Soil Testing Options in High Tunnels

Bruce Hoskins University of Maine

hoskins@maine.edu anlab.umesci.maine.edu

High Tunnel Project Yields (avg. yield ~ 3000 lb/1000 sq. ft. => 65 tons/A)

Calculated (lb/A) fruit content => 180 N, 30 P, 400-500 K

Unique System

Rely on basic soil fertility, as with open field

Enhanced daytime air temperature

Faster growth rates from more heat units

Greater heat gain in soil with black plastic

Enhanced mineralization of organic nutrient sources

No natural rainfall – water must be supplied

Better disease control

Allows fertigation

Unique Problems

Temperature Extremes – Requires ventilation – May aggravate insect problems – Faster growth rates worsen nutrient deficiencies

Nutrient salt buildup

– Faster mineralization, especially under black plastic – Carryover of available nitrogen (Nitrate) – Enhanced evaporation “wicks” salts to the surface – No natural rainfall to wash (leach) excess nutrients – Irrigation usually not sufficient to leach excess salts

Evaporation + Transpiration > = Water input

Similar to field production in Irrigated Desert

Soil-Soil Water-Root Relationships

Most nutrient uptake as water-soluble ions (+) charge cations (Ca+2 K +1 Mg +2)

(-) charge anions (NO3-1 H2PO4

-1 SO4-2)

– Small proportion of total in solution at any time

Replenished as solution levels are depleted From cation exchange sites (Ca K Mg)

From stable compounds or complexes (P S)

From microbial activity/mineralization (N P)

Field Soil Test Traditional soil fertility test

Capacity to supply nutrients over entire season – Treats soil as a nutrient storehouse

Extracts a quantity of available nutrients – Correlates well with uptake and yield for the season

Regional tests

– Specific to mineralogy, climate, and nutrient chemistry Morgan/ modified Morgan (pH 4.8) Mehlich 3 (pH 2.5) Olsen + Ammonium acetate (pH7)

Appropriate Testing System for High Tunnels

Startup houses

– Essentially same as open-field soil management

– Routine field soil test most appropriate

Optimize pH, OM, major & micronutrient reserves

Appropriate Testing System for High Tunnels

Established houses (1 + years)

• Salt buildup can be a problem if not uncovered Monitor total salt level to avoid dessication damage

• Open field soil N management does not apply

Monitor nitrate level to avoid over-fertilizing

Hoop House/High Tunnel Package hybrid test 1

Field soil test to address potential deficiencies

EC (SME) to monitor total nutrient salt buildup

Available nitrogen to address nitrate buildup

Saturated Media Extracts Common Uses

1) Where nutrients applied as water-soluble fertilizers

– Conventional greenhouse bench crops

2) Where nutrient content exceeds retention capacity

High proportion of “free salts”

Soils with accumulated nutrient salts Irrigated desert soils

Long-term high tunnels

Saturated Media Extraction - Add water in a closed vessel just to saturation pt.

- Automatically accounts for moisture retention

- Constant relationship to field capacity (roughly 2X)

Water added at saturation (as % dry soil) Sandy loam: 20 – 35 % added water

Silt loam: 35 – 50 % added water Organic mixes: > 80 % added water

Long-Term High Tunnel Package hybrid test 2

Continuously-covered houses, usually 3+ years

Saturated Media Extraction + Organic matter

Water soluble (nutrient intensity) mgt. system

UVM interpretation guidelines

N-P-K recommendations to adjust SME levels

UVM guidelines

Optimum SME Ranges

GH Tomato/Cuke (Wittwer & Honma)

pH 5.8 – 6.8

NO3-N 125 – 200 ppm

P 8 – 13 ppm

K 175 – 275 ppm

Ca > 250 ppm

Mg > 60 ppm

EC 1.5 – 3.0 mmhos

Greenhouse Media (Warnke)

NO3-N 100 – 200 ppm

P 6 – 10 ppm

K 150 – 250 ppm

Ca > 200 ppm

Mg > 70 ppm

EC 2.0 – 3.5 mmhos

Optimum SME Ranges

GH Tomato/Cuke (Wittwer & Honma)

pH 5.8 – 6.8

NO3-N 125 – 200 ppm

P 8 – 13 ppm

K 175 – 275 ppm

Ca > 250 ppm

Mg > 60 ppm

EC 1.5 – 3.0 mmhos

Current High Tunnel (ME & VT)

pH 6.0 – 7.0

NO3-N 100 – 200 ppm

P 1 – 5 ppm

K 150 – 275 ppm

Ca > 250 ppm

Mg > 60 ppm

EC 2.0 – 4.0 mmhos

Estimated fertilizer rates to increase SME nutrient levels

Pounds/1,000 sq. ft needed to raise N approximately 10 ppm

Blood meal 12-0-0 4.2

Soybean meal 7-1-2 7.2

Alfalfa meal 2.5-2-2 20.2

Pounds/1,000 sq. ft needed to raise P approximately 2 ppm Bone char 0-16-0 25

Rock phosphate 0-3-0 133

Pounds/1,000 sq. ft needed to raise K approximately 20 ppm Sul-Po-Mag 0-0-22-11Mg 2.6

Potassium sulfate 0-0-52 1.1

Alfalfa meal 2.5-2-2 28.6

Pounds/1,000 sq. ft needed to raise Ca approximately 25 ppm Calcium sulfate (gypsum) 7.5

Calcitic lime (low Mag) 7.5

Dolomitic lime (hi Mag) 5.3

Adapted from Wittwer & Honma

Soil Extract Comparison Field Soil vs SME

2011 High Tunnel Calibration Project

Pre-plant Analysis

Field Soil Test Dry soil (mg/kg)

ID NO3-N P K Mg Ca Na B S Cu Fe Mn Zn

R1 116 402 160 1077 12193 176 1.8 357 0.33 7.0 20 13

R2 86 362 154 1074 11074 162 1.7 395 0.35 6.8 19 11

R3 85 383 243 1253 12306 232 1.9 788 0.31 7.9 18 12

R4 117 327 159 988 10847 196 1.5 552 0.29 6.5 15 16

R5 75 319 109 949 11088 105 1.6 204 0.30 5.6 20 12

R6 98 354 126 1043 11489 150 1.6 336 0.27 6.6 19 12

CV -> 18.1 8.9 29.2 9.9 5.4 25.3 8.1 46.6 9.3 11.1 8.9 12.4

Mean-> 96 358 158 1064 11499 170 1.7 439 0.31 6.7 18 13

Ideal -> 30-50 10-20 275-400 250-450 2000-3000 < 200 0.5-1.5 > 25 0.25-0.6 6 - 10 5 - 10 1 - 2

Rating-> High V High Medium V High V High OK High V High OK OK High V High

SME Test Extract (mg/L)

ID NO3-N P K Mg Ca Na B S Cu Fe Mn Zn

R1 86 3.3 16 82 233 77 0.06 179 0.013 1.3 0.13 0.04

R2 75 3.9 21 140 400 104 0.08 407 0.029 2.1 0.20 0.05

R3 70 3.9 49 169 502 140 0.09 524 0.037 1.4 0.10 0.04

R4 105 3.9 28 151 532 130 0.08 485 0.007 2.1 0.15 0.07

R5 68 3.0 9 85 264 55 0.06 210 0.021 1.3 0.12 0.03

R6 76 3.0 9 98 301 70 0.05 257 0.030 1.7 0.13 0.03

CV -> 17.1 12.5 61.4 29.6 32.6 33.9 20.9 40.9 52.9 23.1 24.5 32.7

Mean-> 81 3.6 25 125 386 101 0.07 361 0.021 1.6 0.14 0.05

Ideal -> 100 - 200 1 - 5 150 - 275 > 60 > 250 < 100 0.05-0.50 25-50 0.01-0.5 0.3-5.0 0.1-3.0 0.3-3.0

Rating-> Medium Optimum Low Optimum Optimum OK Optimum V High OK OK OK Low

Soil Extract Comparison Field Soil vs SME

Fundamental differences in nutrient pools

– Exchangeable/extractable vs water soluble (Q vs I)

– Low quantity = Low intensity

– Opt/High Quantity may not reflect in Intensity

Differences in reporting basis

- Dry soil basis (mg/kg) vs extract concentration (mg/L)

- Reflected in NO3-N levels

SME = variable dilution factor

Current Status High Tunnel Soil Testing

For newer houses, routine field soil analysis with additional checks on EC

and available nitrogen works well.

Continuously covered high-EC houses can be effectively managed using SME testing system.

Field soil and SME testing systems access greatly different pools for most nutrients and are reported on a different basis. Each requires discreet interpretation and recommendation systems.

Attempts to verify and/or recalibrate existing SME guidelines had limited success. Further studies are needed on lower fertility soils over a full season.

Questions?