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Nitrogen Removal by Delaware Crops

 

Effective nutrient management minimizes nutrient losses to the environment while maximizing the crop nutrient uptake. Valid numbers for all nutrient inputs and outputs are required to most effectively manage nutrients in agronomic and vegetable crop systems. The amount of nitrogen (N) removed by the harvested portion of the crop is needed to develop nutrient balances. However, N removal by crops can vary considerably from field-to-field and year-to-year. The purpose of this document is to provide average values of N uptake for common Delaware grain, forage, and vegetable crops for use in nutrient management planning activities.

What is “Crop Nutrient Removal”?

Crop nutrient removal is defined as the total amount of nutrients removed from the field in the harvested portion of the crop (e.g., grain, silage, hay). The term crop nutrient removal should not be confused with crop nutrient uptake, which is defined as the total amount of nutrients contained in the entire crop at maturity. For example, this would include N in the grain, stover, and roots of a corn crop. Crop nutrient removal is lower than crop nutrient uptake because a significant percentage of the nutrients taken up by a crop are returned to the soil in the form of crop residues. Nutrients remaining in crop residues are subsequently available for uptake by crops planted in the next season.

Determining Crop Nitrogen Removal for Delaware Crops

Removal of N by crops can be estimated using standard values for the N content in the harvested portion of the crop and crop yield. One reliable source of information about the N content of most Delaware crops is available in the Plant Nutrient Content Database, which was developed by the USDA Natural Resources Conservation Service (NRCS). However, the most accurate way to determine crop N removal is to have a representative sample of the harvested portion of the crop analyzed for N content. Analyzing crop samples for nutrient removal is different than routine plant tissue analysis, which is used to monitor the nutrient content of a crop or to identify nutrient deficiency or toxicity. For example, a subsample of the harvested grain that is collected from the combine or weigh wagon after yield determination is analyzed for N content to quantify N removal at harvest. In contrast, analysis of ear leaf samples collected at initial silking is useful to monitor corn nutrient content during the growing season. For vegetable crops, the use of standard values for N content may be preferable to harvested tissue analysis due to the difficulty encountered when trying to dry vegetables. Because of their high water content, a freeze drier is often required to prevent the vegetable samples from rotting during drying.

Laboratory nutrient analysis reports usually provide nutrient content of plant tissue samples on a dry weight basis (i.e., units of nutrient per unit of dry plant tissue). To determine crop N removal, these dry weight values must be adjusted to account for the moisture content of the crop. In addition, for crops where yield is reported in units other than pounds per acre, the N content of the harvested tissue must be adjusted based on the weight per unit (such as pounds per bushel).

The following example illustrates how to determine crop N removal for corn grain containing 1.45% N based on results of lab analysis:

This value corresponds to 1.45 pounds (lbs) N per 100 dry pounds of corn grain. Because this value is listed on a dry weight basis, it must be adjusted to account for the moisture content of the crop. For corn grain, if we assume a moisture content of 15.5%, which is equivalent to 84.5% dry matter or 0.845 lb dry corn grain per lb corn grain:

Crop N removal must then be adjusted (when applicable) based on the standard test weight. The standard test weight for corn grain is 56 lb/bushel (bu):

Therefore, the actual nutrient removal for corn grain in this example would be 0.69 lb N per bushel.

Nitrogen Removal by Typical Delaware Crops

The N removal rates for typical Delaware grain crops listed in this document were determined by analyzing the harvested portion of selected crops in Delaware (Binford, 2008). Between 2003 and 2007, a total of 668 corn grain samples, 175 soybean samples, 322 winter wheat samples, and 117 winter barley samples were collected at harvest from locations throughout Delaware (with a small number of samples collected from farms located on the eastern shore of Maryland that share similar climate, soil, and cropping conditions as Delaware) and analyzed for N content (Binford, 2008). Nitrogen content of harvested grain samples in Delaware reported by Binford (2008) was comparable to standard values reported in the USDA-NRCS Crop Nutrient Removal database.

Only a small number of vegetable and forage harvest samples were collected from Delaware fields in 2004 due to issues related to drying samples for analysis. Nitrogen values in harvested tissue of the vegetable and forage crops data presented by Binford (2008) were in good agreement with values obtained from the USDA Plant Nutrient Content Database. Therefore, standard values for crop N removal of selected vegetable and forage crops from the USDA Plant Nutrient Content Database are reported in this publication. We then calculated the amount of N removed per acre by grain and forage crops (Table 1) and vegetable crops (Table 2) over a range of realistic yield goals for major Delaware crops, where removal is the product of N content and crop yield.

Table 1. Estimated Nitrogen Removal in the Harvested Portion of Selected Delaware Grain and Forage Crops.

Crop Yield Unit Crop N Content (lbs N/yield unit) Yield (yield unit/ac) Crop N Removal (lbs/ac)
Barley bu (48 lb/bu @ 14% moisture) 0.76 40 30
60 46
80 61
100 76
Corn bu (56 lb/bu @ 15.5% moisture) 0.69 50 35
100 69
150 104
200 138
Soybeans bu (60 lb/bu @ 13% moisture) 3.44 30 103
40 138
50 172
60 206
Wheat bu (60 lb/bu @ 13% moisture) 1.05 40 42
60 63
80 84
100 105
Corn silage ton (@ 70% moisture) 7.75 15 116
20 155
25 194
30 233
Grasss-legume hay ton (@ 12% moisture) 43.6 2 87
3 131
4 174
5 218

Table 2. Estimated Nitrogen Removal in the Harvested Portion of Selected Delaware Vegetable Crops.

Crop Yield Unit Crop N Content (lbs N/yield unit) Yield (yield unit/ac) Crop N Removal (lbs/ac)
Bell pepper, fresh market boxes (25 lb/box @ 92.5% moisture) 0.04 750 30
1000 40
1250 50
1500 60
Bell pepper, processing lbs (@ 92.5% moisture) 0.002 18000 36
21000 42
23000 46
26000 52
Cantaloupe melons (6 lb/melon @ 90% moisture) 0.009 3500 32
5000 45
6500 59
8000 72
Cabbage cwt (@ 91% moisture) 0.32 100 32
115 37
120 38
125 40
Cucumber, pickler processing bu (50 lb/bu @ 95.5% moisture)) 0.055 150 8
200 11
250 14
300 17
Cucumber, slicer boxes (55 lb/box @ 95.5% moisture) 0.061 250 15
300 18
350 21
400 24
Eggplant boxes (32 lb/box @ 93% moisture) 0.058 700 41
800 46
900 52
1000 58
Jalapeno pepper lbs (@ 92% moisture) 0.002 25000 50
30000 60
35000 70
40000 80
Lima bean lbs (@ 69% moisture) 0.011 1000 11
2000 22
3000 33
4000 44
Peas cwt (@ 79% moisture) 0.94 15 14
25 24
35 33
45 42
Potatoes cwt (@ 77.2% moisture) 0.37 150 56
200 74
250 93
300 111
Sweet corn, processing tons (@ 75% moisture) 8 4 32
6 48
8 64
10 80
Squash, fresh market boxes (20 lb/box @ 95% moisture) 0.038 550 21
600 23
650 25
700 27
Squash, processing lbs (@ 95% moisture) 0.002 12500 25
15000 30
17500 35
20000 40
Tomato boxes (25 lb/box @ 94% moisture) 0.038 750 29
900 34
1050 40
1200 46
Watermelon lbs (@ 91% moisture) 0.001 45000 45
60000 60
75000 75
90000 90

Summary

The amount of N removed in the harvested portion of the crop can be determined using the standard crop removal values and the procedures presented above or by analyzing the N content of the harvested portions of the crop. If direct analysis is selected, one should keep in mind that results can be highly variable by field and year and difficult to perform for vegetable crops due to their high moisture content. Once crop N removal is determined, those removal rates can be used in subsequent nutrient management planning calculations to determine the appropriate amounts of N to apply to a particular cropping system to maximize uptake and minimize losses to the environment.

Author(s):
A.L. Shober
Department of Plant and Soil Sciences
University of Delaware
Original Publication Date: June 2013
References:

Binford, G. 2008. Nutrient removal rates for common crops in Delaware: Final report. Submitted to the Delaware Center for the Inland Bays. University of Delaware. Newark.
USDA, NRCS. 2012. The PLANTS Database (http://plants.usda.gov, 10 September 2012). National Plant Data Team, Greensboro, NC 27401-4901 USA.
Peer Reviewers:
Jennifer Volk, Environmental Quality Extension Specialist, University of Delaware
Sydney Riggi, Nutrient Management Extension Agent, University of Delaware

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