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Fertility Management Strategies for the Soils of Pohnpei
Jonathan Deenik, P.hD.Department of Tropical Plants and Soil Sciences
University of Hawaii
Outline
• Soils• Conventional management • Local options• Properties of organic amendments
• Applying organic amendments
Island Food Security
• Multi‐story agroforestry• Relies on nutrients stored in soil organic matter
• Animal production systems linked to cropping systems
• Manure is fertilizer
Old pepper field
Rakied series
Recent pepper field
Native Forest
pH P Ca K OM
ppm %
5.5 3.3 390 26 6.1
pH P Ca K OM
ppm %
6.4 33 6626 129 11.9
pH P Ca K OM
ppm %
5.1 5.4 251 74 12.6
pH P Ca K OM
ppm %
6.0 7.7 2539 59 7.6
Agroforestry System
pH P Ca K Alsat
ppm %
6.0 90 2,500 300 <12
Soil Fertility Requirements Selected Crops
pH P Ca K Alsat
ppm %
6.0 35 2,500 700 <12
pH P Ca K Alsat
ppm %
6.0 35 2,500 700 <12
Taro Banana Chinese Cabbage
Conventional Approach
• Imported lime and chemical fertilizers are effective, but EXPENSIVE
• Prolonged use of chemical fertilizers leads to declines in soil quality
Local Resources
• Conversion of animal manure to compost• Potential pollutants (N & P) become valuable soil amendments
What is Compost?
Compost – The remains of plants and animals after they have decomposed. Can be used to fertilize soil and to improve its structure and ability to hold water.
Benefits of CompostSoil Physical Properties• Improve soil structure• Increase water retention• Decrease bulk density
Soil Chemical Properties• Source of essential nutrients• Increase nutrient retention (CEC)• Detoxify Al
Soil Biological Properties• Enhance life of the soil• Create disease suppressive soils
Optimum Conditions for Composting
• Pile size: 3’X3’X12’• Correct mixture of C and N
• Particle size: <1”• Moisture: 45 – 60%• Oxygen: >5%• Temperature: 130 ‐150°F
Common FeedstocksMixing Ratio:• 1/3 manure, 1/3 high carbon (wood chips), 1/3 green materials (grass, leaves)
• Turning the pile monthly speeds up the composting process
Compost QualityCarbon Material pH C:N OC TN P Ca Mg K
% % % % % %
Mac Nut 5.8 12.8 33.8 2.64 0.69 1.44 0.91 3.35
Tree Trim (TT) 7.1 22.4 42.8 1.91 0.99 2.30 0.72 1.06
Swine NA 13.8 25.8 1.87 0.58 1.91 0.77 1.12
No soil amendment
Using Compost as a Soil Amendment
Swine compost at ≈ 20 Ton per acre
How Much Compost to Add?
Required information:1. Crop N requirement
bok choy = 100 lb N/ac2. Compost C:N ratio
<15 means N available 3. Total N content and
“availability” in the compostIf no lab data assume 1.5%Assume 25% of total N isplant available
How Much Compost to Add?
Example Calculation:1.
. .26,667 /
2. Scaling down to 1,000 ft2
3. How deep a layer?This much compost is equivalent to 0.2 inches deep
Compost Can Overcome Fertility Constraints of Pohnpei Soils
• A source of N, P, K and Ca, which are very low in Oxisols of Palau
• Reduces Al levels and eliminate Al toxicity
• Increases water infiltration decreasing erosion
Compost Quality
Compost with lots of woody materials has high probability of causing N deficiency
Cured compost with little woody material is a high value soil amendment
Summary
1. Compost has multiple benefits to soil
2. It is essential to use manures from animal production systems to make high value compost
3. Compost application can reduce dependence on imported fertilizers
Kalahngan!