University of California Nitrogen Management Training for Certified Crop Advisers Nitrogen management in annual vegetable crops
The Water Quality Control Board will: institute nitrogen use reporting for agriculture use that information to estimate potential environmental N loading through the use of mass balance calculations Basic assumption of a nitrogen mass balance approach: N applied to a field but not removed in harvested products is at risk of eventually leaving the field in gaseous or liquid form
Volatilization Denitrification Fertilizer Organic amendments Irrigation water NO 3 -N Harvested products Leaching Or runoff
Volatilization losses can be significant for: Anhydrous ammonia, especially water-run Topdressed urea Animal manure Losses up to 30% of applied N are possible Volatilization losses to the atmosphere are environmentally damaging when N is deposited in wild lands
Denitrification losses can be significant with: Frequent, saturating irrigation High soil nitrate level Denitrification is usually a minor part of an N balance in San Joaquin Valley cropping, although nitrous oxide (N 2 O) loss is an air quality concern
What about long-term soil N storage? Short-term root zone NO 3 -N carryover is common Significant long-term soil N sequestration is uncommon, and probably limited to conservation tillage management
Nitrate leaching losses are likely to be significant where N loading (from all sources) substantially exceeds crop N removal
Bottom line: Within some level of uncertainty, evaluating agricultural N management on a mass balance basis (inputs outputs) does estimate potential environmental N loading
Bottom line: Within some level of uncertainty, evaluating agricultural N management on a mass balance basis (inputs outputs) does estimate potential environmental N loading At similar yield levels, a grower applying substantially more N than his neighbor is probably releasing more N to the environment over time
N management in a more regulated world: Some crops, and some production systems, will get more scrutiny than others To keep under the regulatory radar, strategic N management will be needed - evaluate N requirement on a field-specific basis, making use of non- fertilizer N sources
Nitrogen planning exercise:
Nitrogen planning exercise:
N fertilization scenarios There is not one right answer!!!
Annual vegetable crops show a characteristic growth pattern
N uptake follows the same pattern N uptake by processing tomato: Data from four high-yield fields
N uptake follows the same pattern N uptake by cantaloupe: 3 high-yield hybrid cantaloupe fields
Fruiting crops have a characteristic pattern of N partitioning N partitioning by processing tomato: General rule: In fruiting crops, fruit typically represents 50-70% of total crop N uptake
Vegetative crops typically harvest near peak N uptake rate Fruiting crops typically harvest after peak N uptake rate
Typical peak N uptake rates for vegetable crops: 3-4 lb / acre / day in cool conditions 4-6 lb / acre / day in warm conditions
Individual fields can differ widely in nutrient uptake High yield tomato fields: Crop uptake (lb/acre) N P 2 O 5 K 2 O Field 1 245 78 273 Field 2 262 92 471 Field 3 341 106 540 Luxury uptake - nutrient uptake that neither increases yield nor product quality - often 10-20% of the total crop N uptake
Accounting for yield effects: lb N / ton Crop type of fresh weight Fruiting Cantaloupe 3.0 Honeydew 2.1 Pepper 3.2 Tomato 3.1 watermelon 2.0 Vegetative Broccoli 11.6 Lettuce 4.0 Source: USDA nutrient removal calculator (http://plants.usda.gov/npk/main )
In a more regulated world, we need think strategically about N management Strategic N management requires attention to field-specific characteristics
Field-specific N management : Develop a reasonable N fertilization template, then modify it for: Residual soil NO 3 -N Soil N mineralization potential Irrigation water NO 3 -N In-season plant analysis???
What is a reasonable N template? N management in lettuce fields: Ave N application Ave N uptake Since N deficiency in commercial fields is very uncommon, seasonal N rates 2004-05 coastal lettuce field survey on the lower end of the normal range should be sufficient in most cases
Field-specific N management : Post-establishment soil NO 3 -N - often called Pre-sidedress Soil Nitrate Testing (PSNT) Often the most important field-specific modification
Why is post-establishment soil NO 3 -N sampling so important? It integrates the main factors influencing soil N mineralization (rapid N mineralization from residues and amendments has already taken place) The measurement is taken after crop establishment, when additional leaching should be controllable (given good irrigation management)
How variable is post-establishment soil NO 3 -N? Processing tomato fields, sampled post-transplanting: Differences among fields are large (PPM x 3.8 = approximate lb NO 3 -N/acre in each foot of depth) NO 3 -N in the top foot typically correlates well with 2 nd foot
How variable is post-establishment soil NO 3 -N? Processing tomato fields, sampled post-establishment: 35 lb N/acre 192 lb N/acre 110 lb N/acre
How to calculate a fertilizer credit for residual soil NO 3 -N? There is no right answer for all situations to what depth? what about spatial variability? Possible approaches: Credit a fraction of residual N (50-75%?) Credit all residual N above a threshold (5 PPM?)
Contribution of soil N mineralization: Between 5-6% of soil organic matter is organic N You can generally count on net mineralization of at least 1-2% of soil organic N content during a vegetable crop season Example: Top 12 inches of soil weighs 3,800,000 lb/acre 2,000 lb organic N per % organic matter 20-40 lb N/acre per % soil organic matter Caution: N mineralization behavior of very high organic matter soils may be different
Contribution of prior crop residue: wheat tomato broccoli Typical residue N content (kg/ha) 60 80 200 Residue %N 1.5 2.5 3.5 In general, more than 90 days after soil incorporation, crop residue N behaves similarly to that of existing soil organic N
Field-specific N management : Irrigation water NO 3 -N 2013 irrigation water NO 3 -N uptake efficiency trial continuously injected varying levels of NO 3 -N from 0-40 PPM measured lettuce biomass N at harvest
Results: Fertilized control Levels of irrigation water NO 3 -N Bottom line: NO 3 -N in irrigation water behaves like fertilizer
Tissue N monitoring for annual crops: Leaf total N overall crop N status Petiole NO 3 -N NO 3 -N taken up but not yet assimilated into organic compounds
Leaf total N monitoring : provides a reliable indicator of plant N status changes relatively slowly over time is poorly correlated with soil NO 3 -N availability early in the season when N uptake is slow, so it has limited value in early season fertilization decisions
Advantages of leaf total N : changes slowly 2007 UCD processing tomato trial lb N/acre Growth stage Total plant N content N uptake/day Daily uptake as % of biomass N Early bloom 25 1 4 Mid fruit set 80 3.5 4 First red fruit 160 4.5 3 Leaf total N substantially above the sufficiency level indicates sufficient biomass N to accommodate 7+ days of crop growth
Limitation of leaf total N: leaf N doesn t reflect soil N availability until the high N uptake period, so it is a flawed guide to early season N fertilizer need Leaf N data from 20 processing tomato fields : Red symbols from fields in which N availability limited yield Green symbols from fields with adequate N to maximize yield Sufficiency level Early flowering Full bloom First red fruit
Advantages of petiole NO 3 -N : easily / quickly measured Disadvantages of petiole NO 3 -N : Environmental factors can affect results more than soil N availability
Limitations of petiole NO 3 -N : Much more variable than leaf total N 2009 Lettuce N trials, cupping stage: Average C.V = 13% Average C.V. = 46%
How much can environmental factors influence petiole NO 3 -N? Six sprinkler-irrigated coastal broccoli and cauliflower fields, sampled every 2 days over a sprinkler irrigation cycle :
Bottom line on plant tissue testing : whole leaf sampling gives a good snapshot of current crop N status but, if it is in the adequate range, does not project forward more than 7-10 days to predict whether additional N application is required maintaining high petiole NO 3 -N throughout the season should ensure crop nitrogen sufficiency; however, because environmental conditions can cause low petiole NO 3 -N even when soil NO 3 -N is adequate, using petiole analysis to determine fertigation requirements often leads to unnecessary fertilization
Nitrogen management: Agronomy vs. regulatory reporting The regulatory interest in N use reporting is to estimate the potential for environmental N loading The role of a CCA will be to help clients maintain productivity while minimizing unnecessary N application
Example N reporting form: CROP NITROGEN DEMAND Crop Expected yield (lbs of production/ acre) Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre)??? PROTOTYPE NITROGEN BUDGET WORKSHEET Total N applied to field (lbs/ac) Dry & Liquid Fertilizers Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) Soil Nitrogen Credits Residual soil NO3-N In-season soil organic N mineralization NO3-N in irrigation water TOTAL N CREDITS (per acre) Total N Credits and Applications: Crop N needs: Balance Ratio Recommended N
CROP NITROGEN DEMAND Crop PROTOTYPE NITROGEN BUDGET WORKSHEET Recommended N Expected yield (lbs of production/ acre) Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) Total N applied to field (lbs/ac) Dry & Liquid Fertilizers Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) Soil Nitrogen Credits Residual soil NO3-N In-season soil organic N mineralization NO3-N in irrigation water TOTAL N CREDITS (per acre) Total N Credits and Applications: Crop N needs: Balance Ratio???
CROP NITROGEN DEMAND Crop Expected yield (lbs of production/ acre) Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) PROTOTYPE NITROGEN BUDGET WORKSHEET Total N applied to field (lbs/ac) Dry & Liquid Fertilizers Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) Recommended N Soil Nitrogen Credits Residual soil NO3-N??? In-season soil organic N mineralization??? NO3-N in irrigation water??? TOTAL N CREDITS (per acre) Total N Credits and Applications: Crop N needs: Balance Ratio
CROP NITROGEN DEMAND Crop Expected yield (lbs of production/ acre) Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) PROTOTYPE NITROGEN BUDGET WORKSHEET Total N applied to field (lbs/ac) Dry & Liquid Fertilizers Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) Recommended N Soil Nitrogen Credits Residual soil NO3-N In-season soil organic N mineralization NO3-N in irrigation water TOTAL N CREDITS (per acre) Total N Credits and Applications: Crop N needs: Balance Ratio
Crop example: Lettuce CROP NITROGEN DEMAND PROTOTYPE NITROGEN BUDGET WORKSHEET Crop lettuce Expected yield (lbs of production/ acre) 48,000 Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) 140 Total N applied to field (lbs/ac) Dry & Liquid Fertilizers Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) Soil Nitrogen Credits Residual soil NO3-N In-season soil organic N mineralization NO3-N in irrigation water TOTAL N CREDITS (per acre) Total N Credits and Applications: Crop N needs: Balance Ratio Recommended N
Crop example: Lettuce CROP NITROGEN DEMAND PROTOTYPE NITROGEN BUDGET WORKSHEET Crop lettuce Expected yield (lbs of production/ acre) 48,000 Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) 140 Total N applied to field (lbs/ac) Dry & Liquid Fertilizers 180 Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) 180 Soil Nitrogen Credits Residual soil NO3-N In-season soil organic N mineralization NO3-N in irrigation water TOTAL N CREDITS (per acre) Total N Credits and Applications: Crop N needs: Balance Ratio Recommended N
Crop example: Lettuce CROP NITROGEN DEMAND PROTOTYPE NITROGEN BUDGET WORKSHEET Crop lettuce Expected yield (lbs of production/ acre) 48,000 Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) 140 Total N applied to field (lbs/ac) Dry & Liquid Fertilizers 180 Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) 180 Soil Nitrogen Credits Recommended N Residual soil NO3-N 40 In-season soil organic N mineralization 20 NO3-N in irrigation water 10 TOTAL N CREDITS (per acre) 70 Total N Credits and Applications: Crop N needs: Balance Ratio
Crop example: Lettuce CROP NITROGEN DEMAND PROTOTYPE NITROGEN BUDGET WORKSHEET Crop lettuce Expected yield (lbs of production/ acre) 48,000 Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) 140 Total N applied to field (lbs/ac) Dry & Liquid Fertilizers 180 Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) 180 Soil Nitrogen Credits Recommended N Residual soil NO3-N 40 In-season soil organic N mineralization 20 NO3-N in irrigation water 10 TOTAL N CREDITS (per acre) 70 Total N Credits and Applications: 250 Crop N needs: 140 Balance 110 Ratio 1.80
N fertilization scenarios
Processing tomato scenario: Smith Block 5 280 lb N/acre is typical N uptake at this yield level, not the critical N uptake
Processing tomato scenario: Smith Block 5 Current fertilization practices recognize that there are significant nonfertilizer contributions
Processing tomato scenario: Smith Block 5 25 * 0.23 * 6PPM = 35 lb NO 3 -N
Processing tomato scenario: Smith Block 5 Crop residue effects probably minor, but not fully reflected in the soil test
Processing tomato scenario: Smith Block 5 180 lb N applied; soil test will not reflect all the N mineralized by spring. During the tomato season N release likely to be minor
Processing tomato scenario: Smith Block 5 Olsen P is high, therefore P fertilizer need is minimal Soil NO 3 -N test probably underestimates residual NO 3 -N after dry winter Higher than normal soil organic matter suggests significant N contribution ( 1.3% OM * 30 lb N/% OM = 39 lb N )
Processing tomato scenario: Smith Block 5 From P fertilizer in transplant water Fertigation amount could be adjusted (probably downward) depending on post-transplant residual soil NO 3 -N lb N/acre Preplant N At-transplanting N 10 Sidedress N Fertigated N 180 Foliar N Total seasonal N application (lb/acre) 190 In-season monitoring? Residual soil NO 3 -N could be very useful in this situation (substantial fall soil NO 3 -N, fall amendment application) Full bloom stage leaf total N??
Processing tomato scenario: Smith Block 5 CROP NITROGEN DEMAND PROTOTYPE NITROGEN BUDGET WORKSHEET Crop tomato Expected yield (lbs of production/ acre) 120,000 Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) 280 Total N applied to field (lbs/ac) Dry & Liquid Fertilizers 190 Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) 190 Soil Nitrogen Credits Recommended N Residual soil NO3-N 40 In-season soil organic N mineralization 40 NO3-N in irrigation water 35 TOTAL N CREDITS (per acre) 115 Total N Credits and Applications: 305 Crop N needs: 280 Balance 25 Ratio 1.09???
Processing tomato scenario: Smith Block 5 CCA respondents at the Fresno meeting : lb N/acre Low 25% Mean High 25% Preplant N 21 22 47 At-transplanting N 18 24 33 Sidedress N 35 33 34 Fertigated N 82 125 131 Foliar N 4 10 21 Total seasonal N application 164 214 267 N balance -1 49 102 N ratio 1.00 1.18 1.36
Cantaloupe scenario: Jones Block B-3 Planting date May 10, 2014 Planting method Seeding Irrigation technique drip Realistic yield goal 1,100 cartons/acre (22 tons/acre) Crop N uptake requirement (lb N/acre) 170 Seasonal transpiration (inches) 12 Irrigation water NO 3 -N (PPM) 1 Typical seasonal N fertilization rates in the area 80-140 Background information : Field location Merced County Prior crop broccoli Residue N left by prior crop (lb/acre) 200 Residue %N (dry weight basis) 3.5 Date of residue incorporation March 10, 2014 Date of soil sample April 15, 2014 Soil amendments applied none Soil analysis: Organic matter NO 3 -N Phosphorus (PPM) Exchangeable K Sample ID ph (%) (PPM) Bray Olsen PPM Soil texture Jones Block B-3 7.7 0.7 24 10 12 331 clay loam
Cantaloupe scenario: Jones Block B-3 Planting date May 10, 2014 Planting method Seeding Irrigation technique drip Realistic yield goal 1,100 cartons/acre (22 tons/acre) Crop N uptake requirement (lb N/acre) 170 Seasonal transpiration (inches) 12 Irrigation water NO 3 -N (PPM) 1 Typical seasonal N fertilization rates in the area 80-140 Minimal irrigation N credit Background information : Field location Merced County Prior crop broccoli Residue N left by prior crop (lb/acre) 200 Residue %N (dry weight basis) 3.5 Date of residue incorporation March 10, 2014 Date of soil sample April 15, 2014 Soil amendments applied none Soil analysis: Organic matter NO 3 -N Phosphorus (PPM) Exchangeable K Sample ID ph (%) (PPM) Bray Olsen PPM Soil texture Jones Block B-3 7.7 0.7 24 10 12 331 clay loam
Cantaloupe scenario: Jones Block B-3 Planting date May 10, 2014 Planting method Seeding Irrigation technique drip Realistic yield goal 1,100 cartons/acre (22 tons/acre) Crop N uptake requirement (lb N/acre) 170 Seasonal transpiration (inches) 12 Irrigation water NO 3 -N (PPM) 1 Typical seasonal N fertilization rates in the area 80-140 Background information : Field location Merced County Prior crop broccoli Residue N left by prior crop (lb/acre) 200 Residue %N (dry weight basis) 3.5 Date of residue incorporation March 10, 2014 Date of soil sample April 15, 2014 Soil amendments applied none Soil analysis: High-N broccoli residue will mineralize quickly; much of the contribution is reflected in the soil sample Organic matter NO 3 -N Phosphorus (PPM) Exchangeable K Sample ID ph (%) (PPM) Bray Olsen PPM Soil texture Jones Block B-3 7.7 0.7 24 10 12 331 clay loam
Cantaloupe scenario: Jones Block B-3 Planting date May 10, 2014 Planting method Seeding Irrigation technique drip Realistic yield goal 1,100 cartons/acre (22 tons/acre) Crop N uptake requirement (lb N/acre) 170 Seasonal transpiration (inches) 12 Irrigation water NO 3 -N (PPM) 1 Typical seasonal N fertilization rates in the area 80-140 Background information : Field location Merced County Prior crop broccoli Residue N left by prior crop (lb/acre) 200 Residue %N (dry weight basis) 3.5 Date of residue incorporation March 10, 2014 Date of soil sample April 15, 2014 Soil amendments applied none Soil analysis: No preplant N needed, but some may come with preplant P Low soil organic matter limits its contribution ( 0.7% OM * 30 lb/% OM = 21 lb N ) but some additional mineralization likely from crop residue Organic matter NO 3 -N Phosphorus (PPM) Exchangeable K Sample ID ph (%) (PPM) Bray Olsen PPM Soil texture Jones Block B-3 7.7 0.7 24 10 12 331 clay loam
Cantaloupe scenario: Jones Block B-3 From preplant P fertilizer lb N/acre Preplant N 15 Sidedress N Fertigated N 50 Foliar N Total seasonal N application 65 High soil residual NO 3 -N minimizes fertigation requirement In-season monitoring? Residual soil NO 3 -N?? Early fruiting stage leaf total N??
Cantaloupe scenario: Jones Block B-3 CROP NITROGEN DEMAND PROTOTYPE NITROGEN BUDGET WORKSHEET Crop cantaloupe Expected yield (lbs of production/ acre) 44,000 Crop nitrogen 'need' to meet expected yield (lbs of Nitrogen per acre) 170 Total N applied to field (lbs/ac) Dry & Liquid Fertilizers 65 Foliar N fertilizers Other N fertilizers Available N from recent organic amendments TOTAL N APPLIED (per acre) 65 Soil Nitrogen Credits Recommended N Residual soil NO3-N 100 In-season soil organic N mineralization 20 NO3-N in irrigation water 0 TOTAL N CREDITS (per acre) 120 Total N Credits and Applications: 185 Crop N needs: 170 Balance 15 Ratio 1.09???
Cantaloupe scenario: Jones Block B-3 CCA respondents at the Fresno meeting : lb N/acre Low 25% Mean High 25% Preplant N 4 22 58 Sidedress N 16 28 24 Fertigated N 56 63 90 Foliar N 0 3 6 Total seasonal N application 64 111 178 N balance 14 61 128 N ratio 1.08 1.36 1.75