PCC January/February 2018

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Table 1 Typical macronutrient uptake and harvest removal of annual vegetable crops at normal yield levels. Continued from Page 29 Crop Seasonal crop uptake (lb/acre) % nutrient removal N P K with harvest Broccoli 250-350 40-50 280-380 25-35 Brussels Sprouts 350-500 40-60 300-500 30-50 Cabbage 280-380 40-50 300-400 50-60 Cantaloupe 150-200 15-25 170-250 50-65 Carrot 150-220 25-40 200-300 60-70 Cauliflower 250-300 40-45 250-300 25-35 Celery 200-300 40-60 300-500 50-65 Head or Romaine Lettuce 120-160 12-16 150-200 50-60 Baby Lettuce 60-70 5-7 80-100 60-75 Onion 150-180 25-35 200-260 65-75 Pepper (Bell) 240-350 25-50 300-450 65-75 Potato 170-250 30-40 250-300 65-75 Processing Tomato 220-320 35-45 300-400 60-70 Spinach 90-130 12-18 150-200 65-75 ISOMATE SUPERIOR MATING DISRUPTION PRODUCTS FOR • CODLING MOTH • NAVEL ORANGEWORM • ORIENTAL FRUIT MOTH • PEACH TWIG BORER • LIGHT BROWN APPLE MOTH ISOMATE ® Mist ISOMATE ® TT PACIFIC BIOCONTROL CORPORATION www.pacificbiocontrol.com Jeannine Lowrimore Northern California ISOMATE ® is a registered trademark of Pacific Biocontrol Corporation 209.603.9244 ® ISOMATE ® Ring Christeen Abbott-Hearn Central and Coastal California 559.334.7664 decisions because, if levels are low, fertilization is necessary, but if levels are high, fertilizer applications can be reduced or skipped. Table 1 shows typical levels of N taken up by several crops grown in Monterey County. The uptake of N can vary to some degree from these values depending on yield potential of the crop and residual N in the soil. During the crop cycle, N uptake by crops follows a typical sigmoidal curve. For instance, in direct seeded lettuce, small amounts of N (about 10 lbs N/A) are taken up by the crop during the first 24–28 days of the crop cycle. This amount of N can be supplied by a modest application of starter fertilizer or by N in an anticrustant. However, during the next 35-40 days to harvest, N uptake is 3-4 lbs N/A/day following a linear uptake pattern. This is the key part of the crop cycle that we evaluate levels of residual soil nitrate to make effective fertilizer decisions. Adjusting fertilizer N applications based on soil nitrate-N Soil nitrate levels are measured prior to post-thinning N applications in the top foot of soil for most cool-season vegetables. Samples can be analyzed for nitrate by a commercial lab. However, the nitrate quick test (http://ucanr.edu/ blogs/blogcore/postdetail.cfm?postnum=4406 ) is used to analyze soil on the same day to facilitate making fertilizer decisions based on the current levels in the soil. If residual soil nitrate levels are low (20 ppm NO3-N) indicate that the fertilizer application can be greatly reduced or skipped. Residual soil nitrate-N levels of 20 ppm NO 3 -N in the top foot of soil is equivalent to 70 to 80 lbs of N (depending on soil bulk density) and this quantity is sufficient to supply 30 Progressive Crop Consultant January/February 2018
the crop for 10-14 days. Soil nitrate levels decline later in the crop cycle due to crop uptake and losses from leaching, and residual soil nitrate can be measured again prior to the next fertilization event to determine further fertilizer N needs. Residual soil nitrate levels of 20 ppm during the critical growth period following thinning indicates sufficient N is available for optimal crop growth. However, in the week prior to harvest soil nitrate levels can decline to below this level without jeopardizing crop yield. Nitrate in Irrigation Water Nitrate in irrigation water can also supply N for crop growth. The quantity of nitrate-N in irrigation water can be calculated from the following formula: ppm NO 3 -N in irrigation water x 0.227 = lb N/acre inch of water Table 2 N in irrigation water and typical crop water usage ppm NO 3 -N in irrigation lbs N/acre inch 10 2.3 16 – 23 20 4.5 32 – 45 40 9.1 64 – 91 60 13.6 95 – 136 lbs N for a crop using 7 – 10 acre inches water Nitrate in irrigation wells along the coast vary from less than 10 ppm NO 3 -N to wells that have greater than 50 ppm NO 3 -N. Calculating the quantity of N supplied by the irrigation water is made by multiplying the seasonal water uptake of the crop by the nitrate concentration of the water. Broccoli and cauliflower take up from 7-11 inches of water and lettuce 5-9 inches of water. As can be seen in Table 2 waters supplying > 40 ppm NO 3 -N can supply significant quantities of N for crop growth. In trials conducted in 2016-17, we observed that fertilization practices can be modified by a small amount (10 – 20 lbs N/A) with irrigation waters with < 20 ppm NO 3 -N, however for wells with > 40 ppm NO 3 -N, fertilization rates can be reduced more substantially (40 lbs to much more). Sources of Residual Soil Nitrate-N Levels of residual soil nitrate build up during production of the first crop which can result in substantial quantities of residual soil N at the beginning of the second crop. Residual soil nitrate-N comes from the following sources: mineralization of crop residues, unused fertilizer, NO 3 -N in irrigation water and mineralization of soil organic matter. The quantity of N that remains in the field following harvest can be substantial (Table 1, page 30) and can vary from 35 to >200 lbs N/A in spinach and broccoli, respectively. The concentration of N in crop residues varies from 2.5 to 5.0. Incubation studies of cool-season vegetable residues indicate more rapid mineralization of N with higher concentrations of N in the tissue; most mineralization Continued on Page 32 January/February 2018 www.progressivecrop.com 31
Page 1 and 2: January/February 2018 Managing Nave
Page 3 and 4: 4 UPCOMING EVENTS: North Valley Nut
Page 5 and 6: Navel orangeworm eggs on an almond
Page 7 and 8: ADVERTORIAL Ensure season-long cont
Page 9 and 10: Liquid Nutrients High Phos TM 8-25-
Page 11 and 12: Exceptional Value. Endless Innovati
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Page 15 and 16: ADVERTORIAL HUANGLONGBING The Growi
Page 17 and 18: or green island symptoms (Figure 3)
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Page 21 and 22: quadrilateral cordons and spur prun
Page 23 and 24: Table 3 Summary of yield and Ravaz
Page 25 and 26: presents imminent threat to the cro
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Page 29: Lettuce. All photos courtesy of Ric
Page 33 and 34: acreage. Other Techniques for Impro
Page 35 and 36: 40 Years of Farming Experience The

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