Oxygen isotope ratio of leaf and grain material correlates with stomatal conductance and grain yield in irrigated wheat.

Theory (Craig and Gordon 1965; Dongmann et al. 1974; Sternberg et al. 1986; Farquhar and Lloyd 1993) suggests that the oxygen isotope ratio (δ18O) of plant material should reflect the evaporative conditions under which the material was formed, so that d

Implementing the Conservation Agriculture Concepts in the Irrigated Wheat Based System of North Mexico; A Dynamic Process Towards Sustainable Production

In this paper we use the example of the irrigated wheat based systems of North Mexico as a typical example of a step-by-step process to advance the use of Conservation Agriculture based Resource Conserving Technologies towards the final goal of the implementation of Conservation Agriculture. Sonora in northwest Mexico. This region is characterized by a desert climate, mostly sunny and dry with a total rainfall of about 381 mm per year with 253 mm during the summer cycle (May – Oct). The Yaqui Valley is one of the main agricultural production areas encompassing nearly 255,000 ha of irrigated land using primarily gravity irrigation systems fed by canals (over 80% of irrigation water) and deep tube wells (around 20% of irrigation water). Crops planted during the winter cycle are wheat (November-May),safflower (January-June), winter maize (September-February), chickpea (December – April) while during the summer cycle summer maize (May – October), sorghum (March – July), dry beans (March – May) are most common. There have been 3 main shifts in farming system practices during the last decades: (1) In 1981, the majority of the farmers were planting with ‘melgas’ (crops planted in solid stands on the flat with flood irrigation in basins) with only 6% of farmers in the valley planting on raised beds. However by 1996, 90% of the farmers had shifted to planting on raised beds. The great benefits from bed planting are reduced production costs, reduced irrigation water use, enhanced field access which facilitates control of weeds and other pests, and timely and efficient application of nutrients, reduced tillage, and crop residue management. (2) Another remarkable change in farmer practices has been crop residue management. In the 1992/93 cycle, residues were burned by 95% of the farmers. This practice was deeply entrenched. By 2001, however, 96% of the farmers are no longer burning but incorporating the residue. (3) Recently there is growing interest to take the next logical step in making raised bed planting more sustainable by reducing tillage and manage crop residues on the surface by reusing permanent raised beds with only superficial reshaping in the furrows between the raised beds as needed before planting of each succeeding crop, following even distribution of the previous crop residues. Therefore in 1991 the crop management team at CIMMYT started research on permanent beds to offer farmers opportunities to further reduce production cost andincrease sustainability of the system through the positive effects on chemical, physical and biological soil quality.status: publishe

Conservation Agriculture and Soil Carbon Sequestration; Summary of a Critical Review

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 poster reports a summary of an extensive review of the potential impact of CA on C sequestration published in Critical Reviews in Plant Sciences. 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 quality, controls erosion and reduces tillage-related production costs.status: publishe

Wheat yield and tillage–straw management system×year interaction explained by climatic co-variables for an irrigated bed planting system in northwestern Mexico

Wheat is an important food and income source and estimated demand for wheat in the developing world is projected to increase substantially. The objectives of this study were to gain insight into (i) the effect of tillage–straw system on yield and yield components (number of grains per m2 and thousand kernel weight), (ii) the relation between climatic conditions and yield and yield components, (iii) the explanation of tillage–straw system×year interaction for yield and yield components by climatic co-variables. Wheat grain yield and yield components were measured in a long-term trial established in 1992 under irrigated, arid conditions in northwestern Mexico. Five tillage–straw management systems (conventionally tilled raised beds [CTB] with straw incorporated and permanent raised beds [PB] with straw burned, removed, partly retained or fully retained) were compared for a wheat–maize rotation. Daily climatic data were averaged over six periods corresponding approximately to advancing wheat growth stages. The PB-straw retained and PB-straw removed had the highest yields (average yield of 7.31 and 7.24 t ha−1, respectively) and grains perm2. The PB-straw burned had the lowest yield (average yield of 6.65 t ha−1) and grains per m2, but the highest thousand kernel weight. Maximum temperature was positively correlated to final grain yield during tillering and head differentiation, but was negatively correlated to thousand kernel weight during grain-filling. For the tillage–straw system year interaction, three groups of management systems were distinguished for yield and grains perm2: PB-straw burned, CTB-straw incorporated and PB where straw is not burned. The CTB-straw incorporated had a positive interaction with year in favorable years with high radiation and evapotranspiration. The PB-straw burned was relatively more affected by excess water conditions and showed positive interactions in years with high relative humidity. The PB-straw retained was the most stable in different climatic conditions, indicating that this management system could contribute to maintaining wheat yield in a changing climate scenario.status: publishe

Soil water content, maize yield and its stability as affected by tillage and crop residue management in rainfed semi-aridhighlands

Rainfed crop management systems need to be optimized to provide more resilient options to cope with projected climatic scenarios forecasting a decrease in mean precipitation and more frequent extreme drought periods in Mexico. Soil water content (0–60 cm) was measured during three crop cycles in maize plots with different agronomic management practices in a long-term rainfed experiment (established in 1991) in the highlands of Mexico. Maize yields of 1997–2009 were reported. Crop management practices varied in (1) tillage (conventional [CT] vs. zero tillage [ZT]) and (2) residue management (full or partial retention and removal). ZT with residue retention had higher soil water content than management practices involving CT and ZT with residue removal which provided a buffer for drought periods during the growing seasons. In 2009, a cycle with a prolonged drought during vegetative growth, this resulted in yield differences of up to 4.7 Mg ha−1 between ZT with (partial) residue retention and the other practices. Averaged over 1997–2009, these practices had a yield advantage of approximately 1.5 Mg ha−1 over practices involving CT and ZT with residue removal. ZT with (partial) residue retention used rainfall more efficiently and resulted in a more resilient agronomic system than practices involving either CT or ZT with residue removal.status: publishe

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

The use of the marasha ard plough for conservation agriculture in Northern Ethiopia

Indigenous tillage systems are often undervaluated in conservation agriculture (CA). In Ethiopia, starting from 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 remains however 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 „bed and furrowing‟. From the socio-economic point of view, implementation of permanent beds and retaining of stubble leads to decreased oxen (and straw) requirements, but also to an increased need of weeding in the first years. To overcome that problem, we have introduced glyphosate herbicide in 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 full benefit of the permanent bed system can only be expected after some years. Overall, this type of resource conserving technologies 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 to long-term food security

The effect of tillage, crop residue management and nitrogen fertilization on wheat crop performance in an irrigated bed planting system in northwestern Mexico

End-of-season yield results do not permit the evaluation of within-season management interactions with the production environment and consequently do not allow full understanding of the applied management practice. Therefore, crop performance was measured twice a week during the 2007/08 crop cycle with a handheld NDVI sensor in a long-term trial established in 1992 under irrigated, arid conditions in northwestern Mexico. Different bed planting systems (conventionally tilled beds [CTB] and permanent raised beds [PB]) were compared for a wheat-maize rotation. Residue management varied from full to partial retention and burning. Nitrogen (N) fertilizer treatments differed in dose (0, 150 or 300 kg N ha-1) and time of application (basal or split application). Wheat crop development throughout the season clearly depends on tillage, crop residue management and amount and timing of N fertilization. Three tillage-straw systems could be distinguished based on their different effect on crop growth: CTB-straw incorporated, PB-straw burned and PB where straw was not burned. When no N fertilizer was applied, the CTB-straw incorporated took off fast compared to the PB systems, but plant performance decreased abruptly two weeks after the first auxiliary irrigation and was lower than in the PB where straw was not burned thereafter. When N fertilizer was applied, the high plant performance in CTB was maintained throughout the season. In the PB-straw burned, plant performance was lower throughout the season than in the other tillage-straw treatments when no N fertilizer was applied. When N fertilizer was applied, the initial growth in the PB-straw burned was equally fast than in the CTB-straw incorporated. However, later in the season plant performance decreased faster in the PB-straw burned than in the other tillage-straw treatments. When N fertilizer was applied, the PB where straw was not burned showed slower initial crop growth than CTB and PB-straw burned. The difference was more pronounced when more straw was retained. Increasing levels of N fertilizer resulted in plant performance closer to that of CTB-straw incorporated later in the season. Increasing the amount of N fertilizer increased plant performance in all tillage-straw treatments, but differences between N fertilizer treatments were small in the PB-straw burned. There is an important interaction between tillage/residue management practice and N fertilizer application practice that needs further research.status: publishe

The importance of crop residue management in maintaining soil quality in zero tillage systems; A comparison between long-term trials in rainfed and irrigated wheat systems

CIMMYT is committed to improving livelihoods in developing countries by improving the productivity and profitability of farming systems while sustaining natural resources. This paper focuses on the influence of crop residue management on soil quality in zero till systems and includes results from two long-term trials established in the early 1990’s in different agro-ecological systems in Mexico: (1) a low-input, semi-arid, rainfed system in the rainfed central highlands (2240 masl) with zero tillage on the flat and (2) a high-input, arid, irrigated system in the northwestern part of the country with zero tilled permanent raised beds. In both zero till systems, the (partial) retention of the crop residues was necessary to maintain soil quality. In the rainfed semi-arid zero tillage system, mean weight diameter obtained by dry sieving, aggregate stability, infiltration, soil moisture content, soil microbial biomass and nutrient status were lower with residue removal than with residue retention. In the irrigated permanent raised bed system, burning of all crop residues resulted in a degradation of soil structure, lower direct infiltration, irrigation efficiency, soil moisture content, soil microbial biomass, lower total N and greater soil sodicity as compared to retaining crop residue at the surface. Practices with partial retention of crop residue showed soil quality similar to practices with retention of all residues. The retention of at least part of the crop residue is essential for the sustainability of zero till systems, although it may be possible to remove part of the residue for other uses, especially in irrigated conditions where biomass production is high.status: publishe