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It’s a message that some may be tired of hearing, but one that will remain every bit as important until the days you stop farming.
Never underestimate the role of lime in underpinning your soil fertility.
Lime is the most basic, but also the most critical element of soil fertility. Maintaining the correct soil pH is the cornerstone for maintaining the productivity of our soils. Developing optimum soil pH levels through the use of lime should be an ongoing action on your farm.
How lime works
If soil pH is not close to optimum, then the availability of major nutrients required for plant growth is decreased. The anti-acidic properties of lime reduce the ions which cause acidity in soils and thus prevent them from binding with the important plant nutrients. This in turn helps nutrient availability for the growing plant.
Maintaining mineral soils in the optimum soil pH range of 6.3 to 6.5 will increase the availability of all the major nutrients such as nitrogen (N), phosphorus (P) and potassium (K). These nutrients include those stored in the soil and those freshly applied.
Extensive work by Teagasc has shown the benefits to crop growth of correcting soil pH. For example, studies have shown that in a wheat crop, where soil pH is raised by 1.0 (ie pH5.5 to pH6.5), a yield increase of 2t/ha was achieved.
Applying lime on to soil can also have beneficial implications on soil biology.
Correcting soil pH levels and creating an environment for plant life to thrive in will, in turn, allow soil biology and earthworms to thrive, breaking down plant residues, animal manures and release nutrients required for healthy plant growth.
How is lime lost
It is possible for lime to be lost through the profile of the soil due to a number of reasons, so it is crucial that farmers check soil pH levels every three to five years.
Lime is lost mainly through rainfall. Rain and soil water are charged with carbon dioxide, which can dissolve the lime contained in the soil. Some of this dissolved lime can make its way down into the soil drainage system and be lost from the soil.
Crop growth can also be a cause of lime depletion in the soil. According to Teagasc, an average crop of hay or silage can utilise up to 75kg/acre of lime. In addition to this, the repeated use of certain fertilisers, such as sulphate of ammonia, can use up lime in the soil.
Practicalities
Liming is the second step to take when aiming to improve soil fertility levels. Soil sampling is the first. A recent soil report (every three to five years) will show the rate of lime required, depending on the soil type, soil pH and crop type. Develop a farm liming plan, targeting fields with largest requirements first.
Lime can generally be applied at any convenient time of the year. In crops and reseeds, spread after ploughing so that it can react with the soil and be thoroughly mixed during cultivations. Teagasc suggests applying no more than 7.5t/ha (3.0t/ac) in one application. Where more lime is recommended, apply the balance after two to three years.
Remember, when soils are over-limed, some crops may suffer from lack of plant nutrients such as boron, iron and manganese. Basing lime applications of recent soil test has never been so important.
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