Sand extraction from agricultural soils in Bangalore region: ecological and economical consequesnces

SAND EXTRACTION FROM AGRICULTURAL FIELDS AROUND BANGALORE: ECOLOGICAL DISASTER OR AN ECONOMIC BOON? – A STUDY
RAJENDRA HEGDE, RAMESH KUMAR, ANIL KUMAR, SRINIVAS AND RAMAMURTHY
National Bureau of Soil Survey and Land Use Planning, RC, Hebbal, Bangalore-24.

Abstract: Sand supply from riverbeds to Bangalore is not able to meet the demand of booming construction sector. Enterprising farmers have taken up extraction of sand by washing surface soils of agricultural fields. Nearly 25 percent of sand supplied is from this source. A field investigation and laboratory analysis was undertaken to understand ecological and economic consequences of sand extraction. Study revealed that significant employment and economic gains are realized at an ecological cost. Loss of surface soils, nutrient losses, crop yield losses, siltation of tanks, excessive ground water exploitation and soil erosion are taking place due to sand extraction. There are no quality differences between riverbed sand and soil extracted sand. Comprehensive policy is needed to make the enterprise ecologically tolerable and safe.
Key words: Soil extracted sand, eco-degradation and ground water exploitation.

INTRODUCTION
Land is a limited resource having competing demands. Need to augment food production also from marginal lands have a serious impact on land use resulting in accelerated land degradation. Progress in S&T has eased out pressure on natural resources to some extent, but urban centric development has resulted in imbalanced growth and exploitation of natural resources. Urban centric economic growth have increased employment opportunities in these areas, whereas mechanization, stagnant prices and production, increased input costs in agriculture have made it unattractive leading to increased rural unemployment and migration. All these factors have put extraordinary pressure on urban infrastructure.
Riverbeds are major sources of sand and its accumulation as layers of deposits is a dynamic phenomenon. Major user of sand is construction sector which is growing exponentially. Due to its increasing demand, sand is being over extracted from different riverbeds. This is resulting in negative externalities on riparian habitats like the riverbeds losing their ability to hold water. As sand is extracted rapidly, ground water evaporates fast, reducing groundwater recharge, increasing initial and premature failure of irrigation wells and associated predicament in farming (Viswanathan, 2002).
Sand mining negatively affecting agriculture, rural livelihoods and also leading to environmental problems like rise in atmospheric temperature (Subash, 2002 and Ojos Negros Research group, 2002). These activities have affected local economies drastically leading to conflicts among rural people and sand players as in case of Karnataka (Upendra Acharya ,2003, Jayaram, 2002 and Gopinath, 2002). Nevertheless there is increased awareness among rural people about negative effects of this activity as evidenced by series of protests. Another major source of land degradation is brick industry. Estimates suggest that clay brick industry is degrading the fertile topsoil to the extent of 20,000 ha every year in India, thereby causing severe land degradation (Kathuria, 2006).
Exponential demand for sand has created many environmentally unsafe situations as river bed sand supply is not able meet the demand. During the last 3-4 years surface soils from tank beds, agricultural fields, village common lands are excavated and washed to produce a kind of artificial sand all around Bangalore to meet enormous demand. For Bangalore, nearly 4000 lorry loads of sand per day are supplied for construction projects. It is reported that nearly 25 percent of sand is from units extracting sand from surface soils of agricultural fields/village tank beds (Belgaumkar, 2005 and Dept. Mines and Geology, GOK 2005). Remaining is mined from riverbeds called AT sand. Under these circumstances, entire gamut of trade of sand extracted from topsoils was analyzed in terms of environmental, economic, technological, institutional, policy and equity dimensions.
What is the driving force?:
Not only the increased demand for sand in Bangalore, but also the less remunerative crop production enterprises and prevailing drought like conditions during the last few years have driven farmers to this enterprise. Sand extraction is providing reasonably gainful employment for many farmers and landless labors in the region.
However, agriculturally essential surface soils have certain unique characters, which make them indispensable for crop production. As such fertile surface soils are the combined result of efforts of farmers and natural forces over a long period of time. When surface soils are removed from agricultural lands for sand extraction, the first negative effect is on soil organic matter (SOM). SOM is very important to the functioning of soil and crop production system by affecting infiltration, water holding capacity, erosion resistance, run off, soil crusting, porosity and ease for tillage. SOM accounts for 50 to 90% of cation exchange capacity (CEC) of surface soils.
Sub-surface soils show reduced biological activity. Organic amendments and fertilization of sub-surface soils are necessary to ensure rapid buildup of microbial populations and initiate nutrient cycling. Once soils are desurfaced for such activities, bulk density of remaining soil increases and hydraulic conductivity decreases. Plant establishment and growth get affected adversely leading crop yields losses (Grewal and Kuhad 2002).
There are no scientific studies on ecological and socio-economic implications of sand extraction from surface soils. Hence the present study was undertaken.
Materials and methods
Study was undertaken at 15 sand extraction units in five villages (Linganahalli, Karahalli, Ancharhalli, Dasagondanahalli, and Rajaghatta) in Bangalore rural district during 2006-07. Farmers and sand extractors were interviewed to get details of economics and input use pattern. Soil (surface and sub-surface), silt and sand samples were collected. Nutrient content (N, P, K, Cu, Fe, Mn and Zn), and pH, sand silt and clay content were analyzed (Sarma et al, 1987). Net return per load of sand at farm gate is estimated by taking into account all expenses incurred.
Results and Discussion:
Set up of sand extraction units: Rectangular pits of dimension: 20 X 8 X 2 feet is normally dug with slight slant towards the end where washed wastes are let out. Pits are covered from all sides with stone slabs. It costs around Rs 5000/- to set up an extraction unit. These are normally set up near to bore-wells. Due to erratic electricity supply, water is pumped during nights to temporary ponds and pumped to extraction units during daytime using 5 HP diesel pumps. Pumps are normally hired @Rs 60/- per lorry load of sand (excluding cost of diesel). Nearly one-foot (30 cm) depth of surface soil is excavated and transported from agricultural fields. It is spread on extraction pit for further processing. Two to three rounds of washing is done with a water jet to wash soil and extract sand. Normally a part of silt, sand and clay flow out. Still a part of these components remain in sand being sold in Bangalore (table 6). In a day three lorry loads of sand is extracted from one extraction unit.
Economics of sand extraction:
Only resourceful farmers or contractors undertake these enterprises, as they have to invest on labors (68% of total cost, table 1), soil, water, diesel etc. It is evident from the study that farmers belonging to lower strata of economic endowment are not able to reap many economic benefits except for employment opportunities as labors. Economic estimates based on the available data and analysis (table 1) revealed that sand extraction enterprises are generating a turn over of Rs 146 crores/annum in the region. It is generating an enormous employment of 33 lakhs man-days, out of which nearly 75 percent is on farms itself. Income generated for labors by this source is to the tune of Rs 71 crores / annum.
Enterprise is showing a favorable effect on rural economy as region has been witnessing drought like situation in the last 6-7 years. Incidence of farmers’ suicides in this region is also rare compared to other drought prone areas in the state. Although farmers are undergoing enormous economic stress due to drought like situation and falling prices of agricultural produces, this kind of employment and income opportunities have helped them to manage critical situations.
For producing one lorry load of sand, 5 HP diesel pump has to run for nearly 3 hours and it consumes 3 liters of diesel. Hence nearly 3000 liters of diesel is consumed every day around Bangalore for sand extraction. That amounted to Rs 4.5 crores worth of diesel in a year.
Sand extractors are earning a net profit of Rs. 2100/- per lorry load of sand. This is based on the fact that, average quality of sand from these units are sold at Rs. 4000/- per Lorry load at farm gate. Normally 30 cm depth of top soil is used for sand extraction. One hectare of land to a depth of 30 cm yields 33 lorry loads (one lorry load=90 m3) of sand. Hence if a farmer himself undertakes sand extraction from his land, he can earn a net profit of Rs. 72,000/-per ha. Instead if he sells surface soil for sand extraction, he earns an income of only Rs. 6600/- per ha.
Ecological degradation:
Nearly 132,000 liters of water is needed for washing 4 tractor loads of soil to produce one lorry load of sand. A conservative estimate suggests that nearly 21900 lakhs gallons of water is used for sand extraction per year around Bangalore. This water is pumped from deep bore-wells. In most regions ground water level has reached precarious status (KLUB, 2001). In the region, it has already gone down to 300 m due to overdrawing. Due to this all open wells in the region without exception have dried up.
Efforts of rainwater harvesting for ground water recharging are very few. Hence, additional burden on ground water for sand extraction is an impending ecological disaster and it needs immediate interventions. There are some extractors who are reusing wash-water by making it to stand in series of lagoons and allowing silt to settle down. This water is reused for one more round of soil washing. The practice is more due to the scarcity of water rather than the concern for ecosystem. Even with this practice, which is quite rare, only 25-50 percent of water is recovered. Remaining is lost in conveyance, evaporation, infiltration etc.

Table1: Economics of sand extraction from agricultural top soils around Bangalore

Details
For one lorry load of sand
(90 cu,mt.)
1000 lorry loads(one day supply)
One year
Remarks
1
Labor for top soil excavation(man days)
3
3000
11 lakhs

2
Cost of labor for soil excavation(Rs)
650(34)
6.5 lakhs
24 crores

3
Labor for soil wash(man days)
3
3000
11 lakhs

4
Cost of labor for soil wash (Rs)
650(34)
6.5 lakhs
24 crores

5
Total cost of labor on farm
1300(68)



5
Cost of soil(Rs)
200(10.5)
2 lakhs
7.5 crores
When purchased from other farmers**
6
Diesel required(Litres)
3
3000
11 lakhs


Diesel pump rent
60(3)



7
Diesel cost(Rs)
120(6)
1.25 lakhs
4.5 crores

8
Quantity of water used(litres)
132000
1320 lakhs (60 lakh gallons)
481800 lakh(21900 lakh gallons)

9
Water cost (Rs)
100(5.5)
1 lakh
3.6 crores
When purchased from borewell owners)
10
Total cost
1720
17 lakhs
63 crores

11
Price at Farm gate
4000
40 lakhs
146 crores

12
Net profit for sand extraction unit owner
2280
23 lakhs
83 crores

12
Sand loading & transport labor(man days)
3
2500
912500

13
Total Employment generated(man days)
9
9000
33 lakhs

17
Income generated for labors(Rs)
1950
20 lakhs
71 crores

(value in bracket are percent of total).
Wash-water contains heavy amounts of silt-clay (table 2). While producing one lorry load of sand, nearly 30 m3 of silt-clay is produced. Hence nearly 11 million m3 silt-clay is produced due to sand extraction in a year. During the washing process itself or during rainy season all the accumulated silt-clay invariably reaches nearest tank. These particles block pores in tank bed or agricultural fields where it is allowed to enter. Net result is reduced infiltration rate and ground water recharging. Naturally it causes enhanced water run off from fields during heavy rains. Hence, wash water coming out of sand extraction units is not safe enough for direct use on agriculture fields or village tanks. Small quantum of settled silt-clay is being used by brick makers for making bed for raw bricks. However this can be made use for mixing to highly sandy soils with caution which is called soil hybridization (Suganya and Sivasamy, 2006 and Butterworth et al., 2003). It is evident from table 3 (columns 6, 7, 8 & 9) that sandy soils of banana plot improved in its physical and nutrient contents after application of tank silt @ 900 cu m per ha over two seasons.
For generating one lorry load of sand nearly 120 m3 of top soil is used (Table 2). In a year nearly 43.8 million m3 of soil is now extracted for sand extraction. Due to this, surface soils from 18600 ha of land is being lost. These lands are not going out of cultivation permanently. Crops are being raised on sub-surface soils which are poorer in physical and biological parameters and plant nutrient status. Hence, in immediate next season, there is a crop yield loss to an extent of 10-20% depending upon crop and management (Grewal and Kuhad, 2002 and farmers own experiences recorded during the study). It takes 5-8 years to regain original status. Yield reduction was observed in desurfaced soils even though soil fertility differences were removed by fertilizer additions (Gollany et al., 1992). Topsoil removal not only lowered yield but also reduced the ability of crops to respond to favorable conditions, whether better landscape position or increased precipitation during growing season.
Farmers use normally use class III or class IV land for sand extraction. Fertile pockets (class I and II) are always used for growing cash crops like Mulberry, Grapes, vegetables etc. Class III and IV lands are dominantly used for growing hardly crop like Ragi in the region. It is found that productivity, area and production of Ragi are going down in recent years (District statistics, Bangalore (rural): 2000-2006). Sand extraction is one of the main reasons for it.
Nutrient loss: (Tables 3, 4 and 5): Silt-clay carries considerable amounts of phosphorus and potassium (Column 3 and 4: table 3). Due to concentration effect, silt-clay showed increased amounts of these nutrients when compared to top soil. Similar is the case with other micro nutrients. It was reported that soils of eastern dry zone in Karnataka (Bangalore region) are generally poor in potassium (Anil Kumar et al, 2003). However in the present study, subsurface soil contained higher quantities of available potassium compared to surface soil (Table 3 & 4). In general, excavation of surface soils from agricultural fields and tank bed for sand extraction resulted in fertility depletion. Estimates suggest that in a year nearly Rs 25 million worth of N and Rs 17.68 million worth of P2 O5 are lost due to sand extraction. Increased bulk density of the sub-surface soils indicated not favorable soil condition for the next crops. Grewal and Kuhad (2002) also reported similar unfavorable soil conditions on desurfaced soils in Haryana. Deep excavations done in village common lands have become source point for gully erosion in many cases.
Table 2: Soil degradation due to sand extraction in peri-urban and rural Bangalore

Details
Per lorry load of sand
In one day (1000 lorry loads)
In one year
remarks
1.
Soil used (m3.)
120
120000
438 lakhs

2.
Are of land used for soil excavation(ha)
0.04
40
18600
0.3 m depth (normally)
3.
Quantity of water used (litres)
132000
1320 lakhs
(60 lakhs gallons)
48180 million (2190 million gallons)

4.
Quantity of silt-clay generated (m3.)
30
30000
11 million


Table 3. Physical and chemical properties of surface soil and silt-clay due to sand extraction. (Available N P,K in Kg/ha and others in ppm).
sample
Sand (%)
Silt(%)
Clay(%)
Texture
Av.N
Av.P2O5
Av K2O
Cu
Fe
Mn
Zn
pH
1
79.7
13.4
6.9
Loamy sand
173
168
249
0.64
19.6
10.6
1.0
7.2
2.
87.0
6.8
6.1
Loamy sand
187
217
170
0.44
10.2
8.8
3.1
8.1
3
59.4
8.1
32.5
Sandy clay loam
231
298
419
0.90
16.2
18
1.1
7.4
4
81.4
6.7
11.9
Sandy laom
158
184
280
0.88
33.2
9.8
0.5
5.7
5
78.8
10.7
10.5
Sandy laom
144
132.2
321
0.82
16.8
19.8
0.8
6.7
6
68.8
21.1
10.1
Sandy loam
144
22.4
175
0.40
15.6
24.6
0.5
6.6
7
69.0
22.2
8.8
Sandy loam
187
132
175
1.38
15.6
17.2
0.4
7.9
8
87
6.8
6.1
Loamy sand
187
217
170
0.44
10.2
8.8
3.1
8.1
9
61.4
13.9
24.7
Sandy clay loam
187
284
628
2.02
14.2
27.6
5.6
7.1

Top soil use for sand extraction(site 1: upland situation)
Top soil use for sand extraction(site 2: valley land situation)
Subsurface soil after removal surface soil for sand extraction (site 1).
Exposed sub soil after removal of surface soil for sand extraction(site 2)
Soils from plot grown with Ginger on subsurface soil for one season (after removal of top soil for sand extraction).
Silt left at the sand extraction site after sand extraction from top soil (site1).
Silt left at the sand extraction site after sand extraction from top soil (site 2)
Soil properties of banana plot before the application of tank silt.
Soils of Banana plot applied with tank silt.

Table 4: Nutrients content and fertility depletion from surface soil of agricultural fields due to sand extraction
Nutrient
Units
Surface soil
Sub surface soil
silt
Fertility Depletion/ha
Fertility depletion /year*
Value of nutrient at present rates(Rs)
N
Kg/ha
319.6
191.8
90.0
127.8
2.38 million
25 million
P2O5
Kg/ha
83.7
25.2
11.7
58.5
1.09 million
17.68 million
K2O
Kg/ha
74.8
158.7
62.1
83.9*
* gained
-
Cu
ppm
0.66
0.3
0.1
0.56
-
-
Fe
ppm
0.38
0.76
0.53
0.15
-
-
Mn
ppm
21.6
14.1
2.96
18.84
-
-
Zn
ppm
18.4
13.13
0.18
18.22
-
-
B.D
g/c.c
1.4
1.7
-
-
-
-
* 18600 ha of land being excavated to a depth of 30 cm in one year.

Table 5: Nutrient content in surface soil of Tank bed used for sand extraction
Nutrient
Units
Surface soil
Sub surface soil
silt
Nutrient Loss / ha
N
Kg/ha
245.5
227.4
100.1
145
P2O5
Kg/ha
15.5
12.5
9.6
5.9
K2O
Kg/ha
188
59.4
49.9
138
Cu
ppm
0.8
0.1
0.32
0.48
Fe
ppm
11.4
7.16
11.2
0.2
Mn
ppm
7.68
1.1
3.42
4.26
Zn
Ppm
0.24
0.14
0.14
0.10
BD
g/cc
1.2
1.4
-
-

Quality differences between River bed sand and Soil extracted sand: (Table 6). Analysis of physical and chemical properties revealed no drastic differences between sand samples extracted from surface soil of agricultural fields or normal riverbed sand (AT sand). Hence the allegation that soil extracted sand is not good for durability of construction may not hold well.


Table 6. Physical and chemical properties of sands used in Bangalore.
Sand source
Sand%
Silt%
Clay%
Organic carbon(%)
pH
N (kg/ha)
P2O5 (kg/ha)
K2O (kg/ha)
Soil-sand
95
2.4
2.7
0.17
8.5
80
35.8
36.4
River bed sand
91
8.5
0.4
0.41
8.6
96
10.1
27.8

Opportunities and management: When soils are removed from tank bed for sand extraction, it increases water storage capacity of tanks. Hence there is scope for higher water storage and recharging. Similarly, ponds are created due to soil excavation to deeper depths. Regeneration of soil structure by organic amendments and tillage system or their combination is considered appropriate for the management of desurfaced soils. As available nutrient status is invariably poor in desurfaced soils, use of higher doses (25%—50%) of fertilizers and water input than for normal soils may prove beneficial for crop growth (Grewal and Kuhad, 2002). By undertaking required modifications, alternative uses of desurfaced lands for social forestry, waste disposal, water harvesting structures, farm ponds or even fish or Azolla rearing ponds can be achieved However, such efforts are very rare.
Government Policy needs:
As of now, State Government is trying to stop this activity citing reasons of ecological degradation. However, the enterprises are still thriving due to huge demand for the sand. Complete banning may lead to unaffordable price rise for sand. This may severely hurt construction and infrastructure projects. Hence there is a need to evolve comprehensive policy to make this activity ecologically tolerable. Areas and type of soils suitable for sand extraction, re-use of wash-water, safe disposal or use of silt-clay residues etc are the issues to be sorted out scientifically.
Future line of work:
Research efforts need to be initiated to improve present techniques of extracting sand from soil to make it more efficient in terms of amount of sand recovered and quantity of water used.
The present technique of re-use of water for sand extraction needs to be made easier and more efficient.
The possibility of using the waste water more efficiently to recharge the ground water needs to be attempted since the location of sand extraction is normally in the vicinity of bore-well.
Feasibility studies to understand the effect of applying the waste material containing mostly the silt and clay to the sandy soils or to the excavated area to change the texture of the soil and making the soil more productive need to be undertaken.
The role of application of organic materials like FYM/compost/green manure/other organic wastes in improving the productivity of the excavated soil need to be attempted.
Conclusions: Sand extraction from top soils of agricultural fields is a significant economic activity which cannot be wished away. It has got significant ecological dimensions in-terms of ground water exploitation, tank siltation, rain water infiltration, nutrient loss, etc. Loss of crop productivity is temporary but significant and can be restored gradually with consistent efforts. Government policy initiatives, technological and research interventions can be of great help in sustaining enterprise with minimum damage to ecosystem and agricultural production.
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