Longitudinal analysis of a long-term conservation agriculture experiment in Malawi and lessons for future experimental design

Abstract

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.

Conservation Agriculture Affects Grain and Nutrient Yields of Maize (Zea Mays L.) and Can Impact Food and Nutrition Security in Sub-Saharan Africa

“…The CA treatments lead to an increased grain yield, resulting in a significantly higher yield of proteins and Se, had no effect on the yield of K, Mg, Mn, P, and Zn, and reduced yield of Fe. Our results on grain yield agree with many previous reports that showed that CA maize yields outperformed conventional practise ( 53 – 58 ). In this study, a higher yield increase was obtained, with 14.8–33% in 2018–29 and 21.7–75.2% in 2019–20 (excludingT2).…”

“…Similar disparities in different years of agronomic trials have been reported in different research stations of Malawi ( 64 ). Previous studies have also shown that rainfall and drought during cropping season can influence maize physiological response and agronomic performance under CA conditions ( 32 , 35 , 53 ). A longitudinal analysis of the long-term CA experiment in Malawi showed a season effect on yield, and highlighted the strong interaction between CA treatments and climatic conditions ( 53 ).…”

“…Previous studies have also shown that rainfall and drought during cropping season can influence maize physiological response and agronomic performance under CA conditions ( 32 , 35 , 53 ). A longitudinal analysis of the long-term CA experiment in Malawi showed a season effect on yield, and highlighted the strong interaction between CA treatments and climatic conditions ( 53 ). Therefore, stability of the effect of CA across years should be considered both for agronomic performance and grain nutrient parameters.…”

Increasing zinc concentration in maize grown under contrasting soil types in Malawi through agronomic biofortification: Trial protocol for a field experiment to detect small effect sizes

“…The design of the experiment was therefore informed by a power analysis to detect a 10% effect. This is a novel approach to agronomic biofortification studies; typically, studies on maize (and other crops) have limited replication and therefore limited power to detect small effect sizes (Button et al., 2013; Lark et al., 2020; Uttley, 2019). A second objective is to determine how the effectiveness of agronomic biofortification will differ between Lixisols and Vertisols, with maize grown on Vertisols expected to have higher baseline grain Zn concentrations (Chilimba et al., 2011).…”

Performance of Push–Pull Technology in Low-Fertility Soils under Conventional and Conservation Agriculture Farming Systems in Malawi

“…Composite samples from each treatment (about 5 cobs) were taken for dry cob weight, grain weight, and grain moisture at harvest. Samples were sundried, and grain moisture content was measured and adjusted to 13% using a handheld grain moisture meter (Dickey-John USA Grain Moisture Tester, Minigac GAC 2500_US, R. K. Enterprises, New Delhi, India) as stipulated in Lark et al [37]. The grain moisture adjustment was performed to help standardise the yield performance of different treatments and eliminate experimental error sources due to differences in drying methods.…”