http://static1.1.sqspcdn.com/static/f/206917/22952968/1371753539597/Conservation+agriculture+and+smallholder+farming+in+Africa+-+The+heretics%27+view.pdf?token=1l3J89raRKJCl7%2F3kEQrssmMonA%3D

Conservation agriculture and smallholder farming in Africa: The heretics' view

One of the primary challenges of our time is to feed a growing and more demanding world population with reduced external inputs and minimal environmental impacts, all under more variable and extreme climate conditions in the future. Conservation agriculture represents a set of three crop management principles that has received strong international support to help address this challenge, with recent conservation agriculture efforts focusing on smallholder farming systems in sub-Saharan Africa and South Asia. However, conservation agriculture is highly debated, with respect to both its effects on crop yields and its applicability in different farming contexts. Here we conduct a global meta-analysis using 5,463 paired yield observations from 610 studies to compare no-till, the original and central concept of conservation agriculture, with conventional tillage practices across 48 crops and 63 countries. Overall, our results show that no-till reduces yields, yet this response is variable and under certain conditions no-till can produce equivalent or greater yields than conventional tillage. Importantly, when no-till is combined with the other two conservation agriculture principles of residue retention and crop rotation, its negative impacts are minimized. Moreover, no-till in combination with the other two principles significantly increases rainfed crop productivity in dry climates, suggesting that it may become an important climate-change adaptation strategy for ever-drier regions of the world. However, any expansion of conservation agriculture should be done with caution in these areas, as implementation of the other two principles is often challenging in resource-poor and vulnerable smallholder farming systems, thereby increasing the likelihood of yield losses rather than gains. Although farming systems are multifunctional, and environmental and socio-economic factors need to be considered, our analysis indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed.

Productivity limits and potentials of the principles of conservation agriculture

In 1999 no-tillage farming, synonymous of zero tillage farming or conservation agriculture, was adopted on about 45 million ha world wide, growing to 72 million ha in 2003 and to 111 million ha in 2009, corresponding to an growth rate of 6 million ha per annum. Fastest adoption rates have been experienced in South America where some countries are using no-tillage farming on about 70% of the total cultivated area. Opposite to countries like the USA where often fields under no-tillage farming are tilled every now and then, more than two thirds of the area under no-tillage systems in South America is permanently not tilled; in other words once adopted, the soil is never tilled again. The spread of no-tillage systems on more than 110 million ha world-wide shows the great adaptability of the systems to all kinds of climates, soils and cropping conditions. No-tillage is now being practiced from the artic circle over the tropics to about 50o latitude south, from sea level to 3 , 000 m altitude, from extremely rainy areas with 2 , 500 mm a year to extremely dry conditions with 250 mm a year. No-till farming offers a way of optimizing productivity and ecosystem services, offering a wide range of economic, environmental and social benefits to the producer and to the society. At the same time, no-till farming is enabling agriculture to respond to some of the global challenges associated with climate change, land and environmental degradation, and increasing cost of food, energy and production inputs. The wide recognition of no-till farming as a truly sustainable system should ensure the spread of the no-till technology and the associated practices of organic soil cover and crop rotation, as soon as the barriers to its adoption have been overcome, to areas where adoption is currently still low. The widespread adoption globally also shows that no-tillage farming cannot any more be considered a temporary fashion or a craze; instead largely through farmers’ own effort, the system has established itself as a farming practice and a different way of thinking about sustainable agro-ecosystem management that can no longer be ignored by scientists, academics, extension workers, farmers at large as well as equipment and machine manufacturers and politicians. Keywords: w orld-wide no-till adoption , zero tillage adoption , conservation agriculture, soil health, climate change, ecosystem services DOI: 10.3965/j.issn.1934-6344.20 1 0.0 1 .0-0 Citation: Rolf D erpsch , Theodor F riedrich , Amir K assam, Li H ongwen . Current status of adoption of no-till farming in the world and some of its main benefits . Int J Agric & Biol Eng, 20 1 0; 3 ( 1 ): <span style="line-height: 140%; font-family:

Current status of adoption of no-till farming in the world and some of its main benefits.

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Conservation agriculture and ecosystem services: An overview

No-till agriculture is generally considered good for soils, and probably also beneficial in relation to climate change adaptation. However, this Perspective argues that the potential for climate change mitigation through soil carbon sequestration that is possible from a change to no-till agriculture has been widely overstated.

Limited potential of no-till agriculture for climate change mitigation

The adoption of conservation agriculture (CA), based on minimal soil movement, permanent soil cover with crop residues or growing plants and crop rotation has advanced rapidly in the Americas and Australia over the last three decades. One of the immediate benefits of CA in dryland agriculture is improved rainfall-use efficiency through increased water infiltration and decreased evaporation from the soil surface, with associated decreases in runoff and soil erosion. This paper focuses on the effect of CA techniques on soil moisture relations in two researcher-managed trials in Zambia and Zimbabwe. In 2005/2006 and 2006/2007, we found significantly higher water infiltration on both sites on CA fields compared to conventionally ploughed fields. At Henderson Research Station, Zimbabwe, on a sandy soil, a direct seeded CA treatments had a 49% and 45% greater infiltration rate than the conventionally tilled plots after a simulated rainfall in both seasons. At Monze Farmer Training Centre, Zambia, on a finertextured soil, the same treatment had 57% and 87% greater infiltration rate than the conventionally tilled control treatment in both seasons. Treatments that included reduced tillage and surface residue retention had less water runoff and erosion on runoff plots at Henderson Research Station, Zimbabwe. On average, soil moisture was higher throughout the season in most CA treatments than in the conventionally tilled plots. However, the full potential of CA in mitigating drought was not evident as there was no significant drought period in either season. Results suggest that CA has the potential to increase the productivity of rainfall water and therefore reduce the risk of crop failure, as was apparent at the Monze Farmer Training Centre, Zambia, in 2005/2006 when a period of moisture stress at tassling affected CA treatments less than the conventionally tilled treatment.

Effects of conservation agriculture techniques on infiltration and soil water content in Zambia and Zimbabwe

Conservation agriculture has been proposed as a widely adapted set of management principles that can assure more sustainable agricultural production. Conservation agriculture removes the emphasis from the tillage component alone and addresses a more enhanced concept of the complete agricultural system. Applying conservation agriculture essentially means altering literally generations of traditional farming practices and implement use. Within the framework of agricultural production, high soil quality equates to the ability of the soil to maintain a high productivity without significant soil or environmental degradation. A comparative soil quality evaluation is one in which the performance of the system is determined in relation to alternatives. Inconsistent effects of a reduction in tillage on the variation in total porosity with depth may be related to differences in traffic on different sites, or on soil quality at the time tillage was reduced or stopped.

Conservation agriculture, improving soil quality for sustainable production systems?

Conservation agriculture (CA) is characterized by surface crop residue retention and minimal soil movement. It is a complex technology that involves not only a change in many of the farmer's cultural practices, but also a change in mind-set to overcome the use of the plow. CA is knowledge-intensive, and success with the system may depend more on what the farmer does than the level of inputs applied. However, smallholder farmers are generally characterized by weak links to information systems outside those of the community, while close community linkages tend to reinforce traditional activities. They commonly manage complex crop-livestock systems, where crop residues play an important role in animal nutrition. This, coupled with communal grazing rights, makes the retention of sufficient surface residues a difficult practice for small farmers, especially in rain-fed systems where residue production levels are low. Smallholders often have weak links to input and output markets, as well as limited ac...

Tailoring conservation agriculture to the needs of small farmers in developing countries: an analysis of issues

SUMMARY Conservation agriculture (CA) systems are based on minimal soil disturbance, crop residue retention and crop rotation. Although the capacity of rotations to break pest and disease cycles is generally recognized, other benefits of crop rotations in CA systems are seldom acknowledged and little understood. We monitored different conventional and CA cropping systems over the period from 2005 to 2009 in a multi-seasonal trial in Monze, southern Zambia. Both monocropped maize and different maize rotations including cotton and the green manure cover crop sunnhemp (Crotalaria juncea) were compared under CA conditions, with the aim of elucidating the effects of crop rotations on soil quality, soil moisture relations and maize productivity. Infiltration, a sensitive indicator of soil quality, was significantly lower on conventionally ploughed plots in all cropping seasons compared to CA plots. Higher water infiltration rate led to greater soil moisture content in CA maize treatments seeded after cotton. Earthworm populations, total carbon and aggregate stability were also significantly higher on CA plots. Improvements in soil quality resulted in higher rainfall use efficiency and higher maize grain yield on CA plots especially those in a two- or three-year rotation. In the 2007/08 and 2008/2009 season, highest yields were obtained from direct-seeded maize after sunnhemp, which yielded 74% and 136% more than maize in the conventionally ploughed control treatment with a continuous maize crop. Even in a two-year rotation (maize-cotton), without a legume green manure cover crop, 47% and 38% higher maize yields were recorded compared to maize in the conventionally ploughed control in the two years, respectively. This suggests that there are positive effects from crop rotations even in the absence of disease and pest problems. The overall profitability of each system will, however, depend on markets and prices, which will guide the farmer’s decision on which, if any, rotation to choose.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S001447971000030X

Rotation in conservation agriculture systems of Zambia: effects on soil quality and water relations.

Experimentation by farmers with conservation agriculture (CA) is increasing in southern Africa, but local longer term data on these new production systems are scarce. This study focuses on CA research at two contrasting on-farm sites and one on-station long-term trial in Zimbabwe. The on-farm trials were conducted at Chikato village on a sandy soil at Zimuto Communal Area with low rainfall and at Hereford farm near Bindura on a clay-rich soil in a high rainfall area. The on-station trial was at Henderson Research Station near Mazowe where more in-depth soil studies were possible. Results of CA systems from the on-station site show on average 38 and 65% greater water infiltration on riplineseeded (RS) and direct-seeded CA treatments compared with conventionally ploughed control treatments. Results from on-farm sites show a 123 and 168% greater aggregate stability at Hereford and 11 and 24% lower dispersion ratio at Chikato on the two CA compared with the conventionally ploughed control treatments. Soil carbon increased by 46% in the first 20 cm on the sandy soils at Chikato in RS and by 104% in direct-seeded CA treatments in four cropping seasons from 2004 to 2008, while it stayed at low levels on the conventionally tilled control treatment. Yields on CA plots were higher on the sandy soils in dry seasons, but lower in very wet seasons because of waterlogging. Yields on clay soils were less affected by the rainfall season. Crop productivity from CA systems increased at all sites over time owing to better management although significant differences between CA and conventional treatments on the three sites were apparent only after several cropping seasons. Conservation agriculture offers practical solutions to small-scale farmers threatened by future soil degradation and fertility loss, but its successful use will depend on weed control and adequate application of fertilizers. The results indicate that there is no immediate increase in maize (Zea mays L.) yield when changing from a tilled to a CA system, but there is gradual improvement in some soil quality indicators over time.

Patrick C. Wall

Papers

Effects of conservation agriculture techniques on infiltration and soil water content in Zambia and Zimbabwe

Conservation agriculture, improving soil quality for sustainable production systems?

Tailoring conservation agriculture to the needs of small farmers in developing countries: an analysis of issues

Rotation in conservation agriculture systems of Zambia: effects on soil quality and water relations.

Effects of conservation agriculture on soil quality and productivity in contrasting agro‐ecological environments of Zimbabwe