A comparison of two farming systems

In the integrated plant crop area (IPC) fertilizers, except P (chapter 2), and pesticides have been applied according to crop needs. In the organic farming area (OF) only manure and no pesticides have been distributed. One aspect of these different modes of farming is shown in Table 1.

TABLE 1. THE EXPORT OF INORGANIC AGROCHEMICALS BY OVERLAND-, INTER-FLOW AND GROUNDWATER RECHARGE UNDER INTEGRATED CROP PRODUCTION (ICP) AND ORGANIC FARMING (OF). MEAN VALUES OVER THE RUN OF THE YEARS 1994 TO 2001.

N [kg/ha year] DOC [kg/ha year] S [kg/ha year] Cl^– [kg/ha year]

OF ICP OF ICP OF ICP OF ICP

1.4 1.7 0.9 2.1 0.5 0.9 0.4 1.0 3.9 14 12 6.7 2.6 4.4 3.9 3.3 Overland-flow

Inter-flow

Groundwater recharge 10 11 2.3 4.9 46 28 7.5 15 Summe 16 27 15 14 49 34 12 19

The export of N and Cl is higher in the ICP than in the OF area, in contrast S- and DOC-export to neighboring water compartments is strongest in the OF area.

As shown, the N-export from ICP is linked mainly to inter-flow. This is, however, not the case in the OF area although the DOC-export from OF is much stronger than from ICP. DOC from manure and DOC from plant disintegration in soils have obviously different co-transport capabilities.

5. CONCLUSIONS

In the study area the partitioning of overland- and inter-flow changes with agro activities; these changes, however, do not influence groundwater recharge within the measurement accuracy.

Groundwater recharge is much more governed by sediment fabrics.

Only mass transport studies contribute to distinguish clearly between preferential- and different forms of matrix-flow in the unsaturated zone; classical hydraulic observations in the unsaturated zone do not.

The velocities of preferential-flow are in the same order of magnitude as overland-flow and produce in hilly terrains inter-flow with a high export potential for sorbing agrochemicals.

DOC reaches surface waters preferentially thorough interflow. Since many agrochemicals are sorbing substances and DOC has a strong sorption capacity, many agrochemicals move through particle transport. Thus, DOC export produces contaminant pulses for surface water, which simultaneously favors groundwater protection. This export potential has shorter mean residence times in the growing season than in the winter season. However, the co-transport capability of DOC depends also on the DOC origin; manure DOC co-transports less agrochemicals than plant DOC.

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44.

MULTI-TRACER TECHNIQUE AND HYDRO-GEOCHEMICAL APPROACH TO ASSESS POLLUTANTS DYNAMICS IN THE UNSATURATED ZONE AT THE IARI FARM SITE, NEW DELHI, INDIA

U.P. KULKARNI, U.K. SINHA, S.V. NAVADA, U. SARAVANA KUMAR Isotope Hydrology Section, Isotope Applications Division,

Bhabha Atomic Research Centre, Mumbai, India Y.K. SUD, P.S. DATTA

Nuclear Research Laboratory, Indian Agricultural Research Institute, New Delhi, India

ABSTRACT

Soil and groundwater pollution from agricultural activity is becoming an important topic of interest worldwide as a result of the increasing public and regulatory concern on groundwater contamination and its impacts on human health and ecological systems. Contaminant behaviour in the soil, and ultimately in the groundwater is governed by coupled complex processes.

Quantitative and qualitative knowledge of such processes is essential to develop optimal strategies to prevent or remedy the adverse effects of these pollutants. While considerable efforts have been made to understand pollutant dynamics in the saturated zone, very little information is available about their behaviour below root zone and up to the saturated zone. Hence, a study was carried out at the farm site of Indian Agricultural Research Institute (IARI), New Delhi to understand the pollutant dynamics and to protect the groundwater from pollution. Extensive agricultural activities were undertaken at the IARI farm for over 5–6 decades with a history of agrochemical loadings onto its soil. In order to understand the pollutant behaviour in two different conditions, two locations in the farm site was selected; one in an irrigated area and the other in a non-irrigated (rainfed) area. Soil cores were taken from these sites and the samples were analyzed for pH, EC, moisture content, major-ions and isotopes (²H, ¹⁸O, ¹³C). Chemical and radioisotope tracers were injected to estimate the mobility of pollutants. Results of the study are reported here. The results of analyses of soil solution, soil pore gas and the injected tracer experiments indicated that the pollutants may reach the saturated zone in the study area in 7–8 years time. The investigation also indicated absence of reducing environment in the vadose zone and decay of the plant residues in the top layers in the study area. The borehole instrumentation carried out during the investigation helped immensely in understanding the pollutant dynamics in real time mode at the study site.

1. INTRODUCTION

Due to the rise in human population, the demand for good quality of water for industrial, agricultural and domestic purposes is increasing tremendously over the last few decades, with groundwater being the major source. Over-exploitation of groundwater for various purposes has resulted in pollution of the groundwater resources in a few countries and hence has become a major concern as it has a direct impact on human health and ecological systems. The behaviour of contaminants in the soil and, ultimately, in the groundwater is governed by various coupled complex processes. A quantitative and qualitative assessment of such processes is essential for developing optimal strategies to prevent or remedy the adverse effects of these pollutants. While considerable efforts have been made to understand pollutant dynamics in the root zone and in the saturated zone, very little information is available about their behaviour in the unsaturated zone beneath the root zone. The study of this topic requires a multi-disciplinary approach involving physics, biology, chemistry, mathematics, geology, hydrogeology, hydrology, agriculture, soil science etc. The driving force for pollutant transport in the unsaturated zone is recharge (natural, artificial). Hence, a thorough understanding on the recharge processes is highly essential for abating groundwater pollution. Tracers (environmental, artificial) can provide an insight about the recharge processes taking place in the unsaturated zone.

Under the International Atomic Energy Agency (IAEA), Vienna, Austria funded Co-ordinated Research Project on “Isotopes in the Study of Pollutant Behaviour in Unsaturated Zone for Groundwater Protection”, environmental (²H, ¹⁸O, ¹³C) and artificial (Li⁺, Br^-, HTO, ⁶⁰Co) tracers were used to understand the various complex processes occurring in the unsaturated zone at the farm site of Indian Agricultural Research Institute (IARI), New Delhi. Also, an estimate on the recharge, mobility of pollutants and related parameters was made. The study was carried out in collaboration with the Nuclear Research Laboratory, IARI.