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www.elsevier.com/locate/jnlabr/yjare

Journal of

Arid

EnvironmentsJournal of Arid Environments 58 (2004) 1942

Effects of surface-applied biosolids on grass

seedling emergence in the Chihuahuan desert

Joanna M. Hahm, David B. Wester*

Department of Range, Wildlife, and Fisheries Management, Texas Tech University,Lubbock, TX 79409, USA

Received 9 December 2002; accepted 9 July 2003

Abstract

Plant establishment in semi-arid rangelands is difficult because of low, unpredictable

soil water and extreme soil temperatures. In these rangelands, biosolids disposal is

limited to topical application; resulting soil coverage ameliorates microenvironmental

conditions and may affect plant establishment. We investigated biosolids effects on soilwater, soil temperature, and seedling emergence and growth of blue grama (Bouteloua gracilis)

and green sprangletop (Leptochloa dubia) in a Chihuahuan desert grassland. Greenhouse

and field experiments were conducted for 2 years. Biosolids did not affect mean soil

temperature (at seed depth) but usually increased minimum and reduced maximum

temperatures. Biosolids generally reduced soil water loss. These benefits may be insufficient

under harsh conditions to promote seedling establishment, and unnecessary under favorable

conditions. Under intermediate conditions, seedling establishment may be enhanced by

biosolids application.

r 2003 Elsevier Ltd. All rights reserved.

Keywords: Biosolids; Blue grama; Green sprangletop; Revegetation; Seedling emergence

1. Introduction

Arid and semi-arid rangelands are characterized by unpredictable and often

unfavorable environmental conditions that limit the opportunity for seedling

emergence and establishment. Soil water is generally the most limiting factor

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*Corresponding author.

E-mail address: [email protected] (D.B. Wester).

0140-1963/$ - see front matterr 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0140-1963(03)00124-1


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affecting seeding success (e.g., Wester et al., 1986; Dwyer and Aguirre, 1987;

Vallentine, 1989). Successful seedling establishment is influenced by total

moisture received as well as the pattern in which moisture occurs (Wester et al.,

1986;Frasier et al., 1987;Wester, 1995, pp. 168-238). Natural plant regeneration inmost semi-arid areas occurs only every 57 years (or less often) when 2 or

more successive favorable moisture years occur (Dahl and Cotter, 1986); even

during seasons when precipitation is highest, probabilities of receiving rainfall in

patterns and amounts conducive to successful germination and emergence

are often less than 20% (Heermann et al., 1971; Wester, 1979). Additionally,

extreme temperatures can reduce emergence even when soil water conditions

are favorable (e.g., Sosebee and Herbel, 1969; Jordan and Haferkamp, 1989).

Cultural practices that improve chances of seeding success include proper seedbed

preparation, application of protective mulches, and supplemental irrigation

(Vallentine, 1989). These practices, however, are usually cost-prohibitive for

rangelands.

Biosolids are a by-product of wastewater treatment. Approximately

6.9 million dry metric tons of municipal biosolids were produced in 1998

in the US, of which 41% was land applied (USEPA, 1999). It is estimated

that biosolids production and land application will increase to 8.2 million dry

metric tons and 48%, respectively, by the year 2010 (USEPA, 1999). Land

application is common in mined land reclamation (e.g., Sopper, 1993; Daniels and

Haering, 1994, pp. 105-121), agronomic settings (e.g., Luttrick et al., 1982;USEPA,

1989; Lerch et al., 1990a, b; Clapp et al., 1994, pp.137-148), and forests (e.g.,Brockway, 1983; Hart and Nguyen, 1994; Henry and Cole, 1994), where

considerable information has been collected to show beneficial effects on plants

and soils. Research on the effects of biosolids on native rangeland vegetation

(e.g., Fresquez et al., 1990a, b; Aguilar et al., 1994a, pp. 211-220, b; Benton and

Wester, 1998;Yan et al., 2000;Jurado and Wester, 2001) has dealt exclusively with

mature plants.

There is little information on the effects of biosolids on seedling emergence

and seedling growth. Composts and manures may release acetic acid, phenols,

ammonia and other organic compounds at phytotoxic levels early in the

decomposition process (Zucconi et al., 1985, pp. 73-86; Ozores-Hampton et al.,1999; Liebman, 2000, pp. 26-31), resulting in reduced seed germination.

However, Al-Jaloud (1999) found no effects of biosolids applied at rates

of 075 Mg ha1 on sorghum [Sorghum bicolor (L.) Moench.] seed germination

in a pot study. Preliminary petri dish laboratory experiments have shown

that biosolids did not affect blue grama seed germination (Wester, unpubl.

data).

The seedling stage in a plants life cycle is critical both to the individual plant as

well as to vegetation dynamics. Long-term improvement in degraded rangelands

begins with successful establishment of desired species. This research was conducted

to document effects of topically applied biosolids on soil water, soil temperature, andseedling emergence and growth of two native Chihuahuan desert grasses in

greenhouse and field settings.

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2. Materials and methods

Greenhouse and field experiments were conducted on the Sierra Blanca Ranch,

10 km north of Sierra Blanca, Texas (Hudspeth Co.). The Natural ResourceConservation Service (NRCS) has not published a soil survey for Hudspeth Co. Soils

included in this study have been provisionally classified as Jal and Armesa

taxadjunct fine sandy loams on a Loamy Range site (B.L. Allen, pers. comm.; also

see Wester et al., 1993). The Jal taxadjunct is classified as a fine-loamy, carbonic,

thermic Ustollic Calciorthid; it is deep; well-drained and occurs on 01% slopes. The

surface horizon, extending to 15 cm, is a fine sandy loam. The Armesa taxadjunct is a

fine, loamy, mixed, thermic Ustic Haplocalcid; it is deep, well-drained, and occurs on

01% slopes. The surface horizon, extending to 14 cm, is a fine sandy loam. Blue

grama [Bouteloua gracilis (H.B.K.) Lag. ex Steud.] is a dominant grass of the site,

and thus blue grama seeds would be expected in the soil seed bank. Green

sprangletop [Leptochloa dubia(H.B.K.) Nees] is adapted to the general area but does

not occur at the field study site and thus would not be expected in the seed bank. In

order to separate germination of seeds from the soil seed bank from germination of

seeds that were planted, we used both blue grama and green sprangletop in

greenhouse and field trials. Additionally, seeds were planted using a template to

control planting location. Results showed little emergence of seeds attributable to the

native seed bank.

2.1. Greenhouse experiment

Greenhouse pots (28 cm wide, 30 cm deep) were filled with air-dried soil collected

from the top 10 cm of an Armesa soil. Pots were placed on benches in a greenhouse

at the Texas Tech University Research Facilities on Sierra Blanca Ranch in late May

1998. Blue grama and green sprangletop seeds were purchased from Bamert Seed Co.

(Muleshoe, Texas). Germination rates were 86% and 85% for blue grama and green

sprangletop, respectively. Twelve seeds of either blue grama or green sprangletop

were planted at a 6-mm depth in each pot. Fresh biosolids were weighed to the

nearest 0.01 g and hand applied to pots at rates equivalent to 0 or 34 Mg ha1.

Biosolids samples were frozen and shipped to the Soil, Water, and Air TestingLaboratory at New Mexico State University for compositional analysis. All pots

were provided with 13 mm of water in the late afternoon for 7 consecutive days,

followed by 1 day without irrigation, 1 day with 6.4 mm of water, 4 consecutive days

with 26 mm of water, and then 6.4 mm every other day for approximately 1 month.

Seedling emergence was recorded daily. Soil water at 5- and 15-cm depths in each pot

was measured with time domain reflectometry (TDR). Seedlings in pots were

harvested at ages of 2 or 4 weeks. Roots were extracted with a low-volume water

flow, and maximum length of roots and shoots were measured to the nearest 0.25 cm.

Roots were then frozen and transported to the USDA Agriculture Research Service

Cropping Systems Research Laboratory in Lubbock, Texas, where total root lengthwas measured in 00.5; 0.51.0; 1.01.5; 1.52.0; and 2.02.5-mm diameter size

classes using McRhizo software (Regent Instrument Co., Quebec).

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2.2. Field experiments

Five field experiments were conducted in 1997 and 1998 on an area dominated by

Jal and Armesa soils. For each experiment, a randomized block design was used with10 blocks. Experimental units within each block were 0.09-m2 plots of undisturbed

bare ground. A factorial combination of biosolids (0 or 34 Mg ha1) and irrigation

(0, 6.4, or 19 mm of water) treatments was randomly assigned to plots within each

block for each species and each planting date. Sixteen seeds were hand-planted at a

depth of 6 mm in each plot. Immediately after planting, biosolids were applied,

followed by irrigation. Plots were irrigated for 3 consecutive days and then every

other day for 3 irrigations; after this period, plots received only natural rainfall.

Emergence that occurred during the irrigation period will be referred to as initial

emergence. Because there was no emergence in June 1998 and July 1998, irrigation

treatments were repeated in these plots in August; emergence that occurred at this

time will be referred to as follow-up emergence.

Soil temperature, seedling emergence, and seedling survival were

monitored throughout each experiment. Rainfall was monitored with an on-site

rain gauge.

Soil water was also monitored in 1998 field experiments. Each emerged seedling

was marked with a colored pin (different color each day) and emergence, wilting day,

and survival were recorded. Afternoon soil surface temperature was measured in

1997 using an Atkins digital thermometer. Soil temperature data in 1998 were

collected with a Stow-Away XTI data logger, using a thermistor at a 6-mm depth(seed depth). Soil water at a 05-cm depth was recorded with TDR. At shallow

depths and/or in dry soils, soil water measurements with TDR technology may be

inaccurate. Under these conditions, measured soil water will typically be slightly

higher than actual soil water. In this research, however, our interest was in the effect

of biosolids on soil water. Thus, even if measured soil water was higher than actual

amounts, differences in soil water were accurately measured, and are attributed to

the biosolids effect.

2.3. Statistical analyses

Greenhouse root and shoot length data were analyzed as a completely randomized

design with two treatments (0 or 34 Mg ha1 of biosolids) and 10 replications (pots)

for each seedling age and species combination. Normality of experimental errors was

tested with theShapiro and Wilk (1965)test.Levenes (1960, pp. 278-292)test was

used to test for homogeneous variances. Soil water and seedling emergence data were

analyzed with a repeated measures analysis of a completely randomized design.

Mauchlys (1940) test was used to test for sphericity. Sphericity was violated

for soil water and seedling emergence data; individual error terms were calculated

for mean separation, with Satterthwaites approximation for degrees of freedom

(Kirk, 1995).Each field experiment was analyzed as a randomized block design with 2 bio-

solids treatments and 3 irrigation treatments in a factorial combination for each

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Table 1

Chemical analyses of biosolids applied in 1997 and 1998. Data are means (standard deviation)

Constituent Date of biosolids application

1997 1998

May 6 July 16 Aug 19 April 23 June 4

(n 5) (n 4) (n 5) (n 5) (n 5)

P (%) 1.98 (0.07) 2.12 (0.07) 1.80 (0.36) 1.79 (0.06) 2.06 (0.06)

K (%) 0.14 (0.007) 0.12 (0.021) 0.10 (0.012) 0.13 ( 0.004) 0.15 (0.008)

Ca (%) 2.38 (0.06) 2.67 (0.25) 2.03 (0.33) 2.48 (0.054) 2.37 (0.047)

Mg (%) 0.70 (0.035) 0.67 (0.018) 0.57 (0.127) 0.98 (0.43) 0.54 (0.021)

S (%) 1.12 (0.03) 1.30 (0.07) 1.14 (0.14) 1.46 (0.047) 1.37 (0.019)

Na (%) 0.11 (0.006) 0.10 (0.006) 0.07 (0.014) 0.31 (0.055) 0.17 (0.004) Zn (mg kg1) 974 (36) 1148 (15) 1121 (216) 1075 (26) 972 (26)

B (mgkg1) 17.4 (0.55) 21.2 (1.30) 21.8 (0.96) 17.0 (0.71) 10.6 (0.55)

Fe (mgkg1) 67338 (3384) 24240 (551) 24920 (3563) 29176 (911) 24516 (1325)

Mn (mg kg1) 661 (21) 460 (8) 307 (55) 213 (6) 2229 (49)

Cu (mg kg1) 910 (448) 1142 (30) 1085 (170) 839 (21) 872 (11)

Al (mgkg1) 8885 (280) 8948 (217) 8133 (879) 10934 (566) 8286 (229)

EC (dS m1) 7.75 (1.44) 5.41 (0.51) 5.38 (0.59) 16.82 (2.40) 15.85 (0.43)

TKN (%) 4.04 (0.26) 2.60 (0.29) 2.40 (0.12) 4.06 (0.11) 5.52 (0.59)

Ni (mgkg1) 30 (0.84) 20 (0.0) 20 (0.0) 44.82 (1.83) 31.58 (1.66)

Cd (mg kg1) 2.20 (0.31) 8.64 (0.39) 3.80 (0.23)

Pb (mg kg1) 223 (7.4) 236 (6.2) 241 (36.4) 387 (25.9) 228 (9.46)

NH4a (mg kg1) 3965 (88) 7968 (344) 6644 (314) 4623 (211) 6729 (135)

aBy KCL extract.


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species. Normality was tested with theShapiro and Wilk (1965)test.Tukeys (1949)

test was used to test for block x treatment interaction. Mauchlys (1940) test

was used to test for sphericity. Significant effects were declared at the 5% significance

level.

3. Results

3.1. Greenhouse experiment

3.1.1. Biosolids composition

Chemical composition of biosolids is shown in Table 1. Biosolids used in this

study were similar in composition to material used byBenton and Wester (1998)andJurado and Wester (2001).

3.1.2. Soil water

Soil was air-dry at the beginning of the experiment. The addition of 13 mm of

water for 7 consecutive days (2329 May) increased soil water at 5- and 15-cm depths

despite daily evaporative losses. Soil water at a 5-cm depth was higher in biosolids-

treated pots on 2 of the first 4 days after the beginning of watering, and also during a

10-day period after the addition of 26 mm for 4 consecutive days (Fig. 1). Soil water

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of municipal biosolids at a soil depth of 5 cm in the afternoon. Bars and left y-axis indicate millimeters of

irrigation. Treatment means with open symbols on the same date are significantly different (po0:05).



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at a 15-cm depth was not affected by biosolids treatment throughout the duration of

the experiment.

3.1.3. Seedling emergence

Blue grama and green sprangletop seedlings began to emerge in biosolids-treated

pots after 6 consecutive days of irrigation at 13 mm day1 and emergence continued

to increase throughout the trial (Fig. 2). Blue grama seedlings did not emerge in

untreated pots until 3 consecutive days of irrigation at 26 mm day1 were provided.

Similarly, little green sprangletop emergence in untreated pots was observed until

irrigation was increased to 26 mm day1. Although emergence began sooner in

biosolids-treated pots than in untreated pots, total emergence at the end of the trial

was not affected by treatment.

3.1.4. Seedling size

Biosolids treatment did not affect blue grama maximum root, shoot, or total plant

length of 2- or 4-week old seedlings (Table 2). Additionally, biosolids did not affect

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treated with 0 (control) or 34 (biosolids) Mg ha1 of municipal biosolids. Bars and left y-axis indicate

irrigation rate at the given date. Treatment means for a species on the same date with open symbols are

significantly different (po0:05).



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blue grama total root length or root length categorized by root diameter, regardlessof seedling age. Green sprangletop maximum root length and total plant length of 4-

week old seedlings were greater in untreated pots. In addition, total root length and

root length in the 01.0-mm diameter classes were greater in 4-week old seedlings in

untreated pots.

3.2. Field experiments

3.2.1. Environmental conditions

Rainfall varied in frequency and amount during the 5 field experiments [see Hahm

(2000) for daily rainfall data]. Some plantings were followed by relatively harshconditions and other plantings were followed by relatively favorable conditions for

seedling emergence. Results below are presented in an order of harshest to most

favorable with respect to seedling emergence.

3.2.2. Planting date: June 1998

Field plots were seeded on 4 June and irrigation commenced immediately

thereafter. Biosolids had no effect on soil water in nonirrigated plots except on 10

June when 10 mm of rain occurred (Fig. 3a). Soil water was generally higher in

biosolids-treated plots that were irrigated (Fig. 3b and c). Daily mean soil

temperatures were similar between treated and control plots regardless of irrigation(Fig. 4). Daily minimum soil temperatures were generally higher (Fig. 5) and daily

maximum soil temperatures were generally lower (Fig. 6) in biosolids-treated plots.

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Table 2

Root, shoot, and plant length (cm) of 2- and 4-week old blue grama and green sprangletop seedlings in

greenhouse pots treated with 0 or 34 Mg ha1 of biosolids

Length (cm) Blue grama Green sprangletop

Plant age Plant age

Two weeks Four weeks Two weeks Four weeks

Biosolids Control Biosolids Control Biosolids Control Biosolids Control

Maximum root 20.46aa 22.53a 25.30a 26.45a 23.07a 25.97a 27.65a 33.20b

Maximum shoot 4.22a 3.28a 5.95a 4.05a 4.47a 4.43a 4.48a 5.40a

Total seedling 24.68a 25.81a 31.25a 30.50a 27.54a 30.40a 32.13a 38.60b

Root length in diameter class

00.5 mm 58.95a 66.70a 104.45a 91.12a 86.38a 129.62a 111.92a 209.00b0.51.0 mm 4.47a 4.00a 7.85a 8.02a 6.35a 12.41a 7.09a 15.82b

1.01.5 mm 0.37a 0.27a 2.50a 0.52a 0.46a 0.94a 1.25a 1.40a

1.52.0 mm 0.10a 0.08a 0.19a 0.12a 0.15a 0.02a 0.10a 0.18a

2.0-2.5 mm 0.08a 0.03a 0.00a 0.00a 0.11a 0.06a 0.00a 0.00a

Total 63.96a 71.08a 114.99a 99.78a 93.44a 143.03a 120.35a 226.40b

aBiosolids treatment means for a given length measurement within a species and a plant age followed by

different letters are significantly different (po0:05).



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Despite the biosolids effects on soil temperature and water, we observed no initial

seedling emergence of either species (Table 3) and little follow-up emergence of blue

grama occurred. However, about 3% follow-up emergence of green sprangletop

occurred in nonirrigated plots (Table 3).

3.2.3. Planting date: August 1997

Field plots were seeded on 19 August. On 20 August, rainfall provided 2.6 mm of

water; supplemental irrigation on these dates was applied to irrigated plots to equal

the prescribed irrigation totals of 19 and 6.4 mm. No additional rainfall wasobserved for the remainder of the month. Soil temperatures were generally not

affected by irrigation or biosolids treatment.

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biosolids and (a) 0, (b) 6.4, or (c) 19 mm of supplemental irrigation. Treatment means on the same date

with open symbols are significantly different (po0:05).



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Initial blue grama seedling emergence occurred only in plots that received 19 mm

of supplemental irrigation. We observed, however, only 2.5% emergence (Table 4).

Initial green sprangletop emergence averaged nearly 25% in plots irrigated with

19 mm; there was little emergence in other treatments. Biosolids did not affect

emergence of either species in August 1997.

During the two-day period between 11 and 13 September, 23 days after biosolids

application and 15 days after supplemental irrigation, over 35 mm of rainfall

occurred. Follow-up blue grama emergence was observed in nonirrigated plots and

in biosolids-treated plots that had received 6.4 mm of irrigation in August. Similarly,there was 15% green sprangletop emergence in nonirrigated plots and 10% follow-

up emergence in treated plots that had received 6.4 mm of irrigation in August.

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34Mgha1 of biosolids and (a) 0, (b) 6.4, or (c) 19 mm of supplemental irrigation.



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Follow-up emergence in September in August-planted plots thus was generally

inversely related to amount of supplemental irrigation provided in August (Table 4).

3.2.4. Planting date: July 1998

Field plots were seeded on 6 July; after field planting 18.5 mm of rainfall occurred.

No additional rainfall occurred until 17 and 19 July. Daily mean soil temperatures

were generally not affected by irrigation or biosolids treatment (Hahm, 2000).

However, irrigation and sampling date interacted in their effects on soil temperature:

irrigated plots had lower minimum soil temperatures than nonirrigated plots on 6 of

the first 10 days following biosolids application (Fig. 7a). Biosolids treatments andsampling date also interacted in their effects on soil temperature (Fig. 7b). Biosolids

treatment increased minimum soil temperature on 12 days during July; however,

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Fig. 5. Daily minimum soil temperature in June 1998 (at seed depth) plots treated with 0 (control) or

34Mgha1 of biosolids and (a) 0, (b) 6.4, or (c) 19 mm of supplemental irrigation.



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differences followed no apparent trend. Neither irrigation nor biosolids affected

daily maximum soil temperatures in July 1998. Biosolids did not affect soil water in

nonirrigated plots (Fig. 8a). However, soil water was often higher in biosolids-

treated plots that were irrigated (Fig. 8b and c).

Initial seedling emergence during July 1998 was observed only in plots that were

irrigated with 19 mm and treated with biosolids (Table 5). Additionally, blue grama

follow-up emergence in August was less than 6% in irrigated plots. However, green

sprangletop follow-up emergence in August, responding to natural rainfall, wasgreater in biosolids-treated plots that had received no supplemental irrigation

in July.

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70

4-Jun

6-Jun

8-Jun

10-Jun

12-Jun

14-Jun

16-Jun

18-Jun

20-Jun

22-Jun

24-Jun

26-Jun

28-Jun

30-Jun

2-Jul

4-Jul

6-Jul

Temperature(C)

(b)

0

10

20

3040

50

60

70

4-Jun

6-Jun

8-Jun

10-Jun

12-Jun

14-Jun

16-Jun

18-Jun

20-Jun

22-Jun

24-Jun

26-Jun

28-Jun

30-Jun

2-Jul

4-Jul

6-Jul

Date

Temperatu

re(C)

Biosolids Control

(c)

Fig. 6. Daily maximum soil temperature in June 1998 (at seed depth) plots treated with 0 (control) or

34Mgha

1

of biosolids and (a) 0, (b) 6.4, or (c) 19 mm of supplemental irrigation.



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3.2.5. Planting date: July 1997

Field plots were seeded on 16 July. In addition to supplemental irrigation, 3

rainfall events totaling 25.3 mm occurred within 8 days of planting. Soil

temperatures ranged from 32

C to 51

C from 17 to 19 July, after which theydeclined until 25 July. Soil surface temperatures were not affected by irrigation and

were generally not affected by biosolids. Blue grama seedling emergence was greater

in irrigated than nonirrigated plots (Table 6). Additionally, green sprangletop

emergence was greater in plots irrigated with 19 mm than in plots irrigated with

6.4 mm of water. Biosolids did not affect emergence of either species on this planting

date.

3.2.6. Planting date: August 1998

Field plots were seeded on 3 August. Biosolids did not affect soil water in

nonirrigated plots (Fig. 9a). In contrast, soil water was usually higher in biosolids-treated plots on the day following supplemental irrigation (Fig. 9b and c). Biosolids

had little effect on daily mean soil temperatures (Fig. 10a), but often increased daily

ARTICLE IN PRESS

Table 3

Blue grama and green sprangletop seedling emergence (%) in June 1998 plots treated with 0 or 34 Mg ha1

of municipal biosolids and 0, 6.4, or 19 mm of supplemental irrigation

Species Emergence event Treatment Irrigation (mm)

0 6.4 19 Mean

Blue grama Initial Biosolids 0.00 0.00 0.00 0.00a

Control 0.00 0.00 0.00 0.00a

Mean 0.00aa 0.00a 0.00a

Follow-up Biosolids 0.00 0.00 3.13 1.04a

Control 0.00 2.50 2.50 1.67a

Mean 0.00a 1.25a 2.80a

Total Biosolids 0.00 0.00 3.13 1.04aControl 0.00 2.50 2.50 1.67a

Mean 0.00a 1.25a 2.80a

Green sprangletop Initial Biosolids 0.00 0.00 0.00 0.00a

Control 0.00 0.00 0.00 0.00a

Mean 0.00a 0.00a 0.00a


Control 5.63 2.50 1.88 3.33a

Mean 3.44a 1.88a 0.94a


Mean 3.44a 1.88a 0.94a

a Irrigation or treatment means for a species and an emergence event followed by different lower case

letters are significantly different (po0:05).



14/24

minimum temperatures (Fig. 10b) and reduced daily maximum temperatures

(Fig. 10c). We observed little green sprangletop and no blue grama emergence in

nonirrigated plots. Although species had significantly higher emergence in irrigatedplots, biosolids did not affect emergence of either species on this planting date

(Table 7).

4. Discussion

This research studied the effects of biosolids on seedling emergence. We measured

soil water and soil temperature as they were affected by biosolids. We did not

measure chemical properties of soils before and after biosolids application. Because

preliminary petri dish studies indicated that blue grama seed germination was notaffected by biosolids, we assumed that any effects of biosolids on seed germination

were manifested indirectly through effects on microenvironmental conditions and

ARTICLE IN PRESS

Table 4

Blue grama and green sprangletop seedling emergence (%) in August 1997 plots treated with 0 or

34Mgha1 of municipal biosolids and 0, 6.4, or 19 mm of supplemental irrigation


0 6.4 19 Mean


Control 0.00 0.00 2.50 0.83a

Mean 0.00aa 0.00a 2.50b


Control 1.25 0.00 0.00 0.42a

Mean 3.13a 0.94a 0.00b


Mean 3.13a 0.94a 2.50a


Control 0.00 0.00 26.87 8.96a

Mean 0.00a 1.56a 24.69b


Control 16.25 3.75 1.26 7.09a

Mean 15.63a 6.88b 1.88b


Mean 15.63a 8.43a 26.87b

a Irrigation or treatment means for a species and an emergence event followed by different lower case




15/24

not through direct effects, e.g., toxic effects that affect the germination process.

When we observed seedling emergence, whether in the greenhouse or the field

experiments, it was never lower in biosolids-treated plots than in nontreated

(control) plots. Therefore, we conclude that the relatively low seedling emergenceobserved in this study was not attributable to the presence of biosolids.

Increased soil water in biosolids-treated pots during the first 4 days of the

greenhouse trial was sufficient to allow seedling emergence. Seedlings did not

emerge, however, in untreated pots until irrigation was increased. Thus, soil water

conditions that were otherwise unfavorable were ameliorated with surface-applied

biosolids.

We found few effects of biosolids on seedling size. In our greenhouse trial, there

were never any differences in soil water between treated and control pots at a 15-cm

depth. However, soil water was lower in untreated pots at a 5-cm depth during the

first week of the trial, and for a 10-day period including weeks 2 and 3 of the trial.These differences may be responsible for increased maximum root lengths and total

root lengths of 4-week old green sprangletop seedlings in untreated pots. It has been

ARTICLE IN PRESS

10

14

18

22

26

6-Jul

8-Jul

10-Jul

12-Jul

14-Jul

16-Jul

18-Jul

20-Jul

22-Jul

24-Jul

26-Jul

28-Jul

30-Jul

1-Aug

3-Aug

Temperature(C)

0.0 mm 6.4 mm 19 mm

(a)

10

13

16

19

22

25

6

-Jul

8

-Jul

10

-Jul

12

-Jul

14

-Jul

16

-Jul

18

-Jul

20

-Jul

22

-Jul

24

-Jul

26

-Jul

28

-Jul

30

-Jul

1-Aug

3-Aug

Date

Temperature(C)

Biosolids Control

(b)

Fig. 7. Daily minimum soil temperature (at seed depth) in July 1998 plots (a) irrigated with 0, 6.4, or

19 mm of supplemental irrigation or (b) treated with 0 or 34 Mg ha1 of biosolids. Treatment means on a

same date with open symbols are significantly different (po0:05).



16/24

reported that water stress can affect root and leaf elongation differently ( Frensch,

1997) and root biomass.It was relatively easy to show biosolids effects on seedling emergence under the

controlled conditions of the greenhouse. However, these results may be of little

practical value if they cannot be applied to field situations. In field experiments, we

found that application of biosolids had a variable effect on seedling emergence. For

example, during the June 1998 planting (when environmental conditions

were the harshest), no emergence was observed even though soil water was

greater in biosolids-treated plots. During the August 1997 planting (when

conditions were harsh), emergence was recorded only in irrigated plots, and even

in these plots there was little emergence. Evidently, environmental conditions during

these experiments were so harsh that the beneficial effects of biosolids in moderatingsoil temperatures and conserving soil water were insufficient to improve seedling

emergence.

ARTICLE IN PRESS

0

10

20

30

40

50

6-Jul

7-Jul

8-Jul

9-Jul

10-Jul

11-Jul

12-Jul

13-Jul

14-Jul

15-Jul

16-Jul

17-Jul

18-Jul

19-Jul

20-Jul

21-JulIr

rigation(mm)

0510

15202530

SoilW

ater(%)

(a)

0

10

2030

4050

6-Jul

7-Jul

8-Jul

9-Jul

10-Jul

11-Jul

12-Jul

13-Jul

14-Jul

15-Jul

16-Jul

17-Jul

18-Jul

19-Jul

20-Jul

21-JulI

rrigation(mm)

05101520253035

S

oilWater(%)

(b)

(c)

0

10

20

30

40

50

6-Jul

7-Jul

8-Jul

9-Jul

10-Jul

11-Jul

12-Jul

13-Jul

14-Jul

15-Jul

16-Jul

17-Jul

18-Jul

19-Jul

20-Jul

21-Jul

Date

Irrigation(mm)

0510152025303540

SoilWater(%)

Irrigation Rain Biosolids Control

(c)

Fig. 8. Soil water (%) at 05cm depth in July 1998 plots treated with 0 (control) or 34 Mg ha1 of


with open symbols are significantly different (po0:05).



17/24

ARTICLE IN PRESS

Table 5

Blue grama and green sprangletop seedling emergence (%) in July 1998 plots treated with 0 or 34 Mg ha1



0 6.4 19 Mean

Blue grama Initial Biosolids 0.00aa 0.00a 2.50a 0.83

Control 0.00a 0.00a 0.00b 0.00

Mean 0.00 0.00 1.25

Follow-up Biosolids 8.75 3.75 4.38 5.63A

Control 0.63 5.60 1.25 2.49A

Mean 4.69Ab 4.68A 2.82A

Total Biosolids 8.75 3.75 6.87 6.46AControl 0.63 5.60 1.25 2.49A

Mean 4.69A 4.68A 4.06A

Green sprangletop Initial Biosolids 0.00a 0.00a 19.37a 6.46

Control 0.00a 0.00a 0.00b 0.00

Mean 0.00 0.00 9.69

Follow-up Biosolids 20.63a 13.13a 3.14a 12.30

Control 7.50b 7.50a 9.30a 8.10

Mean 14.06 10.31 6.20

Total Biosolids 20.63 13.13 22.50 18.75AControl 7.50 7.50 9.30 8.10B

Mean 14.06A 10.31A 15.9A

aTreatment means within a level of irrigation for a species and an emergence event followed by different

lower case letters are significantly different (po0:05).b Irrigation or treatment means for a species and an emergence event followed by different upper case


Table 6

Blue grama and green sprangletop seedling emergence (%) in July 1997 plots treated with 0 or 34 Mg ha

1



0 6.4 19 Mean


Control 0.00 1.25 5.00 2.08a

Mean 0.03aa 2.50b 4.07b


Control 0.00 5.625 26.88 10.84a

Mean 2.18a 8.44b 24.34ca Irrigation or treatment means for a species and emergence event followed by different lower case letters

are significantly different (po0:05).



18/24

Approximately 3 weeks after the August 1997 planting, over 35 mm of rain

occurred, and under these more favorable conditions seedlings emerged similarly in

treated and control plots. In July 1997, natural rainfall added to the supplemental

irrigation that was provided, and emergence was similar regardless of biosolids

treatment. Thus, under these relatively favorable environmental conditions, the

presence of biosolids did not enhance seedling emergence.

However, environmental conditions throughout the July 1998 planting were

neither as harsh as the conditions in June 1998 nor as benign as those in September1997. Irrigation was supplemented with natural rainfall, and under these conditions,

biosolids improved seedling emergence.

ARTICLE IN PRESS

0

10

20

30

40

50

3-Aug

4-Aug

5-Aug

6-Aug

7-Aug

8-Aug

9-Aug

10-Aug

11-Aug

12-Aug

13-Aug

14-Aug

15-Aug

Irrigation

(mm)

10

15

20

25

30

SoilWat

er(%)

(a)

0

10

2030

40

50

3-Aug

4-Aug

5-Aug

6-Aug

7-Aug

8-Aug

9-Aug

10-Aug

11-Aug

12-Aug

13-Aug

14-Aug

15-Aug

Irrigation

(mm)

10

15

2025

30

35

SoilWater(%)

(b)

0

10

20

30

40

50

3-Aug

4-Aug

5-Aug

6-Aug

7-Aug

8-Aug

9-Aug

10-Aug

11-Aug

12-Aug

13-Aug

14-Aug

15-Aug

Date

Irrigation(mm)

10

15

20

25

30

35

SoilWa

ter(%)

Irrigation Rain Biosolids Control(c)

Fig. 9. Soil water (%) at 05cm depth in August 1998 plots treated with 0 (control) or 34 Mg ha1 of


with open symbols are significantly different (po0:

05).



19/24

4.1. A conceptual model

These results can be combined with findings of Wester et al. (1986) to develop a

conceptual model of the effects of biosolids on seeding emergence. Components of

this model include the following considerations:

1. Under extremely harsh conditions, seedling emergence will not take place. Harsh

conditions may be caused by limited soil water or high soil temperatures. High

ARTICLE IN PRESS

10

15

20

25

30

35

3-Aug

7-Aug

11-Aug

15-Aug

19-Aug

23-Aug

27-Aug

31-Aug

4-Sep

8-Sep

12-Sep

16-Sep

Temperature(C)

Biosolids Control

(a)

(a)

10

14

18

22

26

3-Aug

7-Aug

11-Aug

15-Aug

19-Aug

23-Aug

27-Aug

31-Aug

4-Sep

8-Sep

12-Sep

16-Sep

Temperature(C)

Biosolids Control

(b)

152025303540455055

60

3-Aug

7-Aug

11-Aug

15-Aug

19-Aug

23-Aug

27-Aug

31-Aug

4-Sep

8-Sep

12-Sep

16-Sep

Date

Temperature(C

)

Biosolids Control

(c)

Fig. 10. Daily mean (a), minimum (b), and maximum (c) soil temperatures (at seed depth) in August 1998plots treated with 0 (control) or 34 Mg ha1 of biosolids. Mean and maximum temperatures are averaged

over 0 and 6.4 mm irrigation treatments; minimum temperatures are for the 6.4 mm irrigation treatment.



20/24

temperatures, even with adequate soil water, will be unfavorable for emergence

(Sosebee and Herbel, 1969;Wester, 1979;Mayer and Poljakoff-Mayber, 1989).

2. Under favorable conditions, seedling emergence takes place sooner and is greater

than under less favorable conditions. For example, Wester et al. (1986) showed

that at a 30C soil surface temperature, weeping lovegrass [Eragrostis curvula

(Schrad.) Nees]) seeds germinated two days after 2 consecutive days of water at5 mm per day and reached 63% emergence. In contrast, seeds germinating in

response to 1 application of 5 mm of water, followed by 2 dry days and then a

second application of 5 mm of water emerged 5 days after the start of irrigation

and reached only 37% emergence. Similar results were reported by Hahm (2000),

where blue grama and green sprangletop seedlings emerged 0.52.25 days sooner,

and 1 day sooner, respectively, in biosolids-treated plots provided with

supplemental irrigation than in nontreated plots.

3. Seedlings that emerge sooner tend to survive longer than seedlings that emerge

later.Wester et al. (1986)showed that at a 30C soil surface temperature, weeping

lovegrass seeds germinating in response to 2 consecutive days of water producedseedlings that emerged 2 days after the start of watering, and wilted about 4 days

after emergence. If additional rainfall occurred during this period, seedling

survival was lengthened accordingly. In contrast, seeds that germinated in

response to a single day of water (5 mm) followed by 2 dry days and then a second

day of water (5 mm) produced seedlings that emerged 5 days after the start of

watering; however, these seedlings wilted on their emergence day.

These considerations suggest a conceptual model illustrated in Fig. 11. In this

model, there is little or no emergence under extremely harsh environmental

conditions. Further, even though biosolids may reduce soil temperature extremesand soil water loss, these improvements may be inadequate to promote seedling

emergence. Under favorable environmental conditions, emergence takes place

ARTICLE IN PRESS

Table 7

Blue grama and green sprangletop seedling emergence (%) in August 1998 plots treated with 0 or

34Mgha1 of municipal biosolids and 0, 6.4, or 19 mm supplemental irrigation


0 6.4 19 Mean


Control 0.00 5.00 11.87 5.62a

Mean 0.00aa 4.69b 12.19c


Control 0.60 26.25 26.25 17.70a

Mean 0.92a 22.81b 23.12b

a Irrigation or treatment means for a species and emergence event followed by different lower case letters

are significantly different (po0:05).



21/24

relatively quickly and reaches a relatively high level followed by little mortality. In

these settings, untreated plots experience conditions similar to biosolids-treated

plots. However, when environmental conditions are only moderately favorable,

emergence is delayed and reduced and there is more mortality relative to favorable

conditions. In this setting, any effect that can ameliorate soil temperature extremes

and reduce soil water loss may have a beneficial effect on seeding success by

hastening emergence and prolonging conditions conducive for seedling survival. Wesuggest that under these conditions, topically applied biosolids may promote the

chances for seeding success.

5. Conclusions

Topically applied biosolids moderate soil surface temperature fluctuations. Daily

minimum temperatures can be increased and daily maximum temperatures can be

reduced by biosolids. Biosolids also reduce soil water loss through soil water

evaporative loss. Therefore, biosolids may ameliorate the often-harsh environmentalconditions experienced by seeds planted at shallow depths in arid and semi-arid

rangelands.

The effects of biosolids on seedling emergence depend on prevailing environmental

conditions. Extremely harsh conditions may prevent seedling emergence. Even with

supplemental irrigation, any beneficial effects that biosolids have on moderating soil

temperature and conserving soil water may be inadequate to overcome the

forbidding environment. In contrast, when environmental conditions are favorable,

emergence can take place even without the benefits provided by biosolids. However,

when environmental conditions are neither extremely unfavorable or extremely

favorable, the presence of surface-applied biosolids and the resulting reduction insoil water evaporation and moderation of soil temperature extremes may provide

conditions conducive for successful emergence.

ARTICLE IN PRESS

StandDensity

Time

Low

High

+

_

+

_

+

_

Benign

Intermediate

Harsh

Environmental

Conditions

Fig. 11. A conceptual model showing the effects of topical biosolids application (+) or nonapplication

(

) on plant establishment under benign, intermediate, or harsh environmental conditions.



22/24

When positive biosolids effects on extent of seedling emergence were observed,

these effects were usually modest. Although green sprangletop emergence in treated

and irrigated plots in July 1998 was 19% (compared to 0% in nontreated and

irrigated plots), differences due to biosolids treatments were usually much smaller.For example, blue grama emergence was 2.5% in treated-irrigated plots and 0% in

nontreated-irrigated plots in July 1998. It might be suggested that such small effects

are inconsequential. Perhaps more important than increasing the extent of seedling

emergence, however, biosolids may hasten the onset of seedling emergence. Seedlings

that emerge quickly in response to favorable conditions usually have an increased

chance for seedling success.

We have recorded perennial grass densities between 2 and 4 plants m2 in the

vicinity of the study area (Hahm and Wester, unpubl. data). In Chihuahuan desert

grasslands in southern New Mexico, Hennessy et al. (1983) reported densities of

dominant grasses [e.g., Sporobolus flexuosus (Thurb.) Rydb.] at 3 plants m2 or less;

forb densities ranged from 2.4 to 3.2 plants m2. Chihuahuan desert seed banks may

support over 1300 seed m2 representing 15 different species (Guo et al., 1999).

Although most seeds are associated with shrub canopies, many seeds occur in shrub

interspaces as well (Guo et al., 1998). If biosolids enhance the emergence and

establishment of only a small fraction of this potential seed bank, significant long-

term increases in plant density of degraded arid and semi-arid rangelands may be

expected to result from topical application of biosolids.

Acknowledgements

R.E. Sosebee, E.B. Fish, R.E Zartman, and N.W. Hopper contributed to various

aspects of this research. P. Jurado, R. Mata-Gonzalez, D. Burres, P.L. Cantrell, and

J. Dickensen provided assistance in the field. J. Hahm is currently Environmental

Technologist, Water and Wastewater Utility, City of Austin, TX. This research was

supported in part by MERCO, A Joint Venture, and the State of Texas. This is

publication T-9-934, College of Agricultural Sciences and Natural Resources, Texas

Tech University.

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