Organic fertility management

Organic fertility management is much more than adding nutrients into the soil.

Overall goal is to balance nutrient inputs and outputs and ensure a good balance of nutrients for the crop

to achieve this requires a complex mix of soil management activities including tillage, irrigation, residue management, weed management and crop rotation planning

Neglecting any of these components can compromise crop performance.

What is meant by soil fertility and soil quality?

Soil fertility is the capacity of a soil to provide nutrients required by plants for growth, and is one component of soil quality.

Soil quality is a broader concept that can be defined as the capacity of the soil to: Accept, hold, release and mineralize nutrients and other chemical

constituents Accept, hold and release water to plants, streams, and

groundwater Promote good root growth and maintain good biotic habitat for

soil organisms Resist degradation

Requirements

good soil structure to provide adequate aeration (oxygen for respiration)

good water infiltration (movement of water into the soil), moderate pH ( ideally between 6.0 to 7.5), low salinity (dissolved salts in soil water) low levels of potentially toxic elements such as boron,

manganese and aluminum. balanced fertility that provides adequate levels of macro

and micronutrients that plants and microbes require.

Goals of a sustainable fertility/soil management program

To sustain good productivity and crop quality. Provide a balanced nutrient supply for the crop. Time seasonal nutrient availability to correspond with crop demand. Minimize disease/pest susceptibility. Build soil OM as a long term reserve of nutrients and to maintain good soil

structure and habitat for soil organisms

To sustain environmental quality. Maintain or improve soil quality Minimize off-farm impacts, for example:

Avoid non-point source pollution via surface runoff, erosion & leaching. Prevent soil erosion and sedimentation of waterways. Close nutrient cycles as much as possible: within the field, the farm, or within a

watershed, and even at regional and national scales.

It all starts with the soil and understanding how nutrients cycle in agroecosystems.

Soil Development and Agroecosystems

Soils = Climate, Organisms, Relief, Parent Material, Time. Soils=clorpt

Agroecosystems alter soil processes! Practices modify soil properties Farmers manage soil chemistry and

fertility

Processes in the Soil Profile

Source: The Nature of Soils, Brady 1999

AdditionsLossesTranslocations -

movementTransformations

chemical changes

Soil Texture

Soils can be separated into different particles size fractions, e.g.Sand 0.05 mm – 2 mmSilt 0.002 mm – 0.05 mmClay<0.002 mm

Soils are a mixture of different soil particle sizes.

Soil Physical Properties

Texture--particle size distribution.

Structure--aggregate properties.

Tilth--porosity and workability.

Soil Chemistry and Fertility

Soil pH

Cation exchange capacity (CEC)

Organic Matter

Nutrient availability

Cation Exchange Capacity

Source: Brady and Weil, 1996

In many soils, mineral particles are negatively charged, which repel negatively charged ions (anions) and attract positively charged ions (cations).

Soil pH and Nutrients

Source: Brady and Weil, 1996

Farmers try manage soil pH carefully because it:

Affects plant growthaffects nutrient availability

For example, Nitrification (NH4

+ --> NO3-) can reduce soil

pH. Many growers will add lime to increase pH.

Soil Microbial Processes

Decomposition of plant and animal material.

Mobilize (release into the soil) and Immobilize (assimilate) nutrients.

Create Soil Structure by providing the “glue” to hold aggregates together, and creating pore spaces for air and water movement.

Constituents of Soil Organic Matter

Source: Brady and Weil, 1996

Soil food web

Plant macro-nutrients•C, H, O Basic constituents of organic material

•N Proteins, chlorophyll, enzymes etc

•Ca Cell walls , cellular signals

• P Energy transfer - ATP etc

•Mg Chlorophyll, enzymes, protein synthesis

•S Proteins

•Cl Light reaction, ionic balance, stomatal movements

•K Ionic balance, osmosis, enzyme activator

•Micronutrients – Zn, Mo, B, Mn, Cu

Nutrient deficiencies in Tomato

Nutrient Cycles:How nutrients move through the environment

Simple N-cycle

Lightning, pollution

INPUT LOSSCOMPONENT

Nitrogen cycle characteristics

Inputs: fertilizer manures & other organic

materials N2 fixation

atmospheric deposition

Main stores: atmosphere N2 gas

soil OM (>90% soil N)

Outputs/losses crop harvest denitrification leaching erosion volatilization

Microbes rule!!!!!!

Key microbial processes & N transformations Mineralization:

organic N inorganic N (many forms) (ammonium, NH4

+)

Immobilization: inorganic N Organic N (ammonium, NH4

+) (many forms)

(nitrate NO3-)

Nitrification: ammonium nitrite nitrate

Denitrification: nitrate gaseous forms - nitrogen oxides and N2 gas

Ammonia volatization: ammonium, NH4

+ ammonia gas NH3

N2 - Fixation: Conversion of N2 gas into organic forms of N

Root nodules on clover root

Root nodules:symbiosis between legume (plant) & rhizobium(bacterium)

N2 fixation:

•organisms in symbiotic relationships e.g. rhizobium and legumes,frankia and coeanothus, alder

•free living organisms

•N2 NH4+

1. Ammonia release from soils increases as pH increases

2. Denitrification increases in wet soils

3. Both processes increase in warm soils

Gaseous N Losses

INPUT LOSSCOMPONENT

Phosphorous cycle characteristics Inputs:

fertilizer manures & other organic

materials plant residue atmospheric deposition

(small) weathering of rocks

Main stores: soil minerals & rocks soil OM much smaller % of total

soil P than for N

Outputs/losses crop harvest erosion leaching only if soil P

exceedingly high

Soil chemistry and mineralogy rule! - with microbes playing a greater role in high OM soils

Role of mycorrhizae in Plant P uptake

Known to be critical in low P natural ecosystems Some crops are partly dependent on mycorrhizal fungi:

citrus, grapes, avocados, and bananas, Others that benefit from having them include:

melons, tomatoes, peppers, squash, corn, millet, sorghum. Benefit of mycorrhizae highest at lowmoderate P

favored when P is more limiting than C supply, not favored when P less limiting than C supply

Roots colonized by mycorrhizae reduce penetration by root-feeding nematodes

pest cannot pierce the thick fungal network. Can also improve drought tolerance, soil aggregation

and N nutrition

Types of mycorrhizae

VAM or vesicular-arbuscular –found on diverse set of plants except many trees

EctomycorrhizaeTypically on woody plants

VAM

spores

vesicle arbuscule

Ectomycorrhizae on beech tree roots

Root covered withfungal sheath

X-section showing sheath

Hyphae of sheath

Managing Nitrogen

Issue of synchrony between N mineralization and crop demand

Timing of release depends onMoisture, temperatureQuality of organic material being added

What controls net mineralization of N Balance of mineralization vs immobilization

C:N ratio microbes need about 25x as much C as N to grow If C:N ratio of organic amendment is <20-25, then excess

N is released, ---mineralization>immobilization If C:N ratio is around 25, then

---mineralization = immobilization If C:N ratio is >25 then N limits growth so microbes

scavenge nitrogen --- mineralization<immobilization

Presence of resistant or inhibitory compounds slows mineralization

Lignin, polyphenols etc.

I n p u t C :N P e a k N O 3

( p p m )T im in g o f p e a k *

( D a y s a f t e rin c o r p o r a t io n )

L e g u m e +c o m p o s te d m a n u r e 9 - 1 2 3 0 - 4 5 7 - 3 5 ,2 1 - 4 9 , 7

L e g u m e o n ly 1 0 - 1 5 2 2 7 - 5 0 , 2 1 - 4 9 , 7

L e g u m e + s t r a w 1 9 - 2 5 1 5 - 2 0 7 - 3 5 , 2 1 - 4 9 , 7

S t r a w 4 6 - 9 4 5 - 1 0 7 - 7 7 , 2 1 - 7 7 ,7 - 2 1

N o a d d i t io n s - 1 0 - 1 5 7

D a t a f r o m M . V o l a t e t a l , u n p u b l i s h e d . * d a t a f o r 3 s e p a r a t e y e a r s f r o m t r i a l a t U C D a v i s .

T i m e

N r e l e a s e b ym i c r o b e s

C r o p Nd e m a n d

V u l n e r a b l et o l o s s

T i m i n g o f N r e l e a s e w i t h c r o p d e m a n d

FIELD NITROGEN BALANCE

Inputs = Imported fertilizer + atmospheric deposition

+ N2 fixation

Outputs = N exported in crop + N leached into ground water + N in eroded material + N lost by denitrification .

Amounts of nutrients removed by crops (kg/ha)

N P K

Alfalfa hay

Corn – grain

Rice-grain

Tomatoes

cotton

500

200

80

150

55

45

40

15

25

13

350

40

15

200

17

CASFS Farm Nitrogen Budget

% N %P %K

Compost 1992 1.13 0.57 1.18

Compost 2001 0.93 0.45 0.79

Inputs 1

Inputs 2Atmospheric deposition: Less than 1.0 kg/ha/year, of N, P and K, according to EPA data.

Inputs 3Biological nitrogen fixation – legumes

hard to measure – major source of uncertainty in budget

OUTPUTS

1.Leaching – likely to occur in the fall and spring (difficult to measure)

2.Gaseous losses – quantitatively unlikely to be an important component.

3.Erosion – unlikely – CASFS farm fields generate little runoff.

 

SOM

Soil solution

Fields studied

Apples

Tipi

Pears

Potatoes

Strawberries

Plums

Main Field

Onions+GarlicMixed vegetables

RyegrassCSA

Corn+Beans

Mixed vegetables

Garden

N P KVegetables 45.2 7.2 81.6

Onion + garlic 48.2 7.6 46.7

COMPOST* 16.3 7.9 13.9COVER CROP ? BNF 0.0 0.0

Budget balance -77.1 -6.9 -114.4

Output

Input

Main North Field – 1 year budget

* 1/6 of amount applied every 6 years

Simulated budget for one rotation cycle

N P K N P K1 0.0 0.0 0.0 0.0 0.0 0.0

2 108.8 53.8 103.9 0.0 0.0 0.0

3 0.0 0.0 0.0 48.2 7.6 46.7

4 BNF 0.0 0.0 67.5 10.5 92.4

5 BNF 0.0 0.0 115.7 18.2 133.8

6 BNF 0.0 0.0 46.7 12.0 45.5

7 BNF 0.0 0.0 24.6 3.6 30.1

8 BNF 0.0 0.0 67.5 10.5 92.4

TOTAL 108.8 53.8 103.9 370.1 62.4 440.9

BUDGET -261.3 -8.6 -336.9

INPUT CROP EXPORTYEAR

1. Biological N fixation (BNF) is crucial to compensate for the N exports. Cover crops need to fix 52 kg N/ha/year.

2. Do not know how much N lost by leaching

3. Estimation of BNF is needed to allow us to get an estimate of losses (leaching + gaseous)

4. Potassium export is exceeding input - use higher K compost or other sources of K

5. Phosphorus appears to be in balance

Conclusions

Combine information from budgets with soil testing to refine fertility management

SOM

0

1

2

3

4

5

6

7

8

9

%

Up garden

main field

apples

tipi field

soil ex-P

0

50

100

150

200

250

ppm

Up garden

main field

apples

tipi field

Exchangeable K

0

100

200

300

400

500

600

700

800

1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

mg

K/kg

soi

l

main field apples down garden

research up garden meadow

soil pH

4

4.5

5

5.5

6

6.5

7

7.5

pH

Up garden

main field

apples

tipi field