THE USE OI SOIL SOLARIZATION TO CONTROL WEEDS, PLANT

THE USE OI SOIL SOLARIZATION TO CONTROL WEEDS, PLANT DISEASES
AND INTEGRATION O F CHICKEN LITTER AMENDMENT FOR TOMATO
PRODUCTION IN TANZANIA
D. Mushobozy1, V. A. Khan 2 , and C. Stevens2
Department of Crop Science Sokoine University of Agriculture, Morogoro Tanzania.
2
George Washington Carver Agricultural Experiment Station, Tuskegee University,
Tuskegee, AL 36088.
1
Abstract: This study was initiated in 1995 as a transfer of technology research to investigate the
efficacy of soil solarization under Tanzania climatic condition. In first solarization trial (1996)
90% of 16 species of weeds were controlled with purple nutsedge being the most dominant weed.
Root knot gall damage was not as severe on tomato plant roots grown in solarized soil compared to
non-solarized soil. The effect of applied chicken litter (CCL) in combination with soil solarization
was evaluated on tomato yield. The following treatments were prepared: 0, 1, 3, 5, and 8 MT/ha,
of composed chicken litter (CCL). The best solarized treatment was 3 MT/ha CCL with soil
solarization, where the total yield resulted in 19.3 MT/ha of tomatoes compared to 9.5 MT/ha in the
non-solarized soil without CCL. Results from the second solarization trial (1997) showed that
there was a 50% reduction of a foliage disease on 3-week-old tomato seedlings caused by
Didymella lycopersici.
Keywords: soil solarization, chicken litter, tomatoes, weeds
Introduction
Soil solarization is a plasticulture technology that involves the use of a hydrothermic process
where clear plastic mulch is used to trap solar energy to sterilize the soil to control soilborne pests
such as weeds, nematodes, soilborne pathogens and maintain sustainable system that is involved in
producing fertilizer (Katan , 1980). Recently, soil solarization has been reported to control foliage
diseases (5, 6, 11, 12).
Soil solarization has been investigated in many countries situated in the hot regions of the
world. In hot regions of the world such as Africa, soil solarization has been demonstrated in
Egypt, Cameroon, Libya, Morocco, Sudan, Tunisia and South Africa (9). In Africa, Tanzania is a
typical example, were over 80% of the population comprises of subsistence farmers. They live on
the land in rural areas and survive on crops that they grow themselves (4). In Tanzania,
subsistence farmers can't afford to use expensive chemical pesticides to control nematodes,
soilborne pathogens and weeds, that effect their production of crops. Therefore, they disinfest the
soil by using the slash and burn cultural practices of cutting all trees and weeds growing on the
proposed planting sites. By using this method of sterilization, new fields have to be prepared each
season in rotation just before the rainy season, so as to avoid the build up of nematode and weed
populations. The long term cumulative effect of this method have resulted in desertification in
areas, where crops are grown (7) and unless a cheaper and environmentally sound methods are
adopted quickly, the impact from growing crops in Tanzania under this management system would
be environmentally hazardous. Another problem that faces the subsistence farmers is maintaining
an adequate level of soil fertility, because of the unavailability and expense of synthetic fertilizers.
Subsquently, they experience a reduction in the yield of crops.
Scientists from Tuskegee University, Tuskegee, AL, USA and Sokoine University of
Agriculture (SUA), Morogoro Tanzania, in a partnership, sponsored by the US Agency of
International Development, evaluated the transfer of soil solarization technology under Tanzanian
climatic conditions. The main objective of this study was to determine it's efficacy to control weeds
and soilborne pathogens, and to determine the effect of applied chicken litter amendment, in
combination with soil solarization to improve the yield of tomatoes. Also, we wanted to determine
if the soil solarization technique could be promoted and to see if it could replace the slash and bum
279
technique. Prior to our visit Mr. Deus Mushobozy from Sokoine University of Agriculture
(SUA), spent the summer of 1995 at Tuskegee University studying the operational process of
applying soil solarization.
Methods and Materials
All experiments were conducted in field plots at SUA, Department of Crop Science
Morogoro Tanzania. Roundup herbicide was applied in the field before plowing and preparation
for solarization. Two experiments were conducted from 1995 to 1996 on
Oxisols red main clay loam soil using single layer 48 micro-thick clear plastic mulched sheets
(Polyon Barkai Kibbutz Barkai, Israel). Soil was heavily irrigated by sprinkler irrigation prior to
application of plastic mulch, according to procedures described by Stevens et al., (10). In the first
year the temperature was recorded at 5 and 10 cm depth in solarized soil for about 10 days, before
a malfunction of temperature recorder occurred. In both trials, the first one began 9 Jan., 1996 to
10 April, 1996 (solarized for 13 weeks) and the second trial plot was solorized from 5 November,
1996 to 5 February, 1997 (solarized for 14 weeks). The following rates of composted chicken
litter (CCL): 1, 3, 5 and 8 MT/ha were incorporated in the soil before solarization and in the
control. The composted CCL was a three week old mixture of chicken manure and rice husk. A
comparison of tomatoes grown on nonsolarized and solarized soils with different rates of CCL
were made on the total marketable yield in 1996 and 1997, along with the disease incidence of
Didymella stem canker and leafspot in 1997. Also weed count was made on plots without CCL.
Eight-weeks-old 'Money Maker' tomato seedlings were transplanted after removal of the plastic
mulch. Ammoninum nitrate was applied at 5 g per plants, no P and K were added.
In the second trial (1996) the plastic film was reused from the previous trial in 1995. Avissar
et al (1) showed that reusing clear plastic film ensured better results. Therefore, reusing of plastic
film for soil solarization appears to be suitable for farmers under the prevailing economic
conditions in Tanzania.
Results and Discussion
In the first trial during 1995 the average maximum temperature of the air and mulched soil at
5 and 10 cm depths and 5 cm depth of non-mulched soil were: 29, 43, 36 and 29° C at mid day,
respectively. Solarization can heat the soil through repeated daily cycle (average of 10 days of
solarization), at increasing soil depth maximal temperature decrease, were reached later in the day
and maintained for several hours (Figure 1).
More than 90% of the weeds were controlled with purple nutsedge being the most dominant
weed (Table 1). The disease pressure on root knot was not severe. However root knot nematode
galls were not as severe on tomato plant roots grown in solarized soil compared to non-solarized
soil (Data not shown).
The best treatment was solarized soil intergrated with CCL (in 1996) at 3 MT/ha, this
resulted in a total yield of 19.3 MT/ha of tomatoes compared to 9.5 MT/ha in the non-solarized soil
without CCL. Tomato yield showed more than a two fold increase per hectra following soil
solarization with 3 MT/ha CCL compared to the non-solarized convential planting method. The
best yield on bare soil was obtained by using 5 MT/ha of CCL which gave a yield of 12.6 MT/ha
of tomato fruits (Table 2).
In the second trial (3 March 1996) purple nutsedge was the only weed observed in the plots
and there was almost 100% reduction of this weed in the solarized plots compared to the
nonsolarized soil. However, a severe Didymella stem canker (caused by Didymella lycopersici)
destroyed many of the seedlings 3 weeks after transplanting. Soil solarization was not effective in
controlling stem cankers on tomatoes (Table 1). Because of the severe Didymella stem canker, no
yield was determined in 1997. It has been reported that soil sterilization by steam had little effect,
and may even allow the conidia to survive for longer periods compared to unsteamed soil (3). The
incidence and severity of this disease has been reported to be very high in plastic houses and open
fields of tomato regions of Morocco, North Africa. The fungus attacks as a soil and airborne
pathogen, in tomato transplants planted from September to January, when the weather is usually
wet and cool (2). Besri (2) reported that the solarization of tomato supports (stakes) (Eucalyptus
280
stakes and reed canes) by wet soil and then covered with a clear transparent polyethylene sheet,
considerably decreased the incidence of D. lycopersici and delayed disease occurrence. The
maximum temperatures recorded under the polyethylene sheet were always higher than 50°C, the
maximum air temperature varying between 26 and 34°C. However, there was a 50% reduction of
the foliage disease caused by the fungus (Table 1).
Soil solarization in this location appeared to work very well and could possibly replace the
current slash and burn method. Travelling through the Morogoro district it was observed that
subsistence farmers did not use small tractors or even hand tillers to cultivate their one or two
hectare plots. Therefore, if they could solarize their plots it would be much easier to hand cultivate
for the following reasons: 1) The soil compaction is less in solarized vs nonsolarized soil and 2)
along with weed reduction, it would make hand cultivation by subsistence farmers easier. Soil
solarization has the potential to change cultural practice of agriculture in this region but further
investigation would be needed in an outreach research demonstration program with the subsistence
farmers to make this a reality.
Conculsion
The average maximum temperature of the air and solarized soil at 5 and 10 cm depths and 5
cm depth of non-solarized soil were: 29,43, 36 and 29° C, respectively. More than 90% of the
weeds were controlled with purple nutsedge being the most dominant weed following soil
solarization. Tomato yield showed more than a two fold increase per hectare following soil
solarization with 3 MT/ha CCL compared to the non-solarized convential planting method The
best yield on non-solarized soil was obtained by using 5 MT/ha of CCL which gave a yield of 12.6
MT/ha of tomato fruits. Soil solarization was not effective in controlling Didymella stem cankers
on tomatoes (Table 1). There was a 50% reduction of the foliage disease caused by the fungus.
Literature cited
1. Avissar, R., Naot., O., Maher, Y. and Katan, J. 1986. Field aging of transparent
polyethylene mulches: I. Influence on the effectiveness of soil heating. Soil Sci. J. 50:205.
2. Besri, M. 1991. Solarization of soil and agricultural materials in Morocco for control of
Verticillum wilt and Didymella stem canker in tomato. Chapter 17 p. 237 In: Soil
Solarization Eds. J. Katan and J. E. DeVay. CRC Press, Boco Raton, FL.
3. Bollen, G. J. 1969. The selective effect of heat treatment on the microflora of a
greenhouse soil. Neth. J. Plant Pathol. 75:157-163.
4. Chapin, R. and Doerr, S. 1994. Third world irrigation update. ASP
25:13-22.
5. Daelemans, A. 1989. Soil solarization in West Cameroon: effect on weed control, some
chemical properties and pathogens of the soil. Acta Hortic. 255:169.
6. Hassan, M. S. and Yunis, M. A. 1984. Cucumber cultivation with soil solarization and
plastic mulching. Arab J, Plant Prot. 2:65.
7. Janick, J., Schery, R. W., Woods, F. W. and Ruttan, V. W. 1974. Plant Science and
Introduction to world crops. W. H. Freeman and Company, San Francisco.
8. Katan, J. 1980. Solar pasteurization of soils for disease control: status and prospects.
Plant Dis. 64(5):450.
281
9. Katan, J. and DeVay, J. E. 1991. Soil solarization: Historical perspectives, principles, and
uses. Chapter 2 p. 23 Eds. In: Soil Solarization J. Katan and J. E. DeVay. CRC Press,
Boco Raton, FL.
10. Stevens, C., Khan, V. A., Okoronkwo, T., Tang, A. Y. Wilson. M. A., Lu, J. and
Brown, J. E. 1990. Soil solarization and Dacthal: Influence on weed, growth and root
microflora of collards. HortScience 25:1260.
11. Stevens, C., Khan, V. A., Collins, D. J., Rodriguez-Kabana, R., Ploper, L. D. 1992.
Effects of soil solarization on early blight, southern blight and root-knot on tomato. 19901991: Biological and Cultural test for Control of Plant Diseases 7:43.
12. Stevens, C., Khan, V. A., Brown, J. E., Plopper, L. D., Collins, D. J., Wilson, M. A.,
Rodirguez-Kabana, R. and Curl, E. A. 1993. The influence of soil solarization as related
to changes of soil rhizosphere. ASP 24:170-188.
282
Table 1. Effect of soil solarization on weed control (weed count and composition determined
week after removing the plastic mulch).
Number of weeds per/ m2 plot
Weed composition
Solarized soil
Non-solarized soil
Ceiosia angentea
Commeli rna benghalensis
Euphorbia hirta
Amaranthus vidiris
Amaranthus spinosus
Eleusine indica
Cyperus rotundus
Echinocloa coIona
Rottboellia exaitata
Digitaria spp.
Galinsoga parviflora
Cida acuta
Acanthospermum hispidum
Bidens pilosa
Leucas urtici/olia
Tribulus spp.
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
36
24
31
53
78
94
123
10
4
9
15
7
45
37
9
15
Total
3
590
283
Table 2. Comaprsion of differect rates of composted chicken litter (CCL) in solarized (SS) and non-solarized (NS) soils on the total
marketable yield in 1996. Percent diease incidence of Didymella stem canker and leaf spot of tomatoes in 1997.
Treatment *
SS
+
+
+
+
+
+
—
First solarization trial
Marketable yield (MT/ha) in 1996
Second solarization trial
% Disease incidence of
Number of lesion per leafb/
stem canker in 1997
of Didymella leaf spot in 1997
CCL (MT/ha)
0 (fungicide)
0
1
3
5
8
ND&
13.74
17.32
19.33
17.61
18.14
0 (fungicide)
0
1
3
5
8
ND
9.50
9.43
12.62
13.41
12.62
ND
60
67
73
67
67
11.3
24.0
ND
20.3
20.5
21.0
* *
NS
NS
NS
* *
Significance of F test from ANOVA
SS vs NS
CCL
Interaction
* *
NS
ND
55
67
66
61
67
12.0
10.0
ND
12.5
13.0
7.0
* *
*
^ + means soil solarization for 13 weeks; - non-solarized plots
h/ number of lesions per leaf is from the second leaf from the bottom of the seedling. The fungicide treatment was sprayed with Dithane
M-45.
^ ND means not determined.
50
5 cm MULCH
•—
40 -
10 cm MULCH
5 cm No MULCH
o
LU
oc
ZD
\-
S
30 -
LU
Q.
20 -
10
—i—
20
10
30
HOURS
Figure 1. The daily course soil heating by polyethylene at two soil depths for ten days, as
compared to the non-solarized (no mulch) soil at a depth of 5 cm.
285