dasar-dasar ekosistem sawah

DASAR-DASAR

EKOSISTEM SAWAH

Diabstraksikan oleh: Soemarno, PSL-PPSUB 2013

KOMPENDIUM KAJIAN LINGKUNGAN DAN PEMBANGUNAN

GOOD WATER MANAGEMENT PRACTICES FOR RICEFIELD

Diunduh dari sumber: http://www.knowledgebank.irri.org/factsheetsPDFs/watermanagement_FSWaterSavingGeneral.pdf

………. 30/10/2012

BundGood bunds are a prerequisite to limit

water losses by seepage and under-bund flows. Bunds should be well compacted

and any cracks or rat holes should be plastered with mud at the beginning of the

crop season. Also, check for, and repair new rat holes, cracks, and porosity caused by earth worms throughout the growing

season. Plastic sheets can be used to repair especially permeable parts of bunds.

A few principles exist to “get the basics right” for good water management in paddy rice.

Ponded water depth

Keeping the depth of ponded water around 5 cm

minimizes water losses by seepage and

percolation. See the fact sheet on Alternate Wetting

and Drying for more information on fieldwater management.

Good bunds avoid seepage losses

THE SOUND WATER MANAGEMENT

Diunduh dari sumber: http://www.knowledgebank.irri.org/rkb/2-sound-water-management.html………. 30/10/2012

Good water management in lowland rice focuses on practices that conserve water (by eliminating the unproductive water flows of seepage, percolation,

and evaporation) while ensuring sufficient water for the crop. Water management practices are given for the different periods of the crop

cycle from pre-planting activities to the ripening stage.

It is assumed that farmers have access to sufficient irrigation to maintain flooded conditions. Water-saving technologies for conditions of insufficient

water are described in subsequent paragraphs.

Pre-planting

The amount of water used for wet land preparation of lowland rice can be as low as 100-150 mm but can go up to 900 mm in large-scale

irrigation systems with a long land preparation period.

Various options exist to minimize the amount of water used in the pre-planting period. Land preparation lays the foundation for the whole

cropping season and it is important in any situation to “get the basics right” for good water management afterwards.

Especially important for good water management are field channels, land leveling, and tillage operations (puddling, bund preparation and

maintenance).



Field channels to manage water

In many irrigation systems, there are no field channels (or ‘tertiary’ irrigation or drainage channels) and water flows from one field into the other through breaches in the bunds. This is called “plot-to-plot” irrigation. The amount of

water flowing in and out of a rice field can not be controlled and field-specific water management is not possible. This means that farmers may not

be able to drain their fields before harvest because water keeps flowing in from other fields. Also, they may not be able to have water flowing in if upstream farmers retain water in their fields or let their fields dry out to

prepare for harvest. Moreover, a number of technologies to cope with water scarcity require good water control for individual fields. Finally, the water

that continuously flows through the rice fields may remove valuable (fertilizer) nutrients.

Constructing separate channels to convey water to (irrigation) and from (drainage) each field greatly improves the individual control of water, and is the recommended practice in any type of irrigation system. Alternatively, if field channels can not be constructed for individual fields, they should be

constructed to serve a limited number of fields together.



. Thorough puddlingA rice field can be compared with a bath tub: the material of a bath tub is

impregnable and it holds water well – however, you only need to have one hole (by removing the plug) and the water runs out immediately. Rice fields just need a

few rat holes or leaky spots and they will rapidly loose water by seepage and percolation.

Thorough puddling results in a good compacted plow sole that reduces the percolation rates throughout the crop growing period. The efficacy of puddling in

reducing percolation depends greatly on soil properties. Puddling may not be effective in coarse soils, which do not have enough fine clay particles to migrate downward and fill up the cracks and pores in the plow sole. On the other hand, puddling is very efficient in clay soils that form cracks during the fallow period that penetrate the plow pan. Although puddling reduces percolation rates of the

soil, the action of puddling itself consumes water, and there is a trade-off between the amount of water used for puddling and the amount of water “saved” during

the crop growth period by reduced percolation rates.

Puddling may not be necessary in heavy clay soils with low vertical permeability or limited internal drainage. In such soils, direct dry seeding on land that is not puddled but tilled in a dry state is very well possible with minimal percolation

losses.



Bund preparation and maintenanceGood bunds are a prerequisite to limit water losses by seepage and

underbund flows. To limit seepage losses, bunds should be well compacted and any cracks or rat holes should be plastered with mud at the beginning of the crop season. Make bunds high enough (at least 20

cm) to avoid overbund flow during heavy rainfall. Small levees of 5-10 cm height in the bunds can be used to keep the

ponded water depth at that height. If more water needs to be stored, it is relatively simple to close these levees.

Researchers have used plastic sheets in bunds in field experiments to reduce seepage losses. Although such measures are probably financially

not attractive to farmers, the author has come upon a farmer in the Mekong delta in Vietnam who used old plastic sheets to block seepage

through very leaky parts of his bunds.

Liang tikus harus dibuntu



. Separately irrigated seed bedsMost lowland rice is established by transplanting rice plants from a seed bed

into the main field. In large-scale irrigation systems, seed beds are often found in corners of individual farmers’ fields scattered throughout the area. If

there are no field channels to separately irrigate the seed beds, the whole field is flooded while the rice plants grow in the seed bed.

All water losses from the main field through evaporation, seepage, and percolation, are a wasteful loss as no crop grows yet in the field. One remedy is to construct field channels that bring water to the seed beds only so that the

main field only needs to be soaked and puddled a few days before transplanting (3-4 days). Seed beds are best located close to the main canals so that little water is lost by transporting it over long distances through field

channels. Community seed beds may be an option to concentrate the raising of

seedlings in one place to use the irrigation water most efficiently. In some areas, private companies produce seedlings that farmers can purchase so they

save their own irrigation water.



. Early vegetative stageAfter crop establishment, continuous ponding of water generally provides the

best growth environment for rice and will result in the highest yields. Flooding also helps suppress weed growth, improves the efficiency of use of nitrogen and, in some environments, helps protect the crop from fluctuations

in temperatures. After transplanting, water levels should be around 3 cm initially, and gradually increase to 5-10 cm with increasing plant height. With direct wet seeding, the soil should be kept just at saturation from sowing to some 10 days after emergence, and then the depth of ponded water should

gradually increase with increasing plant height. With direct dry seeding, the soil should be moist but not saturated from sowing till emergence, else the

seeds may rot in the soil. After sowing, apply a flush irrigation if there is no rainfall to wet the soil. Saturate the soil when plants have developed 3 leaves,

and gradually increase the depth of ponded water with increasing plant height.

Under certain conditions, allowing the soil to dry out for a few days before reflooding can be beneficial to crop growth. In certain soils high in organic matter, toxic substances can be formed during flooding that can be removed

through intermittent soil drying. Intermittent soil drying promotes root growth which can help plants resist lodging better in case of strong winds

later in the season. Intermittent soil drying can also help control certain pests or diseases that require standing water for their spread or survival, such as golden apple snail. The farmers often practice a period of 7-10 days “mid-season drainage” (during which the soil is left to dry out) during the active

tillering stage. This practice should reduce the number of excess and nonproductive tillers, but these benefits are not always found.

Intermittent soil drying is also used in the System of Rice Intensification (SRI) and is suggested to lead to improved soil health. Other research,

however, shows that nonflooded soil promotes the occurrence of certain soils pests such as nematodes.



. Ripening stage

This period does not necessarily require flooding. Soil that is 80–90% saturated is sufficient. However, for easy operations, keeping the fields flooded may still be the simplest management approach.

Draining the fields some 10-15 days before the expected harvest date hastens maturity and grain ripening, prevents excessive nitrogen

uptake, and makes the land better accessible (because it is dryer) for harvest operations.



. Alternate wetting and drying (AWD)

In alternate wetting and drying (AWD), irrigation water is applied to obtain flooded conditions after a certain number of days have passed after the

disappearance of ponded water. AWD is also called ‘intermittent irrigation’ or ‘controlled irrigation’.

The number of days of nonflooded soil in AWD before irrigation is applied can vary from 1 day to more than 10 days. A practical way to implement

AWD is to monitor the depth of the water table on the field using a simple perforated ‘field water tube’. After an irrigation application, the field water depth will gradually decrease in time. When the water level (as measured in

the tube) is 15 cm below the surface of the soil, it is time to irrigate and flood the soil with a depth of around 5 cm.

Around flowering, from 1 week before to one week after the peak of flowering, ponded water should be kept at 5 cm depth to avoid any water

stress that would result in potentially severe yield loss. The threshold of 15 cm is called ‘Safe AWD” as this will not cause any yield decline since the roots of the rice plants will still be able to take up water from the saturated

soil and the perched water in the rootzone.

The field water tube helps farmers see this “hidden” source of water. In Safe AWD, water savings may be relatively small, in the order of 15%, but there

is no yield penalty. After creating confidence that Safe AWD does not reduce yield, farmers may experiment by lowering the threshold level for irrigation

to 20, 25, 30 cm, or even deeper. Some yield penalty may be acceptable when the price of water is high or when water is very scarce.

IRIGASIIrigasi merupakan upaya yang dilakukan manusia untuk mengairi

lahan pertanian. Ada banyak model irigasi yang dapat dilakukan manusia.

Pada zaman dahulu, jika persediaan air melimpah karena tempat yang dekat dengan sungai atau sumber mata air, maka irigasi

dilakukan dengan mengalirkan air tersebut ke lahan pertanian. Irigasi juga dilakukan dengan membawa air dengan menggunakan wadah kemudian menuangkan pada tanaman satu per satu. Untuk

irigasi dengan model seperti ini di Indonesia biasa disebut menyiram.

PITCHER IRRIGATION

In order to achieve an effective irrigation, unglazed earthenware or clay pots are buried to the neck of the vessel next to plants or small

trees. The pots are filled with water and covered with a lid. Since the unglazed walls of the pods are

porous, the water can seep slowly out and reach the roots of the plants. Instead of a clay or earthenware pod, also the sweet monkey orange fruit

(Strychnos spinosa can be used when it has been dried and the top

cut off.

Diunduh dari sumber: http://www.infonet-biovision.org/default/ct/293/soilconservation………. 28/10/2012

http://id.wikipedia.org/w/index.php?title=Lahan_pertanian&action=edit&redlink=1

http://id.wikipedia.org/wiki/Sungai

Irigasi Permukaan

Irigasi Permukaan merupakan sistem irigasi yang menyadap air langsung di sungai melalui bangunan bendung maupun melalui bangunan pengambilan bebas (free intake) kemudian air irigasi

dialirkan secara gravitasi melalui saluran sampai ke lahan pertanian.

Dalam irigasi dikenal saluran primer, sekunder, dan tersier. Pengaturan air ini dilakukan dengan pintu air.

Prosesnya adalah gravitasi, tanah yang tinggi akan mendapat air lebih dulu.

Bangunan irigasi untuk menyalurkan air irigasi ke swah intensif di Kab. Jember

http://id.wikipedia.org/wiki/Bendung

Irigasi LokalSistem ini air distribusikan dengan cara pipanisasi. Di sini juga berlaku gravitasi, di mana lahan yang tinggi mendapat air lebih

dahulu. Namun air yang disebar hanya terbatas sekali atau secara lokal.

Diunduh dari sumber: http://informasi-budidaya.blogspot.com/2007/06/sistem-irigasi-pertanian-di-niigata.html ………. 28/10/2012

Sistem irigasi pertanian di Niigata

Dari pintu pengeluaran air tersebut dialirkan ke sawahnya melalui pipa yang berada di bawah permukaan sawahnya. Kalau di tanah air

kita pada umumnya air dialirkan melalui permukaan sawah.

http://4.bp.blogspot.com/_w6ZSxCkN18g/RoL1qkpVR-I/AAAAAAAAAEg/YfSmH0mTqDE/s1600-h/DSC03617.JPG

Irigasi Tradisional dengan EmberDi sini diperlukan tenaga kerja secara perorangan yang

banyak sekali. Di samping itu juga pemborosan tenaga kerja yang harus

menenteng ember.

Small-scale drip irrigation systems

BUCKET SYSTEM

The bucket system consists of two drip lines, each 15-30 m long, and a

20-litre bucket for holding water. Each of the drip lines is connected to a filter to remove any particles that may clog the drip nozzles. The bucket is supported on a

bucket stand, with the bottom of the bucket at least 1 m above the

planting surface. One bucket system requires 2-4 buckets of

water per day and can irrigate 100-200 plants with a spacing of 30 cm

between the rows.

For crops such as onions or carrots, the number of plants can be as

many as the bed can accommodate. A farmer growing for the market

can usually recover this investment within the first crop season.


Irigasi Pompa Air

Air diambil dari sumur dalam dan dinaikkan melalui pompa air, kemudian dialirkan dengan berbagai cara, misalnya

dengan pipa atau saluran. Pada musim kemarau irigasi ini dapat terus mengairi sawah.

Sistem irigasi dengan “pompa” untuk mendistribusikan air

Irigasi Pasang-Surut di Sumatera, Kalimantan, dan Papua

Dengan memanfaatkan pasang-surut air di wilayah Sumatera, Kalimantan, dan Papua dikenal apa yang dinamakan Irigasi Pasang-

Surat (Tidal Irrigation). Teknologi yang diterapkan di sini adalah: pemanfaatan lahan pertanian

di dataran rendah dan daerah rawa-rawa, di mana air diperoleh dari sungai pasang-surut di mana pada waktu pasang air dimanfaatkan.

Di sini dalam dua minggu diperoleh 4 sampai 5 waktu pada air pasang.

LAHAN PASANG-SURUTLahan pasang surut adalah lahan yang pada musim penghujan (bulan

desember-mei) permukaan air pada sawah akan naik sehingga tidak dapat di tanami padi.

Pada musim kemarau (bulan juli-september) air permukaan akan surut yang mana pada saat itu tanaman padi sawah baru dapat ditanam (pada

lokasi yang berair). (LIPI Kalimantan, 1994)

Combined drainage

and irrigation

system using tidal differences

(source ESCAP 1978)

Irigasi Tanah Kering atau Irigasi Tetes

Di lahan kering, air sangat langka dan pemanfaatannya harus efisien. Jumlah air irigasi yang diberikan ditetapkan berdasarkan kebutuhan tanaman, kemampuan tanah memegang air, serta sarana irigasi yang

tersedia.Ada beberapa sistem irigasi untuk tanah kering, yaitu:(1) irigasi tetes (drip irrigation), (2) irigasi curah (sprinkler irrigation), (3) irigasi saluran terbuka (open ditch irrigation), dan (4) irigasi bawah permukaan (subsurface irrigation).

Untuk penggunaan air yang efisien, irigasi tetes [3] merupakan salah satu alternatif. Misal sistem irigasi tetes adalah pada tanaman cabai.

DRIP IRRIGATIONIn drip irrigation, water flows through a filter into special drip pipes, with

emitters located at different spacings. Water is discharged through the emitters directly into the soil near the plants through a special slow-release

device.


http://primatani.litbang.deptan.go.id/index.php?option=com_content&task=view&id=86&Itemid=56

SISTEM TANAH-AIR-TANAMAN

PADI SAWAH

TRANSPOR AIR: Tanah – Tanaman - Atmosfir

Air bergerak dari tanah, melalui akar, batang, daun, memasuki atmosfer

Laju aliran air ini merupakan fungsiF (selisih potensial, resistensi)

Potential unit name Corresponding value

Water height (cm) 1 10 100 1000 15850

pF (-) 0 1 2 3 4.2

Bar (bar) 0.001 0.01 0.1 1 15.85

Pascal (Pa) 100 1000 10000 10000 1585000

Kilo Pascal (kPa) 0.1 1 10 100 1585

Mega Pascal (MPa) 0.0001 0.001 0.01 0.1 1.585

TEGANGAN AIRPotential air bernilai positif dalam kondisi “free liquid water”

Potential dalam sistem tanah-tanaman-atmosfir bernilai negatif(dalam tanah sawah tergenang, potential air positif)

Air bergerak dari potential tinggi (top of hill) menuju ke potential rendah (bottom of hill)

Tegangan adalah – potential: air bergerak dari tegangan rendah menuju tegangan tinggi

Diunduh dari sumber: http://www.knowledgebank.irri.org/ewatermgt/courses/course1/modules/module02/m02l03.htm ………. 30/10/2012

Rice plants take up water from the soil and transport it upward through the

roots and stems and release it through the leaves and stems as vapor in the atmosphere (called transpiration). The movement of water through the

plant is driven by differences in water potential: water flows from a high

potential to a low potential (imagine free water flow over a sloping surface: water flows from the top, with a high potential, to the bottom, with a low

potential). In the soil-plant-atmosphere system, the potential is high in the soil and low in the atmosphere. Therefore water moves from soil to plant and to

the atmosphere.

Potential = 0

Potential is +

Potential = -

Potential = 0

Potential = +

POTENSIAL AIR DALAM TANAMAN DAN TANAH

-140

-120

-100

-80

-60

-40

-20

0

20

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

ponded water

muddy suspension

impermeable layer

subsoil

ground water table

Pressure head (cm)

Depth (cm)

Water potential in the flooded rice soil

The unsaturated soil“pulls” at the water and

potential is negative

When a paddy rice field falls dry, the soil water potential becomes negative and decreases

Positive water potential

Potential during the growing season in an aerobic soil

(aerobic rice, Changping, China, 2002)

0

10

20

30

40

50

60

70

80

90

100

175 200 225 250 275 300Day number

Soil moisture tension (kPa)

Panicle initiation Flowering Harvest

TEGANGAN LENGAS TANAH SELAMA PERTUMBUHAN TANAMAN

Potential air di atmosphere (di atas tajuk daun) mendorong laju transpirasi potensial, yang merupakan fungsi dari: F (radiation, wind speed, vapor pressure, temperature).

Siang hari yang cerah dan panas => menarik dengan kuat air dari tubuh tanaman

Potential air dalam tanah dipengaruhi oleh sifat-sifat tanah dan kadar air tanah:

Tanah liat mengikat kuat air • Tanah pasir mengikat longgar air • Banyak air tanah : Potensial tinggi

• Air sedikit : Potensial rendahTanah liat yang kering mengikat kuat air (Air tanah sulit

diserap akartanaman)

When the soil is too dry (high soil water tension), it becomes too difficult for roots to take up water and water flow in the plant gets

reduced:• Reduksi transpirasi

• Reduksi photosynthesis• Reduksi luas daun• Daun menggulung

• Percepatan kematian daun• Gabah hampa.

Dampak KEKERINGAN

USING WATER EFFECTIVELY IN A DRY CLIMATE OR DRY SEASON

Water must be used economically in dry areas. To do this, the home garden manager should:

1. prepare the soil so that the plant will grow in a basin-like or sunken space, to help prevent surface water runoff;

2. select crops that grow well under drier conditions (e.g. cassava, sweet potato, eggplant, guava, mango, groundnut, safflower and nug);

3. grow short-term vegetable crops near a water source such as a water well, a drain from a washing area, or a water tank.

Diunduh dari sumber: http://www.fao.org/docrep/003/X3996E/x3996e30.htm ………. 28/10/2012

Reduksi transpirasi sbg fungsi tegangan lengas tanah (IR72)

leaf (Tact/Tpot)

Soil water tension

0

0.2

0.4

0.6

0.8

1

1.2

1 10 100 1000 10000

Leaf rolling factor (-)

Soil water tension (kPa)

Rolled leaves => less canopy photosynthesis

Leaf rolling

Sterilitas Gabah

Turner (1986): relationship between leaf rolling – increased canopy temperature

Spikelet sterility

Less grains

Less yield

Mempercepat kematian daun

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1 10 100 1000 10000

Drought-induced leaf death factor factor (-)


Daun mati => fotosintesis berkurang

0

0.2

0.4

0.6

0.8

1

1.2

1 10 100 1000 10000

Reduction factor (-)


Leaf expansion,

Leaf death

Leaf rolling,Spikelet sterility

Leaf photosynthesis,transpiration

Pengaruh tenganan lengas tanah IR72

photosynthesis

EFEK KEKERINGAN

Less leaves

Reduced leaf expansion

Less canopy photosynthesis

Less biomas

sReduced partitioning to shoot

Reduced leaf photosynthesis, transpiration

Leaf rolling

Less light interception

Spikelet sterility

Less grainsLess yield

Accelerated leaf death

Soil moisture tension

Less canopy transpiration

Efek waktu terjadinya kekeringan: Paling peka saat pembungaan

O’Toole, 1984