Ekofisiologi tanaman kubis bawah naungan dan pemberian bahan pembenah tanah di lahan pasir pantai

SAPARSO, Promotor Prof. Dr. Ir. Tohari, M.Sc

2008 | Disertasi |

Lahan pasir pantai memiliki potensi besar dalam pengembangan berbagai macam tanaman hortikultura di Indonesia. Tanaman kubis dapat dikembangkan di lahan tersebut dengan tingkat produktivitas menguntungkan apabila dilengkapi dengan teknologi spesifik lokasi. Penelitian bertujuan mengkaji pertumbuhan dan hasil kubis bawah naungan dan pemberian lapisan bentonit di lahan pasir pantai. Penelitian laboratorium bertujuan mengidentifikasi karakter berbagai bahan lapisan kedap, dilaksanakan di Laboratorium Scanning Electron Microscope dan X-Ray Diffraction Lemigas Jakarta, Laboratorium Mekanika Tanah Fakultas Teknik UGM dan Laboratorium Hidrologi dan Hidrolika UGM. Percobaan pot dilaksanakan di rumah kaca kebun percobaan Banguntapan, Fakultas Pertanian, UGM bertujuan menentukan nisbah dan ketebalan optimum lapisan bentonit bagi pertumbuhan tanaman kubis dalam media tanah pasir. Percobaan lapangan dilaksanakan di wilayah pengembangan hortikultura lahan pasir pantai Samas, Bantul, Yogyakarta selama musim hujan dan kemarau (Oktober 2004- September 2005). Penentuan permeabilitas dengan metode Falling Head tidak berbeda nyata dengan permeameter ELE28-290. Vertisol, tanah lempung Kokap dan bentonit Nanggulan memiliki permeabilitas 0,01%, 11,0% dan 23,1% terhadap permeabilitas tanah pasiran 558,3 mm/hari. Bahan baku bentonit Boyolali memiliki permeabilitas tidak berbeda dengan bentonit Boyolali kualitas BK masing-masing 4,32 x 10-2 mm/hari dan 2,43 x 10-2 mm/hari. Bentonit Pacitan dan Boyolali kualitas UB mengandung smektit natrium masing-masing 90% dan 95% dan memiliki permeabilitas tidak berbeda nyata masing-masing 1,4 x 10-2 mm/hari dan 1 x 10-2 mm/hari. Ketebalan lapisan bentonit 0,5 cm memiliki permeabilitas lebih tinggi nyata daripada ketebalan 1,0 dan 1,5 cm. Ketebalan lapisan 1 cm dan 1,5 cm memiliki permeabilitas tidak berbeda nyata. Nisbah campuran bentonit Pacitan 15 % dan 20 % terhadap pasir dapat membentuk agregat yang memiliki pori-pori meso dan memiliki permeabilitas 13,7 dan 10,3 mm/hari. Nisbah bentonit 30-100 % memiliki permeabilitas tidak berbeda nyata berkisar 1,4 x 10-2 mm/hari sampai 7,5 x 10-2 mm/hari. Lapisan bentonit 15 % tebal 1,7 cm dalam pot dengan media tanah pasir pantai menghasilkan lengas tanah 8% di atas kapasitas lapangan dan suhu tanah terendah yang sesuai bagi pertumbuhan tanaman kubis dengan indek panen bobot kering dan hasil krop tertinggi. Pemberian lapisan bentonit 30 % dan 45 % memiliki lengas tanah 157,7 % di atas kapasitas lapangan sehingga menghambat pertumbuhan tanaman. Lapisan bentonit 15 % tebal 2 cm di lahan pasir pantai memiliki total lengas tanah 53,6 mm/30 cm dan dapat menyediakan air selama 2 hari sampai batas kritis lengas siap tersedia sedangkan tanah tanpa lapisan kedap hanya bertahan satu hari dengan total lengas tanah 46,5 mm/30 cm. Naungan 60 % menurunkan intensitas cahaya (Xismh) dari 537,7 μmol/m2/detik menjadi 192,1 μmol/m2/detik. Di lahan tanpa lapisan bentonit, naungan 22,4% memberikan hasil 34,9 t/ha, 7,1% lebih tinggi daripada tanpa naungan (32,6 t/ha) mengikuti persamaan Ybshs.tb = -2,0.10-4 X2 ismh + 0,167 Xismh (R2=0,995**). Di lahan dengan lapisan bentonit, naungan menurunkan hasil kubis mengikuti Y bshs.b = -1,0.10-4 X2 ismh + 0,1329 X ismh (R2=0,987**) dengan hasil tertinggi 44,18 t/ha di lahan tanpa naungan (35,6% lebih tinggi daripada di lahan tanpa lapisan bentonit). Tanaman kubis dapat tumbuh baik di lahan pasir pantai pada musim hujan maupun musim kemarau dengan hasil berkisar 36,96 - 40,01 t/ha. Musim hujan memiliki intensitas cahaya, suhu udara dan suhu tanah lebih tinggi daripada musim kemarau. Air pengatusan musim hujan lebih rendah daripada musim kemarau. Kadar prolin daun tidak berbeda nyata antar musim. Laju pertumbuhan tanaman minggu ke 8-10 ditentukan oleh intensitas cahaya dan air pengatusan sesuai persamaan Ylpta 8-10 = 0,000408 X2 ismh –0,00249 X2 atus –0,572 Xismh +4,549Xatus (R2=0,973 **). Bobot segar hasil kubis ditentukan oleh suhu tanah dan air pengatusan mengikuti Ybshs = –0,050 X2 stnh + 0,000114 X2 atus + 3,435 Xstnh –0,108 Xatus (R2=0,985**). Sistem tumpangsari tanaman kubis dan terong memberikan Nisbah Kesetaraan Lahan (NKL) 2,635 dan tidak berbeda nyata antar musim maupun pemberian lapisan kedap. Tanaman kubis sistem tumpangsari memberikan efisiensi penggunaan air dan energi tidak berbeda dengan tanaman kubis bawah naungan 30%.

Coastal sandy land has a great potential for various horticulture crop development in Indonesia. The cabbage crop could be developed in the land to provide profitable productivity if these were completed by the location spesific technology. The research aimed to study the cabbage growth and yield under shading and application of bentonite layer as soil conditioner. The laboratory research studied the characteristic of various impermeable material, was carried out at the Scanning Electron Microscope and X-Ray Diffraction Laboratory Lemigas Jakarta, Soil Machanic Laboratory in Technical Faculty, Hydrology and Hydraulic Laboratory of Gadjah Mada University. Green house experimental was carried out in of Banguntapan experimental station, Agriculture Faculty of GMU, to determine the optimum of bentonite sand-bentonite ratio and the thickness as impermeable layer in supporting the growth and yield of cabbage. The field experiment was conducted in the horticulture development area of Samas coastal sandy land, Bantul, Yogyakarta in rainy and dry season (October 2004-September 2005). Permeability measurement using Falling Head and ELE28-290 permeameter were not significantly different. Permeability of Sentolo Vertisol, Kokap clay soil and Nanggulan bentonite 0,01 %; 11,0 % and 23,1 % from sandy soil permeability 558,3 mm/day. Bentonite raw material of Boyolali bentonite (RMBL) has similar permeability with grade BK bentonite from Boyolali quality (BLBK) permeability, 4,3 x 10-2 mm/day dan 2,43 x 10-2 mm/day. Bentonit from Pacitan (BPIB) and grade UB bentonite from Boyolali (BLUB) has similar (90 and 95%) Na-smectite content as well as permeability (1,4 x 10-2 mm/day dan 10-2 mm/day). Material of 0.5 cm thick has different permeability compared to that 1.0 and 1.5 cm thick material. The last two have similar permeability. Mixture of sand with 15 % and 20 % bentonite from Pacitan has low permeability to respectively 13.7 and 10.3 mm/day, producing aggregate with meso-pore enabling for water movement but capable for water holding for plant need. However, mixture with bentonite proportion 30 % or greater yield insignificantly different permeability, ranging from 1,4 x 10-2 to 7.5 x 10-2 mm/day. Conditioning coastal sandy soil with 15 % of sand-bentonite mixture of 1.7 cm tick increase soil moisture 8 % above normal field capacity and lower soil temperature, leading to highest harvest index as well as crop yield. With more bentonite (30 % and 45 %), soil moisture is much higher, 157,7% above field capacity which disadvantageous for plant growing, giving the lowest crop yield. Application of 15% and 2 cm thickness bentonite sand mixture retent 53,55 mm/30 cm and supported 2 days to reach the readily available water (RAW) threshold. The land without the bentonite layer retent 46,53 mm/30 cm and only one day to reach the RAW threshold. Shading 60 % of full sunlight decreased light intensity (Xismh) from 537,7 μmol/m2/s up to 192,1 μmol/m2/s. In the land without bentonite layer, shading 22,4% produced 34,9 tons per hectare (7,1% above without shading, 32,6 tons per hectare) according to Y bshs.tb = -2,0.10-4 X2 ismh + 0,167 Xismh (R2=0,995**). In the land with bentonite layer, shading decreased the yield significantly according to Y bshs.db = –0,050 X2 stnh + 0,000114 X2 atus + 3,435 Xstnh –0,108 Xatus (R2=0,987**). With the highest yield 44,18 tons per hecatre attained in the land without shading (35,6% above without bentonite layer). The cabbage crop could grow well either in the rainy or dry season and produced 36,96-40,01 tons per hectare. In the rainy season, light intensity, air temperature and soil temperature are higher than the corresponding figure in dry season. Water drainage in rainy season was less than that in the dry season. Leaf proline content did not differ significantly with season. Plant growth rate was determined by light intensity (ISMH) and drainage water (ATUS) according to the equation Ylpta 8-10 = 0,000408X2 ismh –0,00249X2 atus –0,572Xismh+ 4,549Xatus (R2=0,973 **). The crop yield was determined by soil temperature (STNH) and drainage water as Y bshs = –0,050 X2 stnh + 0,000114 X2 atus + 3,435 Xstnh –0,108 Xatus (R2=0,985**). Land equivalent ratio of cabbage-eggplant intercropping was 2.635, and did not differ with season and bentonite layer use. Water and energy use efficiency under intercropping system did not differ with man made artificial shading of 30 %.

Kata Kunci : Tanaman hortikultura,Tanaman kubis,Tanah lahan pasir