Dampak penerapan teknik konservasi di lahan kering terhadap produktivitasnya

IDJUDIN, Abdullah Abas, Promotor Prof.Dr.Ir. KPH. Tejoyuwono Notohadikusumo

2006 | Disertasi | S3 Ilmu Pertanian (Ilmu Tanah)

Penelitian “Dampak Penerapan Teknik Konservasi di Lahan Kering terhadap Produktivitasnya” dilaksanakan di tiga lokasi lahan kering yang berbeda kondisi geofisika (geologi, bahan induk, tanah, topografi dan iklim) lahannya yaitu Karangasem, Gunung Kidul (Mintakat Agroekosistem/MA II), Nawungan, Bantul (MA III), dan Glagaharjo, Sleman (MA Va) Propinsi DI Yogyakarta. Penelitian dilaksanakan sejak tahun 1993 hingga tahun 2003. Tujuan penelitian ini adalah mempelajari kemempanan teknik konservasi (cara mekanik dan vegetatif) terhadap gatra: 1) pengendalian erosi tanah, 2) perubahan/perbaikan sifat-sifat fisik, kimia dan mutu tanah, dan 3) perbaikan produktivitas lahan. Metode penelitian yang digunakan adalah model Zachar (1982) dan Dradjad (2004) yaitu cara deluometrik (run off dan erosi), cara pedologi (sifat-sifat fisik dan kimia tanah), cara hidrologi (lengas tanah), dan cara vegetasi (produksi tanaman). Cara deluometrik dan pedologi diukur langsung di lapangan pada kondisi hujan alami, sedangkan cara hidrologi dan vegetasi diukur dengan tidak langsung (pengukuran di lapangan dan penggunaan data sekunder yang tersedia). Data dianalisis dengan regresi berganda model statistical analysis system (SAS) untuk mengetahui perbedaan di antara perlakuan teknik konservasi. Uji jarak ganda Duncan (Duncan’s Multiple Range Test) digunakan untuk mengetahui pengaruh teknik konservasi tanah pada waktu yang berbeda. Hasil penelitian menunjukkan bahwa penerapan teknik konservasi tanah cukup mempan dalam mengendalikan erosi tanah, dan berdampak positif terhadap perbaikan sifat-sifat tanah dan peningkatan produksi tanaman. Pada tahun pertama penelitian, penurunan laju erosi tanah sebesar 23-32% (19,92-27,80 t/ha/th) di Karangasem, 62-76% (17,74-24,80 t/ha/th) di Nawungan, dan 58-70% (11,67-14,77 t/ha/th) di Glagaharjo. Selama kurun 9-10 tahun kemudian, penurunan erosi tanahnya semakin besar yaitu di Karangasem sebesar 75% (10,21 t/ha/th) mendekati nilai di bawah ambang batas erosi yang terbolehkan/BET (9,60 t/ha/th), di Nawungan 69% (10,83 t/ha/th) mencapai nilai di bawah ambang BET (14,40 t/ha/th), dan di Glagaharjo sebanyak 79% (6,85 t/ha/th) mencapai nilai di bawah ambang BET (16,80 t/ha/th). Berkat peranan teknik konservasi tanah yang semakin baik, sifat fisik (meningkatkan agihan pori-pori tanah, memantapkan kestabilan agregat dan menurunkan nilai NPD), menjadi lebih baik, sifat kimia (pH, C, dan P, nilai tukar kation Ca, Mg, dan K, dan KPK meningkat) dan meningkatkan mutu (indeks Storie) tanah. Secara kumulatif, peningkatan sifat fisik, kimia dan mutu tanah, mencapai rata-rata 65% (Karangasem), 91% (Nawungan), dan 97% (Glagaharjo). Produksi tanaman meningkat dengan semakin membaiknya kesuburan tanah. Hasil tanaman semusim meningkat 56-216% (Karangasem), 29-173% (Nawungan), dan 48-97% (Glagaharjo). Persentase hidup tanaman tahunan umur 2 tahun mencapai 63-90% (Karangasem), 63-89% (Nawungan) dan 81-97% (Glagaharjo). Produksi rumput gajah mencapai 31,9 t/ha berdaya dukung pakan ternak sapi sebanyak 2,5 unit (Karangasem), rumput raja 17,5 t/ha berdaya dukung ternak sapi 1,4 unit (Nawungan), rumput gajah (37,6 t/ha) dan rumput raja (14,0 t/ha) dapat memenuhi pakan ternak sapi masing-masing sebanyak 29,9 unit dan 1,1 unit (Glagaharjo). Konservasi air aliran limpas permukaan dalam embung atau tandon air meningkatkan produktivitas lahan (melalui peningkatan lengas, intensitas tanaman, dan kebutuhan minum ternak sapi). Adopsi teknologi oleh petani dan kinerja konservasi tanah serta gatra sosial ekonomi juga meningkat dengan nyata.

Field experiments were carried out at three different biophysical environments consisting of geology, parent material, soil, topography and climate conditions. The locations of experiments were at Karangasem, G. Kidul District (Agroecological Zones/MA II), Nawungan, Bantul District (MA III) and Glagaharjo, Sleman District (MA Va) in the Special Territory of Yogyakarta Province. The objective of the studies were to evaluate the effect of soil conservation techniques (mechanical and vegetatives measures) on: 1) Soil erosion control, 2) Changes of the physical and chemical soil properties, and soil quality, and 3) Improvement of the lands productivity. The effectiveness of soil conservation techniques applied in this research was evaluated by using the Zachar (1982) and Dradjad (2004) methods i.e deluometric methods (run off and soil erosion), pedological methods (physical and chemical soil properties), hydrological methods (soil moisture regions), and vegetation methods (crop productivity). The deluometric and pedological methods were implemented by direct determination using secondary data from the field; hydrological and vegetation methods were practised by indirect determination using a secondary data from the fields. Based on the framework, a double regression model SAS was used to test the effect of soil conservation techniques on the deluometric and pedological aspects. Duncan’s Multiple Range Test was used to compare the effect of various conservation techniques in different times of measurements. Results of studies showed that on the average soil conservation techniques reduced effectivelly soil loss and hence physical and chemical soil properties and increased lands productivity. In the first year of research, soil conservation techniques reduced soil loss by 23- 32% (19.92-27.80 t/ha/yr) at Karangasem, 62-76% (17.74-24.80 t/ha/yr) at Nawungan, and 58- 70% (11.64-14.77 t/ha/yr) at Glagaharjo. During 9-10 years of the soil conservation practiced, soil loss reduced drastically when compared with soils loss without conservation. Soil conservation techniques at Karangasem, reduced soil loss by 75% (10.21 t/ha/yr) that was still a little bit higher than permissible rate of erosion/BET (9.60 t/ha/yr); at Nawungan, reduced soil loss by 69% (10.83 t/ha/yr) was lower than its BET (14.40 t/ha/yr); and at Glagaharjo, reduced soil loss as much as 79% (6.85 t/ha/yr) was lower than its BET (16.80 t/ha/yr). Due to the decreasing soil loss, soil physical properties (increased in pores distribution, increase in aggregate stability, and decrease in dispersion ratio value/NPD), soil chemical properties (increase in pH, C, and P, increase in cation exchange of Ca, Mg, and K, and increase in CEC), and soil quality (Storie index) were improved. Cummulativelly, improvement of soil properties and soil quality were increased by 65% at Karangasem, 91% at Nawungan and 97% at Glagaharjo. Crop productivity increased due to the improvement of physical and chemical soil properties. Perennial crops yields increased by 56-216% at Karangasem, 29-173% at Nawungan and 48-97% at Glagaharjo. Annual crops survival increased by 63-90% at Karangasem, 63-89% at Nawungan and 81-97% at Glagaharjo. Increase in grass production as fodder amounted to 31.9 t/ha (was enough feed for 2.5 cattle/hr) at Karangasem, 17.5 t/ha at Nawungan (was enough to support 1.4 cattle/hr), and 14.0-37.6 t/ha at Glagaharjo (was enough to support 1.11 – 2.9 cattle/hr). Conserving excessive water in small reservoirs during the rainy season proved water to improve lands productivity (soil moisture contribution, high value vegetables plantation and using of cattles drink). The level of adoption of soil conservation practices by farmers and its impact on economic aspect were promising and indicated future prospects.

Kata Kunci : Lahan Kering,Teknik Konservasi,Produktivitas,Teknik Konservasi Lahan Kering,Produktivitas Lahan