STUDI NERACA AIR PADA TANAMAN AKASIA, ALBISIA, BALSA DAN KAYU PUTIH DI JALUR HIJAU KAMPUS UGM YOGYAKARTA

Karta Sirang, Dr. Ir. Suprodjo Pusposoetardjo M. Eng

1987 | Tesis | S2 Ilmu Kehutanan

Penelitian ini bertujuan untuk menentukan dan memban dingkan kebutuhan air evapotranspirasi (transpirasi dan e­ vaporasi) aktual, throughfall, aliran batang dan intersep­ si tegakan hutan tanaman akasia, albisia, balsa dan kayu pu­tih. Data tersebut merupakan anasir pokok daur air di hutan yang mencirikan jenis dan keadaan pertumbuhan·tegakannya. Hasil penelitian ini sangat bermanfaat dalam memilih jenis tanaman hutan yang sesuai untuk reboisasi dan perbaikan da­ur air suatu kawasan aliran (watershed). Variabel-variabel curah hujan (P), throughfall (TF), a­liran batang (SF), perubahan lengas tanah dan faktor cuaca seperti temperatur dan radiasi matahari diukur, sedang in - tersepsi dihitung berdasarkan P dikurangi TF dan SF. Evapo­transpirasi potensial (ETP) dihitung menggunakan metoda Jensen-Heise. Evapotranspirasi aktual (ET) dihitung berdasar­kan koefisien transpirasi tanaman dan faktor kelengasan _ta­nah yang kebenaran perhitungannya dibandingkan dengan peruba­han lengas tanah terukur. Untuk mengetahui perubahan lengas .. tanah yang disebabkan oleh adanya hujan dan pengaruhnya ter- hadap transpirasi, maka ET dipisah menjadi Edan T dengan ko­efisien masing-masing KS dan KC (KS+KC=l). Analisis n????raca air menggunakan variabel-variabel di a­tas menghasilkan lengas tanah terhitung (NM). Harga NM diang­gap sama dengan lengas terukur (Sl) bila selisih total sela­ma periode waktu tertentu lebih kecil dari 5 persen. Hasil perhitungan demikian itu memberikan harga KC sebagai karak­teristik transpirasi tanaman yang bersangkutan sesuai dengan keadaan setempat. Penelitian ini masih bersifat penda????uluan, maka tegakan hutan yang dipilih rnerupakan komunitas tunggal. Penelitian dilakukan di Bulaksumur, Yogyakarta. Basil analisis neraca air menunjukkan bahwa harga TF pa­da tegakan akasia 75 persen; albisia 77,6 persen; balsa 70,1 persen dan kayu putih 75,9 persen dari curah hujan. Dan harga SF pada tegakan akasia 7,9 ????ersen; albisia 4,3 persen; Intersepsi pada tegakan albisia 18,3 persen; balsa 17,9 per­sen; ctkasia 15,4 persen dan kayu putih 12,6 persen dari cu???? rah hujan. Kecepatan pertumbuhan yang berbeda menyebabkan laju transpirasi berbeda. Transpirasi pada tegakan balsa 22,8 persen; kayu putih 21, 9 persen; al.bisia 21, 7 persen dan aka­sia 21,3 persen dari curah hujan. Penutupan tajuk dan ukuran daun penyusunnya berbeda menyebabkan evaporasi di bawah te­gakan hutan berbeda. Evaporasi di bawah tegakan akasia 3,5 persen; albisia 3,2 persen; kayu. putih 2,9 persen dan balsa 2,5 persen dari curah hujan. Karakteristik transpirasi tiap jenis tanaman hutan yang diteliti dinyatakan oleh hubungan KC dengan waktu dalam ben­tuk persamaan polinomial dengan koefisien polinomialnya 1. Untuk tegakan akasia : Cl=0,9200135; C2=5,464808E-04 C3=-l, 390412E????·04; CL????=8, 02961E-07; C5=1, 165031E- C6=-l, 101694E-10; C7=2,443396E-13 2. Untuk tegakan albisia : Cl=0,9352872; C2=2,777936E-05 C3=-l,768064E-04; C4=1,830728E-06; C5=4,707473E-09; C6=-l,014891E-10; C7=2,73145E-13 3. Untuk tegakan balsa : Cl=0,9451002; C2=4,278168E-03; C3=-2,858862E-Q4; C4=3,620728E-06; C5=-l,297936E-08; C6=-2,710249E-ll; C7=2,471007E-13; C8=-3,710017E-16 4- Untuk tegakan kayu putih : Cl=0,9397752; C2=2,670495E-03; C3=-2,088771E-04; C4=1,830397E-06; C5=5,089101E-09; C6=-9,762149E-ll; C7=2,563318E-13 Evapotranspirasi aktual pada tegakan balsa 25,2 persen; kayu putih 25 persen; albisia 24,9 persen dan akasia 24,5 persen dari curah hujan. Perbedaan jenis dengan ET yang ber­beda mengakibatkan pemanfaatan lengas tanah berbeda kedalam­annya. Tegakan akasia dan kayu putih memanfaatkan lengas ta­nah tidak melebihi kedalaman 300 cm, sedang pada tegakan al­bisia dan balsa memanfaatkan lengas tanah mencapai atau bah­kan mungkin melebihi kedalaman 300 cm.

A preliminary research on water balance in 4 forest stand has been conducted with two main objectives. The first objec­tive is to determine the value of essential components of wa­ter balance in the forest stand. These essential components of water balance consist of evapotranepiration (evaporation and transpiration), throughfall, stemflow and interception which are representing the growth and morphological characte­ristics of a particular tree. The second objective is to com­pare these values of water balance components among several choosen forest stands; i.e. acasia, albizia, balsa and caje­put. Data of these two objectives will be very useful in choosing the most suitable species for a given physical envi­ronment of a particular watershed with the main aim of water yield improvement. Precipitation (P), throughfall (TF), stemflow (SF) and climatic factors such as temperatur and global radiation were measured daily. Soil moisture content was measured in about 7 days interval as an observed soil moisture (Sl). Intercep­was calculated from P minus TF and SF. Potential Evapotrans­piration (ET:P) was calculated by Jensen-Heise method.· Actual evapotranspiration (ET) was calculated ba????ed on crop coeffi­cient and soil moisture dryine rate factor. The validity of calculated ET was demonstrated by the fitness of calculated soil moisture content (NM) and s1. To account for the contri­bution of rainfall to the change in soil moisture content and its influence on transpiration, ET were separated into evapo- ration (E) and transpir????tion (T) with respective coefficients KS and KC in which KS + KC = 1. The calculated soil moisture was considered to be equivalent with Sl if differences of NM and Sl in a certain period of time was smaller than 5 percent. This preliminary research was carried out in Bulaksumur, Yogyakarta. All of the stands forest choosen in the study we­re pure stands of fully grown trees. The result of water balance analysis showed that TF va­ lues in the stand of acasia was 75.0 percent; albizia 77.6 percent; balsa 70.1 percent and cajeput 75.9 percent of total rainfall. SF values in the stand of acasia was 7.9 percent; albizia 4.3 percent; balsa 11.9 percent and cajeput 9.1 per­cent of total rainfall. Interception in the stand of albizia was 18.3 percent; balsa 17.9 percent; acasia 15.4 percent and cajeput 12.6 percent or total rainfall. Differences in canopy coverage intensity, size of leaves­and their configuration caused different transpiration and e­vaporation rates. 1ranspiration in the stand of balsa was 22. a percent; cajeput 21.9 percent; albizia 2l o 7 percent and a­casia 21.3 percent of rainfall. Evaporation in the floor of acasia stand was 3.5 percent; albizia 3.2 percent; cajeput 2.9 percent and balsa 2.5 percent of to????al rainfall. Transpiration characteristics of each epec????es of the ob­served plantG are indicated by the relationship of KC vs Time in the form of a-polynomial 'regression which its respected coefficients : in the acasia stand Cl=.9200135, C2=5•L????64808E­-04, C3=-l.390412E-04, Cl????=8.02961E-07, C5=1.165031E-08, C6= -l.101694E-10, C7=2.443396E-13???? in the albizia stand Cl=.935 2872, C2=2.777936E-05, C3=-l.768064E-04, C4=1.830728E-06, C5= 4.707473E-09, C6=-l.014891E-10, C7=2.73145E-13; in the balsa stand Cl=.9451002, C2=4-278168E-03, C3=-2.858862E-04, C4=3• 620728E-06, C5=-l.297936E-08, C6=-2-710249E-ll, C7=2°471007E­-13, C8=-3-710017E-16; in the cajeput stand Cl=.9397752, C2= 2.670495E-03, C3=-2.088771E-04, C4=1.830397E-06, C5=5.0891E-09, C6=-9-762149E-ll, C7=2.563318E-13. Actual Evapotranspiration in the stand of balsa was 25.2 percent; cajeput 25.0 percent; albizia 24.9 percent and acasi­a 24.5 percent of total rainfall. The difference in root sys­tems and the rate of ET of each tree species caused differen­ces in soil moisture utilization in soil solum.·Acasia and ca­jeput utilized available soil moisture at a depth of soil la­yer less than 300 cm, while albizia and balsa utilized avai­lable soil moisture up to 300 cm or deeper.

Kata Kunci : Neraca Air, Tanaman Akasia, Albisia, Balsa, Kayu Putih, Jalur hijau