Silage crops such as ryegrass are frequently harvested to feed livestock, which removes vital mineral ions from the soil. One of these ions is nitrate, which plants absorb to synthesise essential organic molecules.
Give two examples of biological molecules containing nitrogen that would be removed when a silage crop is harvested.
Scientists investigated changes in the application of nitrogen fertiliser in a silage-producing region between 1990 and 2020. They also monitored the fertiliser response ratio, which represents the kilograms of silage dry matter (DM) produced per kilogram of nitrogen fertiliser applied.
The table below shows the results of their study:
| Year | Nitrogen fertiliser used (kg ha−1 yr−1\text{kg ha}^{-1}\text{ yr}^{-1}kg ha−1 yr−1) | Fertiliser response ratio (kg DM / kg nitrogen\text{kg DM / kg nitrogen}kg DM / kg nitrogen) |
|---|---|---|
| 1990 | 40 | 28.0 |
| 1995 | 60 | 22.5 |
| 2000 | 90 | 17.0 |
| 2005 | 120 | 14.2 |
| 2010 | 150 | 11.5 |
| 2015 | 180 | 9.8 |
| 2020 | 210 | 8.5 |
Use these data to calculate the difference in the mass of silage dry matter produced per hectare in 1990 compared with 2020. Show your working.
Use the data in the table to evaluate the use of nitrogen fertilisers on silage-producing crops in this region.
