Abstract:

To reveal the dynamic responses of dry matter accumulation (DMA) to silage maize−soybean row ratios and maize planting densities across different altitudes, thereby enabling effective prediction of DMA for this cropping system. A two−year field experiment (2023−2024) in Meigu county, Sichuan province, China was conducted. The experiment adopted a three−factor split−plot design with three altitude levels (1600m, 2000m and 2400m), two maize−soybean row ratios (2:3 and 2:4), and three maize planting densities (52500, 67500 and 82500plants·ha⁻¹). Mono−crop dry matter of silage maize and soybeans was determined at six growth stages of silage maize under 18 treatments. Using normalization methods and based on effective accumulated temperature (EAT), a Richards model for DMA in silage maize−soybean inter−cropping system was fitted through model screening under different altitudes and row ratio−density interactions. In addition, a DMA rate curve was employed to quantitatively analyze the relationship between EAT and DMA dynamics under different altitudes, row ratios and maize density. The results showed that EAT emerged as the key meteorological factor regulating both DMA pre− and post−silking in silage maize−soybean strip inter−cropping systems at different altitudes. A dynamic simulation model of DMA using relative effective accumulated temperature as the independent variable Richards model:  was developed, with fitting degree（R²）of 0.9967, which could well fit the dynamic of DMA in silage maize−soybean strip inter−cropping. DMA increased with rising altitude, and the 2:3 row ratio treatment exhibited higher DMA than the 2:4 treatment. The population relative dry matter accumulation rate (RV) was divided into three phases: a slow increase phase (0.0−0.2), a rapid increase phase (0.2−0.7) and a decline phase (0.7−1.0). With increasing altitude, the EAT requirement showed phase−dependent variability: it first decreased and then increased during the slow increase phase, gradually increased during the fast increase phase and decreased before increasing again during the decline phase. The maximum relative DMA rate followed the order: high altitude>low altitude>medium altitude. Under the three altitudes, the maximum population relative dry matter accumulation rates in the 2:3 row ratio treatment were 3.52%, 6.36%, and 6.41% higher than those in the 2:4 treatment, and the medium density resulted in 1.96%, 5.47%, and 6.52% greater increases compared to the low density, respectively, indicating that optimal row ratio and maize density interactions could enhance the RV. Throughout the whole growth period, the relative dry matter average accumulation rate (ARV) of silage maize−soybean inter−crops did not differ significantly between row ratios at low altitude. In contrast, at medium and high altitudes, the 2:3 row ratio led to significantly higher ARV than the 2:4 ratio. Regarding the plant density, ARV at low altitudes gradually decreased with increasing density, while at medium and high altitudes, it first increased and then decreased with increasing planting density.

Key words: Altitude, Row ratio, Density, Silage maize?soybean strip inter?cropping, Effective accumulated temperature, Dry matter accumulation, Mean rate