Some agricultural chemicals are likely to move with percolating water. These include nitrogen in the form nitrate and some pesticides, particularly herbicides. Other chemicals are unlikely to leach in this way because they chemically bind with soil or other material. These include phosphorus and many pesticides.

I imagine that if irrigation is performed correctly, the irrigation water is unlikely to move to deeper groundwater. This is because irrigation will be balanced more-or-less with evapotranspiration. Instead, leaching of chemicals to groundwater is more likely to be driven by rain events.

Well,

Very good question, am eager to know too, so I will be following

By moving during the layers to the groundwater

Some agricultural chemicals are likely to move with percolating water. These include nitrogen in the form nitrate and some pesticides, particularly herbicides. Other chemicals are unlikely to leach in this way because they chemically bind with soil or other material. These include phosphorus and many pesticides.

I imagine that if irrigation is performed correctly, the irrigation water is unlikely to move to deeper groundwater. This is because irrigation will be balanced more-or-less with evapotranspiration. Instead, leaching of chemicals to groundwater is more likely to be driven by rain events.

In agricultural activities, chemicals are introduced into the soil in the form of fertilizers and pesticides. The illustration given by Dr. Bayan tells everything. For achieving higher yield of crops and also to protect the crops from pest attack, fertilizers and pesticides are applied respectively. The application of these chemicals should be within the prescribed limits. However, some people apply more than the prescribed limits and because of this over dosage, chemical residue will take place, which in turn leaches into the soil and ultimately pollutes the groundwater.

They are carried through the soil layers,as Bayan Hussien 's picture.

No, the groundwater is protected from irrigation water because the infiltration between soil layers deny the vertical transport of pollution

Kouadri Saber , this is not universally true. Unconfined aquifers are hydrologically connected to the surface.

thank you Salvatore S. Mangiafico for the correction, I forgot to exclude some particular cases..

Kouadri Saber , unconfined aquifers are quite common. I did a quick search, and didn't find any document that suggested the percent (by area or population) that use unconfined aquifers on a nationwide or global scale. But for an example, New Jersey, USA: "In 2015 there were 7,288 mgd of surface water allocations, 779 mgd of unconfined groundwater allocations, and 341 mgd of confined groundwater allocations." (New Jersey Water Supply Plan 2017 - 2022, https://www.nj.gov/dep/watersupply/pdf/wsp.pdf). ["mgd" is million gallons per day. A gallon is less than 4 liters.]

So, in NJ, twice as much water is used from unconfined aquifers as from confined aquifers. One reason is that there is the large Kirkwood-Cohansey unconfined aquifer in the southern part of the state. Though the unconfined aquifer use is only 10% of surface water use. One reason for this is that some densely populated areas rely on surface reservoirs.

i'm very thankful for this precious informations and explanations Mr Salvatore S. Mangiafico

Following

Omar Al-Khashman

This document will serve you.

I see that the subject has been well discussed. I have nothing further to add.

Sudip Saha Omar Al-Khashman

Sudip Saha Bamba Zie Aboubakar Armel

By leaching.

Leaching

Leaching of harmful chemical fertiliser. Sudip Saha

Pesticides example from Norway

Hello, Sudip Saha ,agricultural wastes are generally chemicals, and other materials enter the soil through rainwater intermediaries, as a result of damaging the soil, which should always be normal for agricultural land, then because groundwater extraction uses boreholes, sea water enters tens of kilometers damaging groundwater, in Indonesia it has been severe for this, so that agriculture becomes infertile and unproductive for plants, so many owners sell land for housing, I just believe, the fertility of the land turns out to have a limit of some sort of expiration. regards.

Leaching of excessive agrochemicals with irrigation water or rain is the main cause of polluting ground water by agricultural activities.

Overuse of fertilizers and pesticides are the main cause of contaminating underground water. N-fertilizers are the main polluting of underground water because of the excessive use by the growers.