Agriculture Reference
In-Depth Information
aggregate size distribution following perennial grass-clover mixture and
spring wheat crops.
Materials and Methods
The experiment started in 1982 at the Agrophysical Research Institute's
experimental station located ~60 km southwest of St Petersburg. Plots were
stablished on a podzolic loamy sand soil in a seven-course rotation with a
grass-clover mixture ( Phleum pratense and Trifolium pratense ) for 2 years,
potato ( Solanum tuberosum ), spring barley ( Hordeum vulgare ), winter rye
and downy vetch ( Secale cereale and Vicia villosa ), winter rye ( Secale cereale )
and spring wheat ( Triticum vulgare ). All the crops were grown in each year
from 1982. The plots were not replicated and there was only one plot for
each crop in each year. Tillage treatments consisted of spring mouldboard
ploughing (conventional tillage) at a depth of 20-22 cm and spring disking
(minimum tillage) at a depth of 10-12 cm. The size of the plots was
30 m
186 m (for each tillage treat-
ment). No fertilizers were applied to any of the crops. The grass-clover
mixture was used as the only source of nutrients for the crops of all the
seven stages of the rotation. The grass-clover mixture was used for hay. Soil
samples (0-10 cm) were taken from the plots with grass-clover mixtures
(the first and second stages of the rotation) and from the plot with spring
wheat (the seventh stage of the rotation) in May and September of 1998.
Five samples of soil were taken from each plot and mixed. Three sub-
samples were taken from these bulked samples and all the soil properties
were determined from these and used for analysis. Organic matter contents
in the whole soil samples and in the water-stable aggregate size fractions
were determined by wet oxidation according to Tjurin's procedure
(Kaurichev, 1986). Measurements of aggregate size distribution were
carried out by dry and wet sieving with a rotary sieve (Vadjunina and
Korchagina, 1986). Sieve sizes were 0.5, 1.0, 2.0, 3.0, 5.0 and 7.0 mm.
×
186 m (for each crop) and 15 m
×
Results and Discussion
The growing of perennial grass-clover mixtures is known to contribute to a
considerable input of plant residues and hydrophobic organic substances
into soils. Studies have shown that the percentage of water-stable
aggregates increases with increasing content of organic matter originating
from grasses (Ekwue, 1990; Broersma et al ., 1997). Such changes in wet
aggregate stability are very important, especially for light-textured soils,
which usually demonstrate both low organic matter content and a low
percentage of water-stable aggregates.
Search WWH ::




Custom Search