Journal of the NACAA
ISSN 2158-9429
Volume 3, Issue 1 - July, 2010

Editor: Lee Stivers

Nutrient Management with Cover Crops

Alan Sundermeier, Extension Educator, The OhioState University Extension

ABSTRACT

Cover crops can be utilized in a cropping system to absorb and recycle soil nutrients. This ability can be useful when excess fertilizer has been applied to a cash crop and remains available in the soil. Without a cover crop, the fertilizer nutrients may soon become unavailable due to leaching or surface runoff. In the same way, when manure is applied to the soil, a cover crop can absorb nutrients contained in the manure before leaching or runoff occurs. A cover crop with fast growing ability is capable of producing large amounts of biomass in a short period of time. The amount of capturing and recycling of excess soil nutrients in plant biomass is one of the most important features when comparing cover crop species of grasses, legumes, and brassicas. Research conducted in Ohio has shown that oilseed radish cover crop significantly reduces soil nitrate levels by 70% when compared to no cover crop after manure application. Also 9.8 tons per acre of dry matter biomass has absorbed 603 lbs/acre of nitrogen, 126 lbs/acre of phosphorus, and 1060 lbs/acre of potassium. Due to its fleshy composition (and low carbon:nitrogen ratio), the oilseed radish plant material easily decomposes and nutrients become available for the following cash crop.

 

NUTRIENT MANAGEMENT WITH COVER CROPS
 
OVERVIEW
Cover crops can be utilized in a cropping system to produce, absorb and recycle soil nutrients. This ability can be useful to improve fertilizer use efficiency. Without a cover crop, the fertilizer nutrients may soon become unavailable due to leaching or surface runoff. In the same way, when manure is applied to the soil, a cover crop can absorb nutrients contained in the manure before leaching or runoff occurs. A cover crop with fast growing ability is capable of producing large amounts of biomass in a short period of time. In general grasses, legumes, and brassicas all have the capacity to reduce soil nitrate levels and recycle nutrients.  The amount of capturing and recycling of excess soil nutrients in plant biomass is one of the most important features when comparing cover crop species.  
 
RED CLOVER COVER CROP
The use of clover as a nitrogen source for corn production may allow producers to reduce commercial nitrogen rates. To evaluate the effect of clover cover crop and nitrogen rates on corn production, an experiment was conducted at the Ohio State University Research Farm in Wood County, Ohio. The entries were replicated four times in a randomized complete block design. All systems in this comparison were no-till. Medium red clover was frost seeded in wheat on April 18, 2008. After wheat harvest, clover was allowed to grow until 10-29-08 when Roundup and Clarity herbicides were applied to kill the clover. Corn was planted at the same time in all plots as no-till on 5-12-09. Sidedress nitrogen was applied on 6-16-09 at V6 growth stage. Three rates of nitrogen were applied at 0, 80, and 160 pounds per acre. Red clover biomass analysis from late fall 2008 showed 120 lb/acre of available nitrogen.
 
CROP AND SOIL MEASUREMENTS
Chlorophyll content of corn on 8-8-09 ranged from 24.1 SPADD meter reading for no clover and no nitrogen to 53.1 with clover and 160 lb/acre nitrogen applied. In all comparisons, clover increased chlorophyll content of corn leaves.
 
Table 1. SPADD Meter reading 8-8-09
No Clover
O Nitrogen
24.1
Clover
O Nitrogen
26.7
No Clover
80 lb. N
47.9
Clover
80 lb. N
50.1
No Clover
160 lb. N
50.6
Clover
160 lb. N
53.1
                       
 
 
 
 
 
 
 
Table 2. Soil nitrate nitrogen tested on 8-8-09, ppm nitrate. Clover increased the soil nitrate content except at the 80 lb. nitrogen rate.
 
No Clover
O Nitrogen
2.7
Clover
O Nitrogen
5.2
No Clover
80 lb. N
4.7
Clover
80 lb. N
4.5
No Clover
160 lb. N
13.5
Clover
160 lb. N
22.7
 
 
 
 
 
 
 

 

Table 3. Corn yields were significantly increased when clover was included.
 
Cover Crop                 Sidedress N Rate        Corn Yield bu/acre
 
No clover                        0                             39.9    A
Clover                             0                             47.6       B
No clover                      80                             93.3        C
Clover                           80                            103.2           D
No clover                    160                            129.5                E
Clover                         160                            135.4                E
                       
LSD (0.10)                 6.3
 
 
COST OF CLOVER ANALYSIS
Red Clover can effectively increase profitability of corn production.
 
At 80 lb/ac sidedress nitrogen rate, clover cover crop increased corn yield by 9.9 bu/ac.
      Value of Corn = 9.9 bu/ac x $3.50 /bu     = $ 34.65                  
Cost of clover = 12 lb/ac x $1.75/lb   = $ 21.00
Net return on clover    =  $ 13.65
  
OILSEED RADISH COVER CROP
Oilseed radish is a unique cover crop that farmers are planting to improve their soil quality for economic crop production. It has the ability to recycle soil nutrients, suppress weeds and pathogens, break up compaction, reduce soil erosion, and produce large amounts of biomass. Freezing temperatures of 20 to 25 degrees will kill oilseed radish which allows for successful no-till spring planting of subsequent crops. As a fast growing, cool season cover crop, oilseed radish is best utilized when planted after small grain (e.g. wheat) or corn silage harvest. Excess nutrients in manure amended soil are rapidly absorbed by this cover crop, thus preventing leaching or runoff of nutrients into water systems.
 
DESCRIPTION
Oilseed radish (Raphanus sativus [L.] var.oleiferus ), belongs in the Brassicaceae plant family, commonly called mustards. The Daikon type of Oilseed Radish has a large, fleshy taproot that can grow 2 to 3 inches in diameter and one foot or more in length (Fig.1) not including the fine root hairs that spread from the main taproot. Above ground growth consists of wide leaves that are soft, moist and fast growing. The foliage reaches one to two feet in height in a semi-erect stature. Leaf stems easily break from the main root, therefore traffic or grazing will destroy plant growth (Fig. 2). 
 
 
Figure 1
Fig. 1. Oilseed radish taproot compared to one foot ruler.
 
 
 
Figure 2
Fig. 2. Succulent broad leaves on Oilseed Radish grow rapidly by utilizing excess nutrients in soil.
 
PLANTING RECOMMENDATIONS
As a cool season cover crop, Oilseed Radish is best suited for early fall growth. When given 60 days or more of plant development, maximum return on seed investment can be realized. Opportunities for planting Oilseed Radish in a cropping system would include:
·         After small grain harvest (e.g. wheat)
·         After vegetable or sweet corn harvest
·         After corn silage harvest
·         After early maturity soybean harvest
 
Seed is planted to a depth of one-half inch. Seed size is similar to alfalfa, therefore when using a drill a small seeder attachment is necessary. Broadcast seeding of Oilseed Radish can be done successfully if followed by light tillage incorporation. Having the soil level after cover crop planting will allow for no-till planting of the following crop next spring.


 

 
VIGOROUS GROWTH POTENTIAL
Oilseed Radish has the potential to produce a total of  9.8 tons per acre of dry biomass when planted by September 1 in Northwest Ohio.
    Chart 1
Chart 1.
 
NUTRIENT CYCLING
Due to its fast growing ability, Oilseed Radish is capable of producing large amounts of biomass in a short period of time. Capturing and recycling of excess soil nutrients in biomass is one of the most important features of this cover crop. When planted after manure, sludge, or fertilizer application, Oilseed Radish may prevent water quality problems by storing nutrients in its biomass. Due to its fleshy composition (and low carbon: nitrogen ratio), the plant material easily decomposes and nutrients become available for the crop planted the following spring.
 
Table 4: Nutrient content of Oilseed Radish dry biomass.
 
Nutrients                     Concentration %                     Amounts of nutrients (lbs/acre)
 
 
Tops
Roots
Tops
Roots
Total
Nitrogen
3.8
2.5
331
272
 603
Phosphorus
0.7
0.6
 61
 65
 126
Potassium
5.8
5.1
505
555
1060
 
For example, if 10 % of the biomass nutrients are available after decomposition to the following crop planted the next spring, these values would be utilized:
            Nitrogen      –   60  lb/ac
            Phosphorus  -   13 lb/ac
            Potassium    - 106  lb/ac
                       
The absorption of soil nitrate (NO3) by Oilseed Radish and decrease in soil NO3 concentration after fall manure application are illustrated in the following example (Chart 2). Averaged across soils and types of manure application, Oilseed Radish decreased by more than 70% the NO3 concentration in manure amended soil compared with control.
Chart 2
Chart 2
 
 
 
Chart 3
 
Chart 3
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
OATS COVER CROP
 
Oats is another excellent cover crop which can be used to absorb excess soil nutrients. Following wheat harvest in Ohio, a manure application can be applied in July and August. As long as oats were seeded by the middle of August, oats reached a height of 30-45 inches every year, in every plot, regardless of weather variables. The nitrogen in the manure encouraged lush growth. Typically, growth was slow until cool evenings and/or days came. At that point – usually after mid-September – growth became rapid and lush until the end of November. Oats were not winter-killed by light frost. Generally, temperatures below 20 degrees Fahrenheit are required to kill oats. Estimated dry matter production was 3- 5 tons per acre, or more.
  
 
 
MANURE NUTRIENT ABSORPTION BY OATS
(AVERAGE OF 4 SAMPLES OVER 3 YEARS)
 
Nutrient                               Lbs / Ton Biomass                 Lbs. Nutrient / Acre @  4Ton Biomass *
 
Nitrogen                                        69.5                                                      278
Elemental Phosphorus                8.8                                                        35
Elemental Potassium                 81.8                                                      327
         Estimated average biomass from oats. Range 3 to 5 tons / acre.
 
 
ABILITY OF OATS TO ABSORB SOIL NITRATE AFTER MANURE APPLICATION 
 
Chart 4
 
 
Soil nitrate levels consistently showed sharp increases within 4-6 weeks after manure application, and then declined until spring planting. This basic pattern occurred under both oats and no cover crop strips. However, the soil nitrate reduction in the oats strips was in all likelihood due to the oats’ absorption, as the period of rapid growth coincided with the period of nitrate reduction. The reason for the reduction in soil nitrate levels where there was no cover crop was not explored in this project. It can be speculated that since nitrate is water soluble and therefore mobile in the soil, some portion of the loss could have been to drainage tile lines. Research is needed in this area.
 
BIOMASS COMPARISON
Chart 5
Oats, sudangrass, buckwheat, cereal rye and annual ryegrass are also cover crops used to absorb soil nutrients. These cover crops can be planted in late summer in Ohio and have the ability to produce significant plant biomass before winter. This biomass captures the soil nutrients in an organic form and slowly releases nutrients back to the soil when decomposing. The above chart illustrates the amount of growth from summer seeded grass type cover crops on which 100 lb/acre of actual nitrogen fertilizer was applied at planting at Northwest Ohio research location.
 
Without a source of nitrogen, these cover crops had significantly reduced plant growth (red bars are no nitrogen). Annual ryegrass and cereal rye will continue to grow and produce biomass until late November and then regrow in spring. Oats, sudangrass, and buckwheat had reached maximum biomass production on October 8 because of a killing frost stopping further plant growth. 
 
CONCLUSION
 
Nutrient management can be accomplished effectively by using cover crops. Replacing some fertilizer nitrogen with red clover produced nitrogen will improve profitability of corn production. Oilseed radish, oats and grass cover crops can absorb excess soil nutrients thus preventing nutrient loss and improving water quality.
 
The use of cover crops should be considered a part of every nutrient management plan to prevent loss of existing soil nutrients.  
 
 
REFERENCES
 
Cover Crop Fundamentals, Ohio State University
http://ohioline.osu.edu/agf-fact/0142.html
 
Michigan Cover Crops, Michigan State University
 
Cover Crops: Oilseed Radish, Ontario Ministry of Agriculture
 
GoCorn.net , Ontario Ministry of Agriculture
 
Brassica Cover Crops to Alleviate Soil Compaction, University of Maryland
 
Managing Cover Crops Profitably, 3 rd Edition, SARE
 
Midwest Cover Crop Council
http://mccc.msu.edu