Selenium (Se) accumulation in plant foods may be providing dietary Se to minimize the health problems related to Se deficiency. In this study, rice plants were cultivated in different naturally seleniferous soils (0.5–1.5 mg Se kg⁻¹). Se concentration in rice plant tissues was analysed, and the distribution and translocation of Se in rice were also studied. The effect of exogenous Se on yield and Se concentration in rice grain was also investigated by spraying Na₂SeO₃ (15 mg L⁻¹, 15 g ha⁻¹). Results show that Se concentration in root, straw and grain of rice was increased with increased concentrations of Se in seleniferous soils. The root accumulated higher Se than straw and grain under the same naturally seleniferous soil. Spraying Se significantly increased Se concentration in grain, hull, brown rice and polished rice compared with spraying water. Se concentration in the grain fractions was in the following order: Bran > brown rice > whole grain > polished rice > hull. About 13.7% Se in wholegrain was discarded by milling process if about 6.9% of it was polished as bran. Se-enriched rice could be produced in naturally seleniferous soils with Se concentration from 0.5 to 1.0 mg kg⁻¹, and this polished rice would provide enough Se (60–80 μg day⁻¹) to satisfy the human requirement. Therefore, naturally seleniferous soils may be an effective way to produce Se-enriched rice without spraying Se fertilizer, which will be more economically feasible and environmentally friendly for without exogenous Se added to the soils or plants. However, the polished rice and brown rice, produced by spraying Na₂SeO₃ (15 g ha⁻¹) or grown in soil with total Se upto 1.5 mg kg⁻¹ was not suitable for daily human consumption, unless diluted with Se-deficient rice to meet the standard (≤0.3 mg Se kg⁻¹). This study imparted a better understanding of the utilization of seleniferous soils and Se-enriched rice for human health and food safety.

Straw and biochar, two commonly used soil amendments, have been shown to enhance soil fertility and the composition of microbial communities. To compare the effects of straw and biochar on soil fertility, particularly focusing on soil dissolved organic matter (DOM) components, and the physiochemical properties of soil and microbial communities, a combination of high-throughput sequencing and three-dimensional fluorescence mapping technology was employed. In our study, we set up four treatments, i.e., without biochar and straw (B0S0); biochar only (B1S0); straw returning only (B0S1); and biochar and straw (B1S1). Our results demonstrate that soil organic matter (SOM), available nitrogen (AN), and available potassium (AK) were increased by 34.71%, 22.96%, and 61.68%, respectively, under the B1S1 treatment compared to the B0S0 treatment. In addition, microbial carbon (MBC), dissolved organic carbon (DOC), and particulate organic carbon (POC) were significantly increased with the B1S1 treatment, by 55.13%, 15.59%, and 125.46%, respectively. The results also show an enhancement in microbial diversity, the composition of microbial communities, and the degree of soil humification with the application of biochar and straw. Moreover, by comparing the differences in soil fertility, DOM components, and other indicators under different treatments, the combined treatments of biochar and straw had a more significant positive impact on paddy soil fertility compared to biochar. In conclusion, our study revealed the combination of straw incorporation and biochar application has significant impacts and is considered an effective approach to improving soil fertility.

Improvement in fertilization methods, including the optimal matching of nutrient supply and root nutrient absorption by applying nitrogen (N) in the root zone of crop, is necessary to improve N use efficiency (NUE), maintain high stable yield cultivation of maize, and contribute toward future environmental protection. The current practice of split surface broadcasting (SSB) of N is labor-intensive and the surface broadcasting causes a large amount of N to leach into the environment, yet it does not substantially increase maize yield. Root zone fertilization (RZF) has been identified as an efficient way to solve such problems. However, information on the appropriate amount of N fertilizer under RZF for summer maize remains limited. Therefore, in this study, a two-year consecutive field experiment was conducted during 2015–2016 in Anhui province, China, to investigate the effect of N rate and application method on grain yield, nutrient uptake, and NUE of summer maize. The method chosen is not only important to increase grain yield but also critical for reducing N rate and potential loss in the maize cropping system. The experiment comprised six N rates (90, 135, 180, 225, 270, and 360 kg N hm⁻²) and two N application methods in both 2015 and 2016. The two N application methods included SSB and one-time RZF. Results showed that grain yield of summer maize increased first and then decreased with the increase of N rate; however, when the N rate increased to 270 kg hm⁻², the grain yield increased slowly or even decreased. Compared with SSB, RZF increased grain yield by 4%, and the effect of N on grain yield was mainly related to the number of kernels per ear and 1000-seed weight. One-time RZF increased N apparent recovery efficiency by 18% (7.2 percentage points) compared with SSB and also improved the N agronomic efficiency, N physiological efficiency, and N partial factor productivity. In the comprehensive consideration of yield target, NUE, and soil N balance, the optimal N rate for summer maize in the vertisol soil of Anhui province was 180–225 kg hm⁻² for one-time RZF, which reduced N fertilizer by 14% compared with the SSB. Overall, one-time RZF has great potential for green and sustainable agriculture, and thus fertilization machines are worthy of development and application in maize cropping systems.

Straw return utilizes waste resources to reduce the use of chemical fertilizers worldwide. However, information is still lacking on the relative impact of straw return on soil fertility, the nutrient composition of different soil aggregates, and soil microbial communities. Therefore, this study aimed to understand the effects of different management practices on the crop yield, soil fertility, and soil community composition in a 14-year wheat–rice rotation system. The treatments included a control (without fertilizer and straw addition), chemical fertilization (NPK), straw return without fertilizer (S), and straw addition with chemical fertilizer (NPKS). The results showed that NPKS improved the wheat and rice yield by 185.12% and 88.02%, respectively, compared to the CK treatment. Additionally, compared to the CK treatment, the N, P, and K contents of the wheat stem were increased by 39.02%, 125%, and 20.23% under the NPKS treatment. Compared to the CK treatment, SOM, TN, TP, AN, AP, AK, CEC, AFe, AMn, ACu, and AZn were increased by 49.12%, 32.62%, 35.06%, 22.89%, 129.36%, 48.34%, 13.40%, 133.95%, 58.98%, 18.26% and 33.33% under the NPKS treatment, respectively. Moreover, straw addition promoted the creation and stabilization of macro-aggregates in crop soils. The relative abundance of macro-aggregates (0.25–2 mm) increased from 37.49% to 52.97%. Straw addition was associated with a higher proportion of aromatic and carbonyl carbon groups in the soil, which, in turn, promoted the formation of macro-aggregates. Redundancy analysis showed that straw return significantly increased the microbial community diversity. These findings demonstrate that straw addition together with chemical fertilizer could increase the crop yield by improving soil fertility, soil aggregate stability, and the diversity of fungi.

Continuous cropping obstacles (CC), typical of negative plant–soil feedback, have become a non-negligible constraint to the development of agriculture. In order to investigate the main direct drivers influencing the formation of CC soils from the rhizosphere of CC, tobacco fields were collected and their physicochemical properties, microbial community, and metabolomics were measured and analyzed. We also built a mixed linear model to evaluate the impact of these factors on CC. The results suggested that the pH, available potassium (AK), and zinc (Zn) were significantly higher in CC than in normal tobacco (NOR). However, the content of available nitrogen (AN) decreased significantly. Alpha diversity of the bacterial community was significantly reduced. Bacterial community structure also varied significantly in CC. The study identified an ecological cluster with a significant negative correlation with the above-ground biomass of plants. In this cluster, the pathogenic microbiome increased and the beneficial microbiome decreased. The orthogonal partial least squares discriminant analysis (OPLS-DA) indicated clear variations in the metabolomic profiles of the rhizosphere soil between the CC and the NOR. There was an accumulation of toxic compounds and a decrease of beneficial compounds in rhizosphere soils with CC. The mixed linear model showed that only microbiome and metabolites, rather than the soil’s physicochemical properties, significantly affected plant above-ground biomass. According to the model’s standardized coefficients, metabolites contributed more to the continuous crop obstacles than the microbial community. The soil’s physicochemical properties do not directly cause the emergence of CC. The allelochemicals and microbial community are the main direct obstacles to continuous cropping in tobacco, and allelochemicals contribute more than the microbial community.

Phenolic acids are important allelochemicals that contribute to obstacles in continuous cropping systems, significantly impacting soil nutrients, enzyme activities, and the composition of microbial communities. This study explored the effects of treatment time and the concentration of various phenolic acids (salicylic acid and p-hydroxybenzoic acid) on soil nutrients, enzyme activity, and soil microorganisms through cultivation experiments. The results indicated that high-concentration phenolic acid treatment negatively affected the availability of soil nutrients by acidifying the soil, as reflected in the low soil pH, compared to the untreated control. Moreover, the soil extracellular enzymes exhibited varying degrees of improvement when phenolic acids were added. Multi-element analysis revealed that treatment duration, concentration, and the type of phenolic acid significantly affected soil nutrient levels and enzyme activity. Additionally, structural equation modeling indicated a significant correlation between the concentration of phenolic acids and the diversity of microorganisms. Phenolic acids influence the soil ecological environment by altering the relative abundance of functional microorganisms (p_Patescibacteria and p_Mortierellomycota) in the soil. Thus, comprehensive regulation and control of continuous cropping obstacles can be achieved by adjusting the micro-ecological environment of the soil, which, in turn, affects phenolic acid substances present in the soil, thereby alleviating continuous cropping obstacles.