Lime Application and Clover Establishment - Two Sustainable Actions

Anne O’ Malley, Business & Technology Advisor, Teagasc Ballina

Lime programme 2023 has focused attention on soil condition, pasture quality, soil sampling and the importance of lime and good fertility to sustain grass and clover swards on productive silage and grazing areas of the farm. Spreading lime from July to September is ideal when ground conditions are good, after silage is cut and slurry application is completed. Lime application increases grass growth, releases Nitrogen (N), increases microbial activity and unlocks Phosphorus (P) and Potassium (K).

Apply lime based on a recent soil test results. Soil can be sampled from September to March, waiting 3-6 months after the last application of phosphorus (P) or potassium (K) before sampling. It is important to distinguish between mineral and peat soils. Aim to maintain mineral soils in the optimum pH range of 6.3 to 7.0 and peats in the optimum pH range of 5.5 to 5.8, to maximise nutrient availability, improve N recycling and reduce total N requirements.

Establishment of a clover-rich swards requires optimum soil fertility (pH levels of 6.5 to 7.0 and Index 3 for P and K). A warm soil and sufficient moisture are necessary for seed germination. The optimum window for sowing is from early April to the end of May and from mid-July to mid-August. There are several ways to establish clover-rich swards, including ploughing and reseeding, minimum cultivation and surface reseeding.

Surface reseeding or over-sowing white clover has about a 70% success rate. Experience on farms has shown that over-sowing works best after harvest of silage during May or early June, compared to spreading on grazed swards. This is mainly because grass recovers more quickly after grazing than after a silage cut, thus competing against the slower establishing clover seedling. Broadcasting after mid-June can lead to a high rate of failure as moist soil conditions are critical and the risk of drought is higher during this period. In addition, grazing swards tend not to be open in mid to late season which is critical for the soil-seed contact necessary for clover to germinate. Low weed content is critical to establishing clover and this can be a big challenge mid to late season.

The most reliable method of white clover establishment after mid-June is by carrying out a full re-seed through ploughing or minimum cultivation techniques. This work should be completed no later than mid to late August in order to get the sward well established before winter. Tight grazing management post sowing is essential to success of clover-rich swards. New swards should be grazed as soon as the new grass and clover plants are strong enough to withstand grazing. Grazing encourages branching of clover stolons and tillering of grass which increases ground cover and impedes emerging weeds. Frequent grazing of the re-seed in the first year post establishment will have a beneficial effect on the sward long term.

Despite the benefits of clover in fixing Nitrogen and reducing the need for artificial fertiliser the levels of clover in grassland is low. Clover is more affected than grasses by temperature, soil fertility and management. Clover germinates and grows from seed more slowly than ryegrass and other grasses and has a shorter growing season. Research and new technologies are ongoing and proper management and sensitivity to the requirements of clover are critical for the long-term maintenance of highly productive grass and clover pasture. To increase the levels of white clover in swards will require a combination of reseeding and over-sowing on productive areas of farmland.