Table 4.
Changes in amount of organic C from adding farmyard manure every 5 years to continuous arable or ley‐arable rotations; Woburn Ley‐arable experiment (14)a
| Crop rotationb | Treatment | No. of plots sampled | Sampling period | No. of years | Amount of organic C | Rate of increase (t C ha−1 year−1) | Annual increase (‰ /yr) | Notes | |
|---|---|---|---|---|---|---|---|---|---|
| At start (t/ha) | At endc (t/ha) | ||||||||
| Ar | FYM every 5th year | 5 | 1938–1965/74 | 30.5 | 37.0 | 37.0 | 0.00 | 0.0 | 213 t/ha applied from 1938 to the mid‐1960s |
| Ah | ” | 5 | 1938–1965/74 | 30.5 | 37.0 | 40.2 | 0.11 | 2.8 | ” |
| Lu3 | ” | 5 | 1938–1965/74 | 30.5 | 37.0 | 43.4 | 0.21 | 5.7 | ” |
| L3 | ” | 5 | 1938–1965/74 | 30.5 | 37.0 | 50.1 | 0.43 | 11.7 | ” |
Adapted from Tables 2, 4 and S2, Johnston et al., 2017. Although there was not a significant effect of FYM for individual rotations, when all rotations were considered together, there was a significant effect.
Ar: 5‐year arable crops including root crops. Ah: 5‐year arable including 1‐year hay. Lu3: 3‐year lucerne ley followed by 2‐year arable. L3: 3‐year grazed grass/clover ley followed by 2‐year arable.
For L3, the amount of organic C at the end includes additional C present in the soil to an “equivalent” depth; i.e. so that the same mass of mineral soil was being considered both at the start and end of the period.