DASAR-DASAR EKOSISTEM SAWAH

1. KOMPENDIUM KAJIAN LINGKUNGAN DAN PEMBANGUNAN DASAR-DASAR EKOSISTEM SAWAH Diabstraksikanoleh: Soemarno, PSL-PPSUB 2013

2. GOOD WATER MANAGEMENT PRACTICES FOR RICEFIELD A few principles exist to “get the basics right” for good water management in paddy rice. Bund Good 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. 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 field water management. Good bunds avoid seepage losses Diunduh dari sumber: http://www.knowledgebank.irri.org/factsheetsPDFs/watermanagement_FSWaterSavingGeneral.pdf ………. 30/10/2012

3. THE SOUND WATER MANAGEMENT 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). Diunduh dari sumber: http://www.knowledgebank.irri.org/rkb/2-sound-water-management.html………. 30/10/2012

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

5. THE SOUND WATER MANAGEMENT . Thorough puddling A 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. Diunduh dari sumber: http://www.knowledgebank.irri.org/rkb/2-sound-water-management.html………. 30/10/2012

6. THE SOUND WATER MANAGEMENT Bund preparation and maintenance Good 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 Diunduh dari sumber: http://www.knowledgebank.irri.org/rkb/2-sound-water-management.html………. 30/10/2012

7. THE SOUND WATER MANAGEMENT .Separately irrigated seed beds Most 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. Diunduh dari sumber: http://www.knowledgebank.irri.org/rkb/2-sound-water-management.html………. 30/10/2012

8. THE SOUND WATER MANAGEMENT . Early vegetative stage After 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. Diunduh dari sumber: http://www.knowledgebank.irri.org/rkb/2-sound-water-management.html………. 30/10/2012

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

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

11. IRIGASI Irigasi 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

12. 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

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

14. Irigasi Tradisional dengan Ember Di 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. Diunduh dari sumber: http://www.infonet-biovision.org/default/ct/293/soilconservation………. 28/10/2012

15. 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

16. 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-SURUT Lahan 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)

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

18. SISTEM TANAH-AIR-TANAMAN PADI SAWAH

19. TRANSPOR AIR: Tanah – Tanaman - Atmosfir Air bergerak dari tanah, melalui akar, batang, daun, memasuki atmosfer Laju aliran air ini merupakan fungsi F (selisih potensial, resistensi)

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

21. POTENSIAL AIR DALAM TANAMAN DAN TANAH Potential = 0 Potential is + Potential = - Potential = 0 Potential = +

22. The unsaturated soil “pulls” at the water and potential is negative Water potential in the flooded rice soil

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

24. TEGANGAN LENGAS TANAH SELAMA PERTUMBUHAN TANAMAN Potential during the growing season in an aerobic soil (aerobic rice, Changping, China, 2002)

25. 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 rendah • Tanah liat yang kering mengikat kuat air (Air tanah sulit diserap akartanaman)

26. Dampak KEKERINGAN • 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. • 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: • prepare the soil so that the plant will grow in a basin-like or sunken space, to help prevent surface water runoff; • select crops that grow well under drier conditions (e.g. cassava, sweet potato, eggplant, guava, mango, groundnut, safflower and nug); • 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

27. Reduksi transpirasi sbg fungsi tegangan lengas tanah (IR72) leaf (Tact/Tpot) Soil water tension

28. Leaf rolling Rolled leaves => less canopy photosynthesis

29. Sterilitas Gabah Turner (1986): relationship between leaf rolling – increased canopy temperature Spikelet sterility Less grains Less yield

30. Mempercepat kematian daun Daun mati => fotosintesis berkurang

31. Pengaruh tenganan lengas tanah IR72 Leaf death Leaf photosynthesis, transpiration photosynthesis Leaf rolling, Spikelet sterility Leaf expansion,

32. EFEK KEKERINGAN Soil moisture tension Less canopy transpiration Less canopy photosynthesis Less grains Less yield Less leaves Reduced leaf expansion Less biomass Reduced partitioning to shoot Reduced leaf photosynthesis, transpiration Less light interception Leaf rolling Spikelet sterility Accelerated leaf death

33. O’Toole, 1984 Efek waktu terjadinya kekeringan: Paling peka saat pembungaan