(1) INFLUENCE OF LIME IN SOIL
(Continued) |
| (5) Crops and Livestock |
| It is clear that the response of crops to liming is complex. However, the
bottom line is that there must be obvious crop yield increases before lime can be
justified. In the
case of tillage crops, it is generally accepted that lime is essential in order to
maintain pH and optimum nutrient levels. Archer (1995) summarised the results of the long
term liming trials at Rothamsted and Woburn Farms, and yield penalties for barley for
dropping one pH unit below the
recommended pH was
about 2 t/ha. The critical pH for the range of crops is given in the section under lime
requirements. |
| Cutting trials carried out between 1952 and 1974 have shown that response
to liming on grassland approximate to increases of 1500 kg DM/ha on the old pasture and
between 3,000 and 4,000 kg/ha on new pastures (Gately, unpublished data). In some
instances there were also effects on quality, in the new pastures; ryegrasses fail to
establish on the acid plots and poorer species e.g. creeping softgrass (Holcus mollis)
can grow instead. Curtin and Smillie (1986b) showed that ryegrass was apparently much less
tolerant of Al than was bentgrass. |
| A trial was instigated by Johnstown that ran between 1967 to 1971 to study
the response of a range of crops to lime, N, P and K (Murphy, Priv. Communication). Only
five sites had an initial pH below six and for the first three years of the trial a high
rate of nitrogen was applied across all lime treatments. No responses to lime were
observed. The application of nitrogen was discontinued in 1970 and the responses to lime
on three out of five sites were observed on grassland (Table 3). |
| Table 3: Herbage D.M. yields (kg/ha) at different sites and lime rates
(t/ha) after withdrawal of N fertiliser. |
| |
|
Rate of Lime t/ha |
| Site |
pH |
0 |
5 |
15 |
| Limerick Laois
Wexford
Kilkenny
Louth
Mean |
5.4
5.2
5.5
5.4
5.2
5.4 |
5300
5400
3700
5300
3700
4700 |
5200
5800
5300
6500
4500
5500 |
4800
5600
4300
6900
4900
5500 |
|
| Because a considerable amount of nitrogen is recycled through the animal
under grazing, it was thought that this might replace the lime effect and that cutting
trials might exaggerate the benefits from lime. An experiment was started in 1976 to
examine the effects of liming old pasture on the performance of grazing Freisian bullocks
(275 kg). The soil had an initial pH of 5.2 and the sward was of mixed species dominated
by common bent grass (Agrostis tenuis). |
| The liming treatments and the liveweight gains are summarised in Table 4.
The limed treatments were approximately 20% better than the control, but there were no
differences between the two lime treatments. |
| Table 4: Effects of lime on liveweight gain per animal per day (5
animals/ha) |
| Lime (t/ha) |
0 |
7.5 |
15 |
| Liveweight gain (kg/ha/day) |
0.55 |
0.65 |
0.67 |
|
| The amount of grass on offer when the animals entered various grazing
cycles was measured with the following results (Table 5). |
| Table 5: Grass on offer at different grazing periods. |
| |
DM (kg/ha) |
| Lime (t/ha) |
0 |
7.5 |
| First cycle Second cycle
Third cycle |
2369
2899
2688 |
2787
3744
3656 |
|
| This shows that animals had 18-36% more herbage available on the limed
plots. The digestibility and the clover content was higher in the limed plots (Table 6). |
| Table 6: Digestibility of herbage (May) and %clover (July) in limed and
unlimed plots. |
| Lime t/ha |
0 |
7.5 |
| Digestibility % %Clover |
66.5
4.7 |
69.2
14.0 |
|
| |
