[Effects of Biochar and Organic Fertilizer on Saline-alkali Soil N2 O Emission in the North China Plain].

Based on the winter wheat-summer maize rotation field experiment, the effects of biochar and organic fertilizer on saline-alkali soil N2O emissions in the summer maize season were studied in Binzhou in the Shandong Province to provide a theoretical basis for reducing N2O emissions from saline-alkali soil. The experiment includes six treatments with three replications:CK[N:0.2 t·(hm2·a)-1, P2O5:0.12 t·(hm2·a)-1, K2O:0.2 t·(hm2·a)-1], C1[5 t·(hm2·a)-1biochar], C2[10 t·(hm2·a)-1 biochar], C3[20 t·(hm2·a)-1 biochar], M1[7.5 t·(hm2·a)-1 organic fertilizer], and M2[10 t·(hm2·a)-1 organic fertilizer]. The same nitrogen, phosphorus, and potassium fertilizer was applied for each treatment. The results showed that the dynamic trend of the soil N2O fluxes among different treatments were similar. The peak N2O emissions occurred after fertilization (base fertilizer and topdressing). The N2O cumulative emission fluxes accounted for nearly half of the emissions during the whole growth period, and the N2O emissions of the C1, C2, and C3 treatments were lower than that of CK after fertilization. Compared with CK, the N2O cumulative emissions from C1 and C2 were reduced by 45.3% and 31.6%, respectively, but C3, M1, and M2 increased by 17.3%, 37.4%, and 27.6%, respectively. Biochar and organic fertilizer both affected N2O emission fluxes. Applying biochar can reduce N2O emissions, while organic fertilizer can increase N2O emissions. In summary, biochar has a great advantage in reducing N2O emissions in the farmland.

[Effects of different fertilization measures on N2O emission in oil sunflower field in irrigation area of upper Yellow River].

Agricultural soil has become the largest anthropogenic source of atmospheric nitrous oxide (N20). To estimate the impacts of long-term combined application of organic and inorganic fertilizers on N20 emission in a typical winter wheat-oil sunflower cropping system in the Ningxia irrigation area, we measured N20 fluxes using the static opaque chamber-gas chromatograph method and monitored the seasonal dynamics of related factors. Our results showed that nitrogen addition in the previous crop field significantly stimulated N2O emissions during the following oil-sunflower cultivation, and the mean fluxes of N300-OM, N240-OM1/2, N300 and N240 were (34.16 ± 9.72), (39.69 ±10.70), (27.75 ±9.57) and (26.30 ± 8.52) µg . m-2 . h-1, respectively, which were 4.09, 4.75, 3.32 and 3.15 times of the control groups. The total cumulative N2O emissions of fertilizer treatments in growing season was as high as 796.7 to 1242.5 g . hm-2, which was 2.99 to 4.67 times of the control groups. During the growing season, the rates of N2O emission in each month organic and inorganic fertlizers combined treatments were similar at high levels. N2O emission in chemical fertilizer treatments gradually decreased, and the main period of N2O emission occurred at the beginning of growing season. Taking July for example, N2O emission accounted for 41.3% to 41. 8% of total cumulative amount. The amounts of N20 emission under organic and inorganic fertilizers combined treatments were significantly higher than under chemical fertilizer treatments. The N2O emissions were not significantly different between conventional and optimized applications of nitrogen fertilizer under the same fertilizing method, either between N300-OM and N240-OM1/2, or between N300 and N240. On account of the drought, N2O emission in each treatment was mainly affected by soil moisture. N2O emission had a significant positive correlation with soil ammonium nitrogen content under combined applications of organic and inorganic fertilizers, but was not correlated with soil nitrate nitrogen content under all treatments. This showed that adding organic fertilizer could stimulate the NO2 production via increasing the soil ammonium nitrogen content.

[Effect of swine manure application on nitrate leaching in winter wheat field in the Yellow River irrigation area of Ningxia, China].

The effect of swine manure application on nitrate nitrogen leaching was investigated in the Yellow River irrigation area of Ningxia. The field experiment was conducted with 3 Treatments: Traditional fertilization 225 kg N kg x hm(-2) without swine manure (CK), traditional fertilization with swine manure 4500 kg x hm(-2) (T1) and traditional fertilization with swine manure 9000 kg x hm(-2) (T2). Nitrate nitrogen leaching rates were measured for 30, 60, 90 cm depth soil layers with a resin core absorption method. The results indicated that the nitrate leaching losses of T1 and T2 treatments ranged from 9.33 to 14.04 kg x hm(-2) (pure nitrogen), which accounted for 4.2%-6.2% of applied nitrogen fertilizer. Compared to CK, the nitrate leaching losses of T1 and T2 increased by 2.6% and 2.1% at 30 cm depth, increased by 1.5% and decreased by 1.3% at 60 cm depth, decreased by 8.7% and increased by 4.0% at 90 cm depth, respectively. The difference did not reach statistical significance among CK and T1 and T2 in nitrate leaching loss at 30, 60 and 90 cm depths. However, there was a declining trend of nitrate leaching at deep soil layers of treatments. The key period of nitrate leaching loss was from spring reviving to early filling stage, which had a higher daily leaching loss than the average of the whole growth period, and accounted for 58.7%-75.3% of total leaching loss. Compared with CK, the yields of T1 and T2 increased by 9.3% and 12.5%, respectively.

[Effects of seeding-box total fertilization on rice yield and nitrogen loss].

By using seeding-box total fertilization technology, a two-year field plot experiment was conducted to study the effects of applying medium rate of controlled-release urea fertilizer (MN, 80 kg N x hm(-2)), high rate of controlled-release urea fertilizer (HN, 120 kg N x hm(-2)), and conventional urea fertilizer (FP, 300 kg N x hm(-2)) on rice yield and nitrogen loss. As compared with FP, HN did not decrease rice yield significantly, and MN and HN increased the two-year average nitrogen use efficiency (NUE) by 26.2% and 20.7%, respectively (the NUE in treatment FP was 33.2%). In treatment FP, the total N concentration in surface water peaked after 1-3 days of urea application; while in treatments MN and HN, the total N concentration in surfate water peaked after 7-9 days of urea application, and was significantly lower than that in treatment FP throughout the rice growth period. The nitrogen leaching loss in treatment FP mainly occurred at tillering stage, while that in treatments MN and HN delayed to tillering-flowering stage. In all treatments, the NO3(-)-N loss accounted for 59.7% - 64.2% of the total N loss. HN decreased the total N leaching loss by 51.8%, as compared with FP.

Leaching behavior of nitrogen in a long-term experiment on rice under different N management systems.

The leaching behavior of nitrogen was studied in single rice paddy production ecosystems in Tsukuba, Japan after 75 years of consistent fertilization regimes (no fertilizer, ammonium sulfate, a combination of composted rice straw with soybean cake, and fresh clover). During the 75-year period, management was unchanged with respect to rice planting density, irrigation, and net N fertilization for each field to which an N-source was added. Percolation water was collected, from May 2001 to April 2002, using porous suction cups installed in the fields at depths of 15, 40, and 60 cm. All water samples were taken to the laboratory for the measurement of both NH(4) ( + )-N and NO(3) ( - )-N concentrations using a continuous-flow nitrogen analyzer. The result indicated that there were significant differences in N leaching losses between treatments during the rice growing season. Total N leaching was significantly lower with the application of composted rice straw plus soybean cake (0.58 kg N ha( - 1)) than with ammonium sulfate (2.41 kg N ha( - 1)), which resulted in N leaching at a similar level to that with the fresh clover treatment (no significant difference). The majority of this N leaching was not due to NO(3) ( - )-N loss, but to that of NH(4) ( + )-N. The mean N leaching for all fertilizer treatments during the entire rice growing season was 1.58 kg N ha( - 1). Composted rice straw plus soybean cake produced leaching losses which were 65-75% lower than those with the application of fresh clover and ammonium sulfate. N accumulation resulting from nitrification in the fallow season could be a key source of nitrate-N leaching when fields become re-flooded before rice transplanting in the following year; particular attention should be paid to this phenomenon.