Xiangdong Li

Over the last century, anthropogenic greenhouse-gas (GHG) emissions have changed the global climate, and agriculture plays an important role in the global flux of GHG. Agricultural management practices, such as split N applications and the use of controlled-release fertilisers have significantly increased the crop yield and N-use efficiency by balancing the N demand of crops and the N availability of soils. However, the impacts of these practices on GHG emissions (in particular in wheat–peanut relay intercropping systems) have not been evaluated in detail. In this study, a common compound fertiliser and a controlled release compound fertiliser (CRF) were used the day prior to sowing, at the jointing stage of wheat and at the peanut anthesis stage in ratios of 50-50-0% (JCF100), 35-35-30% (JCF70) and 35-35-30% (JCRF70), with a control treatment of 0 kg ha⁻¹. The findings demonstrated that treatment JCF70 achieved increases in yields of 9.7% and 14.6% for wheat grain and peanut pod, respectively, compared to treatment JCF100; however, this treatment also significantly increased soil emissions of CO₂ and N₂O. In addition, cumulative emissions of CO₂ and N₂O were higher in the peanut growing season by 74.4 and 31.7%, respectively, than in the wheat growing season owing to the relatively higher soil temperature during the former season. Fertilisation combined with irrigation, was found to be the main cause of GHG emissions. Under the same fertiliser rate and N-management style, JCRF70 further increased the yield of peanut pods and the total combined yield of peanut and wheat by 10.3% and 8.9%, respectively, compared to treatment JCF70. The cumulative CO₂ and N₂O emissions in treatment JCRF70 were 20.4–45.4% less than those in treatment JCF70. The total global warming potentials of CO₂ and N₂O were lowest in treatment JCRF70 owing to it providing the highest grain yield. Therefore, N application with three splits, together with the use of a slow-release fertiliser, may be a simple and effective approach to enhance the grain yield whilst reducing the GHG emissions.

To explore whether and how source-sink theory was involved in mediating peanut high yield formation, a field experiment was conducted using 13 major peanut cultivars in North China. Principal component analysis and cluster analysis were used to evaluate natural indicators for the characterization and classification of source-sink types such as leaf area (LA) per plant, number of flowers, and pod rate. The results showed that LA per plant, number of flowers, pod rate, and pod plumpness at the pod-setting and pod-filling stages could be the major characteristics to evaluate source-sink relationship. Based on the source-sink indicators and yield components, these peanut cultivars could be classified into four categories, including source-sink coordination type, large source-few sink type, sufficient source-few sink type, and sufficient source-large sink type. The source-sink coordination type varieties could achieve high yield mainly due to the higher net assimilation rate at the pod-setting stage, the moderate florescence and number of flowers, and the higher economic pods ratio and pod fullness. Large source-few sink type cultivars had higher LA, but lower net assimilation rate and smaller contribution of the leaf area to the yield formation, thus decreased the pod yield. Sufficient source-large sink type cultivars had longer florescence and more flowers compared to others types, leading to reduce the pod rate and pod plumpness, which was the main limiting factor to increase the pod yield. On the contrary, both florescence and the number of flowers per plant of sufficient source-few sink type cultivars were less than others types. In summary, to prevent the redundancy of leaf source, more flowers but less pegs, and more pods but less kernels and to promote the effective proportions and pod fullness resulting in higher pod yield in peanut production, corresponding measures should be taken to control leaf area and amount of flowering according to different source-sink types peanut cultivars.

Our objective was to optimize soil management practices to improve soil health to increase peanut (Arachis hypogaea L.) yield. We studied the effects of using rotary tillage with mulching film or without [rotary tillage with no mulching (RTNM)], plow tillage with mulching film or without, and green manure with mulching film (GMMF) or without [green manure with no mulching (GMNM)] over 3 years in Tai’an, China. Results showed that compared with RTNM treatment, GMNM and GMMF treatments significantly (P < 0.05) increased soil organic carbon, enzymatic activity, and the available nitrogen, phosphorus, and potassium content. The dominant bacterial phyla in the soil across all treatments were Proteobacteria, Acidobacteria, and Actinobacteria. Bacterial richness and diversity in the soil were significantly (P < 0.05) enhanced after GMMF and GMNM treatments compared with those after RTNM treatment. The linear discriminant analysis effect size analysis indicated that Chloroflexi abundance in the 0–10 and 10–20 cm soil layers changed significantly (P < 0.05) after rotary tillage with mulching film and RTNM treatments, respectively, whereas that of Bacteroidetes changed significantly (P < 0.05) in the 0–10 layer after GMNM treatment. The abundance of the Xanthobacteraceae family of Proteobacteria in both soil layers changed significantly (P < 0.05) after GMNM and GMMF treatments. Redundancy analysis revealed that soil physical (soil bulk density and water content), chemical (soil organic carbon, available nitrogen, phosphorus, and potassium), and biological (soil enzymatic activity and nutrient content) characteristics affect the soil bacterial community. Changed soil quality indices may be favorable for leaf photo-assimilate accumulation. Compared with RTNM treatment, GMNM and GMMF treatments significantly increased photosynthesis rate in the peanut leaf and decreased intercellular carbon dioxide concentration. Our results showed that compared with that after RTNM treatment, the average pod yield after GMMF and GMNM treatments increased by 27.85 and 21.26%, respectively, due to increases in the pods per plant and plant numbers. The highest yield of all treatments was obtained from the GMMF-treated plot, followed by that from the GMNM-treated plots. Thus, taking into consideration the residual pollution caused by plastic films, we propose GMNM as a suitable strategy to improve soil physicochemical and microbial properties and to increase the peanut pod yield.

Better management of N fertilizer is essential for improving crop productivity. Wheat (Triticum aestivum L.)–peanut (Arachis hypogaea L.) relay intercropping rotation systems are a mainstay of the measures to improve the economic and food security situation in China. Therefore, a 2-year field study (2015–2017) was conducted to evaluate the effect of different N fertilizer management regimes on the photosynthetic characteristics and uptake and translocation of N in peanut in the wheat–peanut rotation system. We used common compound fertilizer (CCF) and controlled-release compound fertilizer (CRF) at the same N–P₂O₅–K₂O proportion (The contents of N, P₂O₅, and K₂O in the two kinds of fertilizer were 20, 15, and 10%, respectively.). The fertilizer was applied on the day before sowing, at the jointing stage or the flag leaf stage of winter wheat, and at the initial flowering stage of peanut in various proportions, with 0 kg N ha^-1 as the control. Results showed that split applications of N significantly increased leaf area index (LAI) and chlorophyll content and improved photosynthetic rate, thus increasing the pod yield of peanut. Topdressing N at the jointing stage (S1) or at the flag leaf stage of wheat (S2) and supplying part of the N at the initial flowering stage of peanut increased pod yield. Withholding N until the flag leaf stage (S2) did not negatively affect wheat grain yield; however, it increased N accumulation in each organ and N allocation proportions in the peanut pod, ultimately improving pod yield. With the same N–P₂O₅–K₂O proportion and equivalent amounts of nutrient, CRF can decreased malondialdehyde (MDA) and maintain a relatively high LAI and chlorophyll content at the late growth stage of peanut, prolong the functional period of peanut leaves and delay leaf senescence, resulting in an increase of pod yield over that with CCF. At S1, CRF resulted in a better pod yield than CCF by 9.4%, and at S2 it was 12.6% higher. In summary, applying N fertilizer in three splits and delaying the topdressing fertilization until the flag leaf stage of winter wheat increases total grain yields of wheat and peanut. This method could therefore be an appropriate N management strategy for wheat–peanut relay intercropping rotation systems in China.