Irigasi

Irigasi pada lahan pertanian di New Jersey

Irigasi merupakan upaya yang dilakukan manusia untuk mengairi lahan pertaniannya. Dalam dunia modern saat ini sudah 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 mangalirkan air tersebut ke lahan pertanian. Namun demikian irigasi juga biasa dilakukan dengan membawa air dengan menggunakan wadah kemudian menuangkan pada tanaman satu-persatu. Untuk irigasi dengan model seperti ini di Indonesia biasa disebut menyiram.
Sebagaimana telah diungkapkan, dalam dunia modern ini sudah banyak cara yang dapat dilakukan untuk melakukan irigasi dan ini sudah berlangsung sejak Mesir Kuno.

Sejarah Irigasi di Indonesia

Irigasi Mesir Kuno dan Tradisional Nusantara

Sejak Mesir Kuno telah dikenal dengan memanfaatkan Sungai Nil. Di Indonesia irigasi tradisional telah juga berlangsung sejak nenek moyang kita. Hal ini dapat dilihat juga cara bercocok tanam pada masa kerajaan-kerajaan yang ada di Indonesia. Dengan membendung kali secara bergantian untuk dialirkan ke sawah. Cara lain adalah mencari sumber air pegunungan dan dialirkan dengan bambu yang bersambung. Ada juga dengan membawa dengan ember yang terbuat dari daun pinang atau menimba dari kali yang dilemparkan ke sawah dengan ember daun pinang juga.

Sistem Irigasi Zaman Hindia Belanda

Sistem irigasi adalah salah satu upaya Belanda dalam melaksanakan Tanam Paksa (Cultuurstelsel) pada tahun 1830. Pemerintah Hindia Belanda dalam Tanam Paksa tersebut mengupayakan agar semua lahan yang dicetak untuk persawahan maupun perkebunan harus menghasilkan panen yang optimal dalam mengeksplotasi tanah jajahannya.

Sistem irigasi yang dulu telah mengenal saluran primer, sekunder, ataupun tersier. Tetapi sumber air belum memakai sistem Waduk Serbaguna seperti TVA di Amerika Serikat. Air dalam irigasi lama disalurkan dari sumber kali yang disusun dalam sistem irigasi terpadu, untuk memenuhi pengairan persawahan, di mana para petani diharuskan membayar uang iuran sewa pemakaian air untuk sawahnya.

Waduk Jatiluhur 1955 di Jawa Barat dan Pengalaman TVA 1933 di Amerika Serikat

Tennessee Valley Authority (TVA) [1] yang diprakasai oleh Presiden AS Franklin D. Roosevelt pada tahun 1933 merupakan salah satu Waduk Serba Guna yang pertama dibangun di dunia [2]. Resesi ekonomi (inflasi) tahun 1930 melanda seluruh dunia, sehingga TVA adalah salah satu model dalam membangun kembali ekonomi Amerika Serikat.

Isu TVA adalah mengenai: produksi tenaga listrik, navigasi, pengendalian banjir, pencegahan malaria, reboisasi, dan kontrol erosi. Sehinga di kemudian hari Proyek TVA menjadi salah satu model dalam menangani hal yang mirip. Oleh sebab itu Proyek Waduk Jatiluhur merupakan tiruan yang hampir mirip dengan TVA di AS tersebut.

Waduk Jatiluhur terletak di Kecamatan Jatiluhur, Kabupaten Purwakarta (±9 km dari pusat Kota Purwakarta). Bendungan itu dinamakan oleh pemerintah Waduk Ir. H. Juanda, dengan panorama danau yang luasnya 8.300 ha. Bendungan ini mulai dibangun sejak tahun 1957 oleh kontraktor asal Perancis, dengan potensi air yang tersedia sebesar 12,9 milyar m3/tahun dan merupakan waduk serbaguna pertama di Indonesia.

Jenis Irigasi

Irigasi Permukaan

Irigasi Permukaan terjadi di mana air dialirkan pada permukaan lahan. Di sini dikenal alur primer, sekunder dan tersier. Pengaturan air ini dilakukan dengan pintu air. Prosesnya adalah gravitasi, tanah yang tinggi akan mendapat air lebih dulu.

Irigasi Lokal

Spray Head

Sistem ini air distribusikan dengan cara pipanisasi.

Drip Irrigation

Drip Irrigation - A dripper in action

Drip irrigation, also known as trickle irrigation, functions as its name suggests. Water is delivered at or near the root zone of plants, drop by drop. This method can be the most water-efficient method of irrigation, if managed properly, since evaporation and runoff are minimized. In modern agriculture, drip irrigation is often combined with plastic mulch, further reducing evaporation, and is also the means of delivery of fertilizer. The process is known as fertigation.

Drip Irrigation Layout and its parts

Deep percolation, where water moves below the root zone, can occur if a drip system is operated for too long of a duration or if the delivery rate is too high. Drip irrigation methods range from very high-tech and computerized to low-tech and relatively labor-intensive. Lower water pressures are usually needed than for most other types of systems, with the exception of low energy center pivot systems and surface irrigation systems, and the system can be designed for uniformity throughout a field or for precise water delivery to individual plants in a landscape containing a mix of plant species. Although it is difficult to regulate pressure on steep slopes, pressure compensating emitters are available, so the field does not have to be level. High-tech solutions involve precisely calibrated emitters located along lines of tubing that extend from a computerized set of valves. Both pressure regulation and filtration to remove particles are important. The tubes are usually black (or buried under soil or mulch) to prevent the growth of algae and to protect the polyethylene from degradation due to ultraviolet light. But drip irrigation can also be as low-tech as a porous clay vessel sunk into the soil and occasionally filled from a hose or bucket. Subsurface drip irrigation has been used successfully on lawns, but it is more expensive than a more traditional sprinkler system. Surface drip systems are not cost-effective (or aesthetically pleasing) for lawns and golf courses. In the past one of the main disadvantages of the subsurface drip irrigation (SDI) systems, when used for turf, was the fact of having to install the plastic lines very close to each other in the ground, therefore disrupting the turfgrass area. Recent technology developments on drip installers like the drip installer at New Mexico State University Arrow Head Center, places the line underground and covers the slit leaving no soil exposed.

Sprinkler irrigation

Sprinkler irrigation of blueberries in Plainville, New York

A travelling sprinkler at Millets Farm Centre, Oxfordshire, UK

In sprinkler or overhead irrigation, water is piped to one or more central locations within the field and distributed by overhead high-pressure sprinklers or guns. A system utilizing sprinklers, sprays, or guns mounted overhead on permanently installed risers is often referred to as a solid-set irrigation system. Higher pressure sprinklers that rotate are called rotors and are driven by a ball drive, gear drive, or impact mechanism. Rotors can be designed to rotate in a full or partial circle. Guns are similar to rotors, except that they generally operate at very high pressures of 40 to 130 lbf/in² (275 to 900 kPa) and flows of 50 to 1200 US gal/min (3 to 76 L/s), usually with nozzle diameters in the range of 0.5 to 1.9 inches (10 to 50 mm). Guns are used not only for irrigation, but also for industrial applications such as dust suppression and logging.

Sprinklers may also be mounted on moving platforms connected to the water source by a hose. Automatically moving wheeled systems known as traveling sprinklers may irrigate areas such as small farms, sports fields, parks, pastures, and cemeteries unattended. Most of these utilize a length of polyethylene tubing wound on a steel drum. As the tubing is wound on the drum powered by the irrigation water or a small gas engine, the sprinkler is pulled across the field. When the sprinkler arrives back at the reel the system shuts off. This type of system is known to most people as a "waterreel" traveling irrigation sprinkler and they are used extensively for dust suppression, irrigation, and land application of waste water. Other travelers use a flat rubber hose that is dragged along behind while the sprinkler platform is pulled by a cable. These cable-type travelers are definitely old technology and their use is limited in today's modern irrigation projects.

Center pivot irrigation

The hub of a center-pivot irrigation system.

Center pivot irrigation is a form of sprinkler irrigation consisting of several segments of pipe (usually galvanized steel or aluminum) joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. The system moves in a circular pattern and is fed with water from the pivot point at the center of the arc. These systems are common in parts of the United States where terrain is flat.

Center pivot with drop sprinklers. Photo by Gene Alexander, USDA Natural Resources Conservation Service.

Most center pivot systems now have drops hanging from a u-shaped pipe called a gooseneck attached at the top of the pipe with sprinkler heads that are positioned a few feet (at most) above the crop, thus limiting evaporative losses. Drops can also be used with drag hoses or bubblers that deposit the water directly on the ground between crops. The crops are planted in a circle to conform to the center pivot. This type of system is known as LEPA (Low Energy Precision Application). Originally, most center pivots were water powered. These were replaced by hydraulic systems (T-L Irrigation) and electric motor driven systems (Lindsay, Reinke, Valley, Zimmatic, Pierce, Grupo Chamartin. Most systems today are driven by an electric motor mounted low on each span. This drives a reduction gearbox and transverse driveshafts transmit power to another reduction gearbox mounted behind each wheel. Precision controls, some with GPS location and remote computer monitoring, are now available.

Wheel line irrigation system in Idaho. 2001. Photo by Joel McNee, USDA Natural Resources Conservation Service.

Lateral move (side roll, wheel line) irrigation

A series of pipes, each with a wheel of about 1.5 m diameter permanently affixed to its midpoint and sprinklers along its length, are coupled together at one edge of a field. Water is supplied at one end using a large hose. After sufficient water has been applied, the hose is removed and the remaining assembly rotated either by hand or with a purpose-built mechanism, so that the sprinklers move 10 m across the field. The hose is reconnected. The process is repeated until the opposite edge of the field is reached. This system is less expensive to install than a center pivot, but much more labor intensive to operate, and it is limited in the amount of water it can carry. Most systems utilize 4 or 5-inci (130 mm) diameter aluminum pipe. One feature of a lateral move system is that it consists of sections that can be easily disconnected. They are most often used for small or oddly-shaped fields, such as those found in hilly or mountainous regions, or in regions where labor is inexpensive.

Sub-irrigation

Subirrigation also sometimes called seepage irrigation has been used for many years in field crops in areas with high water tables. It is a method of artificially raising the water table to allow the soil to be moistened from below the plants' root zone. Often those systems are located on permanent grasslands in lowlands or river valleys and combined with drainage infrastructure. A system of pumping stations, canals, weirs and gates allows it to increase or decrease the water level in a network of ditches and thereby control the water table.

Sub-irrigation is also used in commercial greenhouse production, usually for potted plants. Water is delivered from below, absorbed upwards, and the excess collected for recycling. Typically, a solution of water and nutrients floods a container or flows through a trough for a short period of time, 10-20 minutes, and is then pumped back into a holding tank for reuse. Sub-irrigation in greenhouses requires fairly sophisticated, expensive equipment and management. Advantages are water and nutrient conservation, and labor-saving through lowered system maintenance and automation. It is similar in principle and action to subsurface drip irrigation.

Manual irrigation using buckets or watering cans

These systems have low requirements for infrastructure and technical equipment but need high labor inputs. Irrigation using watering cans is to be found for example in peri-urban agriculture around large cities in some African countries.

Automatic, non-electric irrigation using buckets and ropes

Besides the common manual watering by bucket, an automated, natural version of this also exist. Using plain polyester ropes combined with a prepared ground mixture can be used to water plants from a vessel filled with water. The ground mixture would need to be made depending on the plant itself, yet would mostly consist of black potting soil, vermiculite and perlite. This system would (with certain crops) allow you to save expenses as it does not consume any electricity and only little water (unlike sprinklers, water timers, ...). However, it may only be used with certain crops (probably mostly larger crops that do not need a humid environment; perhaps e.g. paprika's).

Irrigation using stones to catch water from humid air

In countries where at night, humid air sweeps the countryside, stones are used to catch water from the humid air by transpiration. This is for example practiced in the vineyards at Lanzarote.

Dry terasses for irrigation and water distribution

In subtropical countries as Mali and Senegal, a special type of terrassing (without flood irrigation or intent to flatten farming ground) is used. Here, a 'stairs' is made trough the use of ground level differences which helps to decrease water evaporation and also distributes the water to all patches (sort of irrigation).

Pengalaman Penerapan Jenis Irigasi Khusus

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. Teknologi ini telah dikenal sejak Abad XIX. Pada waktu itu pendatang di Pulau Sumatera memanfaatkan rawa sebagai kebun kelapa. Di Indonesia terdapat 5,6 juta Ha dari 34 Ha yang ada cocok untuk dikembangkan. Hal ini bisa dihubungkan dengan pengalaman Jepang di Wilayah Sungai Chikugo untuk wilayah Kyushu, di mana di sana dikenal dengan sistem irigasi Ao-Shunsui yang mirip.

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.

Ketersediaan sumber air irigasi sangat penting. Salah satu upaya mencari potensi sumber air irigasi adalah dengan melakukan deteksi air bawah permukaan (groundwater) melalui pemetaan karakteristik air bawah tanah. Cara ini dapat memberikan informasi mengenai sebaran, volume dan kedalaman sumber air untuk mengembangkan irigasi suplemen.

Deteksi air bawah permukaan dapat dilakukan dengan menggunakan Terameter.

Pengalaman Sistem Irigasi Pertanian di Niigata Jepang

Sistem Irigasi Pertanian milik Mr. Nobutoshi Ikezu di Niigata Prefecture. Di sini terlihat adanya manajemen persediaan air yang cukup pada pengelolaan pertaniannya. Sekitar 3 km dari tempat tersebut tedapat sungai besar yang debit airnya cukup dan tidak berlebih. Air sungai dinaikan ke tempat penampungan air menggunakan pompa berkekuatan besar. Air dari tempat penampungan dialirkan menggunakan pipa-pipa air bawah tanah berdiameter 30 cm ke pertanian di sekitarnya. Pada setiap pemilik sawah terdapat tempat pembukaan air irigasi tersebut. Pembagian air ini bergilir berselang sehari, yang berarti sehari keluar, sehari tutup. Penggunaannya sesuai dengan kebutuhan sawah setempat yang dapat diatur menggunakan tuas yang dapat dibuka tutup secara manual. 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. Sedangkan untuk mengatur ketinggian air dilakukan dengan cara menaikan dan menurunkan penutup pintu pembuangan air secara manual. Pembuangan air dari sawah masuk saluran irigasi yang terbuat dari beton sehingga air dengan mudah kembali ke sungai kecil, tanpa merembes terbuang ke bawah tanah. Pencegahan perembesan air dilakukan dengan sangat efisien.

Pengalaman Irigasi Perkebunan Kelapa Sawit

Ketersediaan air merupakan salah satu faktor pembatas utama bagi produksi kelapa sawit. Kekeringan menyebabkan penurunan laju fotosintesis dan distribusi asimilat terganggu, berdampak negatif pada pertumbuhan tanaman baik fase vegetatif maupun fase generatif. Pada fase vegetatif kekeringan pada tanaman kelapa sawit ditandai oleh kondisi daun tombak tidak membuka dan terhambatnya pertumbuhan pelepah. Pada keadaan yang lebih parah kekurangan air menyebabkan kerusakan jaringan tanaman yang dicerminkan oleh daun pucuk dan pelepah yang mudah patah. Pada fase generatif kekeringan menyebabkan terjadinya penurunan produksi tanaman akibat terhambatnya pembentukan bunga, meningkatnya jumlah bunga jantan, pembuahan terganggu, gugur buah muda, bentuk buah kecil dan rendemen minyak buah rendah.

Manajemen irigasi perkebunan kelapa sawit, yaitu: membuat bak pembagi, pembangunan alat pengukur debit manual di jalur sungai, membuat jaringan irigasi di lapang untuk meningkatkan daerah layanan irigasi suplementer bagi tanaman kelapa sawit seluas kurang lebih 1 ha, percobaan lapang untuk mengkaji pengaruh irigasi suplementer (volume dan waktu pemberian) terhadap pertumbuhan vegetatif kelapa sawit dan dampak peningkatan aliran dasar (base flow) terhadap performance kelapa sawit pada musim kemarau, identifikasi lokasi pengembangan dan membuat untuk 4 buah Dam Parit dan upscalling pengembangan dam parit di daerah aliran sungai.

Lihat pula

• Subak (irigasi)
• Irrigation [4]