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Soil and Leaf Analysis for Fruit Crops

Soil and Leaf Nutrient Analysis
I. Soil testing
Objectives:
1. Evaluate soil productivity.
2. Predict the probability of a profitable plant response to fertilization.
3. Determine specific soil properties which may be improved by fertilization/cultural
practices.
A. Information obtained:
1. Water and buffer pH – lime requirement.
2. Element concentration – major cations, phosphorus (not N).
3. Organic matter – content, chemical composition.
4. Mechanical analysis – soil texture, type.
5. Soluble salts – Irrigation water quality, salt stress. Fruit crops are intolerant of
salts in general, but extremely intolerant of Na
+
and Cl
-
ions.
Salinity threshold % decrease in yield
Crop (mmho/cm) above threshold
———————————————————————————-
Sensitive species
Strawberry 1.0 33
Almond 1.5 19
Blackberry 1.5 22
Plum 1.5 18
Grape 1.5 10
Apricot 1.6 24
Orange 1.7 16
Peach 1.7 21
Grapefruit 1.8 16
Tolerant species
Date palm 4.0 4
Bermudagrass 6.9 6
Cotton 7.7 5
Soils lab routinely does lime requirement and major elements forfree; other analyses cost
extra.B. Sampling procedures
Composite sample – 4-16 cores taken at random throughout field.
Range – one composite for each 5 to 100 acres; management decision.
- one composite for each region that can be treated separately.
- one composite for each soil type.
Depth – sample area where majority of roots reside; about 18-20 inches.
Location – sample under tree canopy, within row. Avoid sampling at field edges.
Timing – Mid-summer to late fall, when foliar samples taken. Important to do at same time
each year to compare results over time.
Fertilizer Sources and Application Methods
I. Sources
A. Inorganic (most common).
1. Dry
a. Granular – Fertilizer salts mixed with sand or some other “filler” or “carrier”;
applied to soil dry.
b. Soluble -Fertilizer salts which readilydissolve in water, applied through irrigation
system, “fertigation” or “chemigation”.
c. Slow release -Fertilizer salts coated with relatively impermeable materials which
slow the rate of solubilization; Osmocote (plastic resin), SCU (sulfur-coated urea).
2. Liquid
NH4NO3 solutions – crystallizes at 52°F, mixed with water or urea solution,
crystallizes at 32°F. Used for fertigation; uncommon.
3. Gas
NH3 gas can be applied to irrigation water (flood), or incorporated into soil when
plowing and deep tilling; uncommon. NH3 gas is very toxic to foliage at low
concentrations.
B. Organic
1. Synthetic – urea, IBDU (isobutylidene diurea).
2. Natural – manures, many different types.
+ Slow-release+ May improve soil tilth, structure
+ Inexpensive (per ton, but not necessarily per unit N)
+ Contains many nutrients besides N.
+ May act as mulch, retain water, suppress weeds
- Low analysis, high shipping costs
- May contain weed seeds
- Irregular availability
- Acidic
C. “Complete” (NPK) v. single element sources.
Principal element needed each year is N; others should be applied on an as
needed basis only (determined from annual soil and leaf analyses).
Ca – Applied and tilled thoroughly during site preparation.
P – ” “
Amount removed by crop (kg/ha/yr) is very small (Westwood table 6-6, p. 154):
Species N P K
Apple 39 10 71
Peach 76 11 96
K removed in appreciable quantities, but also held in soil firmly in most cases.
Trees recycle nutrients (retranslocate); nutrients in leaves withdrawn and stored in
stems, roots, prior to abscission.
Benefit from NPK v. N fertilizers is minimal (Westwood, table 6-7):
N, P, K content of leaf tissue after 10 years of complete (NPK) vs. N-only (N) fertilization.
Species Nitrogen (% dry wt) Phosphorus (%
dry wt)
Potassium (% dry
wt)
N NPK N NPK N NPK
Apple 2.74 2.74 0.19 0.19 1.73 1.66
Peach 2.97 2.93 0.22 0.20 2.00 2.02II. Application methods.
A. Soil applied
1. Broadcast – Truck, tractor, hand. (most common).
- Spread uniformly over area occupied by tree roots (herbicide strip).
2. Preplant, incorporated
a. Broadcast prior to tillage, planting of trees; should be done with lime or
gypsum and especially phosphorus since Ca and P are immobile in soil.
b. Spot or band application – mostly in herbaceous crops, but may be done
for strawberries on raised beds, and tree crops with trunk-to-trunk sod (apply
nutrients below grass roots).
3. Fertigation, or “chemigation”
Works best with low-volume irrigation (drip), but can be done with overhead, center
pivot (“piggyback” configuration), or flood irrigation.
Growing in popularity; unknown 30 years ago, performed on 10.6 million acres of
crop land by 1983.
Application costs are 1/3 to 1/2 conventional application techniques; injection
equipment ranges in price from ca. $1000 – $5000.
Can time nutrient application to crop needs (demand periods); “spoonfeed”
nutrients as crop assimilates them, reduces waste.
Legislation currently being formulated to regulate and ensure safety of fertigation.
Calibration:
1. Prior to injection, ensure that all emitters pressurized.
2. Use detergent or dye, determine the time interval between injection and
appearance at closest and furthest emitter; this is minimum time interval for
injection.
3. Time interval should be ±10% for best uniformity:
first = 12 min (12-12.5)/12 = 0.042 or 4.2% diff.
last = 12.5 min
* Application uniformity only as good as water distribution uniformity.Advantages Disadvantages
1. Reduced application, labor 1. Clogging of emitters;
energy costs. Requires filtration, restricts
use of non-soluble materials.
2. Reduced soil compaction, use
heavy equipment (wear and tear). 2. Uneven application if
not monitored properly;
3. Increased convenience of pressure regulation, flow
operation. control.
4. Reduced operation hazard. 3. Possible contamination
of groundwater; must use
5. Possibility of better uniformity back-flow inhibitors.
and utilization of fertilizers.
4. May require unnecessary
6. Potentially reduced surface irrigations.
and groundwater contamination.
5. Possibility of overdose/phytotoxicity is
high.
6. Requires greater management skills.
B. Foliar applied
Effective for correction of micronutrient deficiencies, especially on high pH soils -
useless to apply metals on high Ca soils. e.g., Zn deficiency in apple, pecan; Cu
deficiency in citrus.
All nutrients can be absorbed through the foliage, but foliar application should be
used as a supplement only.
Leaves, stems, petioles, fruits – all absorb nutrients, younger tissues moreso than
older; less cutinized tissues absorb more than highly cutinized.
- Fruits absorb less under high light, low humidity conditions (Western US)
due to higher cutinization.
Potential injury if overdosed; hot, dry weather accentuates injury due to rapid
evaporation and concentration of salts on foliage.
Some spray materials compatible with pesticides and growth regulators, hence, no
extra application cost.Foliar calcium application.
Calcium-related disorders often occur despite adequate soil Ca levels because
accumulation in fruit is less than in leaves, Ca immobile; must supplement.
Cork spot/bitter pit of apple:
Cork spot – spherical, dead areas in flesh (brown), occurs in field.
Bitter pit – Primarily a storage disorder affecting skin and underlying cells.
Often, cork spot called corking, confused with bitter pit.
In pear “Anjou spot”.
* Both Ca-related disorders, but accentuated by high tree vigor and drought (probably due
to dilution of Ca, and lack of accumulation, respectively).
‘York’ – very susceptible cultivar
‘Red Delicious’ affected more than ‘Golden Delicious’, both moderately susceptible.
Sprays:
Ca(NO3
)
2
or CaCl
2 applied in cover sprays for fungal diseases; this rarely
eliminates, but reduces the problem.
Rate: 18-24 lbs/acre per year, in various concentrations depending on # of times
applied.
1.5 lb/acre – 16 sprays
3.0 lb/acre – 8 sprays