Léon-Étienne Parent

Geostatistics of near-surface moisture in bare cultivated organic soils

The aim of this study was to characterise fine scale patterns of organic soil moisture content in the top 5 cm by means of semi-variogram modelling. Soil moisture content was observed along a transect on 2 occasions, early in the 1999 growing season to avoid any influences originating from vegetation and cultural practices. Soil moisture values were found to be normally distributed and were not significantly correlated with the soil organic matter content. Many similarities were depicted between the exponential semi-variograms characteristics of this study and another one in mineral soils, reported in the literature, except for the much higher sills associated with organic soils. Of particular interest were similar correlation lengths, indicating that a correlation range of the order of 100 m should be expected for mineral soils and for the level of moisture and organic matter contents found in this study.

Opportunities for, and limitations of, near infrared reflectance spectroscopy applications in soil analysis: A review

Near infrared reflectance spectroscopy (NIRS) is a cost- and time-effective and environmentally friendly technique that could be an alternative to conventional soil analysis methods. In this review, we focussed on factors that hamper the potential application of NIRS in soil analysis. The reported studies differed in many aspects, including sample preparation, reference methods, spectrum acquisition and pre-treatments, and regression methods. The most significant opportunities provided by NIRS in soil analysis include its potential use in situ, the determination of various biological, chemical, and physical properties using a single spectrum per sample, and an estimated reduction of analytical cost of at least 50%. Contradictory results among studies on NIRS utilisation in soil analysis are partly related to variations in sample preparation and reference methods. The following calibration statistics appear to be most appropriate for comparing NIRS performance across soil attributes: (i) coefficient of det...

The plant ionome revisited by the nutrient balance concept

Tissue analysis is commonly used in ecology and agronomy to portray plant nutrient signatures. Nutrient concentration data, or ionomes, belong to the compositional data class, i.e., multivariate data that are proportions of some whole, hence carrying important numerical properties. Statistics computed across raw or ordinary log-transformed nutrient data are intrinsically biased, hence possibly leading to wrong inferences. Our objective was to present a sound and robust approach based on a novel nutrient balance concept to classify plant ionomes. We analyzed leaf N, P, K, Ca, and Mg of two wild and six domesticated fruit species from Canada, Brazil, and New Zealand sampled during reproductive stages. Nutrient concentrations were (1) analyzed without transformation, (2) ordinary log-transformed as commonly but incorrectly applied in practice, (3) additive log-ratio (alr) transformed as surrogate to stoichiometric rules, and (4) converted to isometric log-ratios (ilr) arranged as sound nutrient balance variables. Raw concentration and ordinary log transformation both led to biased multivariate analysis due to redundancy between interacting nutrients. The alr- and ilr-transformed data provided unbiased discriminant analyses of plant ionomes, where wild and domesticated species formed distinct groups and the ionomes of species and cultivars were differentiated without numerical bias. The ilr nutrient balance concept is preferable to alr, because the ilr technique projects the most important interactions between nutrients into a convenient Euclidean space. This novel numerical approach allows rectifying historical biases and supervising phenotypic plasticity in plant nutrition studies.

Long-term impact of tillage practices and phosphorus fertilization on soil phosphorus forms as determined by p nuclear magnetic resonance spectroscopy.

Conservation tillage practices have become increasingly common in recent years to reduce soil erosion, improve water conservation, and increase soil organic matter. Research suggests that conservation tillage can stratify soil test phosphorus (P), but little is known about the effects on soil organic P. This study was conducted to assess the long-term effects of tillage practices (no-till [NT] and mouldboard plowing) and P fertilization (0 and 35 kg P ha) on the distribution of P species in the soil profile. Soil samples from a long-term corn-soybean rotation experiment in Québec, Canada, were collected from three depths (0-5, 5-10, and 10-20 cm). These samples were analyzed for total P (TP), total C (TC), total N (TN), pH, and Mehlich-3 P (PM3); P forms were characterized with solution phosphorus-31 nuclear magnetic resonance spectroscopy (P-NMR). Results showed a stratification of TP, TC, TN, pH, PM3, and Mehlich-3-extractable aluminum and magnesium under NT management. The PM3 and orthophosphate concentrations were greater at the soil surface (0-5 cm) of the NT-P (soil treatment with 35 kg P ha) treatment. Organic P forms (orthophosphate monoesters, especially -IP, and nucleotides) had accumulated in the deep layer of NT treatment possibly due to preferential movement. We found evidence that the NT system and P fertilization changed the distribution of P forms along the soil profile, potentially increasing soluble inorganic P loss in surface runoff and organic P in drainage and decreasing bioavailability of inorganic and organic P in deeper soil layers.

Soil phosphorus availability in no-till versus conventional tillage following freezing and thawing cycles

Projected global warming may result in colder soil temperatures and a greater number of soil freezing and thawing cycles (FTC) during the winter in cool temperate and high-latitude regions. We evaluated the effects of seasons and repeated FTC on soil P availability in the topsoil of no-till (NT) and conventional tillage (CT) systems. In order to determine P availability during fall 2007 and spring 2008, soil samples (0-15 cm) were collected in both seasons from a long-term corn-soybean rotation experiment in plots that received 0, 17.5 and 35 kg P ha-1 and 160 kg N ha-1 every 2 yr since 1992. In addition, soil cores (0-5 cm) were collected in fall 2007 in plots that received 35 kg P ha-1 and 160 kg N ha-1 every 2 yr and were enriched or not with 2 g of soybean residues. Under controlled conditions, the cores were subjected to various FTC treatments, with each cycle consisting of 5 d of freezing and 5 d of thawing. The water-extractable P (Pw) and Mehlich 3 extractable P (PM3) contents were higher in soil ...

Laser-induced fluorescence signatures as a tool for remote monitoring of water and nitrogen stresses in plants

We tested the potential of leaf fluorescence as a tool for the remote sensing of water and nitrogen stresses in agricultural crops, as compared to the conventional contact techniques of leaf tissue or soil analysis. Multi-wavelength excitation fluorescence and diurnal behavior of the variable chlorophyll fluorescence were used to monitor nitrogen deficiency in corn (GEOIDE RES#54 network project, Canada) and water stress in pea plants (LURE project, France). Variable chlorophyll fluorescence was found to be a very sensitive tool, giving early indications of the drought stress and general indications of a misfunction of the photosynthetic apparatus. Some fluorescence parameters derived from ultraviolet (UV) and visible light (VIS) excitation of chlorophyll, especially the ratio FRFexUV/FRFexVIS measuring the epidermis UV transmittance, seemed to be more specifically related to the nitrogen content of leaves and precluded an ambiguous response as in the case of the more complex ratio BGF/ChlF. Despite the high variability of the biological material in the field, fluorescence could discriminate between N-deficient and N-saturated plants, and between water-stressed and non-water-stressed plants in the early stages of stress development.

Environmental Mehlich-III soil phosphorus saturation indices for Quebec acid to near neutral mineral soils varying in texture and genesis

The Mehlich-III method (M-III) (Mehlich 1984) is a multinutrient agri-environmental routine soil-testing procedure used in many jurisdictions in North America, but one that is affected by soil texture. The PW determined by the Sissingh (1971) method is an index of surface water contamination and desorbed P that is not influenced by soil texture and that can be used to define specific M-III critical environmental indices by soil texture group. Our objective was to define critical environmental indices by relating (P/Al)M-III to PW. We analyzed 275 soil samples from surface, and 175 from subsurface layers, varying in genesis, texture, and pH. The relationship between PW and (P/Al)M-III was influenced by soil properties, particularly soil texture and genesis. Fine-textured (> 300 g clay kg-1) and gleyed soils tended to release more PW at a given (P/Al)M-III compared with coarse-textured (≤ 300 g clay kg-1) and podzolized soils. Using a critical value of 9.7 mg PW L-1 derived from the literature, critical env...

Acidez do solo e calagem em pomares de frutíferas tropicais

A produtividade agricola nos tropicos e afetada, principalmente, pelos fatores ligados a acidez do solo (pH, saturacao por bases, acidez potencial, disponibilidade de nutrientes). A calagem e uma pratica bem conhecida para corrigir a acidez do solo em culturas anuais, ainda que nao seja praticada com a regularidade necessaria. Entretanto, em culturas perenes, a incorporacao de corretivos e mais complexa, devido as caracteristicas desse grupo de plantas e a carencia de informacoes cientificas sobre o assunto. Em condicoes de acidez, a calagem promove a neutralizacao do Al3+, a elevacao do pH e o fornecimento de Ca e Mg, possibilitando a proliferacao de raizes, com reflexos positivos no crescimento da parte aerea das plantas. Contudo, devido a baixa solubilidade e a lenta movimentacao do calcario ao longo do perfil do solo, ha obrigatoriedade de se fazer distribuicao uniforme e incorporacao profunda, antecedendo a implantacao do pomar, a fim de garantir o eficiente aproveitamento de agua e de nutrientes contidos nessas camadas. A calagem deve ser considerada um investimento, pois seus beneficios perduram alem de um ano ou de uma safra agricola. Isso se deve ao efeito residual dos corretivos de acidez do solo, sendo o tempo de duracao desse efeito dependente de varios fatores, entre os quais: condicoes edafoclimaticas, cultura, manejo da area e tipo de corretivo empregado. Em geral, particulas maiores de calcario tem efeito residual mais prolongado, sendo empregadas na implantacao dos pomares. No entanto, a relacao entre o tamanho da particula e o efeito residual tem sido pouco pesquisada, devido a necessidade de estudos de longa duracao. Em funcao das elevadas doses de adubos nitrogenados utilizadas nos pomares de altos rendimentos, a acidez do solo aumenta, como resultado do processo de nitrificacao. Em pomares ja implantados, o procedimento atualmente utilizado pelos produtores e a incorporacao superficial do calcario na area. As recomendacoes talvez fossem outras, caso houvesse maior subsidio da pesquisa, tendo em vista os diversos problemas fitossanitarios que podem ocorrer, direta ou indiretamente da pratica da incorporacao do corretivo, tais como reducao do sistema radicular, ferimento das raizes e consequente risco de infeccoes, com disseminacao de pragas e doencas no pomar. O objetivo desta revisao e apresentar os principais resultados de pesquisas sobre o assunto, mostrando os efeitos da calagem sobre a fertilidade do solo, a nutricao e a produtividade de frutiferas de grande importância economica para o Brasil, bem como discutir a duracao do efeito residual dos corretivos e a dose mais economica a ser aplicada nos pomares de frutas em implantacao e em producao.

Exploration de l’indicateur standardisé de précipitation à l’aide d’une analyse statistique régionale

A regional analysis of 5-d precipitation is presented as an interpretative tool for the standardized precipitation index (SPI). As a water stress index, the SPI provides an historical context to the precipitation fallen over the last i days. A regional analysis allows the SPI to be used beyond its usual diagnostic function, by quantifying the probability that precipitation to come will put an end to an ongoing drought. The proposed regional analysis relies on the precipitation gathered at 110 meteorological stations within Quebec. Five homogeneous regions have been established through the use of a discordancy test and heterogeneity test. Various normalised regional distribution have been adjusted by L-moments. The best adjustments are achieved for the Pearson type III (gamma) distribution.

Modeling of phosphorus dynamics in contrasting agroecosystems using long-term field experiments

Morel, C., Ziadi, N., Messiga, A., Bélanger, G., Denoroy, P., Jeangros, B., Jouany, C., Fardeau, J. C., Mollier, A., Parent, L. E., Proix, N., Rabeharisoa, L. and Sinaj, S. 2014. Modeling of phosphorus dynamics in contrasting agroecosystems using long-term field experiments. Can. J. Soil Sci. 94: 377-387. Long-term field experiments on phosphorus (P) fertilization were originally designed to study crop needs in different soil types by analyzing the effects of several rates of P fertilization on yields, their P concentrations and dynamics of plant-available soil P. The objective of this study was to test a computer-based model to simulate the P dynamics at the field scale using plant database and analyzing for plant-available P by a hierarchical process-based approach. It predicts both the concentration (CP) of phosphate ions (Pi) in soil solution and the associated Pi amounts that in time equilibrate with Pi in solution. Five experiments, representative of contrasting soil types, land-use, and climates were selected. Our model equilibrates the change in plant-available P in the upper soil layer to the P budget between annual P inputs and outputs. Rates of P fertilization affected simulations following the same expected pattern across sites. Field-observed and simulated values are in good agreements in all sites. The field-observed variations of CP per unit of P budget ranged from 0.007 to 2.49 (µg P L-1) (kg P ha-1)-1. The predictions are of the same order of magnitude. Predictions were compared with empirical long-term data and mismatches were discussed. This investigation highlights the scientific interest of long-term field P experiments to test and validate models describing P dynamics at the scale of the agricultural fields under different agricultural management practices.