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Soil Chemical, Physical, and BiologicalProperties of a Sandy Soil Subjected toLong-Term Organic AmendmentsMonica Ozores-Hampton a , Philip A. Stansly a & Teresa P. Salame aa University of Florida, IFAS, Southwest Florida Research andEducation , Immokalee, Florida, USAPublished online: 18 Mar 2011.

To cite this article: Monica Ozores-Hampton , Philip A. Stansly & Teresa P. Salame (2011) SoilChemical, Physical, and Biological Properties of a Sandy Soil Subjected to Long-Term OrganicAmendments, Journal of Sustainable Agriculture, 35:3, 243-259, DOI: 10.1080/10440046.2011.554289

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Journal of Sustainable Agriculture, 35:243–259, 2011Copyright © Taylor & Francis Group, LLCISSN: 1044-0046 print/1540-7578 onlineDOI: 10.1080/10440046.2011.554289

Soil Chemical, Physical, and BiologicalProperties of a Sandy Soil Subjectedto Long-Term Organic Amendments

MONICA OZORES-HAMPTON, PHILIP A. STANSLY,and TERESA P. SALAME

University of Florida, IFAS, Southwest Florida Research and Education, Immokalee,Florida, USA

Although landfills are the most common destination for organicwaste materials in the United States, these materials might be bet-ter utilized for compost and recycled as organic amendments.However, there is little information available on the effects on soilquality of long-term application of these materials. Over a 10-yearperiod, we applied composted and non-composted amendments,including municipal solid waste (MSW), yard trimmings (YT), andbiosolids to a sandy soil in vegetables production in a replicateddesign with a no amended control. Amendments increased thesoil content of most nutrients including P, K, Ca, Mg, Mn, andZn as well as organic matter (OM) and cation exchange capacity(CEC) by three-fold. Effects on P and OM were restricted to the top30 cm of the soil profile. Bulk density was decreased from 1.6 to1.4 g.cm3 by organic amendments, and available water-holdingcapacity (AWHC) was increased by 35%. Organic amendmentsalso enhanced the overall soil microbial activity (species num-ber and diversity), especially of the desirable groups such asheterotrophic aerobes, actinomycetes, and pseudomonads. Thus,the quality of amended soils was improved by all criteria mea-sured, although increased P content could create a water qualityconcern.

KEYWORDS soil quality, compost, soil water tension, soil micro-bial activity, and soil physical and chemical properties

Address correspondence to Monica Ozores-Hampton, University of Florida, IFAS,Southwest Florida Research and Education, Immokalee, FL 34142. E-mail: ozores@ufl.edu

243

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244 M. Ozores-Hampton et al.

INTRODUCTION

The vegetable production system in Florida, which generally includes raisedbeds, polyethylene mulch, and drip irrigation, has been very effective in pro-ducing high vegetable yields (Olson and Simonne, 2007). Generally, Floridasoils are sandy and low in OM. In addition, they have low CEC, AWHC, andnative fertility (Ozores-Hampton et. al., 1998). Native plants in these areassurvive on a thin but dynamic layer of OM on the soil surface (Ozores-Hampton and Obreza, 1998). Conventional commercial vegetable growers,however, rarely add organic amendments since the use of concentrated,inexpensive, and readily available synthetic fertilizers result in high yieldswith maximum short-term profits.

Arshad et al. (1996) defined soil quality as the capacity of a specifickind of soil function, within natural or managed ecosystem boundaries, tosustain plant and animal productivity, maintain or enhance water and airquality, and support human heath and habitation. The success of long-termvegetable production and maintenance of environmental quality is depen-dent on soil quality (Arshad et al., 1996). Indicators of soil quality includeCEC, OM, total carbon (C), pH, and the number and community structure ofcertain soil organisms (Arshad et al., 1996; Doran and Parkin, 1994).

The use of appropriate composted and non-composted organic amend-ments may improve soil quality and enhance the utilization of fertilizer,therefore improving the performance of vegetable crops (Ozores-Hamptonet al., 1998 and Ozores-Hampton and Peach, 2002). Organic amendmentsmay: improve the ability of a plant to tolerate stress by slowing the releaseof nutrients (Ozores-Hampton et al., 2000; Hernando et al., 1989); addsoil OM (McConnell et al., 1993); increase AWHC and CEC (Serra-Wittlinget al., 1996; Tester, 1990); decrease bulk density (McConnell et al., 1993);decrease erosion by water and wind (Tyler, 2001); increase pH in acid soils(Hernando et al., 1989); and increase soil microbial activity (Perucci, 1992).Microorganisms play a significant role in decomposition of soil OM, whichleads to formation of humus and available plant nutrients. Finally, organicamendments may reduce the levels of organisms that cause stress to plants,such as plant-parasitic nematodes and soil pathogens (McSorley et al., 1997;Hointink and Fahy, 1986).

In areas of high population, there are a variety of non-hazardouswastes generated for which composting and land application can providean economically-sound and environmentally-acceptable option for utiliza-tion, but the majority of these wastes are currently landfilled or burned(Goldstein and Madtes, 2001; Ozores-Hampton et al., 1998). Organic amend-ments from wastes produced by urban populations include MSW; YT; foodwastes from restaurants, grocery stores, and institutions; wood wastes fromconstruction and/or demolition; wastewater (from water treatment plants);and biosolids (sewage sludge). Agriculture produces other organic wastes

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Long-Term Organic Amendments in Sandy Soil 245

that can be land applied or composted: poultry, dairy, horse, feedlot,and swine manures; wastes from food processing plants; spoiled feeds;and harvest wastes (Ozores-Hampton et al., 1998; Ozores-Hampton, 2006;Ozores-Hampton et al., 2005).

Organic waste materials land applied with or without composting canbe incorporated as a soil amendment for vegetables, fruit trees, and nurserycrops; used to replace soil removed with nursery trees and sod; appliedas a mulch to decrease evapo-transporation and control weeds; or usedas all or part of potting media (Ozores-Hampton, 2006; Ozores-Hamptonand Peach, 2002). Long-term application of organic amendments made fromwaste materials that passes Federal and State regulations should be suitablefor producing fruit and vegetables for human consumption (USEPA, 1994and 1995; FDEP, 1989).

The objectives of the research were to study the long-term effects ofapplication of organic amendment on sandy soil chemical, physical, andbiological properties.

MATERIALS AND METHODS

Experimental Design

Experiments were conducted during the 1993 to 2001 seasons at theUniversity of Florida’s Southwest Florida Research and Education Center inImmokalee. The soil was an Immokalee fine sand (sandy, siliceous, hyper-thermic Arenic Haplaquods). The treatments consisted of a yearly applicationof organic amendment or a non-amended control in a randomized completeblock design with four replications. Different organic amendments and ratewere applied every year to simulate grower organic amendment availabilitythroughout long term application (Table 1). Organic amendments were bandapplied at bed formation and incorporated in the bed in the fall each year.A methyl bromide and chloropicrin (98:2) were used and applied at bedformation at the rate of 336 kg. ha−1 each year to fumigate the soil. Bedswere covered with black polyethylene mulch during the 1993–1998 seasonsand white-faced black polyethylene mulch during 1998–2001 seasons. Plantswere irrigated with a combination of drip irrigation and water table manage-ment or seepage irrigation. Drip irrigation tubing was a 0.25 mm biwall typewith flow rates of 3.65 m3.d−1 positioned in the center of the bed prior tothe mulch application. Emission points were located on 30 cm spacing. Dripirrigation duration was 1 h, twice per day. Irrigation amounts were based ontensiometer readings to maintain soil-water potential greater than –15kPa.Tensiometers were located in the plant row at 30 and 60 cm depths in theorganic amendment and non-organic amendment plots and monitored twiceper week.

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246 M. Ozores-Hampton et al.

TABLE 1 History of Organic Amendments Applied to the Soil of Field Site in Immokalee, FL,during the 1993 to 2001 Seasons

Year Organic amendments Rate (Mg.ha−1) Source

1993 Municipal solid waste compost 180 Broward County, FL1994 Biosolids 7.4 Tampa, FL1995 Yard trimmings and biosolids compost 22.4 Palm Beach, FL1996 Yard trimmings and biosolids compost

and cow manure45/27 Palm Beach and Oxford, FL

1997 Yard trimmings and biosolids compost 45 Palm Beach, FL1998 Biosolids (Class B) 38 Miami, FL1999 Biosolids (Class B) 47 Miami, FL2000 Biosolids (Class B) 38 Miami, FL2001 Yard trimmings and biosolids compost 27 Immokalee, FL

Cucumber (Cucumis sativus L.), broccoli (Brassica oleracea ItalicaL.), eggplant (Solanum melongena L.), squash (Cucurbita pepo L.), toma-toes (Lycopersicon esculentum Mill.), and watermelons (Citrullus vulgarisSchrad.), were grown during 1993 to 1998 spring seasons. Rotation crops ofpeppers (Capsicum annuum L.) and watermelons were grown from 1998 to2001 during the fall and spring each year. Vegetable crops were transplantedin the fall or spring onto raised beds 0.81 m wide, 0.1 m high, and 1.8 mbetween centers in 85 m long plots. Fertilizer was applied to the vegetablesby injection through the drip irrigation system following the University ofFlorida Extension guidelines (Hochmuth and Maynard, 1998).

Inorganic N and K application was reduced by 50% in the organicamended biosolids plots in the beginning of 1998 to compensate forthe N mineralized from organic amendments. The Florida Departmentof Agriculture and Consumer Service interim Best Management Practice(BMP) rule states that the contribution of plant-available N from organicmaterials shall be 50% of the total nitrate (NO3) concentration (FDACS,1995). Additionally, mineralization studies of this type of biosolids con-cluded a 50% rate of mineralization per year (Obreza and Ozores-Hampton,2000). Therefore, NO3 contributions from organic amendments are shownin Table 2. Under South Florida environmental conditions, a very lowextractable amount of soil NO3 is present in the soil; therefore we assume noN contribution from previous organic amendments application (Hochmuthand Hanlon, 1998). Peppers and watermelon grown in the organic amendedand non-organic amended plots received no P application, since soil Plevel were very high (Hochmuth and Maynard, 1998). Inorganic fertilizerwas applied to the peppers by injection through the drip irrigation sys-tem at 428N-0P-178K and 377N-0P-157K kg.ha−1 for the non-amended plotsand at 214N-0P-90K and 188N-0P-89K kg.ha−1 for the amended plots inthe 1998–1999 and 1999–2000 seasons, respectively. Fertilizer rates appliedto the watermelon by injection though the drip irrigation system were

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Long-Term Organic Amendments in Sandy Soil 247

TABLE 2 Organic Amendments N (NO3) Contribution Applied to theSoil Based in application Rate, Moisture and Total N Content and 50% NMineralization Rate during the 1993 to 2001 Seasons

Year Organic amendments Rate (NO3 Kg.ha−1)

1998 Biosolids (Class B) 2821999 Biosolids (Class B) 3482000 Biosolids (Class B) 2822001 Yard trimmings and biosolids compost 149

211N-0P-88K for the non-amended and 106N-0P-44K for the amended plotsin the 1999–2000 seasons. In the year 2000, the non-amended plot received2.24 Mg.ha−1 of lime to raise the soil pH.

Plants were monitored for insects and diseases and pesticides wereapplied uniform across treatments and as needed according to Univ. ofFlorida Extension guidelines (Hochmuth and Maynard, 1998).

Chemical Properties of Organic Amendments

The Soil and Water Science Department, Univ. of Florida, Gainesville, mea-sured chemical and physical properties of the organic amendments appliedeach year. Three samples were taken for which moisture concentration wasobtained by oven-drying 10 g (wet weight) of organic amendment at 105 ◦Cfor 24 h. Total N and C concentrations were measured in organic amendmentsamples that were air-dried for 4 days, ground in a Spex 8000 Mixer/Mill,and combusted at 1010 ◦C in a Carlo-Erba NA-1500 C/N/S analyzer. Theorganic amendment samples were acid-digested and analyzed by InductivelyCoupled Argon Plasma Spectroscopy (ICAP) for total nutrients and tracemetals according to EPA Method 3050 (USEPA, 1990). Electrical conduc-tivity (EC) and pH were measured using a 2:1 (by volume) water-to-soilsuspension.

Soil Chemical Properties

Yearly soil samples for nutrient analyses and CEC consisting of 10 soil coresor replications 2.5 cm in diameter and 20 cm deep were collected duringJune each year from each treatment and oven-dried, passed through a 1-mmscreen, and extracted with Mehlich-1 solution. The extract was analyzedfor Ca, Mg, P, K, Cu, Mn, Fe, and Zn (Hanlon and DeVore, 1989). Soil pHwas determined in a 1:2 dilution (v/v) with water; OM was determined byignition (Dellavalle, 1992). The CEC of the soil was analyzed by method9081 with four soil samples collected on February 2002 (USEPA, 1990). Soilbulk density was determined from four-soil samples taken in the first 15 cmof soil using a 5 cm long and a 5 cm wide core sampler in February 8, 1999.

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248 M. Ozores-Hampton et al.

Soil P, OM content and pH were determined over depth by removing soilcores 5.3 cm wide and 2.8 cm long from 15 cm increments down to 1 mdepth in February 8, 1999.

Soil Biological Properties

Three soil samples were collected in February 2002 and sent to BBCLaboratory, Inc. (Tempe, AZ) for analysis of biological properties includ-ing number and species richness diversity (SRD) of six functional groups:as heterotrophic aerobic bacteria, anaerobic bacteria, fungi, actinomycetes,pseudomonads, and nitrogen-fixing bacteria. Species richness diversity mea-sures the number and diversity of each group of microorganisms presentin the soil. This index determines the number of species in each microbialgroup and compares to the total number of microorganisms in each group.In addition to the individual SRD determinations of the various functionalgroups, an index for the total species richness diversity (TSRD) was deter-mined. This index is the sum of the heterotrophic aerobic bacteria, anaerobicbacteria, fungi, actinomycetes, pseudomonads, and nitrogen-fixing bacteriaSRD (Page et al., 1983).

Soil Physical Properties

Available water-holding capacity was determined by removing soil cores 5.3cm wide and 2.8 cm long from 15 cm depth in February 2002. The coreswere covered on the bottom with nylon screen, and saturated with waterby soaking overnight. They were placed in a pressure extractor, and thesoil water characteristic curve was measured according to the proceduredescribed by Klute (1986). Available water-holding capacity was expressedas a percentage on a volume basis (cm3 of water/cm3 of soil). The moisturecharacteristic curve was develop using a pressure extractor measuring from 0to −0.35 bars (0 = total soil saturation; −0.33 bar field capacity [Sodek et al.(1990) and Carlisle et al. (1988; 1989)]. Available water-holding capacity iscalculated as the difference between the soil water contents at field capacityand wilting point (Klute, 1986: Hornsby and Mattson, 1998). In Florida thesoil-water characteristic curve is utilized to determine the soil water tensionlevel that will determine irrigation time (Obreza et al., 1997).

Analysis

Data were subjected to analysis of variance (ANOVA) and mean separa-tion according to Duncan’s Multiple Range Test to compare results fromamended and non-amended soils. Regression analysis was used to evaluatethe relationship between soil P and OM content (SAS, 2000).

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Long-Term Organic Amendments in Sandy Soil 249

RESULTS AND DISCUSSION

Chemical Properties of Organic Amendments

Near neutral to alkaline pH, a C:N ratio below 20, and 0.34 to 5.7% N,0.3 to 2.7% P, 0.13 to 0.5% K and 7.2 to 0.9% Ca were observed from theorganic amendments used (Table 3). Phosphorous content was highest in thebiosolids, which were applied in 1994, and in 1998 through 2000 seasons.Micronutrients such as Mg, Fe, and Mn and heavy metals such as Cd, Cu,Pb, Ni, and Zn were within the normal range for organic amendments cropapplication (USEPA, 1994).

Soil Chemical Properties

Soil OM, pH, and Mehlich 1-extractable P, K, Ca, Mg, Mn, Cu, Fe, and Znconcentrations were higher in the organic amendment treatments than thecontrol, except for Mn (1994;95), Fe (1994, 1995, and 2001), and Cu (1994to 1998 and 2000) (Table 4). Organic matter in most vegetable productionareas in Florida is low usually less than 1% (Obreza et al., 1997). From 1998,the addition of organic amendments tended increase the OM content morethan 200% (three-fold). The higher the OM contents the higher the soil res-piration or biological activity (Hointink et al., 1998). Soil with an ideal stateof biological activity or high respiration has adequate OM content and activepopulations of microorganisms (Evanylo and McGuinn, 2000). Organic mat-ter provides the food or substrate on which heterotrophic soil microbesfeed. Of the soil chemical properties tested P levels increased the most inresponse to applications of biosolids; by the end of the experiment theywere more than ten times greater in the amended soils than non-amendedsoil. Soil CEC of amended soil was about 2.5 times that of non-amendedsoils (Table 6). Similarity, higher OM and CEC content was obtained withaddition of 67 Mg.ha−1 per year of yard waste compost to an organic andconvention pepper farm in south Florida during two years (Chellemi andRosskopf, 2004). Also, Shiralipour (1998) reported that in Florida sandy soilsapplication between 34 and 68 t. ha−1 of compost increased CEC by aminimum of 10%.

Phosphorous Soil Profile

In the soil profile samples taken in 1999 season the higher P content wasobserved at soil depths of 0 to 30 cm in amended soil whereas no differenceswere seen over the profile in non-amended soil (Table 5). Differences in Pcontent between amended and non-amended soils were only observed inthe top 15 cm of soil. Organic matter content was greatest in the first 30 cm

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TAB

LE3

Chem

ical

Anal

ysis

ofO

rgan

icA

men

dm

ents

during

1993

to20

01Se

asons

Pro

per

ty

MSW

zco

mpost

bro

war

dco

unty

(199

3)B

ioso

lids

tam

pa

(199

4)

YTW

yco

mpost

pal

mbea

ch(1

995,

1996

,199

7)Cow

man

ure

pal

mbea

ch(1

996)

Bio

solid

scl

ass

Bm

iam

i(1

998,

1999

,20

00)

YTW

&B

SX

com

post

imm

oka

lee

(200

1)

(%dry

wei

ght)

C20

.3n/aw

26.7

6.5

3615

.4N

1.2

3.0

1.9

0.34

5.7

1.1

P0.

32.

31.

00.

442.

70.

4K

0.4

0.13

0.5

0.28

0.14

0.2

Ca

3.1

1.65

4.1

0.90

6.0

7.2

(mg. k

g−1dry

wei

ght)

Mg

3,00

01,

900

2,72

12,

300

8,34

53,

000

Fe20

,000

39,0

0010

,401

1,13

613

,150

n/a

Cd

2.9

0.7

3.0

n/a

7.2

3Cu

281

662

161

1662

741

Mn

5.8

3,18

011

168

40.0

74Pb

231

5360

.2n/a

98.0

24N

i3.

492

8.2

n/a

153

18Zn

655

700

265.

797

1,39

510

3

Additi

onal

pro

per

ties

Mois

ture

(%)

42.0

49.8

30.3

37.4

74.0

50C:N

ratio

16.9

n/a

14.5

196.

414

pH

7.6

7.0

7.3

8.1

8.6

8.2

E.C

.(S

. m−1

)0.

5n/a

0.5

0.6

1.45

0.3

z MSW

:M

unic

ipal

solid

was

te.

yY

TW

:Yar

dtrim

min

gsw

aste

.XBS:

Bio

solid

s.w

n/a:

Notan

alyz

ed.

250

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14

TAB

LE4

Influen

ces

ofO

rgan

icA

men

dm

ents

on

Soil

Chem

ical

Pro

per

ties

and

Nutrie

ntConte

ntduring

the

1993

to20

01Se

asons

Tre

atm

ents

OM

(%)

pH

PK

Ca

Mg

FeM

nCu

Zn

(mg. k

g)−1

June,

1994

Org

anic

amen

dm

ent

n/ay

6.4∗

56.8

∗22

.6∗∗

930∗∗

35.0

∗∗34

.57.

74.

416

.1∗∗

No

org

anic

amen

dm

ent

n/a

5.4

37.6

6.1

304

16.8

32.7

6.4

3.8

4.7

June,

1995

Org

anic

amen

dm

ent

n/a

6.6∗∗

139∗∗

71.1

∗∗1,

069∗∗

43.1

∗∗31

.18.

15.

122

.7∗∗

No

org

anic

amen

dm

ent

n/a

5.3

68.3

33.7

293

24.7

30.9

7.4

5.0

5.8

June,

1996

Org

anic

amen

dm

ent

1.9∗

6.8∗∗

131∗∗

35.1

∗1,

125∗∗

45.8

∗∗78

.8∗∗

10.3

∗7.

822

.3∗∗

No

org

anic

amen

dm

ent

0.9

4.9

39.0

17.4

204

16.0

37.7

5.9

6.7

4.7

June,

1997

Org

anic

amen

dm

ent

n/a

7.2∗∗

45.7

∗∗23

.9∗∗

2,66

8∗∗80

.8∗∗

n/a

n/a

n/a

n/a

No

org

anic

amen

dm

ent

n/a

5.7

11.7

5.9

386

19.7

n/a

n/a

n/a

n/a

June,

1998

Org

anic

amen

dm

ent

2.8∗∗

6.8∗∗

351∗∗

95.0

∗4,

782∗∗

133∗∗

87.6

∗13

.0∗

17.9

21.1

∗N

oorg

anic

amen

dm

ent

0.9

6.4

44.0

47.0

792

62.0

33.0

4.1

17.5

3.0

June,

1999

Org

anic

amen

dm

ent

2.8∗∗

6.3∗∗

447∗∗

37.0

∗3,

083∗∗

91.0

∗∗69

.4∗∗

28.6

∗∗15

.0∗∗

21.9

∗∗N

oorg

anic

amen

dm

ent

0.8

5.9

50.0

26.0

338

31.0

17.2

5.9

6.7

2.5

June,

2000

Org

anic

amen

dm

ent

2.3∗∗

6.6∗∗

169∗∗

24.0

∗1,

637∗∗

115∗∗

58.9

∗9.

1∗∗5.

930

.0∗∗

No

org

anic

amen

dm

ent

0.8

6.1

40.0

18.0

231

26.0

42.5

3.4

4.8

3.2

June,

2001

Org

anic

amen

dm

ent

2.8∗∗

7.0

342∗∗

31.7

2313

∗∗19

4∗50

.311

.3∗∗

5.8

32.1

∗∗N

oorg

anic

amen

dm

ent

0.9

7.0

30.0

29.8

633

126

32.4

4.0

6.7∗

4.7

z∗∗

Sign

ifica

ntat

p≤

0.01

,w

ithin

each

year

.∗ S

ignifi

cantat

p<

0.05

with

inea

chye

ar.

yn/a:

Notan

alyz

ed.

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252 M. Ozores-Hampton et al.

TABLE 5 Influence of Long-term Organic Amendment (1993–1999) in Soil Organic Matter(OM) Content, pH and Phosphorus at Different Depths in Soil Samples in 1999

Organic amendment No organic amendment

Depth (cm) OM (%) pH P (mg.kg)−1 OM (%) pH P (mg.kg)−1

0–15 2.3a∗ 6.3a∗ 113a∗ 0.7a 6.0a 49a15–30 1.4a 6.2a 101a 0.6a 6.4a 57a30–45 0.14b 5.8a 39b 0.29b 6.0ab 29a45–60 0.05b 6.1a 17b 0.05ab 5.9bc 15a60–75 0.14b 5.6a 23b 0.05b 5.3c 17a75–90 0.19b 6.1a 43b 0.14b 5.9bc 29a

∗Significant differences between amended and no amended soils at p ≤ 0.05.Means in columns by depths (a,b) with different letter are significantly different by Duncan’s MultipleRange Test (p ≤ 0.05).

of amended soil and there were no differences in OM among soils at deeperdepths. Soil pH was higher in the top 15 cm of the amended soil than non-amended soil. No differences in soil pH were observed between amendedand non-amended soil at deeper depths. Application of organic amendmentsto soil did not affect soil pH at any depths. No amended plots had a highersoil pH in the first 45 cm of soil than deeper soil depths. For amended soil,no differences were detected in soil pH among depths. A strong coefficientof determination (R2 = 0.90) was found between soil P and OM contentover all depths.

Soil Physical Properties

Long-term application of organic amendments reduced soil bulk densitycompared with no amendment (Table 6). Arshad et al., 1996, reported simi-lar results with organic amendment application decreasing the bulk densityof the soil to an ideal range of less than 1.6 g/cm3. Bulk densities abovethresholds of 1.8 g/cm3 in sandy soil are an indicator of low soil porosityand compaction (USDA, 2008). High bulk density impaired function suchas restricted root growth and poor movement of air and water throughthe soil (USDA, 2008). Compaction under humid conditions can result in

TABLE 6 Influence of Long-term Organic Amendments on Soil Cation Exchange(CEC) Capacity and Bulk Density during 2002 Season

Parameter Bulk density (g.cm)−1 CEC (meq/100g)

Organic amendment 1.4 14.8∗No organic amendment 1.6∗∗ 6.1

∗Significant at p < 0.01.∗∗Significant at p < 0.05.

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Long-Term Organic Amendments in Sandy Soil 253

Soil Water Tension (-kPa)

0 5 10 15 20 25 30 35

Soil

Wate

r conte

nt by v

olu

me

(%

)

0

10

20

30

40

50

Organic Amendment

Non-organic Amendment

FIGURE 1 Effects of long-term organic amendments (1993–2002) in water retention (satura-tion to field capacity) in samples taken on February 2002.

shallow plant rooting and poor plant growth, influencing crop yield. Also,bulk density gives useful information in assessing the potential for leachingof nutrients and erosion. Runoff and erosion losses of soil and nutrients canbe caused by excessive bulk density when surface water is restricted frommoving through the soil (Evanylo and McGuinn, 2000).

At saturation (0 kPa) the organic amended treatment had higher watercontent than non-organic amendments plots (Figure 1). There were nodifferences between amended and non-amended treatments moisture con-tent during soil drainage −2 to −5 kPa (P ≥ 0.47). Organic amendmentsincreased significantly the soil moisture at field capacity between −8 kPa to−30 kPa by 35% (p ≤ 0.0002). In general, OM physically holds more waterthan mineral soil components such as sand, clay and silt; thus, increasing asoil’s OM content increases its AWHC (Evanylo and McGuinn, 2000). Similarresults were reported in a soil quality study when they compared compostedcotton gin trash and inorganic fertilizer application; the composted materialin this case was a very stabilized organic material which increased fieldmoisture retention by 50% than inorganic fertilizer (Evanylo and McGuinn,2000). In Florida, application of 327 Mg. ha−1 of MSW compost increasedthe soil water-holding capacity by 43% (McConnell et al., 1993). The increasein AWHC in sandy soils by increasing soil OM content is attributed to theimprovement in pore size distribution (Shiralipour, 1998). For Florida veg-etable growers the easiest way to modify sandy soils physical propertiessuch as bulk density and AWHC is by the addition of organic amendmentsusing appropriate soil management techniques.

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254 M. Ozores-Hampton et al.

Soil Biological Properties

The total number of heterotrophic aerobic, anaerobic bacteria, actino-mycetes, pseudomonads were increased by long-term organic amendmentapplication (Table 7). But, there were no differences in the number of fungiand N fixing bacteria between the organic amended and non-amended soils.

The soil total SRD was increased by long-term organic amendmentapplication for four of the six functional groups tested (Table 7). Thelargest increases were SRD for fungi and actinomycetes. The overall TSRDof long-term organic amendment application was significantly improved ascompared to no organic amended indicating the beneficial effects of additionof C to sandy soils.

Similar results were obtained in a study comparing traditional fertil-izer application and ten years of compost application in Canada (Warman,1998; Warman and Harvard, 1996). The study indicated that soil C, Ca, Mgand Zn content were similar or higher in plots with compost applicationthan non-composted plots, but P and K soil content were higher in tradi-tional fertilizer plots (Warman, 1998; Warman and Harvard, 1996). A 6-yearstudy in an orange (Citrus sinensis L.) orchard organically managed resultedin higher total C and N as compared to the inorganic fertilizer managedorchard (Canali et al., 2004). Other study with seven-year application ofMSW compost, sewage sludge, farmyard manure at three rates (25, 50 and100 Mg.ha−1) and one inorganic fertilizer in irrigated wheat–corn rotationresulted in a increased CEC, SOC (soluble organic C) and OM (Hemmatet al., 2010). Application of manure or compost increased the CEC of thesoil by increasing the soil OM content and soil C content (Guibert, 1999).The effect was probably due to the increased of the fine fraction of thesoil C content (Guibert, 1999). Normally, soil Al and Fe can fix P as verycomplex and insoluble forms in acid soil conditions. The addition of OMneutralizes the reactions sites that could fix soil P. Organic lignin has anaffinity for Al and Fe in the soil inhibiting the soil from fixing P. Thefree P can be combined to form OM-P complexes, and then the P canbe slowly released by microbial action into the soil (Brady, 1974). Eventhough sandy soils are less variable in their degree of compaction than finertexture soils, the surface layer (15 cm) is more subjected to compaction.When composted biosolids and beef manure were applied to soils thebulk density was reduced significantly as compared to inorganic fertilizerapplication (Tester, 1990). Other studies in Florida with sandy soils usingMSW compost increased the AWHC significantly creating substantial waterused efficiency (McConnell et al., 1993; Gallaher and McSorley, 1994). Therewere no differences in number of soil fungi between the organic amendedand no amended treatments. These organisms are important for breaking

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TAB

LE7

Effec

tsof

long-

term

Org

anic

Am

endm

ents

inTo

tal

Num

ber

of

Mic

roorg

anis

ms

and

Spec

ies

Ric

hnes

sD

iver

sity

during

the

2002

Seas

on

Tre

atm

ent

Het

erotrophic

aero

bic

bac

teria

Anae

robic

bac

teria

Fungi

Act

inom

ycet

esPse

udom

onad

sN

itroge

n-fi

xing

bac

teria

TSR

Dz

Enum

erat

ion

Colo

ny

Form

ing

Units

/gr

amdry

wei

ghtsa

mple

(CFU

/gd

w)

Org

anic

amen

dm

ent

5.2

×10

7∗

4.0

×10

7∗

10×

105

8.7

×10

3∗

2.4

×10

6∗

2.5

×10

6

Non-o

rgan

icam

endm

ent

1.2

×10

78.

1×

106

10×

105

2.3

×10

31.

1×

106

1.6

×10

6

Spec

ies

rich

nes

sdiv

ersi

ty(S

RD

)O

rgan

icam

endm

ent

2.9

1.4

2.5∗

0.8∗

2.1

0.8∗

10.6

∗N

on-o

rgan

icam

endm

ent

3.0

1.4

1.9

0.4

2.1

0.6

9.3

∗ p<

0.05

.∗∗

p<

0.01

.z T

ota

lsp

ecie

srich

nes

sdiv

ersi

ty.

255

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256 M. Ozores-Hampton et al.

down more complex organic compounds, stabilizing soil aggregates, andcontrolling diseases (Grobe, 1998). Tree and vine crop growers were ableto increase the soil fungal number and diversity by the application of YTcompost and cardboard feedstocks, therefore enhancing nutrient uptake,disease suppression, and drought tolerance (Grobe, 1998). Actinomycetesare important in the nutrient cycling of chemical substances such as chitinand cellulose, improving soil crumb structure, and assisting in the reductionof plant pathogen pressures (Perucci, 1992). Pseudomonads are importantin nutrient cycling, assisting plants with P availability, and in the biologi-cal control of plant pathogens (Broadbent and Barker, 1974). The beneficialspecies of pseudomonads were higher and plant pathogenic oomycete fungi(Phythium and Phytophthora spp.) were lower in an organic production sys-tem than in chemically fertilized soils (Broadbent and Barker, 1974). Theseeffects can be observed within a single season when organic amendmentssuch as are incorporated in the organic system (Broadbent and Barker,1974). Populations of free-living nitrogen-fixing bacteria will increase asthe available N in the soil decreases (Perucci, 1992). In our study organicamendments improved TSRD dramatically indicating the beneficial effects ofaddition of organic amendments to sandy soils. Increased soil total microbialactivity or TSRD by the addition of organic amendments has been widelydocumented (Grobe, 1998; Serra-Wittling et al; Perucci, 1992; Press et al.,1996). The adoption organic amendments by the vegetables industry willhave the potential to create pathogen suppressive soil by improving soilquality (Hoitink et al., 1986 and 1997). In general soil borne diseases developin highly mineralized soils deficient in OM (readily biodegradable OM)since these soils do not support the activity of microflora to suppress soilpathogens (Hointink et al., 1986 and 1997). The goal for a vegetable groweris to shift the microorganism community in the low productive areas towardsthe same number and diversity present in high-yield-soils (Hointink, et al.,1997).

Long-term application of organic amendments can improve physical,chemical, and biological properties of soils by increasing soil OM, C, pH,Mehlich 1-extractable P, K, Ca, Mg, Mn, Cu, Fe, and Zn concentrations, CEC,AWHC and by increasing overall soil microbial activity, and decreasing bulkdensity.

ACKNOWLEDGMENTS

This research was supported in part by USDA - CSREES Regional IPM GrantNo 39109813.

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Long-Term Organic Amendments in Sandy Soil 257

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