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Kasetsart J. (Nat. Sci.) 32 : 56 - 60 (1997)
Drip Irrigation for Small -Scale Tomato Production in the Tropics
R. J Holmer1,2 and W. H. Schnitzler1
INTRODUCTION
Drip irrigation for outdoor vegetable pro-
duction is successfully practised for many years by
farmers in developed countries, particularly in theUnited States, Israel and Germany (M?ller and
Schnitzler, 1993). Research studies on the use of
drip irrigation for tropical vegetable production,however, are scarce (Lin et al., 1983). The benefi-
cial effects of drip irrigation compared to other
forms of water management are attributed to auniform water application, controlled root zone
development and better disease management since
only the soil is wetted whereas the leaf surfacestays dry (Lamont, 1991). Another advantage is the
possibility of injecting fertilizers directly into the
root zone of the crop to enable a uniform andadequate nutrition according to actual plant de-
mand (Bar-Yosef et al., 1980).
In cooperation with a private Philippinetomato processing company, a research study was
conducted in the province of Bukidnon, southern
Philippines, to optimize the production of highquality tomatoes for fresh market and processing
by the use of drip irrigation. The system was
designed to be particularly applicable and suitedfor small farming family enterprises. The standard
open furrow irrigation with the fertilizer applied in
solid form in two side-dressings (dry application)
was compared with drip irrigation and fertigation.
The trials were carried out in the company's experi-mental stations and in ten small farmers' fields in
the different agro- ecological zones of Bukidnon
(low, medium and high elevation). Every on-farmresearch set-up comprised 0.25 ha each for open
furrow and for drip irrigation.
MATERIALS AND METHODS
Soil media preparationRich top soil was well pulverized and
screened to remove coarse particles. The soil was
then mixed thoroughly with chicken dung at a ratio
of four parts soil plus one part chicken dung. For theseedling preparation banana leaves were torn into
a dimension of 2 cm diameter by 15 cm long. The
soil media was put into the rolled banana leaves (=lukong) and placed by rows on a leveled area. Three
to four seeds of 1403, a bacterial wilt resistant
semi-determinate tomato variety provided by theBukidnon Seed Corporation (BUSECORP), were
put into each lukong spaced about 4 to 5 mm apart
and 5 cm deep for easy pricking and uniformgennination. To control damping-off and insects,
N-4-cyclohexene-1,2-dicarboximide and chlorpy-
rifos was sprayed on a as-needed basis. The seed-lings were transplanted at an age of 18 to 22 days (7
to 10 cm tall).
1 Institute for Vegetable Science, TU München-Weihenstephan Alte Akademie 10, 85350 Freising, Germany.2 present address: Xavier University College of agriculture, Periurban Vegetable Production Project (PUVeP), 9000 Cagayan de
Oro, Philippines.
57Kasetsart J. (Nat. Sci.) 32 (5)
Fertilization
Nitrogen was given at 100 kg/ha (urea),
potassium at 240 kg/ha (muriate of potash),
magnesium at 23 kg/ha (kieserite by use of furrow
irrigation, Epsom salt in case of drip irrigation),
zinc at 3 kg /ha (zinc sulfate) and boron at 3 kg/ha
(sodium borate).
Dry application : In furrow irrigated fields,half of the fertilizer amounts for N, K, Mg, Zn and
B was given one week after transplanting. The
remaining balance was applied two weeks.Fertigation : Fertigation started three days
after transplanting and was continued twice a week
for a duration of 13 weeks (Table 1). The fertilizerswere put into a container and thoroughly dissolved
TransplantingPrior to transplanting the planting site was
soaked up to saturation by furrow respectively drip
irrigation to minimize transplanting shock. In both
treatments, organic fertilizer in form of chickendung (2 t/ha) and phosphorous (40 kg/ha) as super-
phosphate (0-18-0) were placed into the planting
holes at a distance of 40 cm between hills and 1.50m between rows and covered with a soil layer of
about 4 cm before setting the plants. Directly on top
of the covered manure and fertilizer four to fiveseedlings per hill were planted. Two seedlings per
hill were maintained after final thinning at 10 to 14
days after transplanting corresponding to a plantdensity of 33,333 plants per hectare.
Table 1 Weekly nutrient amounts (in mg/hill1) applied through drip irrigation.
Weeks after transplanting N K Mg Zn Bmg/hill mg/hill mg/hill mg/hill mg/hill
0 68
1 136 436 136 36 362 272 872 136 36 36
3 410 872 136 36 36
4 682 872 136 36 365 818 1308 136 36 36
6 818 1744 136
7 818 1744 1368 682 1744 136
9 544 1308 136
10 410 1308 13611 272 872
12 68 872
13 436
Total (mg/hill1) 5998 14388 1360 180 180
Total (kg/ha) 100 240 23 3 3
1one hill = two plants
58 Kasetsart J. (Nat. Sci.) 32 (5)
with water. Before the fertilizer solution was in-jected into the drip laterals, water was given for five
minutes to fill up the system (first flushing). This
was done to enable a uniform fertilizer distributionand to avoid fertilizer burning of young roots
through further dilution of the fertilizer solution in
the upper soil surface. With a special injectionhose, the solution was sucked into the irrigation
system for about 20 minutes, passing the pump and
the filtration units before entering the drip laterals.The process of fertilizer injection is illustrated in
Figure 1. After the fertilizer application the system
was flushed again for five minutes with plain waterin order to avoid corrosion of the pump and emitter
clogging by fertilizer residues. Since water and
nutrient uptake are dependent on the transpirationrate, the fertilizer were applied between 8:00 am
and 10:00 am to meet the maximum transpiration
rate of plants between 12:00 nn and 2:00 pm.
Water managementIn the furrow irrigation plots, the water
from the irrigation canals was dammed with stonesand soil-filled bags ans conveyed to the field by a
PVC hose. From there, it was distributed evenly
along the plant lines through small furrow acrossthe field slope. In this system the water sips into the
bottom and sides of the furrows to provide the
desired wetting. The furrows were constructedthree days after transplanting using an animal drawn
moldboard plow. In the drip irrigation plots, the
laterals were installed on the surface of each bed(distance 1.50 m apart) with the emitters on the
upper side to reduce the risk of sucking in of soil
particles. This can happen due to under-pressure inthe laterals following the backflow of water after
switching off the pump. The discharge of 3.6 l/h per
emitter at 1 bar operating pressure corresponded toa water consumption of 60 m3 per ha and hour.
For appropriate water management in the
described trials using drip irrigation, a soil feel and
appearance method was used (Ley et al., 1994).
The procedure involves the use of a soil auger to
obtain soil samples at various depths of the rootingzone to assess the soil water status. The samples
taken were compared to a chart (Table 2) with
characteristics of a fine textured soil (clay and clayloam) in terms of feel and appearance at different
water contents. The method requires some practice
and judgement but was considered as adequateenough under the given circumstances. Scheduling
of furrow irrigation was done twice a week in
periods of low precipitation until the soil wassaturated. The depth of water in the furrows was
always kept ten cm below the base of the plant.
RESULTS
In all research stations as well as in nine outof ten farm-trials (Table 3), the fertigated tomato
plants yielded significantly higher than those irri-
gated by open furrows. Tomatoes under fertigationhad a mean usable yield of 56.8 t/ha in the on-farm-
trials compared to 33.5 t/ha only in the furrow
irrigated field (cv. 21.1 %, LSD1% = 13.9 t/ha). Theyield differences obtained in farmers' field were
Figure 1 Method of fertilizer injection into the
drip irrigation system (Pitts et al., 1988).
Suction hoseValve
Pump
Backflowevention
Fertilizer container
59Kasetsart J. (Nat. Sci.) 32 (5)
Table 2 Soil feel and appearance chart for estimating available soil water in fine textured soils (Ley et
al., 1994).
Available water Fine textured soil (clay and clay loam) Water management
100% appears very dark, leaves slight moisture on hand discontinue irrigation(field capacity) when aqueezed, will ribbon1 out about 4 cm
70-80 % quite dark, ribbons and slicks easily, makes firm no irrigation
ball2
60 to 65 % fairly dark; forms firm ball; ribbons out (0.5 - 1 no irrigation
cm)
50% balls easily; small clods flatten out rather than start irrigationcrumble; ribbons slightly
35 to 40 % slightly dark, forms weak balls; clods crumble continue irrigation
< 20% hard, baked, cracked, light color continue irrigation(wilting point)
1 = ribbon is formed by rolling soil between thumb and forefinger;2 = ball is formed by squeezing soil hard in fist
Table 3 Usable yields (t/ha) of tomatoes from on-farm trials comparing fertigation and open furrow
irrigation.
Farmer Location Date transplanted Usable yield (t/ha)Fertigation Open Furrow
Buzon Kulasihan, Lantapan 07-Dec-94 42.84 47.00
Daluan Sankanan, Manolo Fortich 07-Dec-94 57.68 30.39Baa Sankanan, Manolo Fortich 15-Dec-94 46.45 20.55
Daoayan Kahapunan, Cabanglasan 26-Dec-94 75.49 52.00
Piloton Diklum, Manolo Fortich 06-Jan-95 76.03 38.70Binayo Diklum, Manolo Fortich 08-Jan-95 39.20 22.70
Masong San Carlos, Valencia 24-Jan-95 83.33 47.30
Baula Kisolon, Sumilao 03-Feb-95 76.32 35.60Lim Diklum, Manolo Fortich 14-Feb-95 30.72 15.04
Bacus Diklum, Manolo Fortich 10-Mar-95 39.86 26.11
Mean 56.79 33.54
60 Kasetsart J. (Nat. Sci.) 32 (5)
even more expressed than in the experimentalstations where the conditions, particularly in terms
of water management for the open furrow irriga-
tion, could be better controlled than under theactual working conditions of the small farmers. All
farmers who participated in these on-farm studies
appreciated the simplified way of applying waterand fertilizers to their crop by using drip irrigation.
Areas with limited water supply and competition
among the farmers for water could be utilized forgrowing of high-value crops. The problem of soil
erosion due to the drip-wise water emission out of
the dripper lines was nearly eliminated in contraryto the standard open furrow irrigation. The encour-
aging results obtained with drip irrigation of veg-
etables in the presented research studies also con-vinced the Asian Development Bank (ADB) to
assist the Provincial Govemment of Bukidnon in
funding the Bukidnon lntegrated Area Develop-
ment Project (ADB,1996). Included in the project
is the development of more than 1,500 ha in
northern Bukidnon especially for drip irrigation
and the improvement of farm-to-market roads. The
start of this project is scheduled for the end of 1998.
LITERATURE CITED
ADB. 1996. ADB News Release No. 85.
Bar-Yosef B., et al. 1980. Agron. J. 72:815-822.
Lamont W.R. 1991. Irrigation Journal 4:10-15.Ley T.W., R.G. Stevens, R.R. Topielec and W.H.
Neibling. 1994. Pacific Northwest Publica-
tion No.475. Washington, Oregon, Idaho.Lin S.S., et al. 1983, HortScience 18 (14) : 460 -
461
Müller, J. and W. H. Schnit ler. 1993. Gemuese 30: 109 - 110.
Pitts D.J., A.G. Smajstrala and D.T. Haman. 1988.
Agricultural Engineering Special PublicationNo. SS-AGE-808, University of Florida,
Gainesville, 29 p.