University of California Nitrogen Management Training for Certified Crop Advisers Nitrogen Management in Cole Crops and Leafy Greens
N Loss Pathways in Agricultural Systems: Volatilization Denitrification Fertilizer Organic amendments Irrigation water NO 3- -N Harvested products Leaching Or runoff
Growth and N Demand Rates in Cole Crops and Leafy Greens
Characteristic Growth: Vegetables All vegetables initially have a slow growth rate, when there is little biomass accumulation or N uptake About 30 days after seeding/transplanting, growth becomes rapid and the rate is linear Spinach may grow rapidly until the day of harvest Broccoli & lettuce growth rates may slow prior to harvest
N Accumulation: Vegetables N accumulation closely follows the rate of biomass accumulation Although N concentration in crop tissue may decline a bit, total N accumulation in the crop biomass increases dramatically as crops mature
Growth and N Accumulation: Spinach 0.90 Biomass Tons/A 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 20 24 28 Days after Germination Water 140 120 100 80 Lbs N/A 60 40 20 0 Baby Teenage Bunch
Characteristic Growth: Broccoli Biomass Tons/A 4.50 Biomass Accumulation by Broccoli 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 25 40 57 77 84 Days after Germination Water
Growth and N Accumulation: Lettuce Salinas, Summer: Biomass N (lb/acre) 200 150 y = 3.7x - 109 r 2 = 0.86 100 50 0 0 20 40 60 80 Days after planting Biomass N (lb/acre) King City, Summer: 200 150 y = 4.4x - 109 r 2 = 0.86 100 50 0 0 20 40 60 80 Days after planting
N Uptake in Cole Crops and Leafy Greens
N Uptake: Vegetables Typical peak N uptake rates for vegetable crops: 3-4 lb / acre / day in cool conditions 4-6 lb / acre / day in warm conditions
N Uptake Rates: Vegetables Crop type lb N / ton 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
N Uptake Rates: Vegetables Crop Lettuce (north valley) Lettuce (south valley) Nitrogen Uptake Lbs N/A/Day # of days of rapid nitrogen uptake 3.7 30-35 4.4 30-35 Spinach 5.1 15 Broccoli (summer) Broccoli (winter) 5.7 60 2.6 90
% of total roots N Uptake: Effects of Rooting Depth in Spinach Rooting Depth: 45 40 35 30 25 20 15 10 5 0 88% of all roots found in top 12 of soil at harvest 0-4 4-8 8-12 12-16 16-20 20-24 Depth (in) NO 3 - -N (mg/kg soil) 25 20 15 10 5 Nitrate Distribution Post-harvest: 0 0-4 4-8 8-12 12-16 16-20 20-24 Depth (in)
N Uptake: Effects of Rooting Depth in Lettuce Bed Width (inches) Drip line Plant Line Plant Line 5 10 15 20 25 Drip line Drip tape Plant row Bed width (inches) Plant row 10 20 30 40 50 Nitrate-N (ppm) Nitrate-N (ppm) Depth (inches) 5 10 15 20 0 10 20 30 40 50 60 70 Root Number / 100 cm 2 Depth (inches) 5 10 15 20 0 2 4 6 8 10 12 14 16 18 20 22 24 26 25 25 Rooting Density at Various Depths Soil Nitrate Distribution
N Uptake: Effects of Rooting Depth in Broccoli 50 45 Rooting Depth (inches) 40 35 30 25 20 15 34.1 10 5 0 0.1 0.2 0.3 0.4 0.4 0.5 0.6 0.7 0.8 Early Mid Late Harvest Portion of the Growth Cycle
N Uptake: Rates in Spinach Lbs N/A 250 200 150 100 50 Total N applied (lbsn/a) Biomass N (lbs N/A) 175 lbs N/A applied (66 at planting +109 midseason) 93 lbs N/A uptake 0 Site
N Uptake: Rates in Lettuce Lettuce nitrogen uptake varies from 120 to 140 lbs N/A depending on planting configuration and type: Nitrogen application to lettuce lbs N/A Spring Summer Highest field 392 306 Lowest field 70 27 Overall Average 215 152 Average of highest 50% of fields 281 198 Average of lowest 50% of fields 149 106
N Uptake: Rates in Cole Crops Crop Dry Biomass Lbs/A Percent Nitrogen Harvest Product N/A Residue N/A Scavenged from soil Broccoli 8,585 4.0 99 238 155 Cauliflower 6,930 4.1 61 224 21 Cabbage 11,564 3.0 188 163 97
Field-Specific N Management In Cole Crops and Leafy Greens Tissue and Soil Testing Other N Credits Reporting
Petiole N Monitoring: Limitations in Lettuce Much more variable than leaf total N 2009 Lettuce N trials, cupping stage: C.V = 13% C.V. = 46%
Petiole N Monitoring: Limitations in Cole Crops 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 :
Soil Residual Nitrate Testing: Beginning of winter fallow period Plant 2 nd crop Harvest Harvest 20 ppm threshold Plant 1 st crop Nitrate-N (PPM) Months
Other N Credits: Contribution of Prior Crop Residue spinach spring mix lettuce celery broccoli cauliflower Typical residue N content (lbs/acre) 20-40 60-80 160-240 Typical residue %N 5-6 2.5-3.5 3-4.5
Other N Credits: Contribution of Prior Crop Residue A high percentage of residue N is mineralized within weeks of incorporation Within 4-6 weeks after incorporation, the rate of residue N mineralization slows The majority of residue effects on soil N availability can be directly measured by soil nitrate testing before fertilizing the subsequent crop
University of California Nitrogen Management Training for Certified Crop Advisers Contributing Authors: Tim Hartz, Extension Specialist/Agronomist UC Davis Richard Smith, Extension Specialist UC Cooperative Extension Monterey County