Balancing potato yield, soil nutrient supply, and nitrous oxide emissions: An analysis of nitrogen application trade-offs.

Potato has been promoted as a national key staple food to alleviate pressure on food security in China. Appropriate nitrogen (N) application rate is prerequisite and is crucial for increasing yield, improving fertilizer efficiency, and reducing N losses. In the present study, we determined the optimum N application rates by analyzing field trial data from the main potato producing areas of China between 2004 and 2020. We considered the equilibrium relationships between potato yield, N uptake, partial N balance (PNB), and N2O emission under different soil indigenous N supply (INS) scenarios. The results showed that N rate, INS, and their interactions all significantly affect potato yield and nutrient uptake increment. On average, N application increased potato yield and N uptake by 29.5 % and 56.7 %, respectively. The relationship between N rate and yield increment was linear-plateau, while the relationship between N rate and N uptake increment was linear-linear. Soil INS accounted for 63.5 % of total potato N requirement. Potato yield increment and nutrient uptake increment were exponentially negatively correlated with INS and had a significant parabolic-nonlinear relationship with the interaction of N fertilizer application rate and INS. PNB was negatively correlated with fertilizer N supply intensity as a power function. Based on our analysis, a N application rate of 166 kg N ha-1 was found to be sufficient when the target yield was <34 t ha-1. However, when the target yield reached 40, 50 and 60 t ha-1, the recommended N application rate increased to 182, 211, and 254 kg N ha-1, respectively, while ensuring N2O emissions low with an emission factor of 0.2 %. Our findings will help guide potato farming toward cleaner production without compromising environmental benefit.

Characteristics of rice straw decomposition and bacterial community succession for 2 consecutive years in a paddy field in southeastern China.

The characteristics of long-term rice straw decomposition and succession in the bacterial community in the double-rice system are still unclear. Here a 2-year continuous straw bag decomposition experiment was conducted to explore changes in nutrient release, enzyme activity, and bacterial community composition during rice straw decomposition in the double-rice system in Southeast China. After burial in soil, the cumulative dry matter loss rates of rice straw were 38.9%, 72.6%, and 82.7% after 2, 12, and 24 months, respectively. The change in the release rate of straw nitrogen and phosphorus was similar to the dry matter loss, but 93.5% of straw potassium was released after 1st month. Bacterial abundance and community diversity in straw increased rapidly, reaching peaks after 7 and 12 months, respectively. Straw extracellular enzyme activities were the highest in the first 2 months and then gradually decreased over time, and they significantly and positively correlated with straw decomposition rate. Straw decomposition was dominated by copiotrophic Bacilli and Flavobacteriia in the early stages and evolved to be dominated by oligotrophic Acidobacteria, Anaerolineae, Deltaproteobacteria, Saccharibacteria, and Sphingobacteriia in the later stages. Changes in the C/N and K content of straw are the main reasons for bacterial community succession during rice straw decomposition. This study can provide a scientific basis for developing efficient decomposing bacteria agents for rice straw.

Novel ecological ditch system for nutrient removal from farmland drainage in plain area: Performance and mechanism.

The loading of nitrogen (N) and phosphorus (P) from agricultural drainage as the non-point sources is a worldwide environmental issue for aquatic ecosystem. However, how to remove these nutrients effectively from agricultural drainage remains a big challenge with increasing cemented ditches for better management. Here, we designed a novel ecological ditch system which integrated an earth ditch and a cemented ditch with iron-loaded biochar in the Chengdu Plain to reduce the loss of N and P from farmland. After a two-year monitoring, the removal efficiency of total N and total P reached 24.9% and 36.1% by the earth ditch and 30.7% and 57.8% by the integrated ditch system, respectively. The water quality was evidently improved after passing through the ditch system with the marked decrease in the concentrations of N and P. Dissolved organic N, nitrate, and particulate P became the dominant fractions of N and P loss. Rainfall soon after fertilization increased the concentrations of N and P in the ditch system and markedly affected their removal efficiency. The iron-loaded biochar effectively removed N and P from the drainage, especially at the high concentrations, which was mainly attributed to its high adsorption of the dissolved N and P fractions and the interception of the particulate nutrients. Our results indicate that the designed ecological ditch system has a high potential for alleviating agricultural non-point source pollution in the plain area and can be extended to other lowland agricultural ecosystems.

Soybean yield, nutrient uptake and stoichiometry under different climate regions of northeast China.

Climate and soil fertility influence seed yield, nutrient uptake, and nutrient stoichiometry in the plant. We collected soybean [Glycine max (L.) Merr.] data were collected from field experiments in northeast China (warm and cold regions) to study the effect of temperature variations during the crop growing season on seed yield, nutrient uptake and stoichiometry from 2001 to 2017. Soybean seed yield has been increased in the cold region but not in the warm region, where average seed yield was higher. The indigenous nitrogen (N) supply followed the same trend as yield, greater in warmer environments but also increasing over time. The internal efficiency (IE) of N and potassium (K) performed similarly in both climate regions, but phosphorus (P) IE was 30% greater in the warm region than the cold region. For soybean nutrient uptake ratio, the N/K ratio was similar between both regions; however, the N/P ratio was greater in the warmer region relative to the colder region. Overall, the higher temperature experienced in the warm region increased soybean seed yield relative to the cold region, and high soil P accumulation caused soybean P luxury uptake in the cold region of northeast China.

Yield Gap, Indigenous Nutrient Supply and Nutrient Use Efficiency for Maize in China.

Great achievements have been attained in agricultural production of China, while there are still many difficulties and challenges ahead that call for put more efforts to overcome to guarantee food security and protect environment simultaneously. Analyzing yield gap and nutrient use efficiency will help develop and inform agricultural policies and strategies to increase grain yield. On-farm datasets from 2001 to 2012 with 1,971 field experiments for maize (Zea mays L.) were collected in four maize agro-ecological regions of China, and the optimal management (OPT), farmers' practice (FP), a series of nutrient omission treatments were used to analyze yield gap, nutrient use efficiency and indigenous nutrient supply by adopting meta-analysis and ANOVA analysis. Across all sites, the average yield gap between OPT and FP was 0.7 t ha-1, the yield response to nitrogen (N), phosphorus (P), and potassium (K) were 1.8, 1.0, and 1.2 t ha-1, respectively. The soil indigenous nutrient supply of N, P, and K averaged 139.9, 33.7, and 127.5 kg ha-1, respectively. As compared to FP, the average recovery efficiency (RE) of N, P, and K with OPT increased by percentage point of 12.2, 5.5, and 6.5, respectively. This study indicated that there would be considerable potential to further improve yield and nutrient use efficiency in China, and will help develop and inform agricultural policies and strategies, while some management measures such as soil, plant and nutrient are necessary and integrate with advanced knowledge and technologies.

[Soil C, N and P contents and their relationships with soil physical properties in wetlands of Dongting Lake floodplain].

Eight representative soil profiles were installed on three types of wetland (two profiles on Carex spp. -dominated floodplain, four on Phragmites-dominated floodplain, and two on paddy soil) in Dongting Lake floodplain of China in 2004, and their C, N and P contents, microbial biomass C, N and P, <0.001 mm clay particles, and bulk density were measured. The results indicated the spatial distribution of soil C and N and soil microbial biomass C, N, and P were very similar in the profiles (0-100 cm) of three types of wetland, being decreased gradually with depth, except for soil TP which was constant in the profiles. The percentages of soil microbial biomass C, N and P to soil organic C, total nitrogen and total phosphorus decreased gradually with depth. In top layer (0-10 cm), the contents of soil organic C and microbial biomass C and the percentage of soil microbial biomass C to organic C were 19.63-50.20 g x kg(-1), 424.63 - 1 597.36 mg kg(-1), and 3.17% - 4.82%, respectively, the contents of soil total N and microbial biomass N and the percentage of soil microbial biomass N to total N were 1.85-4.45 g x kg(-1), 57.90 - 259.47 mg x kg(-1), and 3.13% - 6.42%, respectively, and the content of soil microbial biomass P and the percentage of soil microbial biomass P to soil total P was 24.16 - 200.99 mg x kg(-1) and 1.09% - 11.20%, respectively. The bulk density of soil top layer (0 -10 cm) was 0.65 - 1.04 g x cm(-3), and the content of < 0.001 mm clay particles was 26.24% - 39.48%. The contents of soil organic C and N and microbial biomass N and P in 0 - 10 cm layer were the highest in Carex spp.-dominated floodplain, followed by paddy soil, and Phragmites-dominated floodplain. Also in 0 - 10 cm layer, the soil microbial biomass C in Carex spp. dominated floodplain and paddy soil was higher than that in Phragmites-dominated floodplain, while the soil bulk density in Phragmites-dominated floodplain was higher than that in paddy soil, and much higher than that in Carex spp. -dominated floodplain. The amount of soil < 0.001 mm clay particles in Carex spp. -dominated floodplain and Phragmites-dominated floodplain was higher than that in paddy soil. In these three types of wetland, soil organic C and N and microbial biomass C, N and P had a significant logarithm correlation (P < 0.01) with <0.001 mm clay particles, and a significant index correlation (P <0.01) with bulk density.