Editing Green manure (section)

==Functions==
{{More citations needed section|date=January 2021}}
{{cleanup section|reason=should be split between general cover crop functions and specific improvements due to burying biomass into soil |date=February 2022}}
[[File:Nitrogen fixation Fabaceae en.svg|thumb|Nitrogen Fixation by Green Manure Legumes ]]
Green manures usually perform multiple functions that include soil improvement and soil protection:

[[Leguminous]] green manures such as [[clover]] and [[vetch]] contain [[Nitrogen fixation|nitrogen-fixing]] [[symbiotic]] [[bacteria]] in [[root nodules]] that fix atmospheric nitrogen in a form that plants can use. This performs the vital function of [[Fertilizer|fertilization]].

Depending on the species of [[cover crop]] grown, the amount of nitrogen released into the soil lies between 40 and 200 pounds per acre. With green manure use, the amount of nitrogen that is available to the succeeding crop is usually in the range of 40-60% of the total amount of nitrogen that is contained within the green manure crop.<ref name="Sullivan" />

{| class="wikitable"
|-
|+Average biomass and nitrogen yields of several legumes<ref name="Pieters-1927" />
! Crop
! Biomass (tons acre<sup>−1</sup>)
! N (lbs acre<sup>−1</sup>)
|-
| [[Sweet clover]]
| 1.75
| 120
|-
| [[Trifolium alexandrinum|Berseem clover]]
| 1.10
| 70
|-
| [[Crimson clover]]
| 1.40
| 100
|-
| [[Hairy vetch]]
| 1.75
| 110
|}

Green manure acts mainly as [[Soil acidification|soil-acidifying]] matter to decrease the alkalinity/pH of [[alkali soils]] by generating [[humic acid]] and [[acetic acid]].

Incorporation of [[cover crops]] into the soil allows the [[Nutrient management|nutrients]] held within the green manure to be released and made available to the succeeding crops. This results immediately from an increase in abundance of soil microorganisms from the degradation of plant material that aid in the decomposition of this fresh material.  This additional decomposition also allows for the re-incorporation of nutrients that are found in the soil in a particular form such as [[nitrogen]] (N), [[potassium]] (K), [[phosphorus]] (P), [[calcium]] (Ca), [[magnesium]] (Mg), and [[sulfur]] (S).

Microbial activity from incorporation of cover crops into the soil leads to the formation of [[mycelium]] and viscous materials which benefit the health of the soil by increasing its [[soil structure]] (i.e. by aggregation).<ref name="Sullivan" /> The increased percentage of organic matter ([[biomass]]) improves [[water]] infiltration and retention, aeration, and other soil characteristics. The soil is more easily turned or tilled than non-aggregated soil. Further aeration of the soil results from the ability of the root systems of many green manure crops to efficiently penetrate compact soils. The amount of [[humus]] found in the soil also increases with higher rates of decomposition, which is beneficial for the growth of the crop succeeding the green manure crop. Non-leguminous crops are primarily used to increase biomass.

The [[root]] systems of some varieties of green manure grow deep in the soil and bring up nutrient resources unavailable to shallower-rooted crops.

Common [[Cover crop#Weed management|cover crop functions of weed suppression]]. Non-leguminous crops are primarily used (e.g. [[buckwheat]]).<ref name="Lawrence 1980 145"/> The deep rooting properties of many green manure crops make them efficient at suppressing [[weed]]s.<ref>{{cite journal |author1=Vasilakoglou, Ioannis |author2=Dhima, Kico |author3=Anastassopoulos, Elias |author4=Lithourgidis, Anastasios |author5=Gougoulias, Nikolaos |author6=Chouliaras, Nikolaos |date=24 February 2011 |title=Oregano green manure for weed suppression in sustainable cotton and corn fields |journal=Weed Biology and Management |volume=11 |issue=1 |pages=38–48 |doi=10.1111/j.1445-6664.2011.00403.x}}</ref>

Some green manure crops, when allowed to [[flower]], provide [[Forage (honeybee)|forage]] for pollinating [[insect]]s. Green manure crops also often provide habitat for predatory beneficial insects, which allow for a reduction in the application of insecticides where cover crops are planted.

Some green manure crops (e.g. [[winter wheat]] and [[winter rye]]) can also be used for grazing.<ref name="Lawrence 1980 145"/>

[[Erosion control]] is often also taken into account when selecting which green manure cover crop to plant.

Some [[Cover crop#Pest management|green crops reduce plant insect pests]] and [[Cover crop#Disease management|diseases]]. [[Verticillium wilt]] is especially reduced in potato plants.<ref>{{cite journal |author1=Larkin, Robert P. |author2=Honeycutt, Wayne |author3=Olanya Modesto, O. |date=May 2011 |title= Management of Verticillium Wilt of Potato with Disease-Suppressive Green Manures and as Affected by Previous Cropping History |journal=Plant Dis. |volume=95 |number=5 |pages=568–576 |issn=0191-2917 |eissn= 1943-7692 |doi=10.1094/PDIS-09-10-0670|pmid=30731947 }}</ref>

Incorporation of green manures into a farming system can drastically reduce the need for additional products such as supplemental fertilizers and pesticides.

Limitations to consider in the use of green manure are time, energy, and resources (monetary and natural) required to successfully grow and utilize these cover crops. Consequently, it is important to choose green manure crops based on the growing region and annual precipitation amounts to ensure efficient growth and use of the cover crop(s).