There is an increasing need for diagnostic tools that can assess the crop nitrogen (N) nutrition status during the growth cycle. In addition to the leaf chlorophyll (Chl) content, we proposed here ...the use of the leaf content of polyphenolics (Phen) as a potential indicator of crop N status. Because of their absorption features in the visible and in the UV part of the spectrum, both Chl and Phen can be measured by rapid and non-destructive optical methods. Therefore, we used two leaf-clip devices, the Minolta SPAD-502 for Chl, and the Dualex for Phen. The latter is a prototype (patent pending) that measures the UV absorbance of the leaf epidermis, which is related to the leaf Phen content. Dynamics of Phen and Chl were measured on the last fully developed leaves of two winter wheat cultivars subjected to different levels of N availability, from tillering to flowering, in 2001, 2002 and 2003. Both Phen and Chl contents were found to increase along the leaf, starting from the ligula, regardless of the stage of development. Both variables were highly correlated with the N concentration of leaves. The average Chl content of the leaf increased, and the average Phen content decreased, with the increased application of N to the field, irrespective of the growth stage, the cultivar and the year of experiment. Therefore, both Phen and Chl can be considered as probes of the crop N nutrition status. Still, the relationship between Chl and the nitrogen nutrition index (NNI), used as a reference indicator of N deficiency, was influenced by the growth stage, whereas the year of experiment affected the relationship between Phen and the NNI. We also propose the use of the simple Chl/Phen ratio as an indicator of leaf N content at the canopy level, for future application in precision agriculture. This ratio would alleviate, at least partially, the problem of gradients along leaves, and would even accentuate the differences among levels of crop N deficiencies because of the Chl and Phen inverse dependence on the crop N nutrition status.
A new equation for predicting penetration resistance of soil is presented. The equation contains two main additive terms: the first is a measure of the degree of compactness of the soil and the ...second gives the contribution of pore water to the soil strength. It is proposed that these terms are applicable to soils of different texture, at different bulk densities and at different water contents. The equation is calibrated and tested using values of penetrometer resistance measured in the field at a range of locations in Poland. Predictions from the equation are compared with predictions from two other published equations. It is shown that the performance of the proposed equation is superior to the other two, at least for the Polish data set used in this work. On the basis of the assumption that the proposed equation is correct, predictions of penetrometer resistance are made using pedotransfer functions to illustrate typical effects of soil texture, bulk density and water content.
The saturated hydraulic conductivity,
K
sat, was measured on soil samples collected from the plough layer and the subsoil. A range of naturally occurring soil bulk densities was obtained by sampling ...in different years, with different crops and within and without wheel-tracks, etc. It was found that, for the plough layer, quite good linear relationships exist between the logarithm of
K
sat and the bulk density. However, for the subsoils, the value of
K
sat usually lies above the regression line for found for the corresponding plough layer. This “excess” hydraulic conductivity of subsoils is attributed to the presence of biopores, especially root channels. The lower hydraulic conductivity of the plough layer, relative to the subsoil, is attributed to the destruction of these biopores by tillage. A simple model for the separate contributions of soil texture and root channels to the overall value of
K
sat is presented. It is concluded that subsoil tillage could cause significant reductions in
K
sat with potentially serious environmental consequences unless it is repeated periodically.
Starting from grain yield, quality and resistance against multiple diseases, the characterization of the cultivar’s behavior increased in recent decades. Needs in quantitative assessments of a larger ...range of criteria has greatly evolved towards yield stability in a large range of fluctuating environments. Using a large dataset crossing cultivars and environments, we thus explored the relationships between yield and Healthy Area Duration (HAD), as affected by genotype, environment and septoria caused by Zygmoseptoria tritici. A set of indexes was then proposed to properly profile cultivar’s behavior. A curvilinear relationship relating HAD to potential yield was first parameterized. It allows quantifying HAD efficiency. Susceptibility (HAD loss) was differentiated from total tolerance (the ratio between yield loss and HAD loss). Finally the specific tolerance, i.e. not due to HAD level, was quantified. Correlations between indexes pointed out that no trade-off was shown between total tolerance and actual or potential yield as well as disease susceptibility. These correlations partially depended on the nitrogen status of crops, underlining other G×E interactions indexes may trap. Finally, as HAD efficiency appeared more highly linked to actual yield than potential yield we proposed an alternative set on indexes based on Healthy Area Absorption (HAA) that accounted for meteorological variability. Interestingly, these last indexes were insensitive to nitrogen nutrition as well as to cultivar susceptibility to Z. tritici. The developed indexes allowed profiling the cultivars’ behavior under a common range of environments. HAA-based indexes open the way to a useful global characterization of cultivars by breeders. Moreover, HAA can be assessed using high-throughput phenotyping tools. A thorough evaluation of this last point needs to be done.
•A multi way characterization of cultivar response to foliar diseases is proposed.•No trade-off between tolerance and productivity or disease susceptibility was observed.•Alternative characterization by remote sensing rather than sampling is considered.
The effects of climate change on forage and crop production are an important question for the farmers and more largely for the food security in the world. Estimating the effect of climate change on ...agricultural production needs the use of two types of tools: a model to estimate changes in national or local climates and an other model using climatic data to estimate the effects on vegetation. In this paper, we will mainly present the effects of climate change on climatic features, the variability of criteria influencing crop production in various regions of France and some possible effects on crops.
The last two decades are witnessing a decline in the growth trend of cereal yields in many European countries. The present study analyses yield trends in France using various sources of data: ...national and regional statistics, scattered trials, results of agroclimatic models using climatic data. Effects in genetic changes through breeding, agronomy and climate are investigated as possible causes. Our results show that genetic progress has not declined but it was partly counteracted, from 1990 on, by climate change which in general is unfavorable to cereal yields in temperate climates because of heat stress during grain filling and drought during stem elongation. We cannot however, from the decade beginning in 2000, rule out agronomic causes, related to policy and economy, in particular the decline of legumes in the cereal rotations, replaced by oilseed rape and to a lesser extent the decrease in nitrogen fertilization.
In plants, carbon and nitrogen (N) economies are intimately linked at the physiological and biochemical level. The strong genetic negative correlation between grain yield and grain protein ...concentration observed in various cereals is an illustration of this inter-relationship. Studies have shown that deviation from this negative relationship (grain protein deviation or GPD) has a genetic basis, but its physiological basis is still poorly understood. This study analysed data on 27 genotypes grown in multienvironment field trials, representing a wide range of agricultural practices and climatic conditions. The objective was to identify physiological processes related to the genetic variability in GPD. Under most environments, GPD was significantly related to post-anthesis N uptake independently of anthesis date and total N at anthesis. The underlying physiological trait might be related to genotypic differences in either access to soil N, regulation of N uptake by plant N status, or ability to maintain root activity during the grain-filling period. GPD is an interesting potential target in breeding as it appears to be relatively robust across different environments and would be valuable in increasing total N uptake by maturity.
An experiment of sink‐source modifications was performed in field‐grown wheat at flowering on five varieties (four Triticum aestivum and one T. durum); among these, two varieties were non‐awned. The ...sink‐source modifications were blade removal (treatment B) and blade deletion and stalk and sheaths darkening (treatment C). Intact plants (treatment A) acted as a control. In the three awned varieties, the effect of awn removal was also analysed. Two lots of tests were initially performed, with awns (treatments A+, B+, C+) or with awns removed (treatments A−, B−, C−). Yields and carbon and nitrogen isotope compositions were then determined on seeds harvested at maturity. Blade deletion reduced the yield by one third whereas additional stalk and sheaths darkening led to a two thirds decrease. Nitrogen yield was similarly affected but the deprivation due to treatment C was less marked for nitrogen than for carbon. Thus, treatment C produced grains which were notably richer in nitrogen than plants which had received treatment A and B. For each of the five varieties, the decrease in yield was highly correlated with a 13C enrichment of grains (roughly from −28 to −25‰). In contrast with the 13C variations, there was no general trend for 15N evolution among treated plants. The final yield for treated T. durum plants was strongly modified when the awns were removed at flowering whereas no significant variations were noted in the other T. aestivum awned varieties. T. durum seeds obtained from plants deprived of awns were notably depleted in 13C and in 15N compared to control plants. Isotope compositions of C and N of the different pools supplying the grain filling were estimated and discussed in the context of the physiology of the mother plants between flowering and maturity.
DéciBlé is a simulation tool intended to support the design and evaluation of technical management for the wheat crop. Crop management is here considered from a strategic planning point of view, as ...the choice of technical decision rules for the whole growing period rather than day-by-day decisions for each operation. DéciBlé simulates the consequences for technical operations and crop production of a set of decision rules over a wide range of possible contexts (regions, year-to-year weather variation, fields, etc.). It is a simulation in which two models interact: a decision and a crop model. The decision model represents the decision rules through a specific formalisation and generates the operations for each context. The crop model is a set of modules simulating plant development, crop environment and yield accumulation implied by these operations in this context through the generation of loss functions or risk estimates. The crop model consists of a set of empirical models based on agronomic diagnosis and experimental references widely used in France. A general validation of DéciBlé is carried out using observed data from a network of field trials. The wheat development stages are simulated within 4 days of the observed dates in more than 80% of the cases and the yield components and final yield with differences of less than 15% from the real values in more than 75% of the cases. We discuss (i) the causes of unsatisfactory predictions and the prospects for improving the various modules of the crop model; (ii) the use of the simulator in some decision problems; and (iii) the position of DéciBlé among the existing models for crop management decision help, emphasising the originality of the method of decision representation.
PDF
