Effects of biochar application methods on greenhouse gas emission and nitrogen use efficiency in paddy fields.

Biochar application in rice production reduces nitrogen loss and greenhouse gases. We conducted in situ experiments for 3 years, with N210B0 (210 kg N ha-1) as the control. Two biochar application methods (B1:15 t ha-1 biochar applied once and B2: biochar applied three times at 5 t ha-1 yr-1) combined with two nitrogen levels (N210: 210 kg N ha-1 and N168: 168 kg N ha-1) were used. Soil physicochemical properties, CH4 and N2O emissions, functional gene abundance, rice yield, and nitrogen use efficiency were analyzed. Both methods improved the physicochemical properties of the soil, however, B1 was less effective than B2 in increasing soil pH, bulk density, organic carbon, total nitrogen, and microbial biomass nitrogen in year 3. B1 had a higher CH4 emission mitigation effect than B2 in 3 consecutive years, mainly due to the higher pmoA gene abundance. B1 showed a higher reduction effect of N2O emissions compared to B2 in year 1, but the opposite was observed in years 2 and 3. B2 had a higher abundance of AOB, nirK, and nosZ genes compared to B1 in year 3. Compared with N210B0, rice yields were increased by 9.1 %, 9.6 %, and 3.6 % with N210B1, N210B2, and N168B2, respectively, over 3 years, while N168B1 improved yields in the previous 2 years. Biochar improved nitrogen use efficiency over 3 consecutive years directly due to increased use efficiency of panicle fertilizer; the effect of B1 was greater than that of B2 during years 1 and 2, while the opposite was observed in year 3. Both Biochar applied once and three times appeared to be promising practices to increase yield and mitigate GHGs. From the GHGI perspective, the biochar applied once combined with 168 kg N ha-1 can further improve nitrogen use efficiency, and reduce GHGs without hindering improvements in rice yield.

Abnormal video homework automatic detection system.

Automatic abnormal detection of video homework is an effective method to improve the efficiency of homework marking. Based on the video homework review of "big data acquisition and processing project of actual combat" and other courses, this paper found some student upload their videos with poor images, face loss or abnormal video direction. However, it is time-consuming for teachers to pick out the abnormal video homework manually, which results in prompt feedback to students. This paper puts forward the AVHADS (Abnormal Video Homework Automatic Detection System). The system uses suffix and parameter identification, Open CV, and the audio classification model based on MFCC feature to realize the automatic detection and feedback of abnormal video homework. Experimental results show the AVHADS is feasible and effective.

An Integrated Analysis of the Rice Transcriptome and Metabolome Reveals Root Growth Regulation Mechanisms in Response to Nitrogen Availability.

Nitrogen is an essential nutrient for plant growth and basic metabolic processes. Root systems play an important role in the ability of plants to obtain nutrients from the soil, and are closely related to the growth and development of above-ground plants. Root morphology analysis showed that root growth was induced under low-nitrogen conditions and inhibited under high-nitrogen conditions. To better understand the molecular mechanisms and metabolic basis underlying the rice root response to nitrogen availability, an integrated analysis of the rice root transcriptome and metabolome under three environmental conditions (low-, control, and high-nitrogen conditions) was conducted. A total of 262 and 262 differentially level metabolites were identified under low- and high-nitrogen conditions, respectively. A total of 696 and 808 differentially expressed genes were identified under low- and high-nitrogen conditions, respectively. For both the differentially expressed genes and metabolites, KEGG pathway analysis indicated that amino acid metabolism, carbon and nitrogen metabolism, phenylpropanoid metabolism, and phytohormones' signal transduction were significantly affected by nitrogen availability. Additionally, variable levels of 65 transcription factors (TFs) were identified in rice leaves exposed to high and low nitrogen, covering 22 TF families. These results also indicate that there is a significant difference in the transcriptional regulation mechanisms of rice roots between low and high nitrogen. In summary, our study provides new information for a further understanding of the response of rice roots to low-nitrogen and high-nitrogen conditions.

Biochar prepared at different pyrolysis temperatures affects urea-nitrogen immobilization and N2O emissions in paddy fields.

BACKGROUND: Food safety has become a major issue, with serious environmental pollution resulting from losses of nitrogen (N) fertilizers. N is a key element for plant growth and is often one of the most important yield-limiting nutrients in paddy soil. Urea-N immobilization is an important process for restoring the levels of soil nutrient depleted by rice production and sustaining productivity. The benefits of biochar application include improved soil fertility, altered N dynamics, and reduced nutrient leaching. However, due to high variability in the quality of biochar, the responses of N loss and rice productivity to biochar amendments, especially those prepared at different pyrolysis temperatures, are still unclear. The main objectives of the present study were to examine the effects of biochar prepared at different pyrolysis temperatures on fertilizer N immobilization in paddy soil and explore the underlying mechanisms. METHODS: Two biochar samples were prepared by pyrolysis of maize straw at 400 °C (B400) and 700 °C (B700), respectively. The biochar was applied to paddy soil at three rates (0, 0.7, and 2.1%, w/w), with or without N fertilization (0, 168, and 210 kg N ha-1). Pot experiments were performed to determine nitrous oxide (N2O) emissions and 15N recovery from paddy soil using a 15N tracer across the rice growing season. RESULTS: Compared with the non-biochar control, biochar significantly decreased soil bulk density while increasing soil porosity, irrespective of pyrolysis temperature and N fertilizer level. Under B400 and B700, a high biochar rate decreased N loss rate to 66.42 and 68.90%, whereas a high N level increased it to 77.21 and 76.99%, respectively. Biochar also markedly decreased N2O emissions to 1.06 (B400) and 0.75 kg ha-1 (B700); low-N treatment caused a decrease in N2O emissions under B400, but this decrease was not observed under B700. An application rate of biochar of 2.1% plus 210 kg ha-1 N fertilizer substantially decreased the N fertilizer-induced N2O emission factor under B400, whereas under B700 no significant difference was observed. Biochar combined with N fertilizer treatment decreased rice biomass and grain yield by an average of 51.55 and 23.90 g pot-1, respectively, but the yield reduction under B700 was lower than under B400. CONCLUSION: Irrespective of pyrolysis temperature, biochar had a positive effect on residual soil 15N content, while it negatively affected the 15N recovery of rice, N2O emissions from soil, rice biomass, and grain yield in the first year. Generally, a high application rate of biochar prepared at high or low pyrolysis temperature reduced the N fertilizer-induced N2O emission factor considerably. These biochar effects were dependent on N fertilizer level, biochar application rate, and their interactions.