Continuing use of fertiliser N dramatically alters the ryegrass-clover equilibrium, giving 10-40% increases in annual pasture production with no obvious (in the short-term) adverse affects on soil biological activity, provided inputs are not much more than 100-150 kgN/ha annually. Exceeding this – as is now very commonly done on dairy farms – increases the risk of a variety of adverse and interconnected effects occurring.
A frequent consequence is the virtual complete disappearance of clover – a very nutritious and N-fixing plant – from the sward. Adverse effects of increased stocking rate include soil compaction, reduced soil aeration and drainage, pugging, restricted root growth and pasture pulling, reduced soil biological activity, declining soil organic matter content (including carbon of course), increased animal nutrition problems and increased losses of nutrients – particularly N and P – to the environment.
The introduction of serious clover pests such as the stem weevil in recent years have forced many dairy farmers to use greatly increased quantities of fertiliser N to replace N no longer being fixed from the atmosphere by clover, and/or to use increased quantities of brought-in feeds such as palm kernel to maintain milk production. This has tended to exacerbate other problems, including those mentioned above.
More and more farmers are becoming increasingly concerned with what they feel is the ‘health’ of their soil. In a virtual absence of systematic surveying and research by the Crown Research Institutes (CRIs), and a ‘not our problem’ attitude from the big fertiliser companies, more farmers are turning to alternative, largely unproven nutrient mixes and soil amendments.
At the very least, it should be a requirement for suppliers and consultants to supply specific information regarding the quantities of nutrients per hectare that are being applied in any nutrient mix, and why these recommended applications differ from ‘Overseer’ recommendations if this is the case, particularly for the major nutrients. “Overseer’ is a long, long way from being perfect, but it is a long way better than doing nothing to assess actual nutrient requirements and losses. I give it a 6 out of 10. Likewise, companies selling soil ‘amendments’, whether they be aglime, fine lime, humates, seaweed or fish extracts etc, should state what these amendments are specifically intended to achieve at the recommended rate of application.
Sadly, in fact incredibly for a country whose entire economic health is dependent on sustainable agricultural production, New Zealand’s universities and Crown Research Institutes employ a grand total, according to our information, of one, yes that’s one, trained and full-time employed soil microbiologist! It is shocking how little we actually know about the microbes and fungi so vital for so many things, probably the most important of which is maintaining the biological activity and health of our soils.