Cutting fertiliser costs with soil testing

Getting soil analysed is often an overlooked or neglected task on some farms. This year before purchasing or applying any chemical fertiliser, it would be advisable to take soil samples for the farm to determine the soil nutrient levels. Why pay to apply nutrients that are already present in the soil?

In addition, under the nitrates directive, a soil analysis is compulsory for any field which has received compound fertiliser containing phosphorous. This analysis is required to determine crop need and is applicable for four years before needing renewed.

A soil analysis is a practical aid to managing soil nutrients efficiently so that soil fertility is at the correct level for the growing crop. It provides information on soil pH, which is especially important when establishing clover swards. Soil pH for grassland should be between 6.0 and 6.5 for optimum fertiliser utilisation and plant growth.

With grassland, soil should have a target Phosphorous (P) and Potash (K) index of 2. At this nutrient level, grazing ground should only receive a spring application of slurry and then straight nitrogen throughout the year. For first cut silage, slurry and straight nitrogen will again suffice.

A major benefit of soil analysis is being able to reduce fertiliser costs. The potential saving that can be made from efficient use of slurry and farmyard manures, will help the profitability of the farm business. Applying 2000 gallons/acre (22cubic metres/ha) of cattle slurry will provide 14 units (17.5 KG/ha), 22 units (27.5 KG/ha) and 42 units (52.5 KG/ha) of N, P and K respectively.

Collecting a soil sample is a simple task and can be conducted using a specific soil auger or simply a spade. Samples should be taken at regular intervals over the field in a W pattern and each core should be about three inches. One sample should represent 10 acres (4ha) and should contain about 25 soil cores. Smaller fields can be grouped together if they are receiving similar fertiliser applications.

Soil sampling is best carried out between October and February on fields which have not received any lime or fertiliser within a two month period.

For more information on soil analysis and nutrient planning, contact your local DARD development advisor.