roe 93

c 1.

Compost Science & Utilization, (1993) Vol. 1, No. 3,73-84

Utilization Of MSW Compost And Other Organic Mulches On Commercial Vegetable Crops

Nancy E. Roe1, Peter J. Stoffella2, and Herbert H. Bryan3 1. Graduate Student, Horticultural Sciences Department, University of Florida,

Gainesville, Florida 2. Professor, Agricultural Research and Education Center, Ft. Pierce, Florida 3. Professor, Tropical Research and Education Center, Homestead, Florida

Increased availability of commercially derived composts and problems with disposal of polyethylene mulch are factors which precipitated an investigation of the long term effects of organic and polyethylene film mulches on soils, plant growth, and yields. Three experiments were performed comparing polyethylene film mulch (PM) with mulches of commercial municipal solid waste compost (MW), dried sewage sludge (SS) and wood chips (WC). In 1990, bell pepper (Capsicum annum L.) plants on PM yielded 8.9 t-ha-1, which was significantly higher than the 1.9,4.6, and 7.2 t*ha-l produced at MW compost rates of 13,40 and 121 t-ha-l, respectively. Yields increased linearly with increasing rates of compost mulch. In spring, 1992, each organic material was applied at 224 and 336 toha-1 and winter (spaghetti) squash (Cucurbita pepo L.) was seeded. Soil moisture was higher under organic mulches than under PM. Soil temperatures in the mornings were not significantly different among mulches, but in the afternoons: SS>PM>MW>WC. Plants grown on PM had larger shoots and roots and produced more fruit per plant, but, because of plant losses to disease, had lower total yields than plants grown in MW and WC. Higher soil Na content occurred in MW plots and high electrical conductivity (EC) occurred in soils of SS plots. In fall, 1992, bell peppers transplanted into the same plots produced 4.7, 4.5, 3.3, and 2.7 t0ha-l from PM, MW, WC, and SS, respectively. Soil tests detected higher NO,-N in WC plots, higher K in PM, higher Zn in MW, and lower Mn and higher Mg in SS plots, than in other treatments. Vegetables grown on PM produced higher fruit yields than those on organic mulches, however, plant losses to disease were also highest in PM plots. Environmental and economic considerations and governmental regulations may encourage organic mulch utilization by commercial vegetable growers.

Introduction

Mulches can reduce evaporation of water from the soil surface, suppress weed growth, restrict leaching of mineral nutrients, and moderate diurnal and seasonal temperature fluctuations of soil. Vegetable growers in Florida also use polyethylene film mulch as a protective sealant for fumigation. This production system has dramatical- ly increased the yields of some vegetable crops.

Polyethylene film mulch use by Florida agriculture is now estimated at more than 9.5 million kg annually (Servis, 1992). Disposal presents a constantly increasing problem and cost, both to growers and to the environment. Disposal costs in some areas of Florida have increased by as much as 30 percent in one year (Servis, 1992).

Large supplies of organic materials have been made available by Florida’s Sol- id Waste Act of 1988 (Chapter 88-130, Florida Statute). This Florida law mandates a 30 percent reduction in solid waste sent to landfills by 31 Dec. 1994, and prohibits disposal of yard trimmings in landfills after 1 Jan. 1992. Some of the woody materials are now chipped for mulches or nursery soil mixes. Other organic materials that were formerly landfilled are being composted, often on a large scale. In some areas, additional efforts to decrease landfill requirements have resulted in com-

Compost Science & Utilization Summer, 1993 73

Nancy E. Roe, Peter J. Stoffella, and Herbert H. Bryan

posting of municipal solid waste and/or sewage sludge. On sandy soils, organic matter can increase water holding capacity and cation ex-

change capacity; stabilize soil structure and increase permeability; add nutrients; and buffer changes in pH, micronutrients, and heavy metals (Bohn et. al., 1985). Composts have also reduced growth of plant pathogenic organisms such as Rhizoctonia solani on small grains (Chung et. al., 1988), Botrytis cinerea on lettuce (Lactuca sativa L.) (Dittmer et. al., 1990), and Phytophthora capsici on peppers (Lumsden et. al., 1982).

The problems associated with disposal of polyethylene film mulch, and the con- comitant availability of large amounts of composts present an opportunity to use organic materials as mulches for commercial vegetable crop production. Other investigations have generally compared unmulched controls (soil) to polyethylene film mulches or to organic mulches (Earhart et. al., 1992; Lal, 1974; Locascio and Fiskell, 1977). Our objective was to investigate the long term effects of polyethylene mulch and several organic mulches on soil properties, vegetable plant growth, and fruit yields.

Materials And Methods

Each experiment was conducted on a commercial bell pepper farm located in Boynton Beach, Florida. Soil type was a Myakka sand (sandy, siliceous, hyperthermic, Aeric Haplaquad). Beds were mechanically constructed 20 cm high, 92 cm wide, and were spaced 1.7 m apart, center to center. Each plot consisted of a single bed 9.1 m in length.

Total Kjeldahl N was determined for the MW compost used in 1990. The Bray I test was used for P determination. Potassium, Ca, and Mg were extracted in 1N NH4 ac- etate. Zinc, Fe, Mg, and Cu were extracted by DTPA-TEA. Sulfur was extracted by CaP04-500 ppm. Electrical conductivity (EC) was measured in 5:l (v/v) water:soil and pH in 1:l (v/v) water:soil solution,.

Extractions for the MW compost used in 1992 were done with a Morgan solution (Wolfe, 1992). Nitrogen, P, and S were determined by a Gilbert spectrophotometer. Calcium, K, Mg, Zn, Mn, Cu, and Fe were determined by atomic absorption. Electrical conductivity and pH were measured in a 2:l (v/v) water:soil solution.

Total Kjeldahl N was determined for the heat-dried sewage sludge used in 1992. Phosphorus was extracted manually by ascorbic acid. Nitric acid was used for K, Ca, Mg, Fe, Mn, S, Zn, and Cu (EPA Method 3050). The pH was measured in a 1:l (v/v) water:soil solution.

Electrical conductivity, N03-N, NH4-N, and pH of soil were measured in a 2:l (v/v) water:soil suspension. The Walkley-Black dichromate method was used to determine soil organic matter (OM) (Nelson and Sommers, 1982). Phosphorus, K, Ca, Mg, Fe, Mn, S, Zn, and Cu in soil were extracted by the Mehlich I method and analyzed by inductively coupled argon plasma spectroscopy (Hanlon et. al., 1990).

Data collected from each experiment were subjected to analyses of variance using SAS (SAS Institute, 1987). Main effects were partitioned into orthogonal contrasts, or means separated by Duncan’s multiple range test, 5 percent level.

Experiment 1.2990 Pepper crop. A mean of three soil samples taken from the experimental site contained (mgkg-1): 1293 Ca, 65.3 Mg, 25.6 K, 223.8 P, 8.1 Zn, 9.4 Cu, 27.8 Mn. Soil OM averaged 1.3 percent. A pre-plant fertilizer of 90N, 45P, and 15K (kgha- l) was broadcast before bedding. A band of 179N and 177K (kgha-l) fertilizer was applied in the center of each bed. Beds were fumigated with a 98 percent methyl bromide, 2 percent chloropicrin mixture at 202 kgha-l, then immediately covered by white polyethylene film (0.0318 mm thick) mulch (PM). The polyethylene film mulch was removed from the compost plots and compost was applied manually at 13,40, or 121

74 Compost Science & Utilization Summer, 1993

Utilization Of M S W Compost And Other Organic Mulches On Commercial Vegetable Crops

TABLE 1. Characteristics of municipal solid waste composts used in Expt. 1 (MW90), and Expt. 2 and 3

(MW92), and dried sewage sludge (SS) used in Expt. 2 and 3

pH ECZ N F K Ca Mg Fe Mn S Zn Cu Mulch ppm (dry wt) MW90 7.9 7.5 5100 433 1593 3750 342 353 121 317 158 93 MW92 8.2 2.5 7 47 532 2210 164 8 17 378 17 <I ss 7.1 NA 31,900 17,200 1100 149,500 5400 9500 6 13,700 1180 537

ZElectrical conductivity in mmh0s.cm-l

t0ha-l on 21 Aug., 1990. The compost was a commercial municipal solid waste compost from a facility in Pompano Beach, F1. (Table 1). Bell pepper, cv. Pr-893 seedlings, approximately 5 weeks old, were transplanted into the beds on 30 Aug., 30 cm apart within rows with 2 rows per bed spaced 45 cm apart. Plant population was equivalent to 39,120 plants/ha. A randomized complete block experimental design with treatments replicated 4 times was used.

On 19 Oct., soil samples were taken at 0-7.5 and 7.5-15 cm depth from each plot, weighed, dried at 70C for 10 days, and reweighed. Moisture content was calculated on a wet weight basis.

Peppers were harvested on 9 and 26 Nov. 1990, and 11 Jan. 1991, graded, counted, and weighed. Fruit sizes were 65 or fewer, 65-85,85-100, and 100 or more fruit per stan- dard 3.9 dekaliter box for extra-large, large, medium, and small, respectively.

Experiment 2.2992 Squash Crop. On 15 Jan. 1992, a previous commercial bell pepper crop in a different field was removed by mowing. Original beds, size and shape as previously described, were utilized. Sodium N-methyldithiocarbamate (Vapam) at 74 literha-l was injected into the beds using an injection wheel with openings at 30 cm. The white polyethylene film (0.0318 mm thick) mulch used for the previous bell pepper crop was left on the plots as a designated treatment, and was removed from each organic mulch plot. Organic mulches were applied manually at 224 and 336 t-ha-l rates on 14-17 Feb. 1992. Organic mulches were: a commercial municipal solid waste compost from Pembroke Pines, FL (MW); a powdered, dried sewage sludge product from Dade County, FL (SS) (Table 1); and wood chips, principally from Melaleucu quinquen- ervia, which had been piled and aged for about one year (WC).

Winter squash, cv 'Tivoli', was machine seeded on 19 Feb. in hills spaced 30 cm apart in the center of each bed, with 1 seed per bed. Plant population was equivalent to 19,562 plants/ha. A randomized complete block experimental design with treatments replicated 5 times was used.

Plant stands in each plot were recorded on 28 Feb., and 25 Mar., and expressed as a percentage of potential total stand.

Two plants per plot were excavated manually on 10 Mar. Shoots were severed at the soil surface, soil washed from root system, dried at 70C for 7 days, and weighed.

Three plants per plot were manually excavated on 23 Apr. Shoots were severed at the soil surface; soil was washed from the root system; roots were partitioned into taproot, which included lateral roots, and basal roots (roots from the root-shoot junction); and fresh weights were recorded. Soil samples were taken from 0-7.5 and 7.5-15 cm depth on 23 Apr., using a sampling tube with a bottom diameter of 5 cm and a top diameter of 7.5 cm. Soil samples were weighed, dried for 7 days at 70C, and reweighed. Soil moisture was determined on a wet weight basis. The 2 depths of samples for each location were combined and tested for Zn, Cu, Mn, Fe, Na content, and EC.

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Nancy E. Roe, Peter J. Stoffella, and Herbert H. B y u n

Squash was harvested on 17,23,24, and 27 Apr. from each 9.1 cm plot. In the first 3 harvests, marketable fruit was weighed and counted. The last harvest included some fruit which was damaged by insects, but was of marketable size.

Experiment 3.1992 Pepper Crop. Drip irrigation was installed in the identical plots used for Expt. 2, before planting bell peppers. One drip line (Netafim) was laid about 5 cm deep in the center of each bed. Emitters spaced at 45 cm delivered approximately 1.1 literhr-l. Two daily irrigations were used, with each supplying about 9,337 literha-l. Fertilizer, at 1.1N and 0.9K kg0ha-l was added through the irrigation system with each application. Polyethylene film was replaced in the polyethylene-mulched plots, but no additional mulch was added to the organic mulch plots.

Soil samples were taken on 24 Sqt. , and tested for pH, OM, EC, Ca, Mg, P, K, Zn, Cu, Mn, N03-N and NH4-N using the sampling and testing techniques previously described. Soil samples were air dried for 60 days before testing.

Bell pepper, cv. '32008', seedlings (4 weeks old) were transplanted on 6 Oct. 1992. Plants were spaced at 30 cm within rows, with 2 rows per bed, spaced 45 cm apart. Ex- perimental design and plot size was identical to Expt. 2. Plant population was equivalent to 39,120 plants/ha.

One plant from each plot was severed at the soil surface on 25 Nov. A 30 cm square wooden frame was then placed on the soil with the hypocotyl at the center. Mulch within the square was removed, and roots were strained from the mulch. Soil in the next 0-7.5 and 7.5-15 cm depths was similarly removed and roots were washed and separated from the soil. Fruit was removed from the shoots, shoots and roots were dried at 70C for 8 days, and weighed.

Plant stands in each plot were counted on 15 and 21 Jan., 1993, and expressed as the percentage of initial plant population. Peppers were harvested from a 6.1 m length of each plot on 28 Dec. 1992 and 15 Jan. 1993. Only U.S. Fancy (at least 7.5 cm diame-

TABLE 2. Soil conditions under white polyethylene film and organic mulches.

Mulch

Percent water (w/w) at soil depthsZ (cm) Mean temperaturesy (C)

0-7.5 7.5-15 Morning Midday Afternoon

PM 5.2 5.8 23.5 25.0 26.2 Organic mulches (ORM) MW 6.0 6.3 24.5 24.9 bX 26.1 b wc 6.1 6.5 26.5 24.1 c 24.6 c SS Rate(t*ha-I) (R) 224

6.5 6.4 24.7 25.8 a 27.7 a

6.1 6.3 336 6.3 6.5 F-test O R M x R Contrasts

NS NS . NS NS

NS NS NS ** ** PM vs ORM

NS,**Nonsignificant or significant at P=O.Ol zSoil moisture was sampled on 23 April YTemperatures were recorded from 17 April-18 June, 1992. Recording times were: morning 6-9 AM; midday 11 AM-I I'M; afternoon 4-7 PM XMean separation in columns by Duncan's multiple range test, 5 percent level


Utilization Of MSW Compost And Other Organic Mulches On Commercial Vegetable Crops

ter and 8.8 cm in length) and U.S. No. 1 (diameter and length greater than 6.25 cm) fruit were counted and weighed (Hochmuth, 1988).

Results and Discussion

Soil Effects The relatively low rates of compost used in Expt. 1 (13,40, and 121 t0ha-l) were not sufficient to cause significant differences in the soil moisture (data not shown). However, in Expt. 2, soil water content under all the organic mulches was significantly higher than under I'M at both depths (Table 2). La1 (1974) reported higher soil moisture under mulches of rice straw and forest litter. Munn (1992) reported increases in soil moisture under straw and shredded newspaper mulches on a silt loam soil early in a wet season, but no differences during a drier season. Both of these investigations, however, compared the mulches with unmulched soil, not with polyethylene film. Black polyethylene film mulch reduced water use more than compost or straw mulches, but compost mulch had the highest water use efficiency by basil (Palada et. al., 1992). The seepage and drip irrigation methods used in our experiments tend to maintain uniform soil moisture levels, unlike differences that may occur under an intermittent method of irrigation or under rainfall only.

Organic mulches usually moderate diurnal soil temperature fluctuations (Asghar et. al., 1987; Palada at al., 1992). Similar moderation in soil temperature fluctuations occurred under WC and MW mulches (Table 2). Soil temperatures did not differ significantly at the morning readings (Table 2). By midday, soil temperatures under the SS were highest among the organic mulches, followed by MW. Soil temperatures of I'M plots were not significantly different, but were lower than SS plots at all recording times. Af- ternoon temperatures varied in the same order as those at midday. Higher afternoon soil temperatures in the SS plots were probably a result of its black color, and lack of insu- lating value. In south Florida, white coated polyethylene film is used to reduce soil temperatures for crops planted in the late summer and early fall. Black polyethylene film can be used to increase soil temperature for winter-planted crops. Therefore, the benefits of moderation of temperature by organic mulches may depend on the planting season.

Soil element concentration taken during the squash harvest period resulted in few significant differences (Table 3). MW plots had significantly higher soil Na concentration than all other plots, followed by WC, and then SS. This was a result of the high (1000 ppm) Na concentration of the MW compost used in this experiment (data not shown). The SS plots, however, had higher EC than the other treatments. The major ions which contribute to high salinity of refuse composts, NO3-, HI'04-, H2PO4-, Na+, K+, Ca2+, and Mg2+ (Inbar et. al., 1993), are practically all present at relatively high rates in the SS material (Table 1). Iron concentration was also highest under SS mulch. Increased soil Fe concentration in SS and WC plots would probably be an asset in this soil, as Fe solubility can be reduced in high pH soils.

Higher K, Cu, and Mn concentration, and lower Zn, P, and NO3-N in soil of PM plots occurred when compared to the organic mulch plots, just before pepper transplanting (Table 4). Within the organic mulches, significant depth X mulch interaction for NO3-N indicated that NO3-N decreased with depth under MW and SS and in-

was highest in NO3-N, and SS had the most Mg and P, and the least Mn soil concentration. Differences in soil Ca and Cu concentration among treatments were less dis- tinct, and there were no significant differences in EC. Soil organic matter levels were similar among organic mulch and I'M treatments, because these organic materials were utilized as a bed cover, and not incorporated into the soil. No available NH4-N was found in any sample tested (data not shown).

creased under WC. Municipal waste compost plots had the highest pH, K, and Zn; WC ~

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Nancy E. Roe, Peter J. Stoffella, and Herbert H. B y a n

Soil pH at this test date was significantly raised by MW and lowered by the SS (Table 4). Conversion of soil NH4-N to NO,-N lowers pH. Since the SS material is highest in total N, there would be more conversion expected in those plots.

High Zn concentration can be a potential obstacle to agricultural use of municipal

centration than the one used in Expt. 1 (Table l), but the MW plots still had a higher Zn soil concentration than other treatments (Table 4). Cu concentration presents a potential toxicity problem both to plants and the consumers of the crop, especially due to the large amount of Cu fungicides used on many crops, but our soil tests indicated a lower Cu in organically mulched plots. Copper tends to bind with organic matter, so the mulches may have fixed Cu that was sprayed on the crops during the previous growing season, preventing it from moving into the soil. Mays and Giordano (1989) reported minimal movement of Cu into the soil past 30 cm deep, even 19 years after high application rates of a compost containing over 100 times more Cu than the prod- ucts utilized in these studies. When current municipal waste composts are compared to those made in the past 20 years, recycling programs and stricter environmental controls on industry have generally resulted in decreased heavy metal concentrations (Mays and Giordano, 1989). Although further reductions are essential, improved composts may allow for expansion of agricultural uses, with less danger to crops, consumers, and the environment.

Experiment 1: 1990 Pepper Crop. Significantly earlier pepper fruit production from PM plots occurred when compared to the compost mulches, however rate of compost did not significantly influence early yields (Table 5).

Total fruit yield from plants in PM plots was significantly higher than from pepper plants in the MW plots (Table 5). The significant linear relationship of total yields and mulch rates suggested that yields would continue to increase with higher rates of compost mulch. This prompted an increase in compost rates for our subsequent experiments.

solid waste compost. The MW compost used in Expts. 2 and 3 had a lower Zn con- ~~

TABLE 3. Soil nutrient concentration and electrical conductivity (EC) in squash plots with

polyethylene film or organic mulches. (Expt. 2)

Zn c u Mn Fe Na ECZ Mulch (mg-kg-l) (ds0m-l)

I'M 14.5 11.3 32.9 48.7 12.5 0.26

Organic mulches (OW) MW 16.6 11.3 33.7 45.6 by 123.5 a 0.44 ab wc 13.3 10.7 33.6 46.3 ab 56.1 b 0.29 b ss 18.8 10.9 44.5 51.3 a 18.8 c 0.64 a

Rute(t*ha-l) (R) 224 17.4 11.0 36.5 47.9 57.4 0.41 336 15.1 10.9 37.5 47.6 74.9 0.50 F-test NS NS NS NS NS NS O R M x R NS NS NS NS NS NS Contrasts PMvsOM NS NS NS NS

NSt**Nonsignificant or significant at P=O.Ol ZEC was measured in a 2:l water:soil suspension. Fe, Mn, Zn, Cu, and Na in soil were extracted by the Mehlich I method and analyzed by inductively coupled argon plasma spectroscopy YMean separation in columns by Duncan's multiple range test, 5 percent level


NS **

Utilization Of MSW Compost And Other Organic Mulches O n Commercial Vegetable Crops

More fruits of each size except extra-large were harvested from plants grown on PM than from the other mulches (Table 5). Fruit yields of each size, except for small fruit, increased linearly with increasing compost rates.

Experiment 2: 2992 Squash Crop. Initial squash germination ranged from 13 percent in the SS plots to 87 percent in the WC plots (Table 6). The high EC in the SS plots (Table 3) produced low initial stands and stunting (Table 6). High soil Na concentration in MW plots (Table 3) may have contributed to the lower initial germination, as compared to the WC plots (Table 6). By 36 days after seeding, many plants in the I'M and WC

TABLE 4. Soil characteristics before pepper transplanting for Expt. 3 (1992)

pH OM EC Ca Mg K P Zn Cu Mn NO3 Mulch (%) (mmhosxm-l) (mg.kg-l)

I'M 7.2 Organic mulches (ORM) MW 7.6 az wc 7.1 b ss 6.7 c Depth (D) (cm) 0-7.5 7.1 7.5-15 7.2 F-test NS O M x D NS Contrasts PMvsORM NS

1.22 0.31 1408 90.8 50.7 180 9.1 6.9 13.5 .6

1.28 1.30 1.25

0.16 0.23 0.06

1516 a 1162 b 1250 ab

85.0 b 65.9 c

102.9 a

31.8 a 10.3 b 8.4 b

199 b 182 b 232 a

16.0a 6.0ab 13.2 a 1.1 b 9.4b 6.4a 11.3a 7.7a

10.8b 5.0 b 9.1 b 1.2 b

1.27 1.26 NS NS

0.17 0.21 NS NS

1376 1293

NS NS

92.5 80.0 NS NS

28.6 22.0 NS NS

205 193

NS NS

12.4 6.3 11.9 3.3 10.3 5.9 11.6 2.0 NS NS NS NS NS NS NS *

NS NS NS NS ** ** * * x* **

NS,*;'Nonsignificant, significant at P=0.05, or P=O.Ol, respectively ZEC, N03-N, and pH of soil were measured in a 2 1 watersoil suspension. The Walkley-Black dichromate method was used to determine soil OM. P, K, Ca, Mg, Fe, Mn, Zn, and Cu in soil were extracted by the Mehlich I method and analyzed by inductively coupled argon plasma spectroscopy YMean separation in columns by Duncan's multiple range test, 5 percent level

TABLE 5. Bell pepper yields harvested from polyethylene film (PM) or municipal solid waste compost

( M W ) mulch (Expt. 1)

Yield

Extra Early Mulch Large Large Medium Small Totalz HarvestY Fruit size

(kgha-l) (a) (g/fruit)

PM 3190 2240 2090 1350 8870 27 104 MW13' 810 570 140 330 1850 0 101 MW40 2460 1030 520 570 4580 1 112 MW121 4050 1600 980 610 7240 3 122 Contrasts

NS PMvsMW NS -

MW Linear ** MWQuad. NS NS NS NS NS NS NS

NSr*,**Nonsignificant, significant at P=O 05, or P=O.Ol, respectively ZYield is the total from 3 harvests YEarly harvest is the first of 3 harvests XApplication rate of compost in t0ha-l

** ** ** x* ** ** NS ** NS **

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Summer, 1993 79 Compost Science & Utilization


plots had developed symptoms of "damping off" disease and died, while more continued to germinate in the MW and SS. Plant stands in the PM plots were significantly higher than the organic mulch plots, 10 days after seeding, but were significantly lower by 36 days after seeding (Table 6). Martinez (1965) reported that higher numbers of replants were needed in plots mulched with black polyethylene film than in unmulched soil, and the lowest number was needed in plots mulched with sawdust.

Squash plants on WC mulch initially grew vigorously, exhibiting increased shoot and'root weights when compared to other organic mulches (Table 6). Later in the season, these plants expressed N deficiency symptoms. Their early growth was apparent- ly a response to residual fertilizer in the soil. As N was utilized, metabolism of the wood chips further depleted the residual N. A higher N03-N concentration in the deeper soil samples taken after the crop indicates that leaching was also a factor (Table 4).

Higher shoot weights occurred in the PM plots than in the organic mulch plots 19 days after seeding (Table 6). This difference resulted in higher shoot:root ratio in the PM plots. Shoot/root ratios were lowest in the plants in the SS plots, which were under high salt stress. Shoot/root ratios of clover generally increased with increasing N, if water and P were adequate (Davidson, 1969). Shoots and roots of WC plants were heavier than MW or SS plants at both sampling dates. By 60 days after seeding, similarities between the growth rates of WC and PM plants were evident in the shoot weight and the percentage of total root weight comprised of taproot (including lateral roots) and basal roots. Plants from PM plots had a significantly lower percentage of the root biomass attributed to the taproot when compared with the organic mulch plots.

TABLE 6. Plant stands, shoot and root measurements, and yields from squash plants mulched

with white polyethylene film or organic materials (Expt. 2)

Days after seeding

10 36 19 60 Fruit

Stand Shoot2 Root2 Shoot ShootY RootY Shoot RootsX Yield Size % wt(g) wt(g) root wt(g) wt(g) root Tap Basal t-ha-1 kg/plant kg/fruit

PM 74 21

Organic mulches ( O M ) MW 62b 69a WC 87a 49b ss 13c 56ab

Rate(t4za-l) (R) 224 55 63 336 53 53 F-test NS NS O K M x R NS NS

Contrasts PMvsORM' **

2.03 0.05 55

0.89b 0.06b 16a 1.94a 0.11a 22a 0.28~ 0.03b 9b

1.05 .06 15 1.02 .07 16 NS NS NS NS NS NS

NS ** xx

1076

949a 11 89a 526b

940 836 NS NS

NS

21 53 34 66

20b 49 58a 42b 25a 49 40b 60a 9c 55 66a 34b

20 51 53 47 17 50 56 44 * NS NS NS NS NS N-s NS

NS NS * NS

8 3.6 1.3

12a l . lb .9b 13a 2.0a l . l a 5b 0 . 5 ~ .9b

10 1.1 1.0 10 1.3 1.0 NS NS NS NS * NS

NS ** NS

NS,',*'Nonsignificant, significant at P=0.05, or P=O.Ol, respectively %hoot and root weights measured after oven drying YShoot and root weights measured on a fresh weight basis XTaproots and basal roots are presented as a percentage of the total root dry weight W e a n separation in columns by Duncan's multiple range test, 5 percent level


Utilization Of M S W Compost And Other Organic Mulches On Commercial Vegetable Crops

TABLE 7. Bell pepper stands, shoot and root measurements, and yields from plants mulched with white

polyethylene film or organic materials

Stand (%I Shoot Root (%) Yield

Fruit Mulch - 1012 107 wt(g) Mulch 0-7.5Y 75-15 kg.ha-lx EarlyW g/plant size(g)

PM 8 <1 17.8 0 87.5 12.5 4704 100 277 176

Organic mulches ( O M ) MW 43aV wc 46a ss 24b

16ab 25a 7b

11.3ab 8.6b 12.0a

35.6a 16.8b

Ob

55.61, 66.813 94.2a

8.8 16.4 5.8

4471a 329813 2692b

92ab 88b 98a

210a 161b 140b

171 173 173

Rate(t.ha-1) (R)

224 40 336 35 F test NS ORMxR NS

17 15 NS NS

10.6 10.7 NS NS

16.0 18.9 NS NS

75.2 72.3 NS NS

8.8 8.8 NS NS

3532 3443 NS NS

93 92 NS NS

177 164 NS NS

173 172 NS NS

Contrasts PMvsORM ** ** ** ** ** ** NS NS

NS,",*'Nonsignificant, significant at P=0.05, or F=O.Ol, respectively ZDays after transplanting YSoil depth (cm) XTotal of 2 harvests: 28 Dec., 1992 and 15 Jan., 1993 Tercentage of fruit in first harvest "Mean separation in columns by Duncan's multiple range test, 5 percent level

Due to early losses to damping off and later losses to gummy stem blight (My- cosphaerella citrullina), overall squash yields were low (mean=9.5 t-ha-l) (Table 6). The percentage of PM plants (21 percent) which survived to harvest was also very low (Table 6). Although over half of the plants in the SS plots survived, they were stunted and affected by a sweet potato whitefly (Bemisia tabaci Gennadius) mediated disorder known as silverleaf (Maynard and Cantliffe, 1990). Few plots even produced fruit (Table 6). The mulch rates used in Expt. 2 were excessive for a dried sludge product. Bryan and Lance (1991) reported that, as rates of heat-dried sludge (soil-incorporated in strips) increased from 0 to 34 t*ha-l, tomato plant size decreased. Total squash yields from plants in MW and WC plots were higher than SS or I'M plots, but yield per plant was significantly higher in I'M plots (Table 6). High soil Na concentration and low available N in MW plots (Table 3) may have resulted in the smaller size and lower yield per plant than the WC plots (Table 6). Mean fruit size (g/fruit) from PM plants was similar to fruits from organically mulched plants, although fruits from WC plants were significantly larger than those from MW or SS.

Experiment 3: 2992 Pepper Crop. Shoot dry weight was highest in pepper plants on I'M mulch, and lowest with WC (Table 7). There was no discernable root growth into the dried sludge, but more than 16 percent and 33 percent of the weight of roots from the plants on WC and MW, respectively, was located in the mulch layer (Table 7). Plants in I'M plots had a significantly higher percentage of roots at the 0-7.5 cm depth and lower percentage at the 7.5-15 depth when compared to organically mulched plants. This may have been a response to the nutrients in the SS material. Most plants grown on the WC mulch exhibited the small size and light green color which are symp-

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Compost Science 8 Utilization Summer, 1993 81


tomatic of N deficiency, suggesting that the roots grew deeper because of lack of nutrients. Asghar et. al. (1987) reported a higher percentage of corn (Zea mays L.) root growth closer to the plant when fertilizer or fertilizer and mulch were compared with plants with no amendments or mulch only. Transplanting work crews are accustomed to planting in polyethylene film mulches, so many of the transplants were planted into the mulch layer, rather than into the soil, as evident in the high percentage of root growth located in the MW and WC mulches (Table 7). This may have contributed to the N deficiency symptoms in plants in the WC plots. Further investigations are nec- essary to determine if this placement may be advantageous in the MW mulch, which has a higher nutrient concentration and water holding capacity. Knave1 and Mohr (1967) reported that root systems of muskmelons (Cucumis melo L.), summer squash (Cucurbita pepo L.), and tomatoes (Lycopersicon esculentum Mill.) under black polyethylene film or black paper mulch were more spreading and shallow than those under clear polyethylene film or no mulch. The soil temperature, moisture, and light com- ponents which contributed to these results may also be factors in the significantly higher percentage of pepper roots in the top 7.5 cm of soil under the SS mulch (Table 7). However, availability of elements in the SS mulch probably exerted the main influence over root growth.

The high preplant rate of NO3-N detected in the soil from the WC plots (Table 4) was not evident in this crop. This occurrence may have been partly an effect of time between sampling and testing, as the conversion from organic N to NO3-N may have continued after samples were bagged. This suggests that a high rate of organic N was present in these samples.

Over 600 mm of rain fell during this growing season, and plant losses to Phytoph- thora on the rest of the farm were almost 100 percent. Plant survival was highest in plots mulched with MW and WC, and was not affected by rates of mulch or interactions between mulch rate and material. By the second harvest date, only 8 percent of the plants grown in the polyethylene film-mulched plots were viable (Table 7). Phytophthora, a water mold, is encouraged by high moisture, so the environment under the polyethylene film may be more conducive to development of the disease. Water splashing onto stems and leaves also promotes development of this disease (Black et. al., 1991). Less splashing of water onto the plants in the organic mulch plots may have occurred, as compared to the I'M plots. Madden and Ellis (1990) reported increased splashing of simulated rainfall on strawberries mulched with polyethylene film when compared to those mulched with straw. Considerable evidence indicates that compost has disease suppressive properties. Lumsden et. al. (1982) reported significant reduction of diseases caused by Phytophthora capsici in soils amended with a compost of sewage sludge and wood chips. The SS product used in these experiments was not a true compost and was used at excessive rates, so the disease suppressive effect of compost would not be expected in SS plots. However, disease suppression by compost may have been active in the MW and WC plots, where survival was highest (Table 7).

Early yields of peppers were significantly different among treatments (Table 7) and were attributed to stand reduction variations. However, earlier fruit development and a trend toward larger fruit on the plants in PM plots suggested that, even in a more normal year, plants from I'M plots may have had higher early yields similar to Expt. 1. Increases in early fruit production on polyethylene film mulch have also been reported in tomatoes (Brown et. al., 1992). Nutrient leaching, N utilization by microbes metabolizing carbon in the compost, and decreased soil temperatures may be delay- ing crop maturity in the organically mulched plots. La1 (1974) suggests that increased maize (Zea mays L.) yield under organic mulches may be due to decreased soil temperature, improved soil moisture, or chemical or biochemical factors. Locascio and 82 Compost Science & Utilization Summer, 1993

. Utilization Of M S W Compost And Other Organic Mulches On Commercial Vegetable Crops

Fiskell(1977) reported that N leaching from soil under polyethylene film mulch was less than from unmulched soil, resulting in higher yields.

Total pepper fruit yields were exceptionally low due to high disease and insect pressure (Table 7). Plant losses to Phytophthora increased rapidly late in the growing

of a second harvest in this treatment, total yields and yield per plant from I'M plots were significantly higher than from those grown on organic mulch plots. Fruit sizes were similar between I'M and organic mulch plots.

Most research indicates that mulches improve vegetable yields when compared with plants grown on unmulched soil. Organic mulches increased yields of tomatoes (Munn, 19921, eggplant (Solanum melongena L.) (Daisley et. al., 1988) and corn (Lal, 1974). Polyethylene film mulch increased yields of bell peppers (Locascio and Fiskell, 1977), tomatoes (Kovach and Brown, 1992) and triploid watermelons (Citrullus vul- garis Schrad.) (Earhart et. al., 1992). However, there are limited and conflicting reports comparing polyethylene film directly with organic mulches. I'alada et. al. (1992) reported that basil under drip irrigation had higher fresh and dry weights from plots mulched with compost than with black polyethylene film. Highest pepper yields were harvested from plants mulched with white polyethylene film, intermediate yields from plants mulched with compost, and lowest yields from unmulched plants (Roe et. al., 1992). These experiments indicate differences in soil effects and plant growth variables among organic mulch materials, and between polyethylene film and organic mulches.

Most benefits of compost use develop over extended periods of time (Mays and Giordano, 1989; Bryan and Lance, 1991). The use of compost as a mulch may result in even longer intervals before any advantages are realized. Carter and Johnson (19881, reported that eggplant yields were higher from plants mulched with black polyethylene film in the first year, but equal to those grown with a pine-needle or newspaper mulch in the second year, and all were higher than yields from unmulched plants.

season (Table 7) and resulted in premature termination of the harvest. Despite the lack ~~

Conclusions

Compost mulch produced generally favorable effects on soil temperature and disease incidence. Yields of pepper and squash fruit were generally lower when plants were mulched with organic materials than with polyethylene film. However, in one experiment, yields increased with increasing municipal solid waste compost rates. Management of compost mulches is extremely complicated because of the variability of composts, and the numerous edaphic and environmental factors which must be con- sidered. Although the organic mulches resulted in lower yields, organic mulches may be a viable alternative to polyethylene film mulches if environmental and governmental regulations and economic factors are taken into consideration.

University of Florida Agricultural Experiment Station Journal Series No. R-03109.

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