Combined Inorganic Fertilizers Research Articles

Higher soil organic carbon accumulation in the subsoil layer by 37 years combined application of inorganic fertilizers with manure than with rice straw in a double-rice paddy soil

ABSTRACT Organic incorporation is widely recommended to increase Soil Organic Carbon (SOC) content, but little was done to compare the effects of using manure and straw in different soil layers. The study was set up to assess the changes of SOC and oxidizable organic carbon fractions in three soil depths (0–15, 15–30 and 30–45 cm) in a double-rice paddy field subjected to 37 years fertilization schemes [control (CK), combined inorganic fertilization (NPK), inorganic fertilizer NK with pig manure (NKM), and inorganic fertilizer NP or NPK incorporated with rice straw (NPS and NPKS)]. The 37 years’ application of NPK, NKM, NPS and NPKS increased SOC content up to 16.5%, 38.7%, 24.4% and 24.2% across the three soil depths, respectively, compared with CK. Both NPS and NPKS treatment had 77% higher SOC accumulation by sequestering more labile SOC fraction (CHL) in topsoil but not the subsoil layers compared with NPK. Long-term NKM application performed best in SOC accumulation (threefold higher compared with NPK) in all studied soil depths, and in the content of CHL in topsoil. Overall, the integration of inorganic fertilizer with organic manure is more effective than straw incorporation on improving SOC accumulation and stability in not only the topsoil but also the subsoil layers.

Changes in the pH, EC, available P, SOC and TN stocks in a single rice paddy after long-term application of inorganic fertilizers and organic matters in a cold temperate region of Japan

The objective of this study was to determine the changes in the main soil chemical properties including pH, electrical conductivity (EC), available phosphorus (P), soil organic carbon (SOC) and total nitrogen (TN) stocks after long-term (31 years) additions of two types of organic matters—rice straw and rice straw compost, combined with NPK fertilizers in single rice paddy in a cold temperate region of Japan. A long-term experiment on combined inorganic fertilizers and organic matters in paddy rice cultivation began in May 1982 in Yamagata, northeastern Japan. After the 31st harvest, soil samples were collected from five treatments [(1) PK, (2) NPK, (3) NPK + 6 Mg ha−1 rice straw (RS), (4) NPK + 10 Mg ha−1 rice straw compost (CM1), and (5) NPK + 30 Mg ha−1 rice straw compost (CM3)] at five soil depths (0–5, 5–10, 10–15, 15–20, and 20–25 cm). Soil chemical properties of pH, EC, available P, SOC, and TN were analyzed. The pH decreased significantly only at the higher compost rate of 30 Mg ha−1, while EC increased in all the organic matter treatments. Available P significantly increased in the CM1 and CM3 treatments by 55.1 and 86.4 %. The amounts of SOC stock increased by 67.2, 21.4, and 8.6 %, and soil TN stock by 64.1, 20.2, and 8.5 % in CM3, RS, and CM1, respectively, compared to NPK treatment. Significant changes in soil properties were observed after 31 years of organic matter applications with reference to PK- and NPK-fertilized rice paddy soils. A significant decrease in pH was observed with the application of a high rate (30 Mg ha−1) of rice straw compost but not with the conventional rate of 10 Mg ha−1. However, EC increased significantly relative to that of the PK- and NPK-fertilized plots in all the organic matter treatments. Available P significantly increased in the CM1 and CM3 treatments by 55.1 and 86.4 %. The amounts of SOC stock expressed as a percentage of total C applied to the soil were higher from 10 Mg ha−1 compost (28.7 %) than that from 6 Mg ha−1 rice straw (17.4 %), indicating a more effective soil organic C accumulation from rice straw compost than that from original rice straw.

Changes in the soil C and N contents, C decomposition and N mineralization potentials in a rice paddy after long-term application of inorganic fertilizers and organic matter

ABSTRACTA long-term experiment on combined inorganic fertilizers and organic matter in paddy rice (Oryza sativa L.) cultivation began in May 1982 in Yamagata, northeastern Japan. In 2012, after the 31st harvest, soil samples were collected from five fertilizer treatments [(1) PK, (2) NPK, (3) NPK + 6 Mg ha−1 rice straw (RS), (4) NPK + 10 Mg ha−1 rice straw compost (CM1), and (5) NPK + 30 Mg ha−1 rice straw compost (CM3)], at five soil depths (0–5, 5–10, 10–15, 15–20 and 20–25 cm), to assess the changes in soil organic carbon (SOC) content and carbon (C) decomposition potential, total nitrogen (TN) content and nitrogen (N) mineralization potential resulting from long-term organic matter addition. The C decomposition potential was assessed based on the methane (CH4) and carbon dioxide (CO2) produced, while the N mineralization potential was determined from the potassium chloride (KCl)-extractable ammonium-nitrogen (NH4+-N), after 2, 4, 6 and 8 weeks of anaerobic incubation at 30°C in the laboratory. Compared to NPK treatment, SOC in the total 0–25 cm layer increased by 67.3, 21.0 and10.8%, and TN increased by 64.2, 19.7 and 10.6%, in CM3, RS and CM1, respectively, and SOC and TN showed a slight reduction in the PK treatment by 5.2 and 5.7%, respectively. Applying rice straw compost (10 Mg ha−1) instead of rice straw (6 Mg ha−1) to rice paddies reduced methane production by about 19% after the soils were measured under 8 weeks of anaerobic incubation at 30°C. Soil carbon decomposition potential (Co) and nitrogen mineralization potential (No) were highly correlated with the SOC and TN contents. The mean ratio of Co/No was 4.49, lower than the mean ratio of SOC/TN (13.49) for all treatments, which indicated that the easily decomposed organic matter was from soil microbial biomass and soil proteins.