. 2000. Organic C accumulation in soil over 30 years in semiarid southwestern Saskatchewan -Effect of crop rotations and fertilizers. Can. J. Soil Sci. 80: [179][180][181][182][183][184][185][186][187][188][189][190][191][192]. Because crop management has a strong influence on soil C, we analyzed results of a 30-yr crop rotation experiment, initiated in 1967 on a medium textured Orthic Brown Chernozem at Swift Current, Saskatchewan, to determine the influence of cropping frequency, fertilizers and crop types on soil organic C (SOC) changes in the 0-to 15-cm depth. Soil organic C in the 0-to 15-cm and 15-to 30-cm depths were measured in 1976, 1981, 1984, 1990, 1993, and 1996, but results are only presented for the 0-to 15-cm depth since changes in the 15-to 30-cm depth were not significant. We developed an empirical equation to estimate SOC dynamics in the rotations. This equation uses two first order kinetic expressions, one to estimate crop residue decomposition and the other to estimate soil humus C mineralization. Crop residues (including roots) were estimated from straw yields, either measured or calculated from grain yields. The parameter values in our equation were obtained from the scientific literature or were based on various assumptions. Carbon lost by wind and water erosion was estimated using the EPIC model. We found that (i) SOC was increased most by annual cropping with application of adequate fertilizer N and P; (ii) that frequent fallowing resulted in lowest SOC except when fall-seeded crops, such as fall rye (Secale cereale L.), that reduce erosion were included in the rotation, and (iii) the fallow effects are exacerbated when low residue yielding flax (Linum usitatissimum L.) was included in the rotation. Some of the imprecision in SOC values we speculated to be related to variations in soil texture at the test site. In the first 10 yr of the experiment, SOC was low and constant for fallow-spring wheat (Triticum aestivum L.) (F-W) and F-W-W rotations because this land was managed in this manner for the previous 50 yr. However, in rotations that received N + P fertilizer and were cropped annually [continuous wheat (Cont W) and wheat-lentil (Lens culinaris L.)], or that included fall-seeded crops (e.g., F-Rye-W), SOC appeared to increase sharply in this period. In the drought period (1984)(1985)(1986)(1987)(1988)) SOC was generally constant, but large increases occurred in the wet period (1990 to 1996) in response to high residue inputs. The efficiency of conversion of residue C to SOC for the 30-yr experimental period was about 10-12% for F-W, F-W-W and Cont W (+P) systems, and it was about 17-18% for the well fertilized F-Rye-W, Cont W, and W-Lent systems. The average annual SOC gains (Mg ha -1 yr -1 ) between 1967 and 1996 were 0.11 for F-W (N + P), 0.09 for the mean of the three F-W-W rotations (N + P, + N, + P), 0.23 for F-Rye-W (N + P), 0.32 for Cont W (N + P), 0.12 for Cont W (+ P), and 0.28 for W-Lent (N + P). The corresponding mean estimated (by our equation) annual SOC gains for these...

RESUMONo sistema de plantio direto, a ausência de revolvimento do solo, aliada ao tráfego de máquinas, promove a compactação excessiva do solo em superfície. Com o objetivo de estudar alguns fatores que interferem na compactação do solo em plantio direto, foi realizado um experimento no município de Ponta Grossa (PR), nos anos agrícolas de 1989/1990 e 1990/1991. Comparou-se o efeito de três métodos de preparo inicial do solo -com arado de discos, aivecas e rotativo -e dois níveis de calagem sobre algumas propriedades físicas de um Latossolo Vermelho-Escuro argiloso no sistema de plantio direto com tráfego controlado. Utilizou-se a seqüência de culturas em rotação: ervilhaca, milho, aveia-preta e soja. Avaliaram-se a densidade, a porosidade do solo e o teor de água retido entre os potenciais de -0,006 e -0,5 MPa. Não houve efeito significativo da calagem sobre as propriedades físicas estudadas. Os resultados demonstraram efeitos significativos do tráfego, aumentando a densidade do solo e reduzindo a sua porosidade e o conteúdo de água retido entre aqueles potenciais. A distribuição, em profundidade, das cargas aplicadas pelo tráfego de máquinas, principalmente de colheitadeiras, foi, provavelmente, influenciada pelo volume de solo revolvido pelos diferentes sistemas de preparo inicial. Nas parcelas em que a estrutura do solo foi submetida a pressões por meio do tráfego, obteve-se redução na produtividade da soja, em comparação às áreas com ausência de tráfego, no período em que o estudo foi realizado.Termos de indexação: rotação de culturas, estrutura do solo, compactação, densidade do solo, porosidade.

No abstract

Estimating spring wheat yield variability with EPIC. Can. J. Soil Sci. 78: 541-549. The Environmental Policy Integrated Climate (EPIC) model has been used on the semi-arid temperate Canadian Prairies to estimate crop yield, soil erosion loss, and water and nitrate dynamics. While its estimates of long-term average yields are accurate for most purposes, additional model development is desirable to fully reflect year-to-year variability. We tested the precision of EPIC (version 5300) in estimating mean yields and in replicating yearly yield variability as influenced by the potential evapotranspiration (PET) method, using field data from a 27-yr crop rotation experiment at Swift Current, Saskatchewan. Rotations tested ranged from continuous wheat (Triticum aestivum L.) to fallow-wheat-wheat. Mean estimated yields were compared with measured yields (MY) and detrended yields (DY). Estimated yields and MYs were further compared by regression, ratio of variances due to lack-of-fit and to experimental errors (R), and model efficiency (EF). Mean yields estimated using the Penman-Monteith and the Priestly-Taylor PET methods resulted in significant underestimations, associated with high annual PET values, and were not analysed further. The Hargreaves (H) and Baier-Robertson (BR) PET methods resulted in mean yields not different than MY or DY for most cases, especially the BR method. EPIC with the H method accounted for 18 to 66% of the variability in annual yield estimation, whereas the BR method accounted for 29 to 60%. These were slightly, but not significantly, lower than results obtained with regionally derived statistical crop models. Overall EPIC with the BR PET method provided yield estimates accurate and precise enough for long term studies. The relatively high R and low EF values obtained, though, suggest further improvements in EPIC are necessary to better replicate yearly yield variability. Analysis of yield residuals indicated that EPIC may not be simulating accurately enough the water balance and its effects throughout the off-season and in the early part of the growing season. Roloff, G., de Jong, R., Zentner, R. P., Campbell, C. A. et Benson, V. W. 1998. Prédiction de la variabilité du rendement du blé de printemps au moyen du modèle EPIC. Can. J. soil Sci. 78: 541-549. Le modèle EPIC (modèle climatique intégré aux décisions à portée environnementale) a été utilisé précédemment pour prédire le rendement des cultures, les pertes de sol dues à l'érosion et la cinétique de l'eau et des nitrates. Malgré l'exactitude de ces prédictions à l'égard du rendement moyen à long terme, il apparaît nécessaire de lui apporter des perfectionnements pour lui permettre de prendre pleinement en compte la variabilité d'une année à l'autre. Nous avons donc testé l'aptitude du modèle (version 5300) à prédire les rendements moyens et à reproduire la vari-abilité du rendement d'une année à l'autre à partir des données d'une expérience de rotation des cultures de 27 ans conduite à Swift Current en Saskatchewan, en fonction de plusie...

Soil fertility is the result of interactions between the physical and chemical soil attributes, affecting its biological component, which in turn feeds back to the physical and chemical soil attributes. The No-Till System (NTS) is the main modality of Conservation Agriculture, essential to achieving farming sustainability and conserving soil fertility. However, farmers often fail to adopt the three principles of NTS: (a) minimum mechanical soil disturbance, (b) permanent soil cover and (c) plant diversification; therefore, the system currently requires a quality measurement. The NTS Participatory Quality Index (PQI) is a tool to qualify and monitor the farm system and requires the participation of the farmers themselves. The aim of this study was to assess key soil quality attributes associated with the implementation of PQI methodology during a large-scale dissemination campaign in areas under NTS in Paraná State, Brazil (Paraná River Watershed 3), in order to demonstrate the effectiveness of the PQI as a tool to drive the improvement of farmers' management. Spearman's correlation coefficients were established between PQI scores and the chemical and physical soil attributes, as well as the indicators incorporated into the PQI. Data were obtained in the Paraná River Watershed 3 from 40 areas of farmland under different farm systems. Crop rotation was the primary management approach that improved soil and agricultural management quality under Brazilian conditions, and confirmed in the study region. The NTS PQI provided a way to evaluate soil management quality in the areas assessed. The rapid soil structure diagnosis proved to be a good tool for assessing soil structure.

EPIC estimates of soil water, nitrogen and carbon under semiarid temperate conditions. Can. J. Soil Sci. 78: 551-562. The Environmental Policy Integrated Climate (EPIC) model is an important support tool for environmental management. Previous tests of the model have determined that it is suitable for long-term yield estimation, but it is less precise in assessing annual yield variability. To determine the reasons for the discrepancies between estimated and measured yields, we tested the ability of EPIC version 5300 to predict soil water and soil nitrogen dynamics, using data from a long-term spring wheat (Triticum aestivum L.) rotation experiment in the semiarid prairie region of Canada. Potential evapotranspiration (PET) estimates varied among methods tested: Priestley-Taylor and PenmanMonteith methods resulted in PET means that were about twice those obtained with the Hargreaves and Baier-Robertson methods. The higher PET means were associated with an excessive estimation of net radiation. We used the Baier-Robertson method to generate the other estimates reported herein. EPIC generally overestimated total soil water, but it still allowed clear differentiation among rotation phases and times of the year, and provided adequate estimates of water during the critical shot-blade stage. Water estimates by soil layer were also generally overpredicted, especially at depths from 0.15 to 0.60 m, but we were able to differentiate among rotation phases and times of the year. Precision of these latter estimates was generally low, accounting at most for 27% of the variability, and varied by soil layer, rotation phase and time of the year. Nitrate-N estimates tended to be lower than measured values, especially at depths below 0.3 m and during vegetative growth phases. However, the estimates also allowed us to distinguish among the rotation phases and times of the year. Total N and organic C were satisfactorily estimated by EPIC. In general, EPIC provided adequate long-term estimates of the environmental quality indicators tested.

Roloff, G., de Jong, R. and Nolin, M. C. 1998. Crop yield, soil temperature and sensitivity of EPIC under central-eastern Canadian conditions. Can. J. Soil Sci. 78: 431-439. The Environmental Policy Integrated Climate (EPIC) model can be an important tool for agricultural and environmental management. Application of EPIC in central-eastern Canada requires testing to evaluate its performance and to indicate eventual changes that ultimately can lead to a more accurate model. We compared crop yields and soil temperatures estimated using EPIC (version 5300) with measured data from two sites -Barrhaven, Ontario and St. Antoine, Quebec -where corn (Zea mays L.) and soybean (Glycine max L.) were grown during 4 yr. The sensitivity of several EPIC outputs to variations in selected input parameters was also determined. EPIC was run with either the Penman-Monteith (PM) or the Baier-Robertson (BR) potential evapotranspiration (PET) method. Mean estimated and measured soybean yields were not different, independent of PET method and location. Mean corn yields were underestimated at Barrhaven with the PM method, whereas they were overestimated by the BR method at St. Antoine. Using the PM method resulted in no difference between estimated and measured yields in 2 out of 5 corn years, while the BR method ensued in no difference in 3 out of 5 years. For soybean, only the BR method resulted in 1 yr of yield different than measured. Performance of the model in relation to experimental error and efficiency of the model varied with crop and location, and indicated that EPIC caused less error and was more efficient in estimating soybean than corn yields. Comparing limited measured soil temperature data with EPIC estimates reveled that EPIC tended to underestimate soil temperature; however no effect on estimated yield was observed. The relative sensitivity of EPIC outputs was least for yield and greatest for leached nitrate-N. The latter also displayed the highest variability in sensitivity. EPIC studies focusing on leached nitrate-N should require the most accurate crop, soil, hydrological and weather data in order to minimize errors.Key words: Environmental modelling, soybean yield, corn yield, sensitivity analysis Roloff, G., de Jong, R. et Nolin, M. C. 1998. Rendement des cultures, température du sol et sensibilité du modèle EPIC dans le centre-est canadien. Can. J. Soil Sci. 78: 431-439. Le modèle Climatique intégré aux décisions à portée environnementale (EPIC) peut être un important outil de gestion de l'agriculture et de l'environnement. L'application du modèle dans la partie centreest du Canada requiert au préalable une évaluation de ses performances et la mise en évidence des modifications susceptibles d'en accroître l'exactitude. Nous avons comparé le rendement des cultures et les températures du sol prédits au moyen du modèle EPIC (version 5300) avec les données de terrain recueillies à deux emplacements, Barrhaven en Ontario et Saint-Antoine au Québec, où le maïs (Zea mays L.) et le soja (Glycine max L.) étaient cultivés ...

Freqüentemente a adoção do sistema plantio direto está associado ao surgimento da compactação ou adensamento da superfície do solo, quer pelo seu não revolvimento, quer pelo tráfego de máquinas e equipamentos agrícolas e de transporte. Com o objetivo de estudar alguns fatores que interferem na compactação do solo em plantio direto e seus efeitos na cultura do milho, foi instalado um experimento em Latossolo Vermelho Distroférrico Típico, na região sudoeste do Paraná, município de Dois Vizinhos, no ano agrícola de 1999. A superfície do solo foi trabalhada para atingir quatro níveis de possíveis compactações: (1) tráfego de colheitadeira carregada com peso de 12.000kgf; (2) tráfego de um trator agrícola com peso de 4.000kgf; (3) descompactação com subsolador de 4 hastes a 0,40m; (4) uma parcela testemunha. Avaliou-se o desenvolvimento do sistema radicular do milho em perfis através de trincheiras em todas as parcelas, efetuando a contagem do número de raízes e sua distribuição em profundidade no perfil, correlacionando com o rendimento de grãos de milho. Os resultados obtidos mostraram que: (1) o tratamento que sofreu tráfego do trator agrícola apresentou efeito negativo da compactação do solo demonstrada pela menor produtividade obtida; (2) os tratamentos que não sofreram compressão do solo (subsolador e testemunha) apresentaram maiores produtividades e também maior densidade de raízes, com sua distribuição mais homogênea no perfil do solo. Foram observados efeitos negativos da possível compressão do solo pelo trabalho artificial produzido pelas máquinas agrícolas nas parcelas trabalhadas, o que comprometeu a distribuição e quantidade de raízes no perfil do solo, bem como o rendimento de grãos de milho.