Legume cover crop reseeding for strategic field management

地下三叶草（Trifolium subterraneum）似乎是一种适合日本的冬季豆科覆盖作物，因为地下三叶草在秋季通过重新播种来维持自身，并且大种子有助于建立并使早秋生产成为可能。然而，关于日本气候条件下地下三叶草复播与耕作制度的关系的研究很少。基于田间和盆栽试验数据，建立了一个简单的方程模型，以确定三叶草-青贮地下玉米轮作中耕作方式和时间对年复播的影响。将建立的模型插入地下三叶草与杂草生长竞争的生长和制种生命周期模型、土壤中种子库动态的季节变化以及种子成熟后耕作处理下地下三叶草种子在土壤中的运动。模拟结果表明，地下三叶草复播苗的种群数量随耕作方式和耕作时间的不同而变化，与实验结果一致。地下三叶草种子成熟后立即进行旋转式耕作，第二年春天成功地培育出了良好的地下三叶草林。但在种子成熟2个月后进行轮作，地埋三叶草苗木枯萎，田间杂草以冬季杂草为主。这些模拟结果表明，一个合适的耕作制度将能够保持地下三叶草年复一年的成功重建。

Subterranean clover (Trifolium subterraneum) appears to be a suitable winter legume cover crop for Japan because the subterranean clover stands maintain themselves by reseeding in autumn and the large seeds facilitate establishment and enable early fall production. However, there is little information on the relationship between reseeding and tillage system for subterranean clover under Japanese climatic conditions. A simple equation model was developed to determine the effects of tillage method and timing on reseeding from year to year in subterranean clover-silage corn rotation based on data from field and pot experiments. The developed model was inserted into life-cycle models for subterranean clover growth and seed production competing with weed growth, seasonal changes of seed bank dynamics in the soil and subterranean clover seed movement within the soil by tillage treatment after seed maturation. In the simulation results, the population of reseeded subterranean clover seedlings varied according to tillage method and timing and the results agreed with the results of the experiments. Rotary tilling immediately after subterranean clover seed maturation successfully produced a good subterranean clover stand the following spring. However, rotary tillage 2 months after seed maturation withered emerging subterranean clover seedlings and the field was dominated by winter weeds. These simulation results suggest that a suitable tillage system would be able to maintain successful subterranean clover reestablishment from year to year.