Agronomy

The response of chile peppers (Capsicum spp.) to different irrigation systems is an important factor affecting crop yield, quality parameters, and resistance to soil-borne diseases. The choice of irrigation method significantly impacts fruit size development, water-use efficiency, and overall crop production. Research shows that proper irrigation management can increase yields, improve physiological response, and reduce the incidence of Phytophthora blight, a major disease caused by Phytophthora capsici. However, over-irrigation directly harms chile peppers, causing waterlogging, which, together with increasing weed spreads, creates favorable conditions for P. capsici to grow and increase disease susceptibility. Conversely, under-irrigation can induce drought stress that weakens chile peppers and increases their vulnerability to P. capsici. Although the pathogen cannot thrive or spread in dry soils, severely stressed plants become highly susceptible when even brief periods of moisture occur—such as from dew, light rainfall, or a short irrigation event—creating favorable conditions for infection. In addition, lack of proper timing and insufficient irrigation frequency adversely affect fruit quality characteristics, including capsaicin content (spiciness), color, and nutrient composition. Water stress is extremely damaging because it can reduce the biomass of plants, delay flowering, reduce fruit size, or cause significant yield loss. Considering the importance of water management in chile pepper cultivation and optimizing irrigation systems is important to ensure high-quality crops. Disease susceptibility and effects of different irrigation systems, including inadequate irrigation and excessive irrigation, have been reviewed, with an emphasis on the impact of these irrigation methods on plant growth and yield quality, and on Phytophthora blight. This review aims to provide insights into the importance of irrigation management for sustainable and effective chile pepper production and disease control.

Foxtail millet (Setaria italica (L.) P. Beauv.) exhibits varying efficiency in utilizing different nitrogen (N) forms. While selecting the appropriate N form is a recognized strategy for enhancing yield and reducing N losses, the integrated responses of millet productivity and soil N dynamics to specific N forms remain poorly understood. To address this, a three-year field experiment integrated with ¹⁵N isotopic tracing was conducted on the North China Plain. We systematically evaluated six fertilization treatments: control (CK), organic fertilizer (M), ammonium sulfate (AF), potassium nitrate (NF), ammonium nitrate (ANF), and urea (UR). The results demonstrated that M showed the greatest yield stability but a lower mean grain yield. In contrast, AF treatment achieved the highest grain yield (increasing by 0.90–27.68%) and N accumulation (increasing by 1.65–41.45%), along with the second-highest yield stability. During the growing season, the composition of soil inorganic nitrogen changed significantly. Across all treatments, the dominant form shifted from NH₄⁺-N at the heading stage to NO₃⁻-N at the flowering and maturation stages. As demonstrated by the ¹⁵N-labeling experiments, foxtail millet presented a stage-dependent shift in nitrogen uptake preference from NO₃⁻ to NH₄⁺. An in-depth analysis identified that sustaining soil inorganic N within 30–38 kg·ha⁻¹ and optimizing the NO₃⁻:NH₄⁺ ratio (4.5–5.3 at flowering; 1.5–1.8 at maturity) were critical for achieving high productivity. In conclusion, AF enhances yield by synchronizing N availability with crop demand, thereby optimizing N accumulation and reducing losses. These findings provide critical insights for designing sustainable millet production systems through tailored N source selection.

Accurate quantification of the Fertilizer Nitrogen Equivalence (FNE) of manure is crucial for optimizing integrated nitrogen (N) management and reducing chemical fertilizer use in potato production. However, uncertainties persist regarding FNE’s response to varying application rates and estimation methodologies. A two-year field experiment in Inner Mongolia, China, evaluated multi-gradient sheep manure applications in potato systems to determine whether FNE exhibits diminishing returns with increasing manure rates and to assess the influence of different estimation approaches. Potato N uptake, tuber yield, and growth parameters were measured. FNE was estimated using four methods: total N uptake, fertilizer-derived N uptake, absolute tuber yield, and yield increment. The key findings were: (1) Potato yield and total N uptake increased with higher N inputs but followed the law of diminishing returns. Notably, FNE values remained statistically stable across a wide application range (180–1200 kg N ha⁻¹, equivalent to 8–53 t ha⁻¹ of sheep manure), with no significant decline observed (p > 0.05), regardless of the estimation method. (2) Yield-based FNE values were, on average, 41% lower than those based on N uptake, indicating inefficiencies in converting absorbed N into tuber biomass. Among the methods, the yield increment approach demonstrated the highest consistency and robustness across treatments. In conclusion, our study demonstrates that the FNE of sheep manure remains stable across a broad application range in potato systems, with no evidence of diminishing returns. For practical fertilizer substitution, we recommend using the yield increment-based FNE estimation, as it provides a reliable and agronomically relevant measure for guiding manure application aimed at reducing chemical N inputs while maintaining crop productivity.