Green Manures

2004 Green Manure Demonstration

The CSU Specialty Crops Program planted spring and summer green manure demonstration plots in 2004 on certified organic land at the Horticulture Research Center. Green manure seed was planted with a plot drill seeder. Spring green manures were planted on April 14th, and summer green manures were planted on July 6th. The plots were sprinkler irrigated to aid in germination, and furrow irrigated once after they were established, but did not receive supplemental water after that.

More information about green manures appropriate for Colorado is greatly needed to help local growers. We will continue to develop different green manure options, focusing on the timing of green manures to fit into intensive vegetable production cycles in Colorado.

Spring Green Manures

  • Barley – cool season annual cereal grain, exceptional erosion control and weed suppression in semi-arid regions
  • Oats – cool season annual cereal, suppresses weeds, prevents erosion, scavenges excess nutrients, adds biomass
  • Field Peas – summer annual and winter annual legume, can be used as a plow-down N source, weed suppressor, forage
  • Fava Beans – spring annual or winter annual legume, relatively shallow thick taproot useful for opening up heavy soils, easily incorporated into soil, we found that fava beans are slow to establish
Green manures seeded with drill seeder
Oats in mid-July
Barley in mid- July
Peas in mid-July

Summer Green Manures

  • Sorghum-Sudangrass (aka – Sudex) – summer annual grass, great for renewing farmed out soils, weed and nematode suppressor, subsoil loosener , heavy producer of biomass
  • Buckwheat – summer or cool-season annual broadleaf grain, quick soil cover, weed suppressor, nectar for pollinators and beneficial insects, topsoil loosener, rejuvenator for low-fertility soils
  • Forage Soybean – edible summer legume and good nitrogen producer (up to 130 lbs/acre)
  • Fava Beans – spring annual or winter annual legume, relatively shallow thick taproot useful for opening up heavy soils, easily incorporated into soil, we found that fava beans are slow to establish

Fall Green Manures

These were not grown at the HRC in 2004 but are commonly used in this area. Local experience has shown that rye and vetch or pea mixtures perform well for a fall cover crop. Rye continues to put on a lot of biomass in the spring and becomes very tough once it develops a seed head.

  • Rye – cool season annual grass, prevents erosion, improves soil structure and drainage, adds organic matter, suppresses weeds (allelopathic), scavenges nutrients
  • Hairy Vetch – summer annual or winter annual legume, N source, weed suppressor, topsoil conditioner, good with grains, phosphorous scavenger, more drought-tolerant than other vetches
  • Winter Pea – winter annual legume, good weed competitor, does well in heavy soils and fixes 70-125 lb N/acre
  • Winter Wheat – winter annual cereal grain, prevents erosion, nutrient catch crop, soil builder and organic matter source, less likely than barley or rye to become a weed and easier to kill

2005 Green Manure Demonstration

Introduction and Methods

On April 27, 2005, yellow sweet clover and winter rye was planted on approximately 2 acres as a summer green manure to cover the land that we had used for production in 2004. On July 20, 2005, the Specialty Crops Program planted 11 varieties of green manures for demonstration and evaluation in an area that had previously been in alfalfa. All green manures were planted using a drill seeder.

Photos

Green Manure Name
Close-up Photo
Field Photo
Birdsfoot Trefoil
Black-eyed Pea
Buckwheat
Chickory
Cowpea
Japanese millet
Lab lab
No Photo Available
Medic mix
Sesame
Sesbania
Soybean

Soil Test Results

Table 1. Soil test results for the green manure demonstrations at the CSU Horticulture Research Center near Fort Collins, CO. The green manures were planted on July 20, 2005 (except clover/rye which was planted on April 27, 2005), and the soil samples were taken in February, 2006. The “pre-planting” soil sample was taken in the fall of 2004.

mmhos/cm
%
ppm
Green Manure
pH
EC
Lime
OM
NO3_N
P
K
Zn
Fe
Mn
Cu
Texture
pre-planting
7.6
0.3
High
4.1
19.2
14.9
379
2.7
20.4
13.9
3.9
Clay
Clover/Rye
7.5
1.1
High
3.0
27.0
4.9
356
1.82
9.48
1.96
3.18
Clay
Black-eyed Pea
7.4
1.1
High
3.0
27.1
4.3
348
1.82
13.9
2.19
3.25
Clay
Buckwheat
7.5
0.5
High
2.8
28.2
3.7
369
1.78
10.4
2.31
3.28
Clay
Chickory
7.6
1.2
High
2.9
15.1
2.5
334
1.58
10.2
2.30
3.26
Clay
Cowpea
7.6
1.0
High
2.8
26.7
3.1
348
1.73
9.49
2.07
2.94
Clay
Japanese millet
7.8
0.9
High
3.2
29.8
4.3
383
1.82
11.0
2.61
3.10
Clay
Medic mix
7.7
1.1
High
2.9
26.7
3.7
419
1.70
10.0
3.10
3.03
Clay
Sesame
7.6
1.2
High
3.0
32.7
4.0
347
1.68
24.9
5.03
3.82
Clay
Sesbania
7.5
1.2
High
3.1
48.0
4.0
392
1.74
10.5
2.63
3.34
Clay
Soybean
7.5
1.3
High
2.9
32.0
4.3
384
1.71
10.8
2.78
3.00
Clay
Trefoil
7.6
1.1
High
2.8
21.0
3.7
363
1.65
10.8
2.64
3.13
Clay

Comments and Conclusions

Below are some comments based on observations of the 2005 green manure demonstration plots at the CSU Horticulture Research Center.

Green Manure Comments
Bird’s foot Trefoil lower stature and relatively slow growing, poor competitor with weeds, long lived, salt tolerant
Black-eyed Pea too slow for weed competition
Buckwheat quick emergence and canopy cover, good weed competition, quick breakdown
Chickory relatively low stature early, if sown very thickly creates a carpet, limited weed exclusion, perennial herb, long taproot penetrates soil, produces nutritious leafy growth
Cowpea too slow for weed competition, reported to produce quick green manure with excellent drought resistance
Japanese millet very fast emerging canopy cover, excellent suppression of weeds
Lab lab no emergence, reported to produce more biomass and N than cowpeas, drought resistant
Medic mix very slow emergence, but may provide good cover in the following spring if hard seed germinates, grows well in dryland alkaline soils
Sesame slow developing canopy allows weeds to establish, known to suppress nematodes
Sesbania fairly quick germination but small leaf results in poor weed competition, reported to open up subsoil and once established is drought tolerant
Soybean poor emergence, too slow for weed competition
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