Mollisols of Santa Fe have different tilth and load support capacity. Despite the importance of these attributes to achieve a sustainable crop production, few information is available. The objectives of this study are i) to assess soil physical indicators related to plant growth and to soil mechanical behavior; and ii) to establish relationships to estimate the impact of soil loading on the soil quality to plant growth. The study was carried out on Argiudolls and Hapludolls of Santa Fe. Soil samples were collected to determine texture, organic matter content, bulk density, water retention curve, soil resistance to penetration, least limiting water range, critical bulk density for plant growth, compression index, pre-consolidation pressure and soil compressibility. Water retention curve and soil resistance to penetration were linearly and significantly related to clay and organic matter (R2 = 0.91 and R2 = 0.84). The pedotransfer functions of water retention curve and soil resistance to penetration allowed the estimation of the least limiting water range and critical bulk density for plant growth. A significant nonlinear relationship was found between critical bulk density for plant growth and clay content (R2 = 0.98). Compression index was significantly related to bulk density, water content, organic matter and clay plus silt content (R2 = 0.77). Pre-consolidation pressure was significantly related to organic matter, clay and water content (R2 = 0.77). Soil compressibility was significantly related to initial soil bulk density, clay and water content. A nonlinear and significantly pedotransfer function (R2 = 0.88) was developed to predict the maximum acceptable pressure to be applied during tillage operations by introducing critical bulk density for plant growth in the compression model. The developed pedotransfer function provides a useful tool to link the mechanical behavior and tilth of the soils studied.
Indicators synthesizing the state of the structural quality and the function of the porous system are useful for assessing soil production capacity as well as the way it may serve natural ecosystems. This research aimed (i) to determine indicators of the state and function of the porous system, (ii) to use them to derive a global index to characterize the soil physical quality, and iii) to establish a reference pore-size distribution curve for Mollisols from the province of Santa Fe (Argentina). Sixty water retention curves (WRC) of A and B horizons of Mollisols, with clay varying between 119 and 538 g kg . Both the high silt content and low organic matter content confer on the soil characteristics with low stability, excess of small pores and low porosity of the macropore domain. Consequently, the capacity to quickly drain the water excess and allow root proliferation was not optimal, possibly due to the high silt or clay content and the low sand content, characteristic of the soil matrix of these Mollisols.
Plant soil compaction poses a serious problem to agriculture because it produces different types of changes in plant characteristics. No method has been implemented to date to use root morphological changes as indicators of soil compaction levels. Therefore, the aim of the present study was to evaluate whether or not the morphological changes in root apexes of soybean (Glycine max (L.) Merrill) can be used as indicators of soil compaction levels. To this end, a silt-loamy soil material (from a Typic Argiudoll, Esperanza series), sieved through a 2 mm mesh was used and the following soil bulk density levels were determined: 1.1, 1.3 and 1.5 g cm -3 for which the corresponding mechanical resistances were < 0.1, 0.5 and 3.5 MPa, respectively. The distance from the apex to the first tertiary root and the root diameter at 1.5 cm from the apex were measured on the secondary root apexes. A form factor equal to the quotient between these two variables was subsequently calculated. An inverse relationship between soil mechanical impedance and secondary root length and form factor as well as a direct relationship with the secondary root diameter were observed. Changes in rhizodermis cells were also recorded. The following morphological characteristics were found to evidence the highest sensitivity to soil compaction: i) the form factor, ii) rhizodermis papillose cells, iii) apical malformations in root hairs, and iv) root diameter in expansion areas. Taken together, the morphological characteristics of root apexes could be considered to be indicative of soil compaction. Key words: Glycine max, mechanical impedance, root indicator, root hairs Características morfológicas de ápices de raízes de soja como indicadores de compactação do soloRESUMO: A compactação do solo causa severos problemas devido a que gera diferentes mudanças nas características das plantas. Não existem métodos que possibilitem o uso das mudanças da morfologia das raízes como indicadores de níveis de compactação do solo. Avaliaram-se se alterações morfológicas nos ápices de soja podem ser utilizadas como indicadores de graus de compactação do solo. Solo peneirado a 2 mm, classificado como Typic Argiudol (série Esperanza), foi compactado até atingir os seguintes valores de densidade do solo: 1.1, 1.3 e 1.5 g cm -3 , para os quais corresponderam os valores de resistência mecânica de < 0.1, 0.5 e 3.5 MPa, respectivamente. A distância desde o ápice até a primeira raiz terciária e o diâmetro a 1.5 cm desde o ápice foram medidos nas raízes secundarias. Um fator de forma foi calculado fazendo o quociente entre as duas variáveis medidas. Houve uma relação inversa entre o cumprimento da raiz secundaria e fator de forma com a resistência mecânica, e uma relação direta entre esta ultima e o diâmetro das raízes secundárias. Alterações nas células da rizoderme foram determinadas. As seguintes características morfológicas se mostraram muito sensíveis a compactação do solo: i) o fator de forma, ii) as células papilosas da rizoderme, iii) malformações apicais no...
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