wAbstract
@Under long-term cultivation, greater accumulations of soil organic
matter (SOM) and phosphorus (P) are found in the surface soil
layer under no-till (NT) versus moundboard ploughing (MP) practices.
Our objective was to evaluate the effects of NT and MP practices
on concomitant SOM and P distribution and sorption characteristics
among water-stable aggregates and non-aggregated particles. The
study was conducted in Quebec, Canada, as part of a long-term
corn and soybean rotation experiment (established since 1992)
on a clay loam soil of the St-Blaise series (Dark Grey Gleysol).
Soil samples were collected in the fall of 2007 in the 0-5 cm
layer from plots under NT and MP receiving 35 kg P ha-1
and 160 kg N ha-1. samples were separated into three
water-stable aggregate-sized classes (macro, 2000-250Κm; meso,
250-180Κm; micro, 180-53Κm) and (silt + clay)-sized particles
(53Κm) using wet-sieving. Macro aggregates made up 60.2 and 48.5
of total soil weight under NT and MP, respectively. In wet-sieved
soils from NT plots, water-extractable P (Pw) concentration increased
in the order (silt + clay)-sized particlesmicro-meso-macro-aggregates;
under MP, micro-, meso-, and macro-aggregate fractions had the
same Pw concentration, while the (silt + clay)-sized particles
showed the lowest Pw concentration. The hierarchy observed among
aggregate-sized classes under NT in relation to Pw concentration
was also observed for carbon content, indicating that Pw is influenced
by soil aggregation as driven by SOM accumulation. The lower Pw
concentration in (silt + clay)-sized particles could be explained
by a greater retention of P by reactive oxides and highly disordered
alumino-silicates present on (silt + clay)-sized particles, thereby
reducing the soluble P released from these particles. One important
aspect of this study is the contrasting P sorption characteristics
of solid particles under NT and MP. The P sorption maxima (Smax value) of the (silt + clay)-sized particles
was twice that of the water-stable aggregates. Sorption characteristics
reflect the hierarchy observed under NT for organic C and Pw,
indicating a closer link between SOM and P dynamics within soil
aggregates in contrast with MP.
Keywords: No till; Mouldboard ploughing; Soil aggregation; Phosphorus
dynamics; Organic carbonx
1. Introduction
2. Materials and methods
@2.1. Site description and experimental design
@2.2. Soil sampling and aggregate separation
@2.3. Chemical analysis
@2.4. Phosphate sorption experiment
@@2.4.1. Langmuir isotherm
@@24.2. Feundlich isotherm
@2.5. Statistical analysis
3. Results and discussion
@3.1. Aggregate size distribution and associated carbon
@3.2. Water-stable aggregates and silt + clay associated dissolved
inorganic P
@3.3. Phosphorus sorption characteristics of aggregate-sized classes
4. Conclusions
References