K.D. Sayre

Simulated wheat growth affected by rising temperature, increased water deficit and elevated atmospheric CO2

Abstract The cropping systems simulation model APSIM-Nwheat was tested against detailed field measurements representing possible growing conditions under future climate change scenarios. Increasing average temperatures by 1.7xa0°C observed over several seasons at Obregon, Mexico reduced the time to flowering by 11 days and resulted in a decline of total biomass and grain yield. These effects were reproduced by the model, except when the observed total biomass inexplicably rose again in the fourth and fifth year, despite higher temperature and a much shorter growing time. In a water stress experiment, the effects of different timing and duration of water deficit on crop growth and yield were reproduced with the model for a rain-shelter experiment at Lincoln, New Zealand where observed grain yields were reduced from 10 to 4xa0txa0ha −1 due to increased water deficit. In experiments from Western Australia, reduced growth and yields due to extreme terminal water deficit were also reproduced with the model where measured yields fall below 0.5xa0txa0ha −1 . In the Maricopa Free Air Carbon-Dioxide Enrichment (FACE) experiment in Arizona, USA, the largest yield increase occurred with elevated CO 2 in the dry and high N treatments, whereas little or no response was observed in the wet and low N supply treatments, as simulated with the model. Combining elevated CO 2 with increased temperature in a sensitivity analysis, two levels of water supply and a range of N applications indicated a positive effect of elevated CO 2 on yield as long as N was not limiting growth. Increased temperature and reduced water supply reduced yields and the yield response to N supply under ambient and elevated CO 2 . Grain protein concentrations were reduced under elevated CO 2 , but the difference was minor with ample N fertiliser. Evapotranspiration was reduced under elevated CO 2 . Higher temperatures increased evapotranspiration with low N input, but reduced it with ample N fertiliser, resulting in a reduction and an increase, respectively, in drainage below the root zone. In the Mediterranean environment of Western Australia the impact of elevated CO 2 and increased temperature on grain yield was in average positive, but varied with seasonal rainfall distribution. Based on the range of model testing experiments and the sensitivity analysis, APSIM-Nwheat was found suitable for studies on directional impacts of future climate change on wheat production. Due to some large discrepancies between simulated and observed data, field experiments representing only a limited range of possible climate change scenarios and the large possible range of factorial interactions not tested, simulated quantitative effects with the model should be interpreted cautiously.

Influence of permanent raised bed planting and residue management on physical and chemical soil quality in rain fed maize/wheat systems

Densely populated, intensively cropped highland areas in the tropics and subtropics are prone to erosion and declining soil fertility, making agriculture unsustainable. Conservation agriculture in its version of permanent raised bed planting with crop residue retention has been proposed as an alternative wheat production system for this agro-ecological zone. A five years field experiment comparing permanent and tilled raised beds with different residue management under rainfed conditions was started at El Batán (Mexico) (2,240xa0m asl; 19.31°N, 98.50°W; Cumulic Phaeozem) in 1999. The objective of this study was to determine the soil quality status after five years of different management practices. The K concentration was 1.65 times and 1.43 times larger in the 0–5xa0cm and 5–20xa0cm profiles, respectively, for permanent raised beds compared to conventionally tilled raised beds. The Na concentration showed the opposite trend. Sodicity was highest for conventionally tilled raised beds and for permanent raised beds it increased with decreasing amounts of residue retained on the surface. Permanent raised beds with full residue retention increased soil organic matter content 1.4 times in the 0–5xa0cm layer compared to conventionally tilled raised beds with straw incorporated and it increased significantly with increasing amounts of residue retained on the soil surface for permanent raised beds. Soil from permanent raised beds with full residue retention had significantly higher mean weight diameter for wet and dry sieving compared to conventionally tilled raised beds. Permanent raised beds with full residue retention had significantly higher aggregate stability compared to those with residue removal. A lower aggregation resulted in a reduction of infiltration. Principal component analysis (PCA) was performed using these soil physicochemical variables that were significantly influenced by tillage or residue management. The PC1 and PC2 separated the conventionally tilled raised beds from the permanent raised beds and PC3 separated permanent raised beds with at least partial residue retention from permanent raised beds with no residue retention. These clear separations suggest that tillage and residue management have an effect on soil processes. The research indicates that permanent raised bed planting increases the soil quality and can be a sustainable production alternative for the (sub)tropical highlands. Extensive tillage with its associated high costs can be reduced by the use of permanent raised beds while at least partial surface residue retention is needed to insure production sustainability.

Genetic and agronomic contributions to yield gains: A case study for wheat

Genetic and agronomic contributions to yield gains for wheat (Triticum aestivum L.) in the Yaqui Valley of northwest Mexico were estimated for the period from 1968–1990. Five problems associated with estimating sources of yield gains were considered, namely: (1) adjusting yield gains for variation in weather over the study period; (2) considering annual cultivar-by-weather interactions, which are potentially problematic when relative yields of cultivars are generated over only part of the study period; (3) overestimating relative yields of cultivars if the check cultivar(s) become susceptible to disease; (4) ensuring that yields as estimated from research station trials represent cultivar performance under farmers conditions; and (5) allowing for cultivar-by-management interactions. With these factors considered, 28% of the weather-adjusted yield gain of 103 kg ha−1 y−1 was attributed to genetic gain (i.e., cultivar improvement). If the yield gains had not been adjusted for annual weather variation, genetic gain would have been overestimated at 50%. By contrast, 48% of the gain was attributed to increased use of N fertilizer, driven at least in part by a decline in N prices; no N-by-cultivar interactions were apparent. The remainder of the yield gap (24%) could not be attributed to specific factors, although P application rates increased over time, and negative deviations from linearity were associated with years having greater than normal rainfall in November and December (a phenomenon which can delay sowing and/or reduce crop stand). In addition to identifying factors contributing to yield gains, technologies that have contributed benefits not measured by yield are discussed.

Carbon isotope discrimination and grain yield for three bread wheat germplasm groups grown at different levels of water stress

Abstract Carbon isotope discrimination (Δ), yield and other characters were determined for 75 spring bread wheat cultivars and advanced breeding lines in which water availability was varied using a line-source irrigation system. The experiment was carried out in 1989/90 at CIMMYT-CIANO, Cd. Obregon, in northwest Mexico. Forty of the cultivars and advanced breeding lines came from CIMMYT-Mexico, twenty from ICARDA-Syria, and fifteen from CIMMYTs International Drought Trial (IDT). Considering all materials together, grain yield and Δ were markedly reduced by drought (yield declined from 4560 to 1090 kg ha −1 , Δ from 16.9 to 14.0‰, from least to most stressed, respectively). For each group of lines, grain yield was positively correlated with Δ in both the most stressed and least stressed parts of the trial (except for the CIMMYT lines under low stress where the correlation was nonsignificant). In addition, high yield under stress was associated with an early maturity score and with less reduction in mature plant height. Δ may be potentially used to augment selection for high yield based on yield itself, in both low- and high-stressed environments. In the latter environment, early maturity and minimal reduction in plant height should also be considered in a selection program especially under conditions of mid-season to terminal drought and/or heat stress.

Plant traits related to yield of wheat in early, late, or continuous drought conditions

Bread wheats (Triticum aestivum L.) were evaluated for plant characteristics contributing to grain yield and plant adaptation under various drought patterns. The usefulness of these traits as explicit selection criteria in developing drought tolerant wheat varieties was investigated in three experiments. Cultivars from four germ-plasm groups, representing the four relevant major and distinct global wheat growing environments, were grown under the respective simulated early, late, continuous and no drought conditions by manipulating irrigation in north western Mexico. Additionally, 560 advanced lines from the CIMMYT breeding program were grown under late drought conditions, and 16 randomly selected advanced genotypes were studied in more detail under late and no drought conditions. In these three studies, the association between yield in drought-stressed environments and yield in non drought-stressed environments was interpreted to reflect genotypic high yield potential, mainly by way of high biomass development. However, yield potential only partly explained the superior performance under drought. For each pattern of drought stress, particular and often different plant traits were identified that further contributed specific adaptation to the distinct drought stress conditions. Knowledge of these traits will be useful for developing CIMMYT germplasm for specific drought-stressed areas. Ultimately, these studies demonstrate that both yield potential and specific adaptation traits are useful criteria in breeding for drought environments, and should be combined to achieve optimum performance and adaptation to drought stress.

Wheat genetic resources enhancement by the International Maize and Wheat Improvement Center (CIMMYT)

The International Maize and Wheat Improvement Center (CIMMYT) acts as a catalyst and leader in a global maize and wheat innovation network that serves the poor in the developing world. Drawing on strong science and effective partnerships, CIMMYT researchers create, share, and use knowledge and technology to increase food security, improve the productivity and profitability of farming systems and sustain natural resources. This people-centered mission does not ignore the fact that CIMMYT’s unique niche is as a genetic resources enhancement center for the developing world, as shown by this review article focusing on wheat. CIMMYT’s value proposition resides therefore in its use of crop genetic diversity: conserving it, studying it, adding value to it, and sharing it in enhanced form with clients worldwide. The main undertakings include: long-term safe conservation of world heritage of both crop resources for future generations, in line with formal agreements under the 2004 International Treaty on Plant Genetic Resources for Food and Agriculture, understanding the rich genetic diversity of two of the most important staples worldwide, exploiting the untapped value of crop genetic resources through discovery of specific, strategically-important traits required for current and future generations of target beneficiaries, and development of strategic germplasm through innovative genetic enhancement. Finally, the Center needs to ensure that its main products reach end-users and improve their livelihoods. In this regard, CIMMYT is the main international, public source of wheat seed-embedded technology to reduce vulnerability and alleviate poverty, helping farmers move from subsistence to income-generating production systems. Beyond a focus on higher grain yields and value-added germplasm, CIMMYT plays an “integrative” role in crop and natural resource management research, promoting the efficient use of water and other inputs, lower production costs, better management of biotic stresses, and enhanced system diversity and resilience.

Conservation Agriculture in South Asia

The Green Revolution era focused on enhancing the production and productivity of rice and wheat. New challenges demand that the issues of efficient resource use and resource conservation receive high priority to ensure that past gains can be sustained and further enhanced to meet the emerging needs. Extending some of the resource-conserving interventions developed for wheat to rice culture is a major challenge for researchers and farmers alike. The present paper shares recent research experiences on resource conservation technologies involving tillage and crop establishment options and associated agronomic practices which enable farmers in reducing production costs, increase profitability and help them move forward in the direction of adopting conservation agriculture.

Yield potential in modern wheat varieties: its association with a less competitive ideotype

Abstract Field experiments were conducted with modern semidwarf spring wheat cultivars representing a range of yield potential in order to compare their adaptation to levels of interplant competition for resources. Levels of competition were altered, in both leaf canopy and underground, by manipulating rows of plants in eight-row yield plots. Competition for light was decreased by bending adjacent rows away from the central two rows thus permitting greater penetration of light to lower leaves of the central rows (light treatment). Reduced competition underground was realized, simultaneously with reduced competition for light, by uprooting the plants adjacent to the central two rows (root/light treatment). These treatments were implemented at the developmental stage of flag-leaf ligule emergence (FLLE), when interplant competition was assumed to become maximal. While the average yield responses were 25%, and 40% to the light and root/light treatments respectively, there was a significant interaction with genetic material. Low-yield-potential (LYP) lines responded more to reduced competition than high-yield-potential (HYP) lines suggesting that the greater efficiency of the HYP lines, reflected in their higher yield, is related to their better adaptation to interplant competition. Physiological bases for improved performance are examined and discussed in relation to ideas about crop ideotypes and possible implications to breeding. These data appear to support the idea that genes conferming yield potential through improved adaptation to the crop environment are associated with a less competitive phenotype.

Growth and morphology of spring wheat (Triticum aestivum L.) culms and their association with lodging: effects of genotypes, N levels and ethephon

Abstract Lodging behavior and morphological characters of 12 spring wheat ( Triticum aestivum L.) genotypes (four Indian cultivars and eight Mexican cultivars/CIMMYT advanced lines) were studied under disease free condition with different N rates (180, 240 and 300xa0kgxa0ha −1 ), and at 300 N, with ethephon (480xa0gxa0ha −1 ) application at CIMMYT (Centro Internacional de Mejoramiento de Maiz y Trigo), near Ciudad Obregon, Sonora, Mexico, during 1997–1998 and 1998–1999. In both years, the crop lodged, mainly by buckling or bending of the culms, 25–30 days after anthesis. Ethephon application at DC 38 prevented lodging and was associated with reduction in plant height (10.2%), peduncle length (14.2%), length of third internode (8.6%). It also simultaneously increased tillers m −2 (9.1%), stem wall thickness for the first (4.3%), second (6.3%) and third (8.1%) internodes and peduncle (3.6%) when compared at the same N level. Varietal differences in lodging behavior were significant during both years. The lodging tolerant genotype, Baviacora 92, had 31.9, 34.0, 40.7 and 34.1% larger diameter for the first, second, third internodes and peduncle, respectively, when compared to HD 2329, one of the most lodging susceptible genotypes. Furthermore, Baviacora 92 had first, second, third internode and peduncle stem walls that were also 31.7, 33.5, 35.4 and 37.1% greater, respectively, than Pavon 76, which had the thinnest stem walls. Genotypic correlations were better than phenotypic correlations, which suggested that environmental effects did not reinforce the genotypic effects rather they weakened them. Tillers m −2 correlated ( r =0.89, P −2 . Simple linear regression explained that 79% of the variation in lodging score could be due to tillers m −2 and 49–65% due to diameter of different internodes. The best sub-set of the regression showed that number of tillers m −2 and/or stem diameter of internodes were the key variables when deciding two or three important characters for selecting for varieties with lodging resistance. Three variables such as stem diameter of first, second internode and length of first internode or tillers m −2 , height and length of stem or tillers m −2 , stem diameter of first, second internode together explained about 89–91% of the variation in lodging score. Therefore, it was suggested that selection for lodging resistant cultivars should emphasize larger stem diameter and wall thickness of basal internodes and fewer tillers per unit area with heavy spikes.

Conventionally tilled and permanent raised beds with different crop residue management: Effects on soil C and N dynamics

Conservation tillage in its version of permanent bed planting under zero-tillage with crop residue retention has been proposed as an alternative wheat production system for northwest Mexico. However, little is known about the dynamics of C and N in soils under wheat/maize on permanent beds (PB) where straw was burned, removed, partly removed or retained, as opposed to conventionally tilled beds (CTB) where straw was incorporated. We investigated the dynamics of soil C and N and normalized difference vegetative index (NDVI) crop values in zero-tilled PB and CTB after 26 successive maize and wheat crops. Organic C and total N were respectively, 1.15 and 1.17 times greater in PB with straw partly removed and with straw retained on the surface, than in CTB with straw incorporated. Organic C and total N were 1.10 times greater in soils with 300xa0kg Nxa0ha−1 added than in unfertilized soil. Cumulative production of CO2 was lower under CTB with straw incorporated than under PB treatments, and CO2 production increased with increments in inorganic fertilizer. The N-mineralization rate was 1.18 times greater than in unamended soils when 150xa0kg inorganic Nxa0ha−1 was applied, and 1.48 times greater when 300xa0kg inorganic Nxa0ha−1 was added. The N-mineralization rate was significantly (1.66 times) greater in PB where the straw was burned or retained on the surface than in CTB where the straw was incorporated, but significantly (1.25 times) lower than in PB with straw partly removed. The NDVI values reached a maximum 56xa0days after planting and decreased thereafter. The NDVI for unfertilized soil were similar for CTB with straw incorporated, PB with straw partly removed, and PB with straw retained on the surface, but significantly lower for PB with straw burned and PB with straw removed. In soils to which 150 or 300xa0kg Nxa0ha−1 was added, NDVI was significantly lower for PB with straw burned than for other treatments. Among other things, this suggests the utility of rotating maize or wheat with crops whose residues have lower C–N ratios, thus avoiding immobilization of large amounts of N for extended periods. PB with residue burning, however, is an unsustainable practice leading to low crop performance and soil and environmental degradation.