Abstract: Field experiments were conducted at Sanganeh Research Station at North-east of Iran to determining runoff production, soil accumulated moisture and develop semiempirical model to determine the best plant row spacing for reclamation and optimum production of degraded rangelands under natural precipitation. Runoff production and soil accumulated moisture were determined in 80 experimental plot on different combination of soil type, vegetation cover and slop gradient, during autumn, winter and spring precipitations during 1996-2005. Results from 90 precipitation events with various magnitude and intensity indicated that, soil accumulated moisture was not considerable in September to November period and the amount of evapotranspiration was more than precipitation up to 6 fold. The average of soil accumulated moisture, evapotranspiration and surface runoff in winter were calculated around 64, 33 and 3% of precipitation, respectively. In spring, the average of evapotranspiration, infiltration and runoff were 62, 36 and 2% of the rainfalls, respectively. The resulted values for moisture accumulation in the soil and surface runoff on the experimental plots make it possible to estimate the potential deficit of moisture and assess the water supply of the plant. Experimental data was used to develop a semiempirical model for determining the best plant row spacing for optimum production and water requirement of pastures. Generally we concluded that there is a strong possibility for reclamation of eroded rangelands using surface runoff in arid and semi arid regions.
INTRODUCTION
More than 30% of the earth’s land area has characterized as arid and semi-arid regions (Hassani et al., 2008). Historically, wide areas of Iran had been covered with forests and rich rangelands (Rangavar et al., 2004). Fast increasing of human’s food requirements, population, climatic conditions and overgrazing are important factors that affect the eroded areas and rangeland’s species composition in semi-arid ecosystems (Solaimani and Hadian Amiri, 2008; Hassani et al., 2008). Degradation of great area of rangelands in North-east of Iran (Khorasan Province) due to environmental and human factors is an example of this evident. Approximately, 41.7% of Khorasan land surface are rangelands, 12.5 million hectare, with production of 90-312 kg ha-1 dry weight on average. The majority of these areas are classified as medium to poor rangelands. The rest of Khorasan land area, are desert rangelands (Zadbar et al., 2007). Earlier studies have revealed that, traditional grazing can reduce diversity of plants in poor soil (Anderson and Hoffman, 2007). For this reason, in the majority of Khorasan Areas, decreaser plants have replaced with increaser ones (Peganum harmala and Sophora pachycarpa). That has resulted to fodder shortage and other serious problems in that region. Therefore, it is essential to reclaim degraded rangelands by scientific and economic methods.
Precipitation is the only source of moisture supply for rangelands. Therefore, it is necessary to use this potential factor for reclaiming degraded rangelands (Wylie et al., 1992). Recent studies in Iran shows that, the total amount of annual precipitation is about 430 billion m3, out of which about 20% is lost in the form of flash floods (Foltz, 2002). Water and soil characteristics in arid and semi-arid regions are in a form that rain in non-growing and at the beginning of growing seasons is reserved in soil so that deep rooted permanent plants can utilize this water source during the growing season (Karabulut, 2002).
Many studies have discussed about the runoff behavior of different land use types and the effects of land use change on runoff production (Dagnachew et al., 2003; Dunjo et al., 2004). Some of the fodder shrubs species can be developed under cultivation in arid zones between 200 and 400 mm of mean annual rainfall. However, when mean annual rainfall drops below 200 mm, additional water from runoff is essential for improving production (Abu-Zanat et al., 2004).
Rainwater harvesting and its use for rangelands improvement can be a common method in arid and semi-arid regions. Many researches in Central Asia and deserts around Caspian Sea in Russia have been carried out in field of rangeland improvement in arid and semi-arid regions using rainwater harvesting. Results of these researches indicated that agroclimatological approach for reclamation is the most suitable scientific and economic method. Using valuable fodder shrubs in degraded rangelands as a protective green belt and applying surface runoff as well as restoring moisture in soil, enable us to increase plant products up to the potential of each region. Applying this method, the fodder products have been increased together with achievements in natural regeneration of fodder plant species (Nurberdiev and Reizvikh, 1992). Compatible shrubs in arid regions could considerably change the conditions of ecosystems in which they are planted (Farrell, 1990). These plants species with C4 photosynthetic pathway has been found to be a valuable component of arid region’s nature where they can also photosynthesize in moisture and temperature stress (Pyankov and Mokronosov, 1991). The consistency of production in these areas is resulted from actual potential of shrubs in the ecosystem. Compared to other plants, the root of shrub species penetrates deeply in soil, improve soil structure and have influence on nutrient cycling and soil moisture (Gliessman, 1990).
Researches performed for recognition of water and soil resources potential in arid regions in the Middle East, has shown that the average rainfall reservation during non-plant growing season i.e., winter, has been 55, 77, 70 and 2% in loamy sand, sandy, sandy loam and loamy rangelands, respectively. In another research, the runoff coefficient has been determined to be about 8% for steppe deserts in Russia and 5% for lower-side of Volga and desert regions of Caspian Sea (Artykov, 1987). According to the study in a nearby field (Chahchahe), the average of runoff coefficient from November to February has been measured to be about 2% (Rangavar et al., 2004). Based on agroclimatologic approach, reclamation of degraded rangelands depends on relation between runoff productivity, soil accumulation capacity and required moisture of phytomeliorants (Rangavar et al., 2004). The amount of surface runoff potential requirement for meeting the plant moisture storage in rangelands differs with geographic properties of different regions. The main objectives of this research were to measure surface runoff and soil accumulated moisture to estimating additional water requirement for rangelands reclamation. On the basis of this research, a semiempirical model was also developed in order to the best plant row spacing for optimum production and water requirement of pastures.
MATERIALS AND METHODS
Station Description
This research was performed to evaluate in real time runoff phenomenon.
Experimental runoff measurement plots were used to determine the required coefficients
and indices. The research station is located between 60°, 13’, 47"
Northern latitudes and 36°, 41’, 17" Eastern longitudes in the 100
km Northeast of Mashhad, Khorasan Province, Iran, with altitude of 700 m above
sea level. Figure 1 shows the situation of Sanganeh research
station on Iran’s map.
Land type of the research station is plateau and slope ranging from 1 to 50%.
The soil cover of runoff plots in Sangane station is mainly represented by Gray-Cinnamonic
soil, Sierozems, Lithosols and Regosols. Soil’s gravels content, acidity,
electrical conductivity, lime, organic matters and gypsum content varied from
0 to 40, 7.2 to 8.3, 1 to 8 dS m-1, 0.3 to 10.4, 0.8 to 3.3 and 0
to 19%, respectively. Variability of rainfall from year to year is very high.
On average, in wetter year, 10-12 rainfall periods are happened. In the drier
years only 4-6 rainfall periods are experienced. The average annual rainfall
is about 250 mm and climate is semi-arid by using Demartonne method. Dominant
vegetation cover type is Poa bulbosa and Artemisia sieberi. In
some patches other species such as Carex stenphylla and Salsola aucheri
are companion plants with dominant species. The percentage of vegetation cover
in different parts of the station and plots varies from 0 to 50%. Suitable place
for runoff measurement was selected based on the slope, vegetation cover and
top soil which have the most important role in runoff production. Considering
above mentioned factors, 80 experimental runoff measurement plots with 2 m width
and 5, 10, 15, 20 and 25 m lengths were constructed and divided into 23 categories.
Each plot was hydrogeologically isolated for collecting and analyzing precipitation
runoff separately. Steel tanks were also considered at the end of each plot
for collecting runoff. Two recording rain gauge were used for collecting rain
data. Figure 2 shows three kinds of runoff measurement plots
with different conditions and dimensions.
| Fig. 1: | Situation of Sanganeh research station on Iran’s map |
| Fig. 2: | Three kinds of experimental runoff measurement plots in different conditions |
Theory of Modeling
Reclamation of degraded rangelands based on agroclimatological approach
needs some information about moisture content, seed germination requirement
and growth and viability of phytomeliorants. Actual moisture content accumulated
(mm) in furrows and utilized by phytomeliorants per year FE0 was
estimated by Eq. 1 (Rangavar et al.,
2004):
(1) |
where, P1 is the amount of precipitation in the autumn-winter (mm), P2 is the amount of precipitation in the spring (mm), Ka is the coefficient of moisture accumulation in the soil, Kr is runoff coefficient in spring period, W is the amount of soil moisture remained from end of previous inactive growing period (mm), that it was negligible for our study and ignored.
For calculating the parameter of moisture adequacy of phytomeliorants, it is
very important to know the moisture requirements of these plants in different
years. Rychko (1994) calculated and appraised the water
and heat parameters for hydroclimatic zoning of the Chu arid region of Kirghizestan.
Zoning was performed based on the average of established zonal parametric natural
moistening (K and W) and elements of the moisture and heat resources in the
active growing period of vegetation expressed in Eq. 2 and
3.
(2) |
(3) |
where, P is the precipitation (mm), Vi and Vf are the amount of reserved moisture along the rooting zone (mm), Rg is the amount of moisture in rooting zone supplied by ground water table (mm), E0 is the evaporability or the maximum total evaporation of agrocoenosis (mm).
To simplify evaporability determination, following equation has been established
based on total daily average temperature of the air (Rychko,
1994).
(4) |
where, E0 is the evaporability during vegetation growth period (mm) and t is the sum of daily average air temperature in the same period (°C).
For the present case study the optimal total evaporation, E0, corresponds
approximately to the demand of the rangeland plants for moisture in a specific
year. Consequently, the ratio between the actual amounts of moisture spent in
a given year on the total evaporation and the required amount of moisture for
the maximum total evaporation in the same year, expresses the value of the coefficient
of moisture adequacy for the phytomeliorants (Kma) in the moisture
accumulating furrows (Eq. 5):
(5) |
where, 0.30xT5-20°C is the total evaporation, E0 is 0.30 T, during active vegetation growth period in arid rangelands within the limits of the average daily temperature of 5-20°C (Nurberdiev and Reizvikh, 1992).
The accumulation coefficient of the autumn-winter precipitation (Ka) in the moisture accumulating furrows was calculated by Eq. 6:
(6) |
where, ΣP is the sum of precipitation in the given case (mm), I is total evaporation from the moment of one precipitation to the following case (mm), S is surface runoff from the inter-row space into the moisture accumulating furrows (mm).
The amount of precipitation runoff (S) from rangeland surface (mm) is determined by Eq. 7:
(7) |
where, Hw is the height of water in reservoir (mm), Ar is reservoir area (cm2) and As is the area of the runoff plot (m2).
Consequently, the runoff coefficient (Kr) is determined by Eq.
8:
(8) |
Measurements
The amount of precipitations in different seasons and related runoff were
measured directly during 1996-2005 in Sanganeh research station. Consumed moisture
for total evaporation was calculated by Rychko (1994)
method.
RESULTS AND DISCUSSION
Table 1 shows average runoff coefficients, evaporation and
accumulation moisture in soil subjected to 90 precipitation events during 1996-2005
in Sanganeh research station. In early June when the weather is hot and dry,
the soil moisture changed from 1.2-1.3% in the 0-5 cm layer, to 2-4% at a depth
of 15 cm, 4-8% at a depth of 60 cm and 7% at a depth of 100 cm. It serves as
an evidence of the fact that the active life of plants discontinues because
the soil moisture was much lower than the wilting point. The results of evaporation,
soil moisture and runoff from 90 precipitation events (with different intensity)
obtained from 23 groups of experimental runoff measurement plots showed that
during autumn there was not considerable moisture in soil and evaporation was
three to six times more than amount of rainfall. Moisture accumulated in soil
from the beginning of winter, were 47% in Dec., 70% in Jan. and 75% in Feb.
with respect to total precipitations.
| Table 1: | Coefficients of accumulation (Ka), evaporation (Ki) and runoff (Kr) in Sanganeh station, during winter and spring (1996-2005) |
| Table 2: | Average long term climatic parameters and their distribution in Mashhad climatological station |
The average of consumed moisture in winter was 33% and the amount of runoff was estimated as 3%. In spring time, the amount of precipitation was noticeable and average evaporation was 62% in Mar. and Apr. Water infiltrated in to the soil was changed to 36 and 2% was used for surface runoff. Table 2 for example shows the exerted achieved results from this research to the average long term climatic parameters in the nearest climatological station i.e., Mashhad.
The comparison of amount of surface runoff and soil accumulated moisture obtained from this research is correspond with the similar study in the central Asian countries, steppe deserts and desert regions of Caspian Sea in Russia. This shows, an existing climatic potential in different regions for reclamation of degraded rangelands or creating artificial pastures.
These results are in agreement with those obtained from central Asian countries, steppe deserts and desert regions of Caspian Sea in Russia (Artykov, 1987).
The accumulated moisture and runoff coefficients obtained from the experimental runoff measurement plots in various years make it possible to calculate the deficiency of the precipitation compared to optimal moisture for the phytoameiorants. Based on results, one can simulate the most rational schemes for creating shrub pasture plantings in various agroclimatic regions of Khorasan Province.
Amount of precipitation deficit (Dr) of a specific agroclimatic
district needed for the stable growth and development of phytoameliorants on
the moisture accumulating furrows can be expressed by the difference between
the required and the actual amount of precipitation in the given district, plus
the surface runoff. This can be expressed in Eq. 9:
(9) |
Finally, the model of Optimal Moisture Adequacy (OMA) for the phytomeliorants
can be expressed in Eq 10:
(10) |
The deficiency of the atmospheric precipitation for the optimal moisture adequacy of phytomeliorants in various agroclimatic regions can be replenished by the surface runoff resulted from atmospheric precipitation. The data shown in Table 3, allow us to select the proper inter row spacing that provides an additional water for the growth and development of phytomeliorants in pastures.
For instance, based on data obtained from Gharatikan meteorological station (near the research station), average rainfall during autumn-winter and spring are 80 and 125 mm, respectively. The required amount of moisture in the active vegetation period of the phytoameiorants is 260 mm. By using the Eq. 9, the precipitation deficit is 83 mm. So, the average runoff with different values of runoff coefficient (Kr) and the inter row spacing, provides 83 mm of additional water for the plants in the spring time. Using Table 3 for Kr = 0.02 and regarding 125 mm spring rainfall, the runoff generated from 30 to 40 m interval, can provided deficit moisture for the optimal moisture adequacy of phytomeliorants.
CONCLUSION
Agroclimatic approach proposed in the present research could be an efficient
pathway to improve the degraded rangelands productivity. It helps forecasting
and determining the seed inter row spacing and providing the optimum use of
surface runoff. Plant water requirement shortage in soil can be reduced by using
the surface runoff. A model was elaborated to calculate the optimum water supply
using the surface runoff properties for North-East of Iran (Khorasan Province).
The model is also applicable for forecasting the possibilities of rangeland
productivity improvement up to its optimal level. A range of standard criteria
was proposed for calculation of the optimum water supply with respect to inter
row spacing (Table 3).
| Table 3: | Possible runoff volume with different values of inter row spacing runoff coefficient and precipitation, (distance between seeds in row, 1 m) |
The proposed model can be applicable to calculate the duration of vegetation period in respect to water supply.
ACKNOWLEDGMENTS
Honorable authorities of Agriculture and Natural Resources Research Center of Khorasan (KANRRC) are highly appreciated for supplying necessary materials and instruments for this research and especially the researcher’s sincere thanks goes to the all staffs and co-workers of the Soil Conservation and Watershed Management Research Department who offered their valuable help in all phases of this research.