manuals for the control structures and the recommended water management are
available with the Ministry of Public Works. Areas are grouped in Water Management Zones.
For each Water Management Zone in a Scheme there is a detailed description for operation
depending on the crops grown, their growth stage and a number of physical
Factors having an
influence on the soil and water management:
Plowing of the rootzone followed by sun-drying up to
two weeks of the clods improves the effect of the following leaching and puddling of the
soil. Together with the puddling, the Plowing is the most efficient way to leach out the
toxic elements from the root-zone.
||Puddling (with pump irrigation). Leaching and Puddling
will require pump irrigation to make the soil sufficiently wet. Puddly and soft wet soil
is a requisite to the growth of rice up to the end of the tillering stage. When the soil
is puddly and soft there are relatively wide spaces between the soil particles, there is a
low percentage of the solid phase and both bulk density and hardness are low. These
conditions favour rice plant growth and absorption of nutrients. After a number of years,
with repeated cycles of puddling, the formed plow-layer will encourage much better water
||Sun-drying (mid-season). Drainage of the
rice field between the end of the tillering stage and the panicle differentiation stage
will lead to higher yields. Rice roots will extend more deeply and stems grow more
strongly. Drainage will increase the portion of the most active white roots of the rice
plant and will decrease the number of non-active black roots. This drainage will also
cause the soil to become more hard and compact by sun drying. According Cheng (1984) the
presence of white roots against black roots is a good indicator that sufficient drainage
has been applied.
||Leaching/percolation. The main aim for the
water management is to promote leaching/percolation by controlled drainage during periods
with rainfall. It will be difficult to provide sufficient water for 8 mm/day percolation.
It appears that leaching is most essential during planting and early growth of the
transplanted rice. Pump irrigation during this period should be highly recommended for
real high yields. Water supply may include acid canal water as it has little effect on the
yield and can be used to provide sufficient percolation.
||Water levels up to 30 cm below land surface
during the growth period of rice in areas no pump irrigation will be applied. Water
levels are preferred to drop up to 30 cm below surface in
very acid soils which has not be puddled and leached by extra pump
irrigation. These water level below surface does not affect the yields in these rice
fields of the swamp lands. During periods with high rainfall mostly the groundwater levels
will be higher. The groundwater level should not drop below 30 cm below land level. The
groundwater levels drop up to 30 cm below surface will not be necessary anymore in soils
subject to several cycles of plowing, leaching and puddling with pump irrigation.
||Ripe soils. Ripe soils are in advantage over
less-ripened, soft soils for high yields. These soils can also be better puddled and
are less subject to toxic conditions. Ripe soils in the swamplands will be formed after
long periods of dryness during the dry season.
||Groundwater drop below 60 cm during dry season. A
long dry period in the dry season when groundwater levels drop below 60 cm depth will have
a very positive effect on the next crop.The positive effect is attributed to better
aeration of the soil, oxidation of toxic organic compounds and increased permeability by
crack forming in the poorly drained clay soils. In wet years the drop of groundwater will
hardly occur during the dry season. Therefore an field drainage system is required. For
the Acid Sulphate soils it is essential that sufficient percolation can be applied after
the dry season, during the next growing season. In these conditions the El Niņo effect of
1997/98 resulted in peak high yields for the following growing season in the Telang
project of South Sumatra province.The same positive effect in acid sulphate soils has been
recorded for the Saleh project (South Sumatra) in 1994/95, also after an extreme long dry
season. Computer Model Simulations based on acid sulphate soil oxidation and leaching,
also show that a deep drop of groundwater below the pyrite layer does not influence the
toxicity in the next growing season, when normal percolation quantities (4-8 mm/day) are
applied during the growing season of the rice.
||Flushing and avoiding slackwater
conditions. From an environmental point of view it is necessary to
avoid acid conditions in the canals. Potentials for fisheries will increase with better
quality water. Better quality water can be obtained by avoiding the slackwater conditions
in canals. It is a matter of Design to improve water
movements in the Primary and Secondary canals.
Without mechanised land preparation
including pump irrigation during land preparation and early planting of the rice crop
there will be no high yields possible!
So what are the main (most important)
objectives of the soil & water management system?
drainage. During most of the time in the wet
season: Groundwater levels should not exceeding 30 cm below land surface. During the
dry season groundwater levels should be at about 60 cm below surface for most of the time.
of canal water and avoiding slackwater conditions. Double
connected canals and one-way flow in the main canals in areas far away from the river.
(2-3 km and more)
Objectives for soil/water management are fulfilled by
the operation of the control gates. A gate
usually consist of a sliding gate and stoplogs. Four types of operation are defined for
the Tidal Swamp Schemes: Retention, Controlled Drainage, Supply and Maximum Drainage. Of
these operations the Controlled Drainage is the most important operation which will be
functioning for most of the time in Indonesia.
The operation of the gates has been practiced
and monitored in the Model areas. It proves that the most difficult operation is water
supply, because it requires frequent visits to the gates and careful watch of the tides
for a good result. For that reason water supply operation should be preferable carried out
near the home-stead's. (SPD secondary canal). Controlled drainage is the most easy
operation and should be preferable carried out on the other side (SDU secondary canal).
See Design Macro.
A description of the operation guidelines is
given in WebPage Model Area.
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