Gatra fisiologi dan agronomi kacang tanah akibat kekeringan

HARSONO, Arief, Promotor Prof.Dr.Ir. Tohari, M.Sc

2005 | Disertasi | S3 Ilmu Pertanian (Agronomi)

Kekeringan dapat menurunkan hasil kacang tanah hingga 96% dan menjadi kendala utama untuk mencapai hasil optimal. Penelitian untuk menentukan tingkat ketahanan kekeringan, gatra fisiologi dan agronomi genotipe tahan kekeringan, kebutuhan air pada periode kritis kekeringan dan tipe ketahanan kacang tanah terhadap kekeringan dilaksanakan pada tanah Alfisol di rumah kaca Balitkabi – Malang dan di kebun percobaan Probolinggo. Di rumah kaca, tanggapan genotipe Singa, Badak, Mahesa, Gajah, ICGV/TBN- 93-B-31, LMG/TBN-93-B-54, JPR/ICGV 87123-93-B1-34 dan LMG/ ICGV 87123- 93-B-66 pada lengas tanah 100% hingga 40% kapasitas lapangan dikaji pada musim kering (MK) 2001. Dua genotipe terpilih tahan dan dua rentan kekeringan untuk penelitian selanjutnya, pada MK 2002 tanggapannya dikaji dari 100% hingga 20% kapasitas lapangan. Tanggapan keempat genotipe tersebut terhadap kekeringan dengan pengairan 500 hingga 47,5 mm, pada MK 2002 dikaji di lapangan, dan tanggapannya terhadap kekeringan pada periode pertumbuhan berbeda juga dikaji di rumah kaca dan di lapangan pada MK 2003. Perbedaan ketahanan kekeringan antara genotipe kacang tanah tampak pada lengas tanah 60% hingga 40% kapasitas lapangan. Pada kisaran lengas tanah tersebut, genotipe Singa lebih tahan kekeringan dibandingkan genotipe lain. Kekeringan pada periode kritis (R5-R8) hingga lengas tanah sekitar 50% kapasitas lapangan, genotipe Singa mampu memberikan hasil 1,58 t/ha polong kering atau 65% dari hasil optimal (2,43 t/ha polong kering), genotipe lain memberikan hasil 37% hingga 61% dari hasil optimal. Genotipe kacang tanah tahan kekeringan pada lengas tanah 60% kapasitas lapangan menunjukkan 28,94% lebih efisien dalam penggunaan air (0,49 g/liter), transpirasi 15,13% lebih rendah (1,85 g H20/dm2/jam), fotosintesis 29,27% lebih tinggi (16,69 mg CO2/dm2/jam) dan prolin daun 23,07% lebih rendah (0,10 ppm) dibandingkan genotipe rentan kekeringan. Akar tumbuh 18,28% lebih panjang (205,42 cm), warna daun lebih hijau gelap dengan klorofil 11,73% lebih tinggi (2,38 mg/g daun segar) dibandingkan genotipe rentan kekeringan, daun berukuran sempit lebih dari 75% dan hasil optimal didapatkan pada indeks luas daun sekitar empat. Genotipe tahan kekeringan mampu memberikan hasil 65 hingga 90% dari hasil optimal apabila pada periode R2 hingga R7 diairi lima kali masing-masing sebanyak 29 hingga 49 mm. Ketahanan genotipe Singa terhadap kekeringan tergolong pada avoidance, dengan indikasi pada kekeringan 60-20% kapasitas lapangan berkandungan air relatif daun lebih tinggi dibandingkan genotipe rentan kekeringan masing-masing 88,59-87,32% dan 85,54- 74,62%.

Drought can reduce the yield of groundnut by up to 96%, and has become the main constraint to achieving optimum yields. Research to determine the droughttolerance of groundnut genotypes, physiological and agronomic characteristics of the drought-tolerant genotype, crop water requirements during the period critical for drought risk, and types of groundnut drought-tolerance were conducted in the Balitkabi-Malang glasshouse and in the Probolinggo field experimental farm on Alfisol soils. The responses of Singa, Badak, Mahesa, Gajah, ICGV/TBN-93-B-31, LMG/TBN-93-B-54, JPR/ICGV87123-93-B1-34, and LMG/ ICGV 87123-93-B-66 genotypes grown in soil moisture conditions rangin g from 100% to 40% of field capacity were studied in the glasshouse during the 2001 dry season. Two droughttolerant and two drought-sensitive genotypes were selected for further study under soil moisture conditions of 100% to 20% of field capacity during the 2002 dry season. The responses of the four genotypes to drought under irrigation regimes of 500 mm to 47.5 mm of water were also studied in the field. The influence of drought during different periods of plant growth were studied in the glasshouse and in the field during the 2003 dry season. Differences in the drought-tolerance of the groundnut genotypes were apparent at soil moistures between 60% to 40% of field capacity. Singa was the most drought-tolerant genotype within this soil moisture range, and produced an average yield of 1.58 t/ha (dried pods) or 65% of optimal yield (2.43 t/ha dried pods) following the application of drought stress (soil moisture approximately 50% of field capacity) during the critical period R5-R8. In comparison, drought-sensitive genotypes produced average yields equivalent to 37% to 61% of optimal yield. The drought-tolerant groundnut genotypes, grown in a soil moisture of 60% field capacity, were characterized by 28.94% more efficient water use (0.49 g/liter), 15.13% lower transpiration rate (1.85 g H2 O/dm2/hour), 29.27% higher photosynthesis rate (16.69 mg CO2/dm2/hour) and 23.07% lower proline content (0.10 ppm), compared to the drought-sensitive genotypes. The drought-tolerant genotypes had 75% narrower leaves, 18.28% longer roots (205.42 cm), and darker leaves containing 11.73% more chlorophyll (2.38 mg/g fresh weight), compared to the drought-sensitive genotypes, and the optimal yield obtained at the leaf area index of around four. The drought-tolerant genotype was able to produce yields equivalent to 65 to 90% of optimal yield when irrigated five times with 29 to 49 mm water for each irrigation during the R2 to R7 growth stages. The Singa genotype capacity for drought-tolerance was found to be due to an ‘avoidance’. It was indicated by the relative leaf water content of Singa genotype on the drought 60-20% of field capacity which was higher than the drought-sensitive genotypes, i. e. 88.59-87.32% and 85.54-74.62%, respectively.

Kata Kunci : Tanaman Kacang,Kekeringan,Gatra Fisiologi dan Genotipe