Tillage Management on Sustainable Rainfed Agricultural Resources
The aim of this study is to investigate the effects
of plowing treatments on the volume of surface runoff, soil loss and crop
yield, a research plan was implemented on hillslopes of the Sohrain Gharacharian
floodwater spreading station in Zanjan province, Iran. Rainfall, surface
runoff, sediment and crop yields were monitored in 1.8 wide x22.1 m long
erosion plots. Two plowing treatments of contour and up and down the slope
were compared on three slope classes of 0-12, 12-20 and 20-40% in triple
replication and randomized complete block design in a regional wheat cropping
experiment. Results demonstrated that contour plowing significantly reduced
the volume of surface runoff and sediment yield in all slope classes.
The amounts of reduction in all three slope classes were 83, 88 and 57%
for runoff and 92, 97 and 95% for sediment, respectively. The volume of
surface runoff and sediment yield from contour plowing of the 12-20 and
20-40% slopes were significantly lower compared to up and down the slope
plowing of 0-12%. Similar results were obtained when comparing volume
of surface runoff and sediment yield from contour plowing of 20-40% slope
to up and down the slope plowing of 12-20%. Contour plowing resulted in
soil loss that was 6.11, 7.73 and 7.73 times less than the soil loss threshold
in 0-12, 12-20 and 20-40% slopes, respectively. The quantity and quality
of crop yield did not change by plowing treatments. But, contour plowing
increased the crop yield by 19, 21 and 9% on 0-12, 12-20 and 20-40% slopes,
Degradation and mismanagement of resources pose a great tragedy in recent
times, these resources should be conserved and utilized to the maximum
possible extent. The prevention of soil erosion, which means reducing
the rate of soil erosion to approximately that which would occur under
natural conditions, relies on selecting appropriate strategies for soil
conservation. Although it is impossible to stop soil erosion completely
under natural conditions, there is a great need to control erosion for
proper land and water use planning. A practical measure of soil resistance
to erosion used by pedologists is the Soil Loss Tolerance (SLT). The term
SLT denotes the maximum rate of soil erosion that can occur and still
permit crop productivity to be sustained economically. Bhattacharyya et
al. (2008) computed SLT minimum limits of 2.5 t ha-1 for
Shivalik-Himalayan region in India. Regarding the time needed for soil
formation under different climatic, topographic and biological conditions,
Bybordi (2001) concluded that 100-300 years required developing 2.5 cm
of soil and 1.16 t ha-1 annual SLT.
Shrestha (1997) evaluated the magnitude of soil erosion in a middle mountain
region of Nepalese, Himalaya. Results showed that the highest and the
lowest rates of soil loss of 56 and 1 t ha-1, belong to rainfed
cultivation areas and dense forest, respectively.
Although irrigation is relatively more important in cereal production
in developing countries, with nearly 60% of cereal productions coming
from irrigated areas, Rosegrant et al. (2002) contend that globally,
69% of all cereal area is rainfed including 66% of wheat. Based on National
Statistical Calendar (2006), from 17.6 million ha of agricultural lands
in Iran, 53% are rainfed, from which 69% are under cultivation of annual
crops, 29% fallow and 2% under orchards. Inadequate moisture and periodic
droughts reduce the periods when growing plants provide good soil cover
and limit the quantities of plant residue produced. Erosive rainstorms
are not uncommon and they are usually concentrated within the season when
cropland is least protected. Water, as rainfall and runoff, is the active
agent for the basic process of water erosion. Water erosion is a serious
problem in sub-humid, semiarid and arid regions and the need for conservation
has become critical in many countries. Soil erosion resulting from improper
management of landuse activities has environmental and economical impacts
(Nikkami et al., 2002). The eroded soil covers bottom lands and
man-made structures as sediment. Gullies, sand dunes and other obvious
signs of erosion are examples of improper land management. Deterioration
in the quality of cropping and grazing lands as a result of erosion, reduces
productivity and increases expenditure on fertilizers. In extreme cases
yields become so poor that land has to be taken out of cultivation (Morgan,
1986). Many researchers have observed declining crop yields with decreasing
topsoil depth. For example, more than half of India`s cropland is losing
productivity because topsoil is being washed or blown away faster than
natural forces can replace it.
Perhaps the single most important factor contributing to erosion of sloping
cropland is tillage. Clearing the land exposes the soil to the effects
of weather. The amount of soil erosion that occurs depends on the kind,
the amount and the direction of tillage operations in relation to the
slope of the land and the timing of tillage. The maximum rate of soil
erosion was recorded in the plots with the variant of conventional up
and down the slope tillage and it was much smaller in the no-tillage variant
and in all variants with tillage across the slope (Basic et al.,
2000). Moldboard plow on different slope gradients resulted in down slope
translocation and dispersion. Both translocation and dispersion are strongly
affected by slope gradient (Oosta et al., 2000). Surface residue
and surface clod mass were consistently reduced by 45% or more in conventional
tillage compared with minimum tillage and delayed minimum tillage (Schillinger
et al., 2001). Soil condition, opening angle and tillage velocity
were also critical factors affecting the translocation coefficient for
the harrow disk in a research conducted in Portugal (Marques Da Silva
et al., 2004). Subsoiling resulted in the highest increase in moisture
storage and lowest evaporation during the fallow period when four soil
tillage practices of conventional tillage, no tillage, subsoiling and
reduced tillage were compared by Cornelis et al. (2002). Alberts
and Neibling (1994) found that surface runoff and soil loss exponentially
decrease with increasing vegetal residue and reducing soil preparation
practices. They indicate the role of canopy cover on reducing destructive
effect of rain drops on soil and reducing surface runoff.
Considering rainfed farm slope in many areas, which is usually much more
than FAO recommendations, applying improved agricultural practices prevents
soil erosion and conserves natural moisture of rainfall at dropping points.
Many developing countries located in arid or semi-arid regions experience
significant problems in securing adequate amounts of water for rainfed
crop production. Water scarcity problems in arid regions result simply
from the lack of sufficient rainfall (Rosegrant et al., 2002).
Rockstrom and Falkenmark (2000) note that due to high rainfall variation
in semi-arid regions, a decrease of one standard deviation from the mean
annual rainfall often leads to the complete loss of the crop. In situ
soil moisture conservation practices like ridges and furrows, compartmental
bounding, tied ridges and mulching as useful moisture conservation practices
in rainfed agriculture were compared by Ramesh and Devasenapathy (2007).
Results showed that moisture conservation through tied ridges along with
mulching recorded significantly higher soil moisture and improved grain
yield of pigeon pea in Tamil Nadu, India. Keeping these views, a field
experiment was planned to investigate the effect of different tillage
directions on the volume of surface runoff, soil erosion and crop yield.
MATERIALS AND METHODS
The research plan was implemented on steep lands of Sohrain Gharacharian
floodwater spreading research station located in northwest, 30 km from
Zanjan city in Iran during September 2003 to August 2005. Covering an
area of 15,000 ha the station lies on quaternary sediments beside the
Gharacharian River with maximum and minimum elevations of 1900 and 1500
m from sea level. Most of the lands in this area are under wheat rainfed
farming. Annual precipitation is between 350 and 400 mm in lower and upper
lands, respectively with Mediterranean to cold semiarid climate.
Two treatments of up and down the slope and contour plowing on three
slope classes of 0-12, 12-20 and 20-40% with three replications and randomized
complete block design were studied under regional wheat planting (first
year) and fallow conditions (second year) in 18 erosion plots of 1.8 wide
x22.1 meter long. Plowing treatments in the plots were simulated manually
by shovel and measured plow depth (25-30 cm) and furrow space (35-40 cm)
in the actual field that was prepared by conventional tractor-drawn moldboard
plow. For enrichment, ammonium phosphate at the rate of 50 kg ha-1
were added at the time of preparation in the first year and conventional
amount of 100 kg ha-1 wheat seeds were used for planting. Soil
fractions and characteristics such as sand, silt and clay percentage,
organic carbon and saturation percentage were extracted from soil samples
of 0-5, 5-20 and 20-40 cm depth of a soil profile in each slope class
at the first year.
During September 2003 to August 2005, 22 rainfall events which produced
surface runoff were monitored by a recording rain gauge in the station.
After each rainfall the volume of surface runoff and the amount of its
sediment content were measured in the tanks located at the lower end of
|| Runoff and sediment sampling from collecting tank
Using a pipe, two 220 L collection tanks were connected to
each other to ensure having enough space to collect all produced runoff
in each rainfall. Using a tube, these tanks were connected to the plots
to carry surface runoff and sediment. A 10 L bucket was installed under
the carrying tube, within the main collection tank, to trap coarse materials.
Using these buckets and a cylindrical sampler (Fig. 1)
increases the computational accuracy of sediment concentration by sampling
from collection tanks (Nikkami et al., 2004). Quantity and quality
of produced wheat seeds during first year were also measured.
RESULTS AND DISCUSSION
Physicochemical analysis of soil samples from 0-5, 5-20 and 20-40 cm depth
of each profile on 0-12, 12-20 and 20-40% slope classes are indicated in Table
1. The volume of surface runoff and the amount of sediment yield resulting
from 22 rainfalls during September 2003 to August 2005 were calculated. Table
2 show the amount of surface runoff and sediment yield from 0-12, 12-20
and 20-40% slope plots, respectively. The quantity and quality of produced wheat
crop are also shown in Table 3 and 4. Analyzing
the results by Least Significant Difference (LSD) method demonstrated that the
contour plowing significantly reduced the volume of surface runoff and the amount
of soil loss in all slope classes compared to up and down the slope plowing.
The amount of reduction with 99% confidence in 0-12, 12-20 and 20-40% slopes
were 83, 88 and 57% for runoff and 92, 97 and 95% for sediment, respectively.
The volume of surface runoff and sediment produced from contour plowing of 12-20
and 20-40% was significantly lower compared to the results of up and down the
slope plowing of 0-12%. The same result was noted when comparing volume of surface
runoff and sediment yield from contour plowing of 20-40% to the results of up
and down the slope plowing of 12-20%. The quantity and quality of crop yield
did not change significantly by plow treatments. But, contour plowing increased
the crop yield by 19, 21 and 9% on 0-12, 12-20 and 20-40% slopes, respectively.
The contour plowing significantly reduces surface runoff and sediment
yield compared to the up and down the slope plowing. The average reduction
on surface runoff and sediment yield was 76.5 and 91.9%, respectively
and shows the effectiveness of plowing direction on steep lands. The amount
of reduction on sediment yield was 91.16, 92.31 and 92.31% and the amount
of reduction on surface runoff was 83.28, 89.24 and 56.84% in 0-12, 12-20
and 20-40% slopes, respectively. The volume of surface runoff and sediment
yield produced from contour plowing of 12-20 and 20-40% were significantly
lower compared to up and down the slope plowing of 0-12%. The volume of
surface runoff and sediment yield produced from contour plowing of 20-40%
was significantly lower compared to up and down the slope plowing of 12-20%.
|| Physicochemical analysis of soil samples
|1Saturation percentage, 2Total
neutralizing value, 3Nitrogen, 4Phosphorus,
|| Surface runoff and sediment yield of 0-12, 12-20 and
20-40% slope plots
|| The quantity of produced wheat seeds
|| Wheat seed quality analysis
Compared to annual SLT of 1.16 t ha-1 (Bybordi, 2001), up and
down the slope plowing of 0-12, 12-20 and 20-40%, increased the soil loss
1.85, 1.68 and 1.68 times, respectively. Contour plowing of the slopes
of 0-12, 12-20 and 20-40% decreased the soil loss 6.11, 7.73 and 7.73
times less than the amount of soil loss tolerance. The quantity and quality
of wheat crop yield did not show significant difference among different
treatments. But, contour plowing increased the yield by 19, 21 and 9%
on 0-12, 12-20 and 20-40% slopes, respectively. The average wheat production
of rainfed croplands in Iran was 1069 kg ha-1 in 2005 (National
Statistical Calendar, 2006). The results of this research showed 1136,
820 and 612 kg ha-1 for contour plowing and 924, 647 and 561
kg ha-1 for up and down the slope plowing of 0-12, 12-20 and
20-40%, respectively. This means 15.7% increase in wheat production on
lands with 0-12% slopes compared to the country`s average wheat production.
This study is the result of a research project entitled The Effects of
Plough on Soil Erosion and Determining Land Slope Threshold for Dry Farming,
Grant No. 80-0500035000-04, implemented in the Soil Conservation and Watershed
Management Research Institute, Tehran, Iran. The authors acknowledge the
financial support of this Institute.
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