4(j) Ways in which farmers can increase the nitrate content of soil

As plants grow they will use up the available nitrates in soil, which can become deficient in essential nutrients.  When the crops are harvested, the nitrate content of the soil is now reduced - its ended up as protein in the grain.  Unless the nitrate is replaced, the nitrate content in the soil will decrease with each crop grown.  To avoid the soil becoming infertile leading to poor plant growth and deficiency disease, the nitrate must be replaced.

There are four ways of doing this.

(i) Spreading an organic fertilisers like animal manure or some composted plant material which is decomposed by bacteria/fungi to release nitrogen compounds into the soil. This is a good method because it is essentially recycling organic substances from animal waste or plant material, both returning nitrogen compounds to the soil on decomposition.

(ii) Spreading synthetic fertilisers (e.g. NPK products) made from ammonium and nitrate ion compounds. Can you name them?

However, the use of artificial fertilisers can create pollution problems like eutrophication if overused. See the notes on ...

Biodiversity, land management, waste management, maintaining ecosystems - conservation and already mentioned in Part 4b.

(iii) Crop rotation avoids growing the same crop in the same field over and over again. Several different crops are grown each year in a seasonal cycle. The cycle should include a leguminous plant (nitrogen-fixing crop) like beans or peas that will naturally return nitrates to the soil for another crop the following year - the plant itself can also be ploughed into the field.