Soil physical quality of Mollisols quantified by a global index

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 kg1, organic matter between 5 and 40 g kg1, and soil bulk density between 1.09 and 1.49 Mg m3, were used. The indicators measured were: pore size distribution, macroporosity (PORp), air capacity (ACt) and plant-available water capacity (PAWC) among others. Soils were classified into four groups according to their physical properties and a reference WRC was determined. From this WRC and considering a total porosity of 0.514 m3 m3, PORp was 0.035 m3 m3, ACt 0.153 m3 m3, field capacity 0.361 m3 m3, permanent wilting point 0.136 m3 m3 and PAWC 0.225 m3 m3. 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.

Soil physical quality of Mollisols quantified by a global index

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 kg1, organic matter between 5 and 40 g kg1, and soil bulk density between 1.09 and 1.49 Mg m3, were used. The indicators measured were: pore size distribution, macroporosity (PORp), air capacity (ACt) and plant-available water capacity (PAWC) among others. Soils were classified into four groups according to their physical properties and a reference WRC was determined. From this WRC and considering a total porosity of 0.514 m3 m3, PORp was 0.035 m3 m3, ACt 0.153 m3 m3, field capacity 0.361 m3 m3, permanent wilting point 0.136 m3 m3 and PAWC 0.225 m3 m3. 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.(AU)

Soil water dynamics and litter production in eucalypt and native vegetation in southeastern Brazil

High productivity of eucalypt plantations is the result of advances in research that have led to gradual improvements in intensive silvicultural technology. High productivity notwithstanding, eucalypt plantations remain the focus of environmental concerns. Our study aimed to compare the soil water regime, litter fall and nutrients dynamics either in a fragment of native forest or in an adjacent stand of growing eucalypt. We took field measurements during the first three years of eucalypt plantation in a sandy soil in the southeastern region of Brazil. Soil moisture and internal drainage were higher during the early stages of growth of the eucalypt stand, as compared with native vegetation. However, one and a half years after planting, available soil water was similar in both vegetations. Higher water availability under the eucalypt stand during the first year occurs because of silvicultural operations (soil preparation and weed control) and the small size of eucalypt trees; these factors increase water infiltration and decrease transpiration. Total leaf fall, over the study period, was similar for both ecosystems; however, differences were observed in the winter and early spring of 2010. The transfer of nutrients to soil by leaf fall was similar except for N and S, which was higher in native vegetation. Nitrogen concentration in the soil solution was higher in native vegetation, but K was higher under the eucalypt stand, mainly to a depth of up to 0.2 m.

Soil water dynamics and litter production in eucalypt and native vegetation in southeastern Brazil

High productivity of eucalypt plantations is the result of advances in research that have led to gradual improvements in intensive silvicultural technology. High productivity notwithstanding, eucalypt plantations remain the focus of environmental concerns. Our study aimed to compare the soil water regime, litter fall and nutrients dynamics either in a fragment of native forest or in an adjacent stand of growing eucalypt. We took field measurements during the first three years of eucalypt plantation in a sandy soil in the southeastern region of Brazil. Soil moisture and internal drainage were higher during the early stages of growth of the eucalypt stand, as compared with native vegetation. However, one and a half years after planting, available soil water was similar in both vegetations. Higher water availability under the eucalypt stand during the first year occurs because of silvicultural operations (soil preparation and weed control) and the small size of eucalypt trees; these factors increase water infiltration and decrease transpiration. Total leaf fall, over the study period, was similar for both ecosystems; however, differences were observed in the winter and early spring of 2010. The transfer of nutrients to soil by leaf fall was similar except for N and S, which was higher in native vegetation. Nitrogen concentration in the soil solution was higher in native vegetation, but K was higher under the eucalypt stand, mainly to a depth of up to 0.2 m.(AU)

Parcelamento da adubação nitrogenada na cultura do milho e utilização do N residual pela sucessão aveia preta-milho / Nitrogen fertilization splitting in maize and residual N utilization for the-black oats-maize succession

Com o objetivo de avaliar a eficiência de utilização do N pela cultura de milho (Zea mays L.), usando-se fertilizante marcado com 15N, aplicado parceladamente (duas formas), e o efeito residual deste fertilizante nas duas culturas subseqüentes em sucessão (aveia preta e milho), sob implantação do sistema plantio direto, foi conduzido um experimento, no sudeste do Brasil, nos anos agrícolas 2003/2004 e 2004/2005, sob um solo de textura areno-argilosa (Hapludox). Os tratamentos consistiram da dose de 120kg ha-1 de N, na forma de sulfato de amônio marcado (15N) e dois parcelamentos de N 30-90 e 60-60kg ha-1. Nas plantas de milho e aveia preta, avaliaram-se o N total acumulado, o N proveniente do fertilizante e a recuperação de N-fertilizante. O incremento da dose de fertilizante nitrogenado aplicado na semeadura (60kg ha-1 de N), no ano agrícola 2003/2004, proporcionou aumento no aproveitamento de N pela planta (65 por cento) em relação ao tratamento que recebeu 30kg ha-1 de N na semeadura (45 por cento).(AU)

The objective of this research was to evaluate: a)the N use efficiency by a maize (Zea mays L.) crop, using 15N labeled fertilizer applied in two splittings, and b) the residual effect of this fertilizer in two subsequent crops in succession (black oats and maize), under the introduction of the no tillage system. The experiment was carried out in Southest Brazil, in the cropping seasons 2003/2004 and 2004/2005, under a sandy-clayey loam soil (Hapludox) The first maize crop was in 2003/2004, the second one in 2004/2005 and the black oats crop in between. Treatments consisted of two ways of application of two N splittings (30-90 and 60-60kg ha-1) as 15N labeled ammonium sulphate fertilizer. In the maize and black oat plants, the following were evaluated: accumulated total N, nitrogen in plant derived from fertilizer and N fertilizer recovery. The treatment with 60kg ha-1 of N applied at sowing, in the 2003/2004 crop, increased the plant N use (65 percent) in relation to the treatment that received 30kg ha-1 of N at sowing (45 percent).(AU)