Background: Continuous cropping is a significant obstacle to sustainable development in the pea (Pisum sativum L.) industry, but the underlying mechanisms of this remain unclear. In this study, we used 16 S rDNA sequencing, transcriptomics, and metabolomics to analyze the response mechanism of roots and soil bacteria to continuous cropping and the relationship between soil bacteria and root phenotypes of different pea genotypes (Ding wan 10 and Yun wan 8). Results: Continuous cropping inhibited pea growth, with a greater effect on Ding wan 10 than Yun wan 8. Metabolomics showed that the number of differentially accumulated metabolites (DAMs) in pea roots increased with the number of continuous cropping, and more metabolic pathways were involved. Transcriptomics revealed that the number of differentially expressed genes (DEGs) increased with the number of continuous cropping. Continuous cropping altered the expression of genes involved in plant-pathogen interaction, MAPK signal transduction, and lignin synthesis pathways in pea roots, with more DEGs in Ding wan 10 than in Yun wan 8. The up-regulated expression of genes in the ethylene signal transduction pathway was evident in Ding wan 10. Soil bacterial diversity did not change, but the relative abundance of bacteria significantly responded to continuous cropping. Integrative analysis showed that the bacteria with significant relative abundance in the soil were strongly associated with the antioxidant synthesis and linoleic acid metabolism pathway of pea roots under continuous cropping once. Under continuous cropping twice, the bacteria with significant relative abundance changes were strongly associated with cysteine and methionine metabolism, fatty acid metabolism, phenylpropanoid biosynthesis, terpenoid backbone biosynthesis, linoleic acid, and amino sugar and nucleotide sugar metabolism. Conclusion: Ding wan 10 was more sensitive to continuous cropping than Yun wan 8. Continuous cropping times and pea genotypes determined the differences in root metabolic pathways. There were common metabolic pathways in the two pea genotypes in response to continuous cropping, and the DEGs and DAMs in these metabolic pathways were strongly associated with the bacteria with significant changes in relative abundance in the soil. This study provides new insights into obstacles to continuous cropping in peas.

Density and fertilization mode are the key factors regulating crude protein synthesis in forage maize; however, there is a lack of systematic understanding of the regulation mechanism. Here, the nitrogen/potassium ratio (N/K), free amino acid (AA) content, crude protein synthesis key enzyme activities (nitrate reductase (NR), glutamine synthetase (GS) and glutamic pyruvic transaminase (GPT)) and crude protein content and yield in leaves, stems, and grain of forage maize, as well as the relationships among them, were explored. The results showed that the N/K of DL-40 (60,000 plants per ha⁻¹, 40% N topdressing at large trumpet stage) and DH-50 (75,000 plants per ha⁻¹, 50% N topdressing at large trumpet stage) significantly increased in leaves, stems, and grain, and correspondingly, NR, GS, and GPT activities in leaves, NR activities in stems, NR and GPT activities in grain, and delayed the decline in AA content. After tasseling, for DL-40 and DH-50 the crude protein content increased by 74.1% and 39.8% in leaves, respectively, 19.9% and 25.6% in grain, respectively, and crude protein yield increased by 16.7% and 35.2% in leaves, respectively, and 23.5% and 25.9% in grain, respectively. There were significant quadratic parabolic relationships of NR, GS, and GPT activities with proportion of topdressing. There was a significant relationship of crude protein content with NR activity in leaves, with NR, GS, and GPT activities in stems and with GPT activity in grain. Regulating the key enzyme activity by adjusting the density and fertilization can significantly improve the crude protein yield of forage maize. Treatments DL-40 and DH-50 significantly increased crude protein content and yield by increasing plant N/K, NR activity in leaves, NR activity in stems, and GPT activity in grain, but slowed the decrease in AA content in leaves, stems, and grain.

Although plastic film mulching is commonly utilized to enhance crop water use efficiency (WUE) in semi-arid areas, the combined effect of plastic film mulching and fertilizer application on Tartary buckwheat yield is still unknown. To address this gap, a four-year field experiment was conducted from 2018 to 2021 to investigate the effect of plastic film mulching and fertilizers on the soil water storage, plant growth, yield, and WUE of Tartary buckwheat in semi-arid environments. The treatments comprised traditional planting without fertilizer (TNF), traditional planting with fertilizer application (N–P₂O₅–K₂O: 40–30–20 kg ha⁻¹) (TF), plastic film mulching with fertilizer application (N–P₂O₅–K₂O: 40–30–20 kg ha⁻¹) (MF), and plastic film mulching without fertilizer (MNF). The results indicated that MF treatment significantly increased leaf area index and SPAD values compared to the other treatments. The yield of Tartary buckwheat under the film mulching increased by 23.3% in comparison to no-mulching treatments, and under fertilizer application it increased by 18.2% compared to no fertilizer. WUE under film mulching exhibited an increase of 3.1% in 2018, 34.9% in 2019, 45.5% in 2020, and 34.6% in 2021, respectively, compared to no mulching. The impact of film mulching on WUE was more significant in years with lower precipitation compared to those with normal or higher precipitation levels. Overall, MF significantly enhanced both the yield and WUE of Tartary buckwheat. This approach proved to be an effective strategy for bolstering drought-resistant yield and optimizing resource efficiency in Tartary buckwheat cultivation in semi-arid regions. Moreover, the positive effects of plastic mulching and fertilizer application on grain yield and water use efficiency were more pronounced in drier years.