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Date
2011
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Publisher
IARI, DIVISION OF AGRICULTURAL ENGINEERING
Abstract
Groundwater is a major source of water in many parts of the world. Pollution of
groundwater either from anthropogenic activities or from inherent aquifer material composition
reduces its supply, posing a threat to development and a challenge to water managers and
strategists. In India, the groundwater quality is deteriorating day by day and is at an alarming state.
The major reason of nitrate pollution in groundwater is due to indiscriminate use of chemical
fertilizers and unscientific disposal of human and animal waste in farms. Quantification of nitrogen
transformation and its subsequent transport in the unsaturated zone is a complex phenomenon due
to interaction of many factors such as land use practices, above-ground nitrogen loading,
groundwater recharge, soil nitrogen dynamics, soil characteristics, and depth to water table. This
complexity in the movement of nitrate through the unsaturated zone can be explained by use of
process based models. A meticulous review of different models developed for prediction of nitrate
leaching below the crop root zone and joining the groundwater table of unconfined aquifer,
necessitated development of GIS based interface of Hydrus-1D model to simulate moisture and
nitrate profile under different cropping systems of semi-arid region. Keeping this in view, the
present study was carried out in different agricultural experiment blocks of IARI farm to have an
insight into the nitrate dynamics in soil-water-plant environment and develop a GIS based nitrate
prediction model to quantify the nitrate leaching to aquifer. Further, the developed model was
simulated for different crops and nitrogenous fertilizer application rates to generate alternative
scenarios of nitrate leaching through the vadose zone leading to groundwater pollution.
In the first phase of the study, the potential groundwater recharge was quantified using the
soil water budgeting protocols under different cropping environments. It was observed that the soil
texture played a dominant role in the recharge process and so also the nitrate concentration, due to
its high solubility in water. The potential groundwater recharge during kharif 2008 was measured
to be 1.19 m. Further, during rabi 2007-08 and 2008-09, the potential recharge below crop root
zone under different experimental blocks of IARI farm were 77.6 and 85.9 mm, respectively. It was
observed that among kharif crops, the maximum potential recharge was under rice and it was 68.4
per cent of supplied water. Subsequently, the dynamics and budgeting of nitrate leaching to the
groundwater was investigated. Different nitrogen transformation and transportation pathways in the
crop root zone indicated that amongst all the crops, the volatilization was found to be maximum in
rice (24. 01 kg ha-1) followed by wheat (21.8 kg ha-1) with application of total 120 kg ha-1
nitrogenous fertilizer. Leaching loss below the crop root zone in rice (34.18 kg ha-1) was found to
be the highest among all other crops. The order of nitrate leaching loss in different crops were rice
ii
> maize > cotton > wheat > mustard. Moreover, the measured nitrate concentration in groundwater
of IARI ranged from a minimum of 6.9 mg l-1 to a maximum of 26.2 mg l-1 and mean value was
found to be 14.0 mg l-1. The nitrate concentration in groundwater was found to be maximum during
kharif season, indicating that there was movement of nitrate to groundwater due to combined effect
of fertilizer application, irrigation and rainfall.
Finally, a GIS based interface of Hydrus-1D model named as “ArcGISHydrus-1D”
interface was developed to simulate the moisture and nitrate concentration below the root zone
depth of the rice, wheat and maize cultivated in IARI farm. Moisture and nitrate migration and
transformation processes below root zone quantified in preceding objectives were used in the
calibration and validation processes of Hydrus-1D model. The model efficiency (E) was found to
be maximum (0.894) at 120 cm depth and minimum (0.625) at 30 cm, for maize crop. Index of
agreement (AI) values in most soil depths were close to one (i.e. ranged from 0.808 to 0.894).
Therefore, values of MAE and RMSE close to zero and E and AI approaching one indicated that the
Hydrus-1D model validation results were in line with the observed values corroborating its
subsequent use in prediction of soil moisture and nitrate leaching through the vadose zone. Further,
the simulation of the validated Hydrus-1D showed that the moisture could leach up to 180 cm
depth below ground surface during rabi season in mustard and maize and up to 240 cm under
wheat cropped area of the farm. In kharif maize, the movement of moisture was up to 270 cm.
Similarly, the simulations of Hydrus-1D showed that the nitrate could leach up to 180 cm, both
during rabi and kharif season. Hydrus-1D predicted nitrate concentrations in the groundwater
occurring at 14 m depth for wheat, maize and rice growing season were 6.4, 7.9 and 9.1 mg l-1 as
compared to the observed N concentration of 5.5, 7.8 and 9.3 mg l-1 leading to model efficiency of
0.88 and prediction error below ± 20 per cent. Further, the model predicted fertilizer use scenarios
up to 50 per cent more than the recommended dose indicated that nitrate leaching to groundwater
increased by 10.9 to 34.4 per cent, 10.1 to 30.4 per cent and 4.4 to 24.2 per cent for wheat, maize
and rice, respectively. Moreover, it was observed that for all crops, nitrate leaching increased with
increase in fertilizer doses and decreased with the increase in depth below the root zone and
extending through the vadose zone up to the groundwater. Nonetheless, this study contributed
significantly in development of protocols of nitrate and water budgeting and subsequent estimation
of nitrate leaching to groundwater under wheat, maize and rice. The developed protocol on
dynamics and budgeting of nitrate leaching to groundwater was also validated. Developed ArcGIS
Hydrus-1D interface was calibrated and validated using the observed data and simulated to
generate the nitrate leaching under changing fertilizer use scenarios for different crops grown in the
experimental blocks of IARI farm.
Description
T-8363
Keywords
research methods, sampling, productivity, mechanization, animal husbandry, economic systems, fruits, markets, packaging, economic resources