Cover Crops
Beginning Farmer and Ranchers Development Program
Kohala Center
NOTES from class on August 10, 2019 by Jim Crum
Presentations by Koon-hui and Amjad (for registered students):
– PAN Calculator
Prescription for Soil Health: Cover Crop Management
with Koon-hui Wang, PhD
CTAHR, Plant and Environmental Protection Services, University of Hawaii
https://cms.ctahr.hawaii.edu/wangkh/Research-and-Extension/Cover-Crops
“Insectary plants of Hawaii” $10/ or online
Basics of Soil Health Management: cover crops!
1. Cover the soil at all times
2. Grow a living root 24/7
3. Reduce soil disturbances: minimal tillage – narrow strip only 2′ wide
4. Synergism with diversity: Crop Rotation
Cover Crops
– benefits (High C/N ratio)
– Till it back in when it is rich and green, before it goes to seed and puts energy into growing the seeds
A. reduce fertilizer costs
– 30-60% of Nitrogen (if tilled in) can be available to subsequent crops
– Have and continue working on a cover crop calculator for Hawaii
– sun hemp, cowpea, lablab, yellow sweet clover, white clover, hairy vetch
– oil radish draws Ca and K up and leaches it to where next crops can get them and can grow down 5 feet
– can make Phosporus more available to plant for uptake
B. add organic matter and improve fertility
– helps infiltration and hording of water an nutrients
– Active Fraction: rich with sugar, proteins and microbial cells = release of most NPK from organic matter
– Stable fraction: rich in cellulose and lignins = real organic matter, dark content, water holding, cation exchange capacity
C. improve yields by enhancing health
– speed infiltration of surface water
– relieve compaction and improve structure
– beneficial microbial life
– enhancing nutrient cycling ensuring health soil long term
D. Pest suppression: weeds, nematodes, insects, and pathogens
– sudangrass and rye produce alleopathic compounds that provide natural herbicides
– smother and out-compete weeds for water and nutrients like buckwheat, yellow sweet
– Can reduce the need for herbicides by 25%
– clover, wollypod, vetch
– shading weeds like sun hemp
E. Prevent erosion
– up to 40% less if used before wind or rain
– no till oil radish is most efficient
F. conserve the soil moisture
G. protect water quality
– reduce nitrogen leeching
No till with roller-crimper: invented in 2003 for organic use
No till with Flail mower is a good combo
C:N ratios
Bacteria is 8:1 C:N ratio.
24:1 is ideal microbial diet
Target for composting: 30:1 to feed microbes but lease some in the soil
How to terminate cover crops: best time to terminate a legume is during the early to mid blooming stage
N release is more rapid when cover crops are plowed in
Cover Crop Chart for Hawaii: low temperature = high elevation
– Lallab, pigeonpea, sunnhemp (2-3 months then mow it in)
– stabilized organic matter (aka humus) is a sponge and can absorb 6 times its weight in water
– each pound of organic matter can hold 18-20 pounds of water
wet blade management of Guinea Grass (video)
Best Method: Mow/Till/Black Plastic (MTBP)
No-Til weed management by Joe DeFrank using flail mower, herbicide, no till drill, then weed mat to share out weeds and “Light Out” or “Turn-the-page” weed management
For compacted soils: Cover cops with Deep Roots: Sorghum-sudangrass, rapeseed, yellow sweet clover
Different cover crops for different needs:
– Dry out web soil: Rye grass
– Bring beneficial insects: buckwheat, white clover
– Reduce nematodes pests: sunnhemp, sudangrass, marigold
– add beneficial nematodes: sunnhemp
Have cover crops as your alley way, then switch the alley to the where the crops were the next year
Beneficial insects: just grow in one area and see the benefits throughout
*It can take 5 years to build soil from depleted to good soil *
BEST: Sun Hemp (30-60 pounds per acre) produces good nematodes but sometimes hard to find the good stuff locally. till stips for the plants, then cut back the other rows of sun hemp to a couple feet high and use the cuttings for mulch. It keeps white flys and solver leaf problems and pickle worms
*Buckwheat is a great one. can let it just die and timing is good compliment for things like zucchini. plant the buckwheat a month ahead of time, then till it, then plant it 2-3 weeks after seeding, then let the
maximum soil organic matter will be 5% can be tested at UH and private labs
You may need to burn the weeds to really get rid of them
a mix of 6-12 different types of cover crops is ideal because of the different benefits
Seed Rate Calibration: 10/160 method = 1 oz seeds applied on 272 ft2 = 10 pounds per acre. 272 sq ft is 1/160th of an acre.
Management of Soil Fertility and Crop Diversity
Amjad A. Ahmad, PhD
CTHAR, University of Hawaii at Manoa
alobady@hawaii.edu
Hanai’Ai Extension Bulletins Website
Sustainable and Organic Agriculture Program (SOAP)
Free Publications:
– “Tea Time in the Tropics” Compost Tea Manual
– “Agroforestry Landscapes for Pacific Island“
– Newsletter
Facebook and Twitter for workshops
Sustainable vs. Organic
Sustainable includes Organic
Triple bottom line: People, Planet, Profit = in balance
Organic vs. Certified Organic
Commercial farming requires certification
Synagro in Honolulu is taking human waste into the plant and processing it for weeks to break down to a chemical granulate
How much fertilizer and when? it depends upon
– crop requirements
– soil fertility status
– fertilizer characteristics
– crop peak uptake stages
Organic fertilizers usually have a much lower concentration so much more is needed. (Urea @ 46 vs. Blood Meal @ 10 for example). However the organic add additional nutrients that will not appear in the synthetic
Liquid fertilizer gives it immediately and readily available but may require an injection system (video)
Macronutrients (needed in big quantities): N/P/K/Ca/Mg/S
Micronutrients (in small quantities): Fe/CI/Zn/Mo/B/Cu/Mn
Mobile nutrients (first seen in older or lower leaves) N/P/K/Mg/Cl/Mo
Immobile (seen in younger or upper leaves): S/Ca/B/Cu/Fe/Mn/Ni/Zn
Soil and Plant tissue testing
– Soil: go below 4 inches, take from a few areas, and either send each individually or mix them together
– Tissue: University Laboratory ADSC at CTHAR or Private Lab
Rapid Testing: Minolta SPAD Meter for chlorophyll. Cardy meters
Hanna meter: pH/EC/Dissolved oxygen meter in solutions and great for hydroponic and Aquaponic
Soil food pyramid: Build it with compost (1/2) and compost (40% and organic and synthetic fertilizers at only about 10%
Soil Organic Matter requires good:Biological: Energy, Nutrients, Resilience
Physical: Stable, Water retention, Thermal properties
Chemical: Cation exchange, pH, binding to minerals
Biochar: corncob, manure, scrapped wood burned in the absence of or low oxygen> higher temp and more closed the condition the better the biochar. Any organic waste can be used for it. adds hundreds or thousands of time the surface area to make more area for nutrients to stay with the soil as it will take much longer to become saturated.Usually has a high pH so will help increase it where needed. Josiah Hunt making it from Mac Nuts but moved to California. Farmers now getting carbon credits. recommend 2% of soil weight It’s not fertilizer, but a conditioner. One application can last for a decade
Invasive algae: Ogo, Eucheuma, Kappaphycus. Important to wsa to address salt in them. dry them and kill them to ensure they dont spread. Available from volunteerst that harvest them in the ocean cleanup. or Maxicrop from the mainland
Keep a pH between 6 and 7.5
If to acid, then lime needs to be applied every three months but is only beneficial to the surface where applied