Soil Carbon Decomposition, Nitrogen Mineralization, and Rice Yield in Organic Farming Paddies after Lands were Reconstructed in Andisols Tochigi, Japan

RIZA KURNIA SABRI, Dr. Ir. Benito Heru Purwanto, M.P., M.Agr, Prof. Weiguo Cheng

2020 | Skripsi | S1 ILMU TANAH

Jepang memiliki topografi yang luas dari pegunungan tinggi hingga pantai. Sebagian lahan padi di Jepang terletak di jurang, yang merupakan model lansekap desa pertanian Jepang yang disebut sebagai yatsuda di Jepang dengan teras ukuran kecil. Untuk meningkatkan efek produksi pertanian, teras ukuran kecil direkonstruksi menjadi ladang ukuran besar di banyak daerah baru, termasuk bekas lahan pertanian organik. Untuk memahami dinamika nitrogen di sawah pertanian organik yang terkena dampak rekonstruksi tanah, kami mengumpulkan sampel tanah dan tanaman padi dari tujuh sawah pertanian organik baru yang direkonstruksi di Tochigi, Jepang, pada musim panen padi pada akhir September, 2018. Ada adalah profil tanah yang berbeda di sisi yang ditambahkan (sisi timur, ketinggian lebih rendah, sungai terdekat) dan terangkat (sisi barat, ketinggian lebih tinggi, bukit terdekat). Lahan berisi dua sisi yang berbeda sebagai 3 tahun (3A dan 3U) dan 5 tahun setelah direkonstruksi (5A dan 5U). Sampel tanah diambil dari tanah bagian atas (0-15 cm) dan sub-lapisan (kedalaman 15-30 cm) di setiap bidang. Hasil padi dan komponen-komponennya diselidiki dan dianalisis sampel tanamannya. Eksperimen anaerobik dilakukan untuk mengukur dekomposisi C tanah dan mineralisasi N sampel tanah setelah pengukuran sifat-sifat tanah, seperti karbon organik tanah (SOC), total nitrogen (TN), pH, EC, dan tersedia fosfor. Hasil penelitian menunjukkan bahwa 5A memiliki jumlah tertinggi SOC dan TN, C dekomposisi dan tingkat mineralisasi N dibandingkan sisi lain. Selain itu, ada parameter hasil dan pertumbuhan padi yang jauh lebih tinggi di sisi 5A dibandingkan yang lain. Pada penyerapan nitrogen, sisi-sisi yang ditambahkan memiliki perbedaan yang lebih tinggi dan signifikan dibandingkan dengan sisi-sisi tanah yang terangkat setelah direkonstruksi. Secara umum, mineralisasi nitrogen sangat berkorelasi dengan hasil padi (R2 = 0,6277; p <0,001), biomassa padi (R2 = 0,6951; p <0,001), penyerapan nitrogen (R2 = 0,7169; p <0,001), dan penyerapan karbon (R2 = 0,6923; p <0,001). Berdasarkan hasil ini, kami menyimpulkan bahwa tanah setelah direkonstruksi di sisi tambahan memiliki kesuburan tanah tertinggi daripada sisi terangkat karena perbedaan ketebalan profil tanah.

Japan has a wide topographic gradient with the landscape ranges from high mountains to coastal plains. The most paddy field in Japan were located on the ravines, which is the model landscape of Japanese farming village called as yatsuda in Japanese with small size terraces. For improving the agricultural production effect, the small size terraces were reconstructed to big size fields in many areas recently, including former organic farming fields. For understanding the nitrogen dynamics in organic farming paddies as affected by land reconstruction, we collected the soil and rice plant samples from the seven new reconstructed organic rice farming fields in Tochigi, Japan, at the rice harvest season in end of September, 2018. There are different soil profiles in the added (east side, lower elevation, nearby river) and upraised (west side, higher elevation, nearby hill) sides. The fields contained of two different sides as 3 years (3A and 3U) and 5 years after reconstructed (5A and 5U). Soil samples were taken from the top soil (0-15 cm) and sub-layer (15-30 cm depths) in each field. Rice yield and its components, and rice absorbed N were investigated and analyzed by the plant samples. Anaerobic incubation experiment was conducted to measure soil C decomposition and N mineralization of the soil samples after soil properties measurement, such as soil organic carbon (SOC), total nitrogen (TN), pH, EC, and available phosphorous. Results showed that 5A had highest amount of SOC and TN, C decomposition and N mineralization rate compared other sides. Furthermore, there were significantly higher rice yield and rice growth parameters in 5A sides compared the others. On the nitrogen uptake, added sides had higher and significantly different compared to upraised sides of land after reconstructed. Generally, nitrogen mineralization had highly correlation with rice yield (R2=0.6277; p<0.001), rice biomass (R2=0.6951; p<0.001), nitrogen uptake (R2=0.7169; p<0.001), and carbon uptake (R2=0.6923; p<0.001). Based on these results, we concluded that land after reconstructed in added sides have highest soil fertility than the upraised sides due to the differences thickness of the soil profiles.

Kata Kunci : Soil organic carbon, nitrogen mineralization, land reconstruction, organic farming paddies