Resilient cropping systems are required to achieve food security in the presence of climate change, and so several long-term conservation agriculture (CA) trials have been established in southern Africa – one of them at the Chitedze Agriculture Research Station in Malawi in 2007. The present study focused on a longitudinal analysis of 10 years of data from the trial to better understand the joint effects of variations between the seasons and particular contrasts among treatments on yield of maize. Of further interest was the variability of treatment responses in time and space and the implications for design of future trials with adequate statistical power. The analysis shows treatment differences of the mean effect which vary according to cropping season. There was a strong treatment effect between rotational treatments and other treatments and a weak effect between intercropping and monocropping. There was no evidence for an overall advantage of systems where residues are retained (in combination with direct seeding or planting basins) over conventional management with respect to maize yield. A season effect was evident although the strong benefit of rotation in El Niño season was also reduced, highlighting the strong interaction between treatment and climatic conditions. The power analysis shows that treatment effects of practically significant magnitude may be unlikely to be detected with just four replicates, as at Chitedze, under either a simple randomised control trial or a factorial experiment. Given logistical and financial constraints, it is important to design trials with fewer treatments but more replicates to gain enough statistical power and to pay attention to the selection of treatments to given an informative outcome.

中文翻译：

---

马拉维长期保护性农业实验的纵向分析和未来实验设计的经验教训

在存在气候变化的情况下实现粮食安全需要有弹性的种植系统，因此在南部非洲建立了几项长期保护性农业 (CA) 试验，其中一项试验于 2007 年在马拉维的奇特泽农业研究站进行。目前的研究侧重于对 10 年试验数据的纵向分析，以更好地了解季节变化的联合影响以及处理之间的特殊对比对玉米产量的影响。更令人感兴趣的是治疗反应在时间和空间上的可变性，以及对具有足够统计能力的未来试验设计的影响。分析显示了平均效应的处理差异，这些差异随种植季节而变化。轮作与其他处理之间的处理效果较强，间作与单作之间的处理效果较弱。没有证据表明保留残留物的系统（与直接播种或种植盆地相结合）在玉米产量方面优于常规管理。尽管厄尔尼诺季节轮换的强大好处也降低了，但季节效应很明显，突出了处理和气候条件之间的强烈相互作用。功效分析表明，在简单的随机对照试验或因子试验下，仅用四次重复可能不太可能检测到实际显着量级的治疗效果，例如 Chitedze。鉴于后勤和财政限制，