Mineral NutritionMineral Nutrition& Management& Management

Dr. Richard RosecranceCalifornia State University, Chico

Productivity & ProfitabilityProductivity & Profitability

OutlineOutline

1. Nutrient pathways to plants2. N fertilization efficiency. 3. N budgeting, a method of accounting

for tree N demand & sources 4. N fertilizer selection & timing

How do nutrients get to the How do nutrients get to the plant roots?plant roots?

1.

2.

3.

Nutrient Pathways to RootsNutrient Pathways to Roots

1. Root interception: Ca, (Zn)2. Mass flow of water: N, Ca, Mg, S, B, (K), (Zn)3. Diffusion: P, K, (Zn)

Cation Exchange Capacity

Nitrate In GroundwaterNitrate In Groundwater

y = 0.7153x - 1372.9R2 = 0.7081

20

30

40

50

60

70

80

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Pa

rtia

l Fa

cto

r P

rod

uc

tiv

ity

(k

g g

rain

kg

N-1

)Nitrogen fertilizer efficiency trend in Nebraska

Even with these improvements, average N fertilizer uptake efficiency is only about 40% of applied N with average yields of about 10 Mt per hectare. A 2-fold increase is possible!

N efficiencyN efficiency

1. Amount & and seasonal patterns of N use by trees

2. N availability from nonfertilizer sources (i.e.irrigation water, cover crops)

3. dynamics of fertilizer N availability4. relationships between timing, amount of

fertilizer, and irrigation water applied

Part 1 Concepts of Part 1 Concepts of FertilizationFertilization

Midsummer leaf N Midsummer leaf N ConcentrationsConcentrations

< 2.3% deficient 2.3 – 2.7% adequate > 2.7% excessive

Mid-Shoot Leaf SamplesMid-Shoot Leaf SamplesTerminal leaflet on spurTerminal leaflet on spur leavesleaves

When to sample leaves?When to sample leaves?Seasonal Variation in Leaf-Seasonal Variation in Leaf-

nutrient Concentrationsnutrient Concentrations

Using Leaf Analysis Results Using Leaf Analysis Results to Adjust Fertilizer Practicesto Adjust Fertilizer Practices

If Leaf N > above critical value, fertilizer can be reduced or eliminated for a year without impacting growth & yield (esp. on heavy-textured soils)

N Use by the TreeN Use by the Tree

Forms of N absorbed by the treeNH4+

NO3-

N Uptake -- Greatest between onset of active shoot growth until late stages of nut fill

N removal in cropN removal in crop

Walnut -40 lbs of N/ton of cropN removal calculators -

http://npk.nrcs.usda.gov/

Whole Tree N Contents by Whole Tree N Contents by Organ in Almond.Organ in Almond.

Excavation Date

3/20

5/20 8/29 9/29

N contents (g)

0

500

1000

1500

2000

2500

3000

rootstrunkcanopyleavesfruit

Harvest

2/20

UptakeUptake

Nitrogen budgeting to Nitrogen budgeting to determine how much to applydetermine how much to apply

N Losses

Nitrogen budgeting to Nitrogen budgeting to determine how much to applydetermine how much to apply

N Losses

Volatilization-N lost directly to Volatilization-N lost directly to atmosphereatmosphere

N in ammonium and urea fertilizers may be released to the atmosphere as ammonia gas. (NH4+→ NH3)pHs >7.5 ↑ volatilization. Volatilization from fertilizers

can be ↓ by rapid incorporation

Effect of rainfall on Urea N Effect of rainfall on Urea N volatilization lossesvolatilization losses

RainfallWithin days

after application

N Volatilization

Losses, %

0.4 2 0

0.4 3 10

0.1 to 0.2 5 10 to 30

0 5 30+(Fox and Hoffman, Pennsylvania – N on no-till corn)

DenitrificationDenitrification

1. soil microorganisms: soil nitrates → N2.

2. N loss ↑ when soils are warm and wet. 3. Denitrification losses are typically less

than 5% but can be higher under low- oxygen conditions

Losses with ureaLosses with urea

Urea has no electrical charge, so it moves readily in the soil with rain or irrigation water.

Volatilization losses from urea fertilizers are low if urea fertilizers are incorporated into the soil shortly after application.

Nitrate LossesNitrate Losses

Nitrate fertilizers are generally more costly per unit of nitrogen than are ammonium fertilizers. Nitrate is highly mobile in the soil.

Choosing & Using N FertilizersChoosing & Using N Fertilizers

Su

Source: Ca Plant Health Association 2002

Worksheet InstructionsWorksheet Instructions

In order to use the nitrogen budgeting approach you will need:

1.yield data for the past few years2. irrigation records3. irrigation water nitrate analyses4. records of compost/manure applications5.estimates of cover crop yield and nitrogen

content6.calculator

Nitrogen Fertilizer TimingNitrogen Fertilizer Timingand Placementand Placement

Nitrogen recovery. Fertilizer recovery is greatest when application coincides with periods of high nitrogen demand by trees

Split applications.Split applications.

A good rule of thumb is to apply one-half to two- thirds of the fertilizer nitrogen in spring, so it is available during the main flush of spring shoot growth. The remainder should be applied by later during nut fill

Best Management Practices Best Management Practices

Successful N management delivers enough N to the crop to optimize yield and profitability while ↓ losses to water and air. Everyone wants the nitrogen to end up in the crop. Thus, the best management practices (BMPs) presented here are identified as sound practices from economic, production and environmental viewpoints.