, 6; Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn
Assumptions Can we assume that most of the corn N uptake in unfertilized strips comes from soil? Can we assume corn will use all available soil N? Can we assume that N is the primary yield-limiting factor in corn production?
Denitrification The N Cycle N 2 O NO N 2 9 8 N 2 N 2 O NO NO 2 NO - 3 NO - 3 N Transformations (Italics) Volatilization NH 3 NH 3 NH 4 + NO - 2 Nitrification Plant Uptake 4 NO 3 - NH 4 + solution NH 4 + Ammonification Fertilizer NH 4+ NO 3 - Immobilization R-NH 2 Aminization Mineralization NO - 3 NH 4+ Fixation 5 N 2 Fixation Fixation 7 Lighting Rainfall Soil Surface 2:1 Clay Atmosphere N 2 Plant & Animal Residues Readily Decomposable Residues (1-2%) 1 Microbial Biomass (<1%) Fungi, Bacteria, Protozoa Actinomycetes, Algae Nematodes, Fauna N2 Fixation Fixation Legumes Non-symbiotic Symbiotic NO 3-6 NO 3- Leaching 3 2 Stable Humus (7-9%) SOIL ORGANIC MATTER (Organic N)
Nitrogen in Agriculture Nitrogen (N) Most dynamic nutrient in soil Many phases, many loss pathways Often nutrient needed in largest quantity Most N in soil is in organic fraction (>9%) Needs to be mineralized for plants to take up
Inputs Predicting Soil N Status Losses 2. Crop Residue & Amendments 1. Fertilizer 1. Crop Uptake 2. Denitrification or volatilization (Lost as gas) 3. Soil Organic Matter Soil Nitrogen (NO 3 + NH 4 ) 3. Nitrate Leaching (Lost with water)
Inputs Predicting Soil N Status Greenhouse Study Losses 2. Crop Residue & Amendments 1. Fertilizer 1. Crop Uptake 2. Denitrification or volatilization (Lost as gas) 3. Soil Organic Matter Soil Nitrogen (NO 3 + NH 4 ) 3. Nitrate Leaching (Lost with water)
Inputs 1. Fertilizer Predicting Soil N Status Greenhouse or pot study Field study Losses 2. Crop Residue & Amendments 1. Crop Uptake 2. Denitrification or volatilization (Lost as gas) 3. Soil Organic Matter Soil Nitrogen (NO 3 + NH 4 ) Lab incubations 3. Nitrate Leaching (Lost with water)
Inputs Predicting Soil N Status Losses 2. Crop Residue & Amendments 1. Fertilizer 1. Crop Uptake 2. Denitrification or volatilization (Lost as gas) 3. Soil Organic Matter Soil N Supply Soil Nitrogen (NO 3 + NH 4 ) 3. Nitrate Leaching (Lost with water)
3 Pools of Organic Matter Passive Slow Very stable organic material Extremely slow decomposition and cycling 6 8% of OM Turnover: decades - centuries Active Recently deposited organic material Rapid decomposition and cycling 5-15% OM Turnover: days few years Intermediate organic material Slow decomposition and cycling 1 3% of OM Turnover: years - decades Active organic matter can be considered an integrator of soil biology and chemistry
Developing a Test to Predict Soil N Availability + years of work in soil science Incubation methods (since 1972) Incubate soils and measure mineralization Can be accurate but takes a long time Other methods have been developed with limited success and adoption Either target organic or inorganic fraction of soil N
Soil Health Indicators Should Be: Sensitive to management changes But not too sensitive/ variable Reflect some aspect of soil or plant function Reliable, robust Exist across every field (universal property) Inexpensive to measure Amendable to commercial testing framework (high throughput)
Quantifying Soil Nitrogen Pools Total N: Combustion Inorganic Labile, Biotic Clay-Fixed Recalcitrant Soil Nitrogen Inorganic N: KCl Extraction Soil Nitrate and Ammonium Pre-sidedress nitrate test Labile, organic pool Mineralizable N Amino sugar N ISNT N-STaR Protein Respiration
Sensitivity of Soil Nitrogen Pools Total N Soil Nitrogen Labile, organic N Inorganic N Time
Amino Sugar Tests Measure amount of soil N present as amino sugar Illinois Soil Nitrogen Test Success: Khan et al., 1; Klapwyk and Ketterings, 6; Mulvaney et al., 5; Sharifi et al., 7 Negative: Barker et al., 6; Marriott and Wander, 6; Laboski et al., 8; Osterhaus et al., 8; Spargo et al., 9 Solvita Labile Amino-Nitrogen (SLAN) University of Arkansas (N-STAR test for rice)
Carbon-Nitrogen-Microbial Activity Respiration (Microbial Activity) Active C (Carbon Pool) Soil Protein (Nitrogen Pool)
Active C = Permanganate oxidizable C 2.5 g soil + Shake for 2 2 ml KMnO 4 minutes Settle for 1 minutes.5 ml of solution + 49.5 ml H 2 O Read color intensity (on spectrophotometer)
8 7 r 2 =.4 - um What is Active C? 6 4 3 - um Active C related to: Smaller POC fractions Heavier POC fractions POXC (mg C kg 1 soil) 8 7 6 4 3 r 2 =.31 53 - um Active C reflects a more processed pool of available C Smaller C:N Larger portion of MBC Slower turn-over times 8 7 6 r 2 =.63 More sensitive to management and environmental changes than SOC, MBC, POM 4 3 4 5 6 7 log POC (mg C kg 1 soil) Culman et al., 212, SSSAJ
Soil Respiration Dried soil + water Seal in jar Incubate for 24 hours Measure concentration of CO2 in jar via GC or IRGA Measure color change in Solvita paddle
Respiration Related to Soil N Release Haney et al., 1, Biol Fert Soils Yost et al., 218, JSWC Franzluebbers 218, SSSAJ Total N and flush of CO 2 determined after 3 d produced the best multiple regression for predicting potentially mineralizable N (R 2 =.85) Schomberg et al., 9, SSSAJ Carbon mineralization was a better predictor of corn agronomic performance than any other measure, both as a single indicator, and in combination with other indicators. Culmanet al., 213, AJ
Relationship Between Active C and Respiration Explore the relationship between respiration and other measures of active organic matter (e.g., Active C) Gain insight into the functional role these measures play Hurisso, Culman, et al., 216, SSSAJ
Soil Protein Abundant in both plant- and microbial-derived biomass Represents the largest pool of organic N in soil Protein è Amino Acids è NH 4 + Rate limiting step to soil N cycling
Soil Protein 3 g soil + buffer Shake and autoclave for 3 minutes Cool, shake for 5 minutes Read color development on spectrophotometer Centrifuge, transfer solution to plate, add BCA regent to react with proteins Incubate plate 1 hr to allow protein to react Hurisso, Culman, et al., 218, AEL
Infrared Spectroscopy (DRIFTS) Non-destructive, very rapid Measures reflectance of energy (reflected vs.) Can predict a wide number of soil properties
On-Farm Corn N-Rate Trials in Ohio
On-Farm Corn N-Rate Studies Study Revising Tri-State Fertilizer Recommendations Multiple N rates (,,,, lbs N/ acre) Replicated 3-4 times and randomized Data Collected Management Info R1 Ear Leaf N, Stalk Nitrate Yield, Grain N at Harvest
Active OM vs. Corn Yield @ Zero N Corn Grain Yield (bu/acre) 4 5 6 7 Soil Protein (g/kg soil) Corn Grain Yield (bu/acre) R 2 =.5 R 2 =.24 R 2 =.7 POXC (mg/kg soil) Corn Grain Yield (bu/acre) 2 4 6 Respiration (mg/kg soil) Corn Grain Yield (bu/acre) 4 5 6 7 Soil Protein (g/kg soil) Year 215 216 R 2 =.17 R 2 =.7 Corn Grain Yield (bu/acre) POXC (mg/kg soil) Year 215 216 R 2 =.24 Corn Grain Yield (bu/acre) 2 4 6 Year 215 216 R 2 =.34 Respiration (mg/kg soil) R 2 =.7
Soil Health Measure Source vs. Sink
Can Soil Health Indicators Complement Routine Soil Testing?
Conclusions Soil scientists still toiling away trying to find perfect N indicator measure One likely doesn t exist, as soil N availability will always be a function of soil type, weather, other factors Active pools of organic matter/ soil health measurements may help inform available soil N Much more work needs to be done ALL work will have to be locally calibrated for soils in a region
Thank You Steve Culman Soil Fertility Ohio State University Wooster, Ohio culman.2@osu.edu 33-822-3787 soilfertility.osu.edu