Crop Management School 2016 Patricia Steinhilber

UMCP/ENST Agricultural Nutrient Management Program

Beneficial Use of Gypsum in Soil Management:

Reduction in Erosion and Soluble P Loss

Today’s Emphases

•what is gypsum and why the current interest?

•role of gypsum in reducing soil erosion and soluble P

•expands info from March 2016 webinar

What is Gypsum? •calcium sulfate dihydrate

−CaSO4-2H2O •a neutral salt •naturally occurring mineral •can be synthesized •by-product of several industries

By-product Gypsum (acceptable for use)

•flue-gas desulfurization gypsum −FGD-gypsum −formed during removal of sulfur dioxide in stack gases of coal-fired electric generating plants

−wet limestone scrubbers −10 million tons/yr produced in US (2012) −projected 20 million tons/yr produced by 2020

By-product Gypsum (unacceptable for use)

•phosphogypsum (PG) −produced in phosphorus fertilizer production

• sulfuric acid + rock phosphate = calcium phosphate and calcium sulfate (gypsum)

−EPA does not allow land application if residual radioactivity is 10 picocuries/gram

−billions of tons stacked in Gulf coast states, especially Florida & Louisiana • 1 stack covers 340 acres and is 200’ high

What’s Driving the Current Interest?

•USDA-NRCS adopted a standard for use of gypsum as a soil amendment −Dec 2015

•by-product gypsum is available and its use as a soil amendment is an economical way of dealing with a potential “waste”

Gypsum vs Limestone

•CaCO3 vs CaSO4-2H2O

•gypsum is 200 times more soluble than limestone

•2.5 gram/liter @ 25⁰C −“moderately soluble”

Reduction of Dissolved P in Runoff and Drainage Water

•Ca+2 ions react with phosphate ions to form a new secondary mineral, calcium phosphate

•one of the mechanisms whereby P is “fixed” in soils

Does Gypsum Reduce P Export in Runoff? •Penn State & USDA Watershed Lab

−JEQ, 2000, v. 29 •variety of materials, including gypsum •soils from PA & MD

−Hagerstown, Klineville & Watson •runoff boxes at a 5% slope, 2” per hour

−bare soil and grassed

Psol (ppm) from Bare and Grassed Runoff Boxes (Hagerstown soil, FIV = 149)

Surface Condition and Application Method

Tons Gypsum per Acre

0 5 10 bare soil (mixed) 0.45 0.31 0.32

grassed (surface-applied) 1.69 1.32 0.72 *

Bare condition represented a tilled soil early in the season before canopy closure, while the grassed condition simulated hay, pasture or buffer strip.

Field-scale Runoff Simulation •Norton, USDA-ARS, JSWC, 2008, v. 63 •Indiana, Blount loam soil •very high soil P levels, no-till corn-bean •4 treatments

−control, poultry litter, gypsum and litter + gypsum (co-applied)

•1 ton gypsum per acre •simulated rainfall at 2” per hour

Value of Gypsum Over Time •Auburn (Bulletin no. 680)

−6 tons poultry liter on bermudagrass pasture −0, 1, 2, 3 tons of FGD gypsum/acre over litter

•rainfall simulation - 3.5”/hr. −immediately after application −5 weeks later −7 months later

Gypsum-treated Grass Buffers (JEQ,2009)

•tall fescue pasture, Alabama −fsl in the Sand Mountain region

•upper slope – litter at 120 # N/acre •runoff sampling zone •lower slope – 0, ½, 1 ¼, 2 ½ T/A gypsum

−5 feet wide •water dispersion device

−continuous flow of water −high intensity rainfall event

Conclusions (Watts & Torbert)

•gypsum reduced P runoff in first major rainfall event

•greatest benefit for lowest rate •P runoff in second rainfall event not impacted by gypsum (1 month later) −temporary effect

Can Gypsum Enhance Infiltration and Reduce Runoff and Erosion?

•Sometimes, under certain conditions

•Let’s look at some soil chemistry concepts

•Let’s talk about soil crusting and soil sealing

Ionic Strength •ionic richness of the soil solution

−sum (all cations x valence) −“saline” soil has ionic strength that reduces plant growth in some plants

•electrical conductivity (EC) −mmhos/cm or deciSiemens/m −component of typical soil test suites W of 100 meridian

Sodic Soils

•sodium-affected soils

•exchangeable sodium percentage (ESP) ≥ 15%

•saline sodic – OK; sodic - trouble

Ionic Strength and Dispersion of Clays

If sodic, dispersion of clays

Dispersion and Flocculation

Clays are surrounded by a swarm of adsorbed cations bathed in a solution full of dissolved ions.

Van der Waals – weak ion to ion attraction caused by induced dipoles

Soil Crusting •thin, compacted layer at soil surface with a lower permeability than the underlying soil −low infiltration high runoff increased erosion

−worse on bare soils after heavy rainfall

•high soil strength −decreased seedling emergence/poor stands

Crust Formation (soil sealing)

•physical processes −aggregate destruction −raindrop compaction −clays become suspended

•chemical processes −dispersion of clays followed by clays clogging pores

−worse when EC is low

Will the increase in ionic strength caused by the addition of a moderately soluble material like gypsum cause flocculation and lead to decreased runoff and reduced erosion?

Gypsum on Runoff and Soil Loss

•Zhang et al., Trans ASAE, 1998 •Georgia, Cecil sandy loam •after CT soybeans, disked, unprotected soil surface

•natural rainfall from November to March

(mm runoff)

(Kg/ha ~ pounds/acre)

How effective is gypsum at increasing infiltration and reducing erosion in fields that have been in no-till?

Impact of Gypsum on Tilled and No-till Fields (Wallace et al., 2001)

•Indiana, Iva silt loam (loess), 5% slope •corn-soybean rotation •field plots with rainfall simulation (2”/hr.)

−after soybeans; residue removed

•gypsum – 1 ton/acre

Conclusions of Wallace •On tilled area, gypsum increased EC at soil surface, keeping clays flocculated and preventing seal formation

•Under no-till, greater aggregate stability led to less aggregate destruction so the increase in EC was not helpful

“Emerging” Technologies

•research has shown effectiveness

•process for acceptance as a BMP is under consideration −ditch filters −curtains

Ditch Filter (Bryant et.al., JEQ v.41, 2012, UMES)

•designed to treat as much of the water passing through ditch as possible −measured amount of Ptotal and Psol in bypass flow

•sampled upstream of filter and downstream of filter

•assessed “chemical efficiency” and “system efficiency”

Efficiency •chemical efficiency

−Casol reacts with Psol to form calcium phosphates −annually – 57% to 90% −per storm event – -11% to 99%

•system efficiency −“disappointingly low” −17% to 30% −93% bypass in exceptionally large storm

Gypsum Curtains (CIG Project)

•trench adjacent to ditch −intercept shallow ground water before it reaches the ditch

•fill with a P-sorbing material like gypsum

•eliminates the problem with bypass flow

•data suggests large reductions in Psol

reduction from 5 ppm Psol before the curtain to 0.2 ppm after the curtain

Local Source

•PBCo, Inc. − Buffalo, NY − “relationship” with many electric generating plants on East Coast

− market and ship FGD gypsum − not yet registered as an amendment in MD − intend to seek registration as SYNGYP ™

White Sands National Monument in south-central New Mexico

Guadalupe National Park, Texas