Nitrate Leaching

Nutrient Management: Nitrate Leaching.

Nitrate leaching is a very common occurrence among the arable farming industry, it is also a “natural occuring process” (Resilient Cropping, 2015). Nitrates are introduced on farms in the form of fertilisers. The way in which nitrate leaching occurs is when the nitrates from the soil seep into drainage water. There is no problem when nitrates are in the roots but once they enter the ground water and fresh water it immediately becomes a pollutant in the environment (Resilient Cropping, 2015). Nitrate leaching mainly is caused by farmers when they weaken the soil by the repetition of planting and excessive amounts of it. The farmers then try to replenish the soil by putting large amounts of fertilisers –which are nitrogen based- on their land. This is in order to try keep the same constant crop yeilds (Reopure.com, 2015).

The diagram above (Fertilizer & Lime Research Centre, 2014), shows the nitrogen cycle. It shows the ways in which nitrogen is introduced into the soils and how it leads to leaching. The steps provided by the Fertilizer and Lime Research Centre (2014) tell us in further detail what is occuring in each stage:

A. N is taken up by the plant

B. The fixation of N by the legumes

C. Ammonium is formed by the decomposition of organic matter

D. Soil organic pool form from the plant residue and dung

E. Urea is converted to Ammonium by enzyme conversion

F. Nitrification – Ammonium converting to Nitrate

G. Denitrification – Nitrate converting to Nitrous Oxide gas and then to Nitrogen gas.

Nitrate leaching is most likely to occur in Winter, in the regional weather records it could be seen that winter was the season that it would most likely have long wet periods which would cause saturated soil (Resilient Cropping, 2015).

As stated by Lilburne and Webb (2002) “Nitrates in groundwater is a major environmental contaminant internationally and in New Zealand”. Rising nitrate leaching concentrations are to be blamed on agricultural systems such as Arable farms (Di & Cameron, 2002), this is a major issues that has to be dealt with by the farmers as there are many negative side effects to excessive nitrate pollution in groundwater and fresh water systems. These side effects not only harm people but animals as well, the following are examples of health effects due to nitrates found by Self and Waskom (2014):

Methemoglobinemia (Blue Baby Syndrome): This is a conditon that is mostly found in infants six months and under. The stomach acid in infants is much weaker than that of an adults, which causes the increase of bacteria in their stomach. This bacteria can convert nitrates into nitrites. The nitrite is harmful as is absorbed by the blood and hemoglobin (“the oxygen-carrying component of blood” (S & W, 2014)) and is the converted into a methemoglobin (S & W, 2014).
The reason for this being dangerous is that the methemoglobin can not efficiently carry oxygen. This is then causing a reduction in oxygen supply to vital organs such as the brain. This can occur in pregnant women as well who have a reduced stomach acidity. Many symptoms occur fro example, bluing of the skin, dizziness, headache, weakness and difficulty breathing.
In animals such as sheep and cattle they a susceptible to nitrate poisoning. Which can cause symptons such as pain in the abdomin, muscular weakness and diarrhea (S & W, 2014).

In the research that I have done, both Di and Cameron (2002) and authors of ‘Do Organic Farming Practices Reduce Nitrate Leaching?’ (2015) agree that agricultural applications that could reduce nitrate leaching in the arable industry are highly needed. The following range of nitrate leaching management options have been suggested by Di and Cameron (2002):

The reduction of the rates of Nitrogen application
Matching the supply of nitrogen to the amount of plant demand
Ploughing at better times
Improving the stock management
Precision farming and regular measures

Looking forward into the future, if farmers have not found a new product to fertilise crops they will very much face the same issues as they do today, as nitrate leaching will always occur when using Nitrogen based fertilizer. Unless farmers have begun to follow a nutrient management regime as well, we will continue to see the same issues occuring every year to follow.

References:

Di, H., & Cameron, K. (2002). Nutrient Cycling In Agroecosystems, 64(3), 237-256. doi:10.1023/a:1021471531188

DO ORGANIC FARMING PRACTICES REDUCE NITRATE LEACHING?. (2015). Communications In Soil Science And Plant Analysis. Retrieved from http://www.tandfonline.com/doi/abs/10.1081/CSS-100104101#.VfCpQ9Oqqko

Fertilizer & Lime Research Centre,. (2014). Inputs, Outputs and Transformations of nitrogen in farming cycles. Retrieved from http://www.massey.ac.nz/~flrc/shortcourses/SNM_information.html

Lilburne, L., & Webb, T. (2002). Effect of soil variability, within and between soil taxonomic units, on simulated nitrate leaching under arable farming, New Zealand. Australian Journal Of Soil Research, (7), 1187.

Mathers, D., & Pearson, A. (2012). Nutrient Management Plans. Far Focus, (6).

Millner, J., & Roskruge, N. (2013). The New Zealand Arable Industry. Lincoln: Manaaki Whenua Press. Retrieved from http://www.landcareresearch.co.nz/__data/assets/pdf_file/0005/77036/1_8_Millner.pdf

Resilient Cropping. (2015) (1st ed.). Retrieved from http://www.far.org.nz/mm_uploads/Nitrogen_leaching.pdf

Reopure.com,. (2015). NITRATE POLLUTION OF GROUNDWATER. Retrieved 10 September 2015, from http://www.reopure.com/nitratinfo.html

Self, J., & Waskom, R. (2014). Nitrates in Drinking Water. Colorado: Colorado State University. Retrieved from http://www.ext.colostate.edu/pubs/crops/00517.html

Ayumi Sleegers