replacement cost approach. This approach ... Replacement costs â i.e., the costs of replacing live storage lost annually .... computer hard disk malfunctioned.
1
Management of Soil Erosion Consortium: An Innovative Approach to Sustainable Land Management in The Philippines Duque, C.M., Sr.1, R.O Ilao2, L.E. Tiongco3, R. S. Quita1, N.V. Carpina4, B. Santos4, M.T. de Guzman2
1.
Introduction
Soil erosion threatens several million hectares of lands in the world today. In the Philippines, soil erosion is a major threat to sustainable production in sloping lands where mainly subsistence farmers carry out food and fiber production. Sloping lands occupy about 9.4 million hectares or one third of the country's total land area of 30 million hectares. The topography together with the high rainfall, subject the cultivated sloping lands to various degrees of erosion and other forms of land degradation. Field experiments conducted in the IBSRAM ASIALAND Network sites in the Philippines showed that up-and-down slope cultivation resulted in annual erosion rates averaging about 100 t ha-1, depending on the rainfall and kind of soil. It was estimated by the Bureau of Soils and Water Management that about 623 million metric tons of soil is lost annually from 28 million hectares of land in the country. The collaborative project being undertaken by the Management of Soil Erosion Consortium (MSEC) heeds the call for integrating the activities of the research community for the development of a new paradigm for research on sustainable land management that meets the twin needs of increased productivity and resource conservation. While research and development activities are slowly experiencing a paradigm shift in the study of natural resources like soil, the approaches used in organizing and using data and information on soil erosion and conservation have not yet reflected this change. To address the above mentioned concerns, particularly on soil erosion management, the involvement of the different stakeholders from resource users to policy makers is needed. The catchment, which is a topographically delineated land area drained by a common stream system, is used as a unit of management and provides a venue for addressing the basic concerns. Assessment of resource use management and planning is done at the catchment scale. In particular, there is a need for the following: (1) incorporation of indigenous knowledge related to land use management into resource use evaluation systems, (2) capability to assess the implications of these indigenous practices for soil erosion and its on- and off-site effects, and (3) establishment of practical indicators of sustainability that relate to both the state or condition and process. Thus, the MSEC project in the Philippines adopts a new paradigm for research and development that requires the participation of the whole range of stakeholders from land users to policymakers in trying to generate and promote improved land use practices on a catchment scale. 1.1
Goal and objectives In general, the MSEC project in the Philippines adopts the catchment approach as a strategy in addressing and looking for options regarding soil erosion problems. Specifically, the objectives of the MSEC Philippines Project are: 1. To enhance the transfer of sustainable and acceptable community-based land management system for the Mapawa catchment; 2. To assess the on-site and off-site impacts (biophysical, socio-economics, environmental) of soil erosion in Lantapan and surrounding areas; 3. To generate reliable information for formulating scientifically-based guidelines in improving catchment management;
1
Central Mindanao University (CMU), Musuan, Bukidnon, Philippines Philippine Council for Agriculture, Forestry and Natural Resources Research and Development (PCARRD), Los Banos, Laguna, Philippines 3 Department of Environment and Natural Resources (DENR), Region X, Malaybalay, Bukidnon 4 Local Government Unit of Lantapan, Lantapan, Bukidnon 2
1
2 4. To enhance R & D capability on integrated catchment management and soil erosion control; and 5. To enhance institutional arrangements for R and D information exchange, sharing and dissemination. 2.
Methodology
In general, the methodology is anchored on the adopted new research paradigm based on a participatory and interdisciplinary catchment approach. The various activities that were carried out support three major components, as indicated below: a. Catchment research to evaluate the effects of different land management practices on water and nutrient flows in the Mapawa catchment; b. Capacity building of concerned institutions in research and development on integrated catchment management and soil erosion; c. Dissemination of R & D results for enhancered adoption of land management technologies and for more accessible information as concrete basis for decision making. The project is a holistic study of the important biophysical and socioeconomic aspects of land management in the catchment areas. Experiments conducted are expected to address on-site and off-site erosion effects. The project uses as much as possible the existing knowledge and models and undertakes needed field observations and trials for the different activities. The major activities carried out are catchment inventory and characterization; hydrological studies; land use changes; information systems and modeling; institutional and policy changes; and people empowerment. 2.1
Instrumentation of microcatchments
A main weir for the whole catchment and four smaller weirs for each microcatchment were constructed from July to September 1999. The main weir was twice damaged by strong floods and repairs had to be done. An automatic weather station (AWS) was installed in the lower half of the Mapawa catchment and 5 manual rain gauges were also put up. Water level recorders were installed in each of the weirs. Instrumentation was completed last April 2000. The coordinates of the weirs, rain gauges and AWS were taken using a GPS GARMIN III Plus. Likewise the coordinates of all farms, foot and animal pathways, houses and creeks were taken using the same instrument. A draft of the field manual on instrumentation and measurements of discharge, bed load, sediment load, runoff and average rainfall in the Mapawa catchment has been prepared. This serves as guide for the research team in instrumentation and data collection processes. Other guidelines include: communication, data collection for weather station (Cimet and Cimbase) and all the water level recorders (Orphemedes and Thalimedes), soil and water sampling, analysis in office, data processing, data base and GIS. 2.2
Data collection and monitoring
Rainfall. Rainfall data were collected using the manual rain gauges and the automatic weather station. Streamflow velocity. In measuring velocity of flow, a current meter (Model 2100 series) was used. The current or velocity of flow was taken at the middle of uppermost lining of the structure, by following the steps below. 1. Divide the width of the lining into sub-sections (20 cm or 30 cm). 2. Measure the velocity of water at 0.20 and 0.80 of the depth at the middle of each subsection. 3. The average of the two velocities are then calculated. 4. Measurement is taken during the entire run-off event in each weir. (When run-off event is greater than the previous one, discharge measurement at the same weir is necessary). In each run-off event, velocity of flow is taken at 5-10 minute interval during rising phenomenon, and increased to 20 minutes when water level is receding. 5. Data on stream flow is used to generate a runoff hydrograph for each weir. Water level. This is recorded automatically by water level recorders and taken from the staff gauge if an observer is present during the runoff event.
2
3 Volume of runoff. The volume of runoff is generated from the runoff hydrograph. In the absence of a rating curved, empirical formulas are used in calculating discharge. As the weir is two-notch shaped, the following equations are used to calculate discharges. Gourley formula for determining discharge using the v-notch. Q = 1.32 tg(a/2)h2.47 where: Q = discharge, l/sec tg = tangent a = angle of v-notch h = height of water from water level recorder For the rectangular notch this equation is used. Q=3.33(L-.2H)H3/2 where: Q= discharge, m3/s L= with of the notch, m H= height of flow, m Suspended load. Two methods has been used in collecting samples for suspended sediment in the runoff water. The first one, by taking samples during runoff event in the notch of the weir when an observer is present during the event and samples are taken every five minute interval. The other one is with the use of improvised runoff sampler. The sampler collects samples at different runoff depths. The limitation is that it can only take samples during rising period. In every run-off event, the eroded soils that are trapped in the Bed load. sediment basin is weighed. This is considered as bedload. The stagnant water is drained through the drain pipe. Five to six soil samples are collected at different depths, mixed, and a representative sample of 200 grams is taken to the laboratory for dry weight determination. This sample is used in determining the amount of soil loss from the catchment. The organic matter content (OM), extractable P, exchangeable Ca, Mg, K, and pH are also determined using standard procedure. Crops and cropping patterns. Data on crops, cropping patterns and farmers practices are gathered through interview with farmers, key informants and participatory rural appraisal. Prices of farm inputs and produce. Prices of farm products and inputs are monitored through personal interview with the farmer and middleman if necessary. 2.3
Evaluation of on-site cost of soil erosion
The approach that was used in estimating on-site costs of soil erosion is the replacement cost approach. This approach provides cash value to the amount of nutrients and organic matter lost during erosion. The rationale is that soil erosion leads to a decline in crop production unless nutrients are replaced in the soil. Therefore, a good indicator of the economic loss may be the cost of replacing those nutrients. The following data are needed for evaluating the on-site cost of soil erosion: 1) bed load, 2) sediment load, 3) nutrient content (NPK) of eroded soil. The data used in this report were those collected from the four microcatchments from April 2000 to August 2001.The local prices of urea (46-0-0), Di-ammonium phosphate (18-46-0), and muriate of potash (0-0-60) were used to estimate the cost of nutrients needed to replace lost nutrients. Transport cost is considered in the cost estimation. 2.4
Evaluation of off-site effect of soil erosion
Francisco (1998) discussed the activities that need to be undertaken to come up with a crude calculation of the magnitude of off-site cost. These activities are: 1. Identify the water body (e.g. reservoir, catchment, lake, etc) where the runoff carrying soil sediments from the study site drains 2. Define the watershed where the project site belongs (Assess relative contribution of the sediments from the project area to the total volume of sediments observed in the water body) 3. Collect information on the sedimentation rate of the water body
3
4 4. Gather information on the water-based economic activities of the downstream communities most vulnerable to the pollution of the water body (e.g. irrigation, hydroelectric power, domestic and industrial water uses) 5. Measurement of the impact of sedimentation-induced water pollution 6. Valuation of the off-site impact of erosion Identification of potential off-site impacts. The identification of potential environmental impacts is based from a careful evaluation of the activity or processes involved. For soil erosion, the processes involved are not confined to the farm where erosion occurred. During rainfall events, part of the soil lost from the upper parts of the catchment are transported by runoff down to the lower parts of the catchment, others are carried further to the water bodies downstream. The detached soil that are carried to the water bodies downstream either end up as bed load or sediment trapped in dams or reservoirs, or are further carried away to the lower water bodies as suspended solids. The sediments and suspended solids carried by runoff cause off-site impacts to water-based activities downstream. Barbier (1996) identified possible downstream or off-site impacts of soil erosion that results from water-borne runoff and sedimentation. These impacts include: reservoir sedimentation; losses to navigation; irregular flow of irrigation; effects on agricultural, fishing and industrial production in lowlands and coastal regions; impacts on water supply and potability; and impacts on drought or flood cycles. Evaluation and analysis. Off-site costs are normally measured in terms of the net present value (NPV) of forgone benefits from any loss of downstream economic activities (loss of income due to crop production losses) or of additional operating costs, such as dredging costs for canals, reservoirs or port facilities). Methodologies employed in estimating off-site costs are specific to the off-site impacts. Soil erosion from the MSEC Philippines site end up as sediments to the reservoir of the Manupali River Irrigation System which is located in the lower part of the Manupali watershed. The MSEC catchment is one of the catchments that contribute to the sedimentation of the reservoir. For a reservoir or dam, Barbier (1996) identified the type of impacts that are usually measured and included as the costs of sedimentation: Reduction in service life of the dam Increase sedimentation of active storage Increase sedimentation of dead storage (planned or unplanned) The following are the common valuation approaches that may be employed in calculating the costs of excessive sedimentation in reservoirs (for irrigation) (Grohs, 1994 as cited by Enters, 2000): Change of productivity – i.e., evaluating the income forgone from not being able to irrigate fields due to reduction in water yields, increased operation and maintenance costs of irrigation schemes, and the high operation and maintenance costs for removing sediments through dredging and replacing damaged equipment Replacement costs – i.e., the costs of replacing live storage lost annually Preventive measures – i.e., the costs of constructing dead storage to anticipate the accumulation of sediments Sedimentation results in reduction in the system’s capacity and thus reduces the area served by irrigation. Assuming that the formerly irrigated area which are not anymore served by irrigation will still be cultivated but without irrigation, then the cost of sedimentation is measured by the difference in the returns from crop production with and without irrigation. Another approach to estimate the cost of sedimentation is to use the cost of desilting or dredging. For the MSEC site, the costs of dredging was used to estimate the costs of soil erosion. Regular dredging of the system has been done since 1995. The actual costs of dredging from 1995 to 2000 was taken from MRIS. The potential contribution of the MSEC site to the total cost of soil erosion in the system was estimated by the
Soil Erosion
Loss of soil and fertility
Loss of water as runoff4
5
Ruined fields and unproductive soils
Drought Reduced WHC
Figure 1. Schematic diagram of the effects of soil erosion Source: Villano. 2001.
3.
Results and Discussion
3.1
Land use and hydrological behavior of the catchment
3.1.1
Land use characteristics and changes
The vegetation and land use of the MSEC catchment area is composed of forest plantation of Eucalyptus, Mangium, Falcata and mixed with Jackfruit; openland with cogon and fern; coffee, crop land (corn and vegetables); and shrubs and bamboo. The distribution per catchment is shown in Table 1. Open grassland occupy the biggest area. This is followed by crop land and forest plantation. Shrubs/bamboos are concentrated along the creek escarpment zones.
5
6 It is observed that there has been no considerable change in land use in the catchment area until the present. In the Kalainingon small microcatchment, there has been no additional land conversion or opening for crop production. But rather the farmers on this catchment are continuously cultivating their areas for crop production. Our recent observation shows that farmer’s starts opening some of the grass land in the area. But they are still on the clearing stage of the operation, some of them are still burning the grasslands which would later be converted to croplands. This activity of the farmers will be closely monitored to determine its effect later on the amount of soil loss in the catchment. Table1. Vegetation and land use coverage of the Micro-catchment Vegetation or land Kalainigon Big Kalainigon Small used 1999 2000 2001 1999 2000 Forest plantation 8 8 8 5 5 Open grassland 32 29.8 29.8 14 14 Coffee 0 0.2 0.2 4 4 Cropland 16 18 18 2 2 Shrubs/Bamboo 4 4 4 6 6 3.1.2
2001 5 14 4 2 6
Rainfall, run-off and discharge
Rainfall intensities which are above 25mm/hr (Hudson, 1971) are more likely to produce high runoff rates and runoff volume. In the case of the MSEC site in the Philippines, rainfall intensities would even sometimes reach to as high as 105 mm/hr. This rainfall intensity coupled with long duration would cause runoff overflow in most of the weirs. Thus, there may be under-estimated runoff data collected from the weirs. The amount of rainfall when runoff occurred is presented in Table 2. Runoff volume is converted into depth of runoff. It is observed that the Direct Runoff Ratio (DRR) which is the ratio of runoff depth and rainfall depth in the main catchment during the period ranges from 1.12 during the month of June 2001 to 7.78 in the month of July 2001. The lower the value of DRR would mean that the catchment has good infiltration rate and therefore a minimal surface runoff which are the carriers of eroded soil. DRR values of the other three microcatchments are presented in Table 3, 4 & 5. DRR of MC1 ranges from 0.66 to 4.37, while in MC2 and MC3, these values range from 4.21 to 11.63 (MC2) and 1.36-6.67, respectively. We can say that MC1 has better infiltration rate than MC2 and MC3. This can be attributed to the smaller percentage of cropped area in MC1. Table 2. Rainfall, runoff and direct runoff ratios in the Main weir Month Rainfall ,mm Runoff, mm DRR (%) May 2000 452.7 25.3 5.60 June 449.8 16.7 3.70 July 180.7 4.5 2.48 August 371.1 24.7 6.66 September 135.0 6.8 5.03 October 341.0 10.0 2.94 November 186.8 8.7 4.67 May2001 349.7 * * June 190.2 2.14 1.12 July 342.7 26.66 7.78 August 205.5 6.02 2.93 * runoff volume has not been computed yet, data loss were experience when the computer hard disk malfunctioned. Table 3. Runoff, Rainfall and Direct Runoff Ratios of Microcatchment 1 Month Rainfall ,mm Runoff, mm May 2000 440 9.3 June 453.9 19.8 July 154.7 1.0
DRR (%) 2.12 4.37 0.66
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7
August September October November
353.8 137.7 340.9 185.8
7.1 2.6 10.7 0.7
1.99 1.86 3.13 0.38
Table 4. Rainfall, runoff and direct runoff ratios of microcatchment 2 Month Rainfall, mm Runoff, mm May 461.0 41.1 June 457.7 53.2 July 187.2 7.9 August 387.6 30.5 September 235.0 0.5
DRR (%) 8.92 11.63 4.21 7.87 0.20
Table 5. Rainfall, runoff and direct runoff ratios of the microcatchment 3 Month Rainfall, mm Runoff, mm May 461.0 14.9 June 457.7 14.9 July 187.2 2.5 August 387.6 25.8
DRR (%) 3.23 3.26 1.36 6.67
Figure 2 shows the runoff hydrograph for the main weir of one of the runoff events that occurred last May 23-24, 2001. The behavior of runoff showed that the catchment is poorly managed since it peaks up in a very short period. Well-managed catchment hydrograph would show a gradual increase in runoff or a gradual rising event. The peak runoff discharge of this hydrograph is 1.05 m3/s with a water level recorded at 1.5 m. During this period, there was also a runoff overflow in the weir. Usually, there is runoff overflow when the water level is greater than 1.4m. Almost all of the runoff in the main weir followed the same hydrograph pattern.
1.2
1
discharge, m3/s
0.8
0.6
runoff, m3/s 0.4
0.2
9:40
9:05
8:30
7:55
7:20
6:45
6:10
5:35
5:00
4:25
3:50
3:15
2:40
2:05
1:30
0:55
0:20
23:45
23:10
22:35
22:00
21:25
20:50
20:15
19:40
19:05
18:30
17:55
17:20
16:45
16:10
0
time
Figure 2. Runoff hydrograph of one runoff event in the main weir May 23-24, 2001 Table 6 and Fig. 3 show the total monthly rainfall and temperature values of the MSEC catchment from May 2000 to July of 2001. This shows that rainfall was more or less
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8 distributed through out the period. Rainfall during the months of May to October 2000 are high although July and September 2000 are quite low. Rainfall during the months of November to February is quite low. High rainfall resumes in the month of May 2001.
Jul-01
May-01
Mar-01
Jan-01
Nov-00
Sep-00
Jul-00
500 450 400 350 300 250 200 150 100 50 0 May-00
Rainfall, mm
Table 6. Monthly mean rainfall of MSEC catchment from March 2000-August 2001 Mean Rainfall Temperature Month (mm) Minimum Maximum Mean May 452.7 16.2 27.1 20.4 June 449.8 15.5 27.2 20.0 July 180.7 14.9 27.5 20.1 August 371.1 15.3 26.6 19.8 September 135.0 15.6 27.1 20.5 October 341.0 16.1 27.2 20.2 November 186.8 15.5 26.6 19.8 December 135.3 14.7 27.0 20.0 January 135.0 13.9 27.1 19.4 February 164.5 12.5 27.6 19.6 March 344.9 13.0 27.6 20.1 April 218.0 14.5 28.5 20.5 May 349.7 14.9 27.4 20.3 June 190.2 15.1 26.9 20.2 July 342.7 14.9 28.9 19.7
Months Figure 3. Total monthly rainfall of Mapawa catchment from May 2000 to June 2001
Table 7 show the total rainfall, number of rainy days and erosive rainfall events of the main weir from April to December 2000. There were about 153 rainfall events during the period with 30 of them producing runoff in the main weir and only 28 in the MC1. Among the runoff events which occured in the main weir, only 9 were considered strongly erosive. These carried with them bedload which are deposited in the weir. The rest of the runoff event in the main weir has a very little or zero amount of bedload. On MC1, there were 15 erosive runoff events out of the 28. We only considered bedload as the source of soil erosion since we do not have enough data for suspended load. suspended load were only measured in the main weir and only when an observer is present. Table 7. Rainfall and soil loss in the MSEC catchment, April to December 2000
8
9
No.
%
30
21
13.7
No. of slightly erosive rainfall 9
28 26* 19** 14***
13 12 11 14
8.5 7.8 7.2 9.2
15 14 9 -
No. of rainy days
Rainfall, Mm
No. of runoff
Main
153
2623
1 2 3 4
153 153 153 153
2574 2659 2659 2443
Weir
Erosive rainfall
Soil Loss in Kg 38,089 2,055 12,353 7,23 48,510
* data until September 1 only ** runoff data until end of August only ***Base on the no. of bedload collection, data logger is not recording properly Table 8. Rainfall and soil loss in the MSEC catchment, January-July 2001 Weir
Main Weir 1 Weir 2 Weir 3 Weir 4
No. of rainy days 143 143 143 143 143
Rainfall, Mm 1723.0 1554.6 1554.6 1554.6 1390.7
No. of runoff
Erosive rainfall No. 4 4 5 4 5
3.2
Nutrient loss and on-site cost of soil erosion
3.2.1
Soil fertility changes on-site
%
No. of slightly erosive rainfall
Soil Loss in Kg
22,062.3 1,105.9 10,871.6 3,002.5 13,752.7
The nutrient distribution of the microcatchment follows a decreasing trend with depth (Table 9). It follows that nutrient are concentrated in the topsoil and is expected that with continued soil erosion, the amount of nutrient loss with time will decrease as the upper layers are removed. Future measurement will determine if the nutrient loss will decrease with time. Table 9. Organic matter, phosphorus and potassium content in 2 soil profiles at Mapawa catchment. Available P Exchangeable K Depth(cm) OM% Ppm Me/100 gm soil Pedon 1 0-113 5.93 4.72 0.33 13-49 4.11 3.32 0.35 49-94 1.31 3.46 0.14 94-184 1.10 3.60 0.67 Pedon 2 0-13 5.44 4.00 0.47 13-30 3.90 2.52 0.11 30-72 2.53 2.54 0.06 72-127 1.10 2.68 0.05 In general, the soil in the four microcatchments has moderate to high level of organic matter (3.2 –5.93 %) and potassium (66-408 ppm) but generally deficient in phosphorus (0.80-13 ppm) (Table 10).
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10
Table 10. Some chemical properties of the soils in the four microcatchment, Mapawa, Lantapan, Philippines P K Microcatchment pH OM% ppm Ppm MC1 Cultivated Area 4.4 - 4.9 4.9 – 5.1 3.90 - 10.2 120 - 144 Newly opened area 4.9 5.65 29 408 MC2 Cultivated area Grassland MC3 Forest MC4 Cultivated area
4.4-5.1 4.8
4.11
2.7-12.9 0.8-2.7
144-375 267
4.4
5.93
2.6
87
4.8
3.18
3.3
66
The change of soil fertility of the catchment with time is very noticeable (Table 11). Both organic matter, phosphorus and potassium increases with time. Application of organic and inorganic fertilizer especially in areas grown to vegetable and some areas grown to corn could have caused the increase in soil fertility through time. The pH of the soil on the other hand decreases as time progresses, farmers on the area are not applying lime to their farm and repeated use of the land could have increased the pH of the soil. Table 11. Soil fertility change in the MSEC catchment Parameters 1998 PH 5.55 OM (%) 5.34 Extr. P (ppm) 3.89 Exch. K (ppm) 86.00 3.2.2
April 2000 4.69 7.20 6.90 126.00
September 2000 4.83 9.20 9.22 151.00
Amount of nutrients lost by erosion
Table 12 shows the erosion rates, land use and shape of the four microcatchments. On a per hectare basis, the magnitude of erosion is in the order of MC 4>>>>> MC 2> MC 3>> MC 1. MC 4 has a total soil loss of 48,510.17 kg and 13,752.7 kg in a per hectare basis, this volume of soil loss increased in the succeeding period with a total soil loss of 51,606.56 kg and 14,325.73 kg in a per hectare basis. This increase is attributed to the harvesting of cassava during this period which are planted along the creek of the microcatchment. MC1 on the other hand has the lowest soil loss among the microcatchments, with a total of 2,875.68 kg from May-December 2000, or 115.35 kg on a per hectare basis and 1105.9 kg from January – August 2001, 44.36 kg per hectare. The big difference in soil loss of MC1 and MC4 could be that MC4 occupies only 0.94 ha or 1.1 % of the aggregate area of the four microcatchments. Almost 50 % of it is cultivated to crops, while MC1 is mostly occupied by grassland and bamboos, hence the very low soil loss. Soil erosion in the whole catchment which is 38,088.71 kg from May- December 2000 has decreased to 22,062.3 kg during the period January- August 2001. This decrease is attributed to the number of highly erosive rainfall events in the latter period (21, highly erosive rainfall events) compared to only 4 from January-August 2001. Table 13 shows the nutrient content of the sediment. The amount was computed by taking into account the soil test values for OM, extractable P, exchangeable K and the weight of eroded soil for each weir per month. For example the sediment load of 105.6 kg collected in the month of July at weir 4 has 5.7% OM, 1.575 ppm exctractable phosphate and 111 ppm exchangeable K. This translates into 6.05 kg OM, 0.2 g of P and 11.7 g of K. If the OM contains 5-6 % N, the N content of the sediment amounts to 302.5 g of nitrogen. 3.2.3
Valuation of nutrients lost and determining on-site cost of erosion
In the replacement cost method, the cost of replacing the nutrients lost with the eroded soil is taken as the measure of economic loss. Tables 14 and 15 show the cost of
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11 nutrient losses in the whole catchment and the four microcatchments for the period April 2000 to December 2000 and January 2001 to August 2001. As in the case of soil loss, the equivalent amount of nutrient loss in MC4 is very high (59.82% in May-Dec2000 and 48.36% in Jan-Aug 2001, respectively) among the four microcatchments. On a per hectare basis MC4 is 19 times greater than the three microcatchments combined for May to December 2000 and 14 times greater during Jan to Aug 2001. The total cost of soil erosion in the whole catchment is PhP 2267.55 in May to Dec 2000 and PhP 835.38 January to August 2001. It is evident that there is a decrease in the cost of soil erosion in 2001. This is because soil loss in the year 2001 is only one half of the soil loss in 2000. On a per hectare basis, cost of soil loss is PhP 26.83 for May to Dec 2000 and PhP 9.89 for Jan to Aug 2001. Losses in the microcatchment may not be a loss in the whole catchment because some of the sediments that are carried by the runoff water are reentrained along the creeks before they reaches the monitoring station of the whole catchment hence they are considered separately. There are two basic considerations in the estimation process made. First, in areas with no production, nutrient loss would have no on-site cost. Second, due to the differences in erosion rates for each microcatchment as affected by factors like land use, type and nature of the microcatchment, location of the cultivated patches relative to the streams, “averaging” of soil erosion for the entire catchment may not be desirable. In fact, each microcatchment has to be categorized according to land uses, farming practices and other factors to come up with a more accurate economic valuation.
11
13
Table 12.
Drainage area, soil loss, land use and shape of the microcatchments, Mapawa catchment from May-Dec. 2000 and January to August 2001 Microcatchment Soil loss, kg Area Total Mean, Kg/ha Land use Shape (ha) No 2000 2001 2000 2001
Whole
84.5 (100%)
MC 1
24.93 (29.5%)
38,088.71
2,875.68
22,062.3
1,105.9
450.75
115.35
261.1
44.36
MC 2
17.88 (21.16%)
9,141.54
10,871.6
511.27
608.03
MC 3
7.96 (9.4%)
8,343.57
3,002.5
1048.19
131.68
MC 4
.94 (1.1%)
48,510.17
13,752.7
51,606.56
14,325.73
20% cultivated to vegetables, root crops 80% grassland, bamboo, Eucalyptus, falcata, settlement 2% cultivated to vegetable and root crops 98% falcata, bamboos,eucalyptus, grassland 10% cultivated 85% grassland/forest 10% settlement, 15% cultivated 75% grassland 40% cultivated (14% of cultivated area is left bare) 60% grassland, trees
Elongated
Triangular
Elongated Elongated Rectangular
2000 – from May to December 2001 – from January to August
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14 Table 13.
Amount of nutrient losses due to soil erosion at the MSEC catchment from April2000 to August 2001 Year/Month/Weir Soil loss, kg Organic matter, kg Ext. P, kg Exch. K, kg Main weir April 2000 500.1 20.8 0.0016 0.1926 May 14,323.0 868.8 0.0269 3.8275 June 13,207.2 784.9 0.0202 4.9877 July 858.0 51.9 0.0020 0.3037 August 7,202.0 435.8 0.0172 2.5495 October 1,880.6 85.1 0.0033 0.6657 November 117.5 6.1 0.0002 0.0413 April 2001 507.6 18.3 0.0005 0.2482 July 20,396.5 749.6 0.9980 6.3336 August 1,158.2 43.5 0.0039 0.3266 Sub-total 60,150.7 3,064.8 1.0737 19.4764 Weir 1 April 2000 366.9 21.6 0.0015 0.1530 May 138.9 91.4 0.0005 0.0480 June 589.5 79.8 0.0014 0.2768 July 268.7 22.6 0.0007 0.1314 August 433.4 36.4 0.0012 0.2119 October 209.1 8.5 0.0003 0.0627 November 48.2 1.9 0.0001 0.0214 April 2001 40.2 2.0 0.0000 0.0229 July 1,056.4 61.6 0.0037 0.4222 August 9.3 0.5 0.0000 0.0037 Sub-total 3,160.6 326.3 0.0095 1.3540 Weir 2 April 2000 689.4 32.8 0.0021 0.1530 May 2,698.8 178.4 0.0175 0.5339 June 4,646.2 342.1 0.0007 0.0590 July 1,285.0 86.1 0.0048 0.4357 August 2,345.8 156.9 0.0088 0.7952 October 602.8 33.8 0.0007 0.1790 November 84.6 5.2 0.0001 0.0317 April 2001 39.1 2.4 0.0001 0.0151 July 10,730.7 459.9 0.0332 4.0218 August 101.8 3.4 0.0004 0.0329 Sub-total 23,224.2 1,301.0 0.0684 6.2573 Weir 3 April 2000 501.3 33.8 0.0016 0.0883 May 3,650.7 247.5 0.0088 0.6242 June 2,560.1 436.5 0.0091 0.6459 July 1,285.2 11.8 0.0005 0.0799 August 272.4 25.1 0.0007 0.0580 October 60.9 4.1 0.0002 0.0119 November 13.1 0.9 0.0000 0.0025 April 2001 23.1 1.5 0.0001 0.0083 July 2,957.0 168.7 0.0118 0.5627 August 22.4 1.3 0.0001 0.0042
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Sub-total Weir 4 April 2000 May June July August October November April 2001 July August Sub-total
11,346.2 648.9 16,022.4 6,251.7 105.6 11,466.1 9,770.4 4,245.0 6,607.8 7,107.7 43.2 62,268.8
931.2
0.0328
29.7 969.1 371.6 6.0 657.3 440.6 198.7 485.9 239.2 1.4 3,399.5
0.0060 0.0238 0.0116 0.0002 0.0181 0.0098 0.0043 0.0114 0.0241 0.0001 0.1095
2.0858 0.0981 2.0656 0.7690 0.0117 1.2727 1.0777 0.4330 1.1894 0.9596 0.0058 7.8826
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Table 14. On-site cost of soil erosion of the MSEC main catchment and the four microcatchment, April 2000- December 2000. N (PhP P (PhP) K (PhP) Cost, PhP Catchment Area Soil loss, Kg Total ha-1 Total Ha-1 Total ha-1 Total Ha-1 2,267.6 26.8 Main 84.50 38,088.7 2,082.2 24.6 3.4 0.04 182.0 2.2 255.9 10.3 MC 1 24.93 2,875.7 242.3 9.7 0.3 0.01 13.4 0.5 734.9 41.1 MC 2 17.88 9,141.5 702.9 39.3 1.5 0.08 30.5 1.7 725.3 91.1 MC 3 7.96 8,343.6 702.0 88.2 1.0 0.13 22.3 2.8 2,555.4 2,718.5 MC 4 0.94 48,510.2 2,468.9 2,626.5 3.5 3.74 82.9 88.2 Table 15. On-site cost of soil erosion of the MSEC main catchment and the four microcatchment, January to August 2001. N (PhP P (PhP) K (PhP) Catchment Area Soil loss, Kg Total ha-1 Total Ha-1 Total ha-1 Main 84.50 22,062.3 670.2 7.9 29.8 0.4 135.4 1.6 MC 1 24.93 1,105.9 56.0 2.2 0.1 0.0 7.9 0.3 MC 2 17.88 10,871.6 384.7 21.5 9.9 0.6 71.9 4.0 MC 3 7.96 3,002.5 141.7 17.8 0.4 0.1 10.2 1.3 MC 4 0.94 13,752.7 600.1 638.4 1.2 1.1 38.1 40.5
Cost, PhP Total Ha-1 835.4 9.9 64.0 2.6 466.5 26.1 152.2 19.1 639.2 680.0
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3.3
Socioeconomic characteristics and changes
3.3.1
Farmers’ agricultural practices
Monoculture of maize is rampant in the area. About 41.66% of the farmers had this kind of cropping system while 37.50% practiced mixed/multiple-cropping system (Table 16). The later was done by dividing the farm area into compartments. Different crops such as maize, sweet peas, potato, etc. are grown at the same time within each compartment. Few farmers practiced crop rotation, coffee-maize combination/Eucalyptus-maize combination. There are about 10 corn farmers in the area. Fifty (50) percent of them don't apply fertilizer because they are only planting the native variety of corn due to lack of capital. Twenty (20) percent of them applied the combination of chicken dung and complete fertilizer (Table 17). On the average, about 2 bags chicken dung and 6 bags complete fertilizer (14-14-14) per hectare are applied for corn (Table 18). A hectare of sweet peas was applied with 10 and 5 bags of chicken dung and complete fertilizer, respectively. Potato was applied with higher rate of 52 and 10 bags of chicken dung and complete fertilizer, respectively. Cropping patterns of the farmers varies from farmer to farmer. But majority of them follow certain pattern of crop planting. Some farmers usually plant corn after a vegetable crop and some of them practice fallow after a corn crop. There are also farmers who practices single cropping pattern through out the year and only plant corn in their area the whole year round. Based on actual observation and actual interview with the farmers in the area, about 84.38% (refer to Table 19) all the cultivators are plowing their farms. The remaining number is using hoes in cultivating the soil. These farmers who use hoes are those who do not have farm animal and could not afford to hire labor to plow their areas. Among this 84.38%, only 2 farmers or 6.25% use harrow. Harrows are very rare in the area. The rest use hoes in pulverizing the clods after plowing. All farmers however manually weed their farms using the traditional weeding practice (off barring and hilling up or using trowel to remove grasses). The use of inorganic and organic fertilizers varies with each cropping season. Most farmers only apply fertilizers if the crops grown are vegetables. There are very few who apply fertilizer to corn crops. Usually corn crops are planted after a vegetable crop.
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Cropping pattern of farmers in the project site Month Jan Feb Mar Apr May Jun Jul ------------
