Ken D. Sayre

The role of conservation agriculture in sustainable agriculture

The paper focuses on conservation agriculture (CA), defined as minimal soil disturbance (no-till, NT) and permanent soil cover (mulch) combined with rotations, as a more sustainable cultivation system for the future. Cultivation and tillage play an important role in agriculture. The benefits of tillage in agriculture are explored before introducing conservation tillage (CT), a practice that was borne out of the American dust bowl of the 1930s. The paper then describes the benefits of CA, a suggested improvement on CT, where NT, mulch and rotations significantly improve soil properties and other biotic factors. The paper concludes that CA is a more sustainable and environmentally friendly management system for cultivating crops. Case studies from the rice–wheat areas of the Indo-Gangetic Plains of South Asia and the irrigated maize–wheat systems of Northwest Mexico are used to describe how CA practices have been used in these two environments to raise production sustainably and profitably. Benefits in terms of greenhouse gas emissions and their effect on global warming are also discussed. The paper concludes that agriculture in the next decade will have to sustainably produce more food from less land through more efficient use of natural resources and with minimal impact on the environment in order to meet growing population demands. Promoting and adopting CA management systems can help meet this goal.

Conservation agriculture and soil carbon sequestration: between myth and farmer reality.

Improving food security, environmental preservation and enhancing livelihood should be the main targets of the innovators of todays farming systems. Conservation agriculture (CA), based on minimum tillage, crop residue retention, and crop rotations, has been proposed as an alternative system combining benefits for the farmer with advantages for the society. This paper reviews the potential impact of CA on C sequestration by synthesizing the knowledge of carbon and nitrogen cycling in agriculture; summarizing the influence of tillage, residue management, and crop rotation on soil organic carbon stocks; and compiling the existing case study information. To evaluate the C sequestration capacity of farming practices, their influence on emissions from farming activities should be considered together with their influence on soil C stocks. The largest contribution of CA to reducing emissions from farming activities is made by the reduction of tillage operations. The soil C case study results are not conclusive. In 7 of the 78 cases withheld, the soil C stock was lower in zero compared to conventional tillage, in 40 cases it was higher, and in 31 of the cases there was no significant difference. The mechanisms that govern the balance between increased or no sequestration after conversion to zero tillage are not clear, although some factors that play a role can be distinguished, e.g., root development and rhizodeposits, baseline soil C content, bulk density and porosity, climate, landscape position, and erosion/deposition history. Altering crop rotation can influence soil C stocks by changing quantity and quality of organic matter input. More research is needed, especially in the tropical areas where good quantitative information is lacking. However, even if C sequestration is questionable in some areas and cropping systems, CA remains an important technology that improves soil processes, controls soil erosion and reduces production cost.

Aggregation and C and N contents of soil organic matter fractions in a permanent raised-bed planting system in the Highlands of Central Mexico

Permanent raised bed planting with crop residue retention is a form of conservation agriculture that has been proposed as an alternative to conventional tillage for wheat production systems in the Central Highlands of Mexico. A field experiment comparing permanent and tilled raised beds with different residue management under rainfed conditions was started at El Batán (State of Mexico, Mexico) in 1999. The percentage of small and large macroaggregates and mean weight diameter (MWD) was significantly larger in permanent raised beds compared to conventionally tilled raised beds both with full crop residue retention (average for maize and wheat), while the percentages free microaggregates was lower. The percentages of small and large macroaggregates and mean weight diameter (MWD) was significantly larger in permanent raised beds with residue retention compared to permanent raised beds with removal of the residue (average for maize and wheat), while the percentages free microaggregates and silt and clay fraction was lower. Cultivation of maize significantly reduced the large macroaggregates, while wheat reduced the silt and clay fraction (average over all systems). Cultivation of maize reduced the C and N content of the free microaggregates compared to soil cultivated with wheat, while removal of plant residue reduced the C and N content of the silt and clay fraction compared to soil where residue was retained. The C and N content of the coarse particulate organic matter (cPOM) and microaggregates within the macroaggregates was significantly larger in permanent raised beds compared to conventionally tilled raised beds both with full residue retention, while C and N content of the cPOM was significantly lower when residue was removed or partially removed compared to the soil where the residue was retained. The δ13C ‰ signatures of the macroaggregates, microaggregates, the silt and clay fraction, cPOM and microaggregates within the macroaggregates were not affected by tillage or residue management when wheat was the last crop, but removal of residue reduced the δ13C ‰ signatures of the macro-, microaggregates and microaggregates within the macroaggregates significantly compared to soil where the residue was retained. Retaining only 30–50% of the organic residue still improved the soil structure considerably compared to plots where it was removed completely. Permanent raised beds without residue retention, however, is a practice leading to soil degradation.

Conservation Agriculture in Maize- and Wheat- Based Systems in the (Sub)tropics: Lessons from Adaptation Initiatives in South Asia, Mexico, and Southern Africa

Conservation agricultures underlying principles—minimal soil disturbance, soil cover and crop rotation—are increasingly recognized as essential for sustainable agriculture. This article summarizes three contrasting cases of adapting conservation agriculture (CA) to smallholder conditions in the (sub)tropics: a) irrigated rice-wheat systems in South Asia; b) rainfed maize/wheat and irrigated wheat systems in Mexico; and c) rainfed maize in Southern Africa. In the South Asia case, farm surveys show rapid and widespread adoption of zero tillage wheat—primarily due to a substantial cost saving (15–16%). In the other cases, uptake so far has been limited—although long-term trials show continuously higher and more stable yields both for maize and wheat. Under marginal conditions CA can generate substantial yield increases—averaging some 50% over conventional smallholder maize yields of 1 ton per ha over 6 years in on-farm trails in Southern Africa. The diverse experiences attest to the wide adaptability of CA systems, which can generate clear economic and potentially enormous environmental benefits. The case studies and wider literature however also reiterate the substantial challenges in terms of targeting, adapting and adopting CA—particularly for smallholders in the (sub)tropics. CA systems are best developed in situ through a multi-stakeholder adaptive learning process to create viable CA-based options that are technically sound, economically attractive, and socially acceptable.

Soil quality as affected by tillage-residue management in a wheat-maize irrigated bed planting system

There is a clear need to develop conservation agriculture technologies appropriate for surface irrigated conditions, and the adoption by small-scale farmers. The objective of this paper is to evaluate the effect on soil quality of five different tillage-crop residue management systems (conventionally tilled raised beds [CTB] with residue incorporated and permanent raised beds [PB] with residue burned, removed, partly retained or fully retained). Data were collected in a long-term trial established in 1992 with a wheat-maize rotation under irrigated, arid conditions in north-western Mexico. Three groups of tillage-straw systems with different characteristics in relation to the soil environment were distinguished: PB-straw burned, CTB-straw incorporated, and PB-straw not burned. The PB-straw burned had high electrical conductivity, Na concentration and penetration resistance and low soil resilience and aggregation, showing that the combination of PB with the burning of residues is not a sustainable management option. The CTB-straw incorporated was distinguished from the PB practices by the soil physical variables, especially the low direct infiltration and aggregate stability, indicating degradation of physical soil quality in this system. The practice of PB, where all or part of the residue is retained in the field, seems to be the most sustainable option for this cropping system.

The Use of the Marasha Ard Plough for Conservation Agriculture in Northern Ethiopia

Indigenous tillage systems are often undervalued in conservation agriculture (CA). In Ethiopia, since the 1970s there have been several attempts to develop and implement often major modifications to the marasha, the traditional ox-drawn ard plough, with the main aim of creating various types of surface depressions. The establishment of furrows and ridges increases soil moisture and grain yield and reduces soil loss. Dissemination of the modified tools, however, remains limited. Recent tendencies are towards testing relatively simple conservation agriculture tools. Major challenges remain, however; the need for capacity building and problems in marketing the tools. From experimental plots, often worked with exotic tools, there is a long road to real adoption by farmers. Rather than developing yet another CA tool, we investigate whether CA-based resource-conserving technologies might be achieved successfully with simple changes to the use of the marasha. On-farm observations on traditional conservation techniques were carried out throughout the northern Ethiopian highlands, and experiments were conducted involving resource-conserving technologies. Farmers traditionally use the marasha ard plough for various types of in situ soil and water conservation by creating surface depressions, either at the moment of sowing (terwah, derdero) or after crop emergence (shilshalo). Building upon this indigenous knowledge, we further developed resource-conserving technologies into a system named derdero+, whereby the traditional ard plough was found suitable for a “bed-and-furrow” system. From the socio-economic point of view, implementation of permanent beds and retention of stubble leads to decreased oxen (and straw) requirements, but also to an increased need for weeding in the first years. To overcome that problem, we introduced glyphosate herbicide into the tillage system. The decreased runoff (−51%) and soil loss (−81%) allow protection of the downslope areas from flooding, but soil nutrient build-up and soil structure improvement are slow processes, and hence the full benefit of the permanent bed system can only be expected after some years. Overall, this type of resource-conserving technology can be part of the ongoing intensification process which includes physical soil and water conservation, slope reforestation and irrigation development. It has, however, its own niche: the cropped land sensu stricto, i.e. the most important part of the land, both for the farmer and for a nation that is striving for long-term food security.

Identifying factors that determine kernel number in wheat

Abstract Understanding variation in kernel number per unit area (KNO) is of major importance in understanding yield and in identifying opportunities to increase yield potential. Factors that determine KNO should therefore be identified considering wide ranges in both crop and environmental conditions. Several field experiments with various spring wheat cultivars were conducted over three years in Mexico. Wide ranges in crop and environmental conditions were obtained by varying N application rates and timing and by different planting dates and locations. Crop development from emergence (DC10) to physiological maturity (DC90) was divided in three phases, with the intermediate phase II ranging approximately from early booting (DC40) to final anthesis (DC70). A photothermal quotient (PTQ) during phase II failed to explain the variation in KNO. Biomass at anthesis explained 72% of the variance, but could not explain some deviant situations and the relation was strongly cultivar specific. Biomass accumulation during phase II more accurately (80%) explained the deviant situations, except one particular location, and cultivar differences became even more pronounced. At this location KNO was also well explained by non-grain spike weight at a week from anthesis, with a constant number of kernels per unit spike dry matter, while differences among cultivars tended to disappear. Factors that are identified to determine KNO are discussed.

Evaluating spatial within plot crop variability for different management practices with an optical sensor

It is essential to have an indication of the sustainability of an agricultural system in addition to the potential, immediate benefits well before the catastrophic consequences of non-sustainability become apparent. Long-term experiments are best suited to test sustainability of a given system. This paper has a dual objective: (1) evaluate the Greenseeker handheld NDVI sensor as a tool for measuring within plot spatial variability, (2) address the question whether different management practices affect spatial within-plot crop growth variability and what this spatial variability tells us about the cropping system performance. Therefore, spatial and time variability of crop performance were measured during the 2004 and 2005 crop cycle for all plots of the different management treatments of a long-term (started 1991) tillage and residue management trial. The NDVI readings measured with the handheld sensor correlated well with the visual scoring in the field. The hand-held sensor is time-efficient and gave reproducible results. The potential for using this tool to detect spatial crop variability, both within and between plots/treatments, is promising. The coefficient of variation (CV) for the NDVI measurement sequence in each plot was determined. The CV’s throughout the crop season reflected the canopy expansion and senescence curve of maize and wheat. The CV was high at the beginning of the crop season, however, once the canopy began to close, leaves from larger plants covered the leaves and whorl of smaller plants, extending further into the linear row. Measurements to investigate spatial variability related to crop performance should thus be done after this initial stage at the end of the vegetative period when the vegetative biomass of the crops is fully established. Zero tillage systems without surface residue retention produced high CVs of the NDVI sequence and high spatial crop variability throughout the season, even after the vegetative period. As the only factors differing between the different plots are the tillage/residue/rotation practices and as similar patterns were found for all plots representing repetitions of the same management practice (zero tillage without residue retention), increased variability is an indicator of agronomic mismanagement or, conversely, of sound agriculturally production practices.

The natural abundance of 13C with different agricultural management by NIRS with fibre optic probe technology.

In the present study the natural abundance of (13)C is quantified in agricultural soils in Mexico which have been submitted to different agronomic practices, zero and conventional tillage, retention of crop residues (with and without) and rotation of crops (wheat and maize) for 17 years, which have influenced the physical, chemical and biological characteristics of the soil. The natural abundance of C13 is quantified by near infrared spectra (NIRS) with a remote reflectance fibre optic probe, applying the probe directly to the soil samples. Discriminate partial least squares analysis of the near infrared spectra allowed to classify soils with and without residues, regardless of the type of tillage or rotation systems used with a prediction rate of 90% in the internal validation and 94% in the external validation. The NIRS calibration model using a modified partial least squares regression allowed to determine the delta(13)C in soils with or without residues, with multiple correlation coefficients 0.81 and standard error prediction 0.5 per thousand in soils with residues and 0.92 and 0.2 per thousand in soils without residues. The ratio performance deviation for the quantification of delta(13)C in soil was 2.5 in soil with residues and 3.8 without residues. This indicated that the model was adequate to determine the delta(13)C of unknown soils in the -16.2 per thousand to -20.4 per thousand range. The development of the NIR calibration permits analytic determinations of the values of delta(13)C in unknown agricultural soils in less time, employing a non-destructive method, by the application of the fibre optic probe of remote reflectance to the soil sample.

Use of Conservation Agriculture to Improve Farming Systems in Developing Countries

Farmers in both developed and developing countries are confronting new challenges related to the globalised economy, accelerating production costs and now climate change. Conventional farming practices that involve tillage for land preparation and weed control, removal or burning of crop residues and mono-cropping are associated with soil erosion and degradation of the soil health needed for efficient water productivity and sustainable crop production. Over the past 30 years, a new approach to farm management to address these issues includes reduced tillage, retention of crop residues and the use of more diversified crop rotations. This is now referred to as Conservation Agriculture. The results of research to compare the productivity and profitability of Conservation Agriculture (CA) with that of conventional farming are outlined in this chapter. Since achieving the benefits of CA requires major changes in attitude from conventional production, the successful extension and farmer adoption of CA requires farmer participation in the development and adaptation of CA technologies.