The effect of erosion on soil productivity and related soil properties
Date
1988-04
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Degree Level
Masters
Abstract
It is generally agreed that erosion reduces soil productivity by changing various soil
properties that are important to plant productivity. The purpose of this study was to
estimate the reduction in yields and changes in soil properties that relate to plant
productivity, with increasing levels of erosion. Experiments were located near Viscount
Saskatchewan, an area dominated by crop-fallow cereal grain rotations. Dark Brown soils
developed on glacial till were used in this study.
Various soil properties and dry matter yields were measured along and between
catenas with moderate and severe erosion. Grain yields were lowest on upper slopes, and
generally increased downslope, often to yields that were double the upper slope yields.
The relationship between yields and relative distance downslope was described best by a
third order polynomial equation, in that yields on the shoulder were slightly less than on the
crest, increased steadily through mid-slopes to maximum values on the lower or foot slope,
then decreased again as sampling moved from the slope to the generally lower part of the
fields. The moderately eroded catena outyielded the severely eroded catena at the crest
position.
The impact of varying degrees of erosion on productivity was estimated by adding
back incremental depths of topsoil to eroded knolls. Grain yields were increased by 45 to
58 % by adding 5 cm of topsoil. Further topsoil additions increased yields, but generally at
a decreasing rate. Fertilizing eroded soil to soil test recommendations produced yields
similiar to the 5 cm treatment, but never greater than the 10 and 15 treatments.
Changes in soil quality with increasing erosion were measured on otherwise similar
soils of increasing length of cultivation (0 to 75 years). Much reduced 137Cs contents on
eroded compared to native soil indicated that erosion increased with time of cultivation.
Losses in silt plus fine sand fractions suggested that wind erosion had dominated. Organic
matter and total N (NT) were lost at the rate of 0.62 and 0.02 Mg ha-1year-1, respectively, over a 75 year period. Potentially mineralizable N (N0) decreased rapidly over the first 40
year period of cultivation, beyond which losses occurred at a slower rate. The relationship
between potentially mineralizable S and years of cultivation was linear, indicating that the
former was lost at a constant rate. Changes in the N0/NT ratio suggest that potentially
mineralizable N was being lost faster than total N. Changes in the S0/ST ratio indicates that
total S is being lost faster than potentially mineralizable S. Organic phosphorus decreased
with increasing years of cultivation, while inorganic phosphorus showed no significant
trends with cultivation.
Field capacity and permanent wilting point decreased with increased erosion due
mainly to losses in organic matter, resulting in a slight decrease in available water capacity.
Cloddiness, as indicated by an increase in the mean diameter of dry aggregates, increased
with erosion, but these aggregates were not stable in water.
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Degree
Master of Science (M.Sc.)
Department
Soil Science
Program
Soil Science