Fertilizer decisions

Waimarino Bulletin, Volume 6, Issue 262, 8 November 1988, Page 8

Fertilizer decisions

Fertiliser decision making is becoming more complex as an increasing number of products become available at a wide range of prices.

As fertiliser is one of the main expenditure items for farmers, any application programme must be carefully planned and evaluated. The basis for fertiliser choice must be the return for dollars invested says Masterton MAFTech agricultural consultant Tony Scarfe. "Fertiliser choice on any property depends firstly on the results of soil tests and herbage analysis, and secondly on the fertilisers available, their nutrient makeup and their comparative on-farm costs. "Soil tests carried out every two years provide a good guide as to the current status of farm soil fertility. Several tests are required from different areas of the farm to give an overall picture of the property, but these areas must be carefully selected to be representative of the whole farm." The nutrient requiremcnts for the property are determined from the soil test results togcther with other farm data. The fertiliser choice is based on the most cost-effective method of providing the nutrients needed. "Many farmers still dccide on fertiliser products by their dollar per tonne price. This method however could result in inefficiencies and wasted money. "For example, to apply 15 kg of phosphate per hcctare you could use superphosphate at $246 per tonne applicd, or DAP at $574 per tonne applied. The higher phosphate contcnt of DAP more than compcnsates for its higher price, so to apply the rcquired phosphate in this case would cost $43 per hectare for

DAP compared to $46.20 for superphosphate", said Mr Scarfe. "This gives a significant saving if you don't need all the sulphur that superphosphate provides, and if you require nitrogen".

Major savings can also be made by changing the product used. "Taking the same example where 15 kg of phosphate per hcctare is required, this could be providcd by a fertiliser containing 12N:10P:10K:IS and costing $88.40 per hectare or by a 15:10:10:7 fertiliser T urn page 8

Fertilizer decisions

From page 9 costing $69.20. The latter not only provides more nitrogen and sulphur but also saves $20.20 per hectare. This is worth over $4,000 in just three years on a 70 hectare dairy farm". Mr $carfe said that the early dry autumn meant that dairy farmers faced a shortage of feed at calving time. "Many farmers plan to use nitrogen to boost grass growth to overcome this situation. Whilc this is

good policy, recent soil tests have shown that a number of farms have low sulphur levels. Using a nitrogen sulphate fertiliscr like ammonium sulphate rather than straight nitrogen may give better responses in these cases. However, if sulphur levels are adequate and ammonium sulphate is applicd, its extra cost (or about $12.90 per hectare) would be wasted". Mr $carfe said that where farmers were in doubt about their fcrtiliser programme they should consult an agricultural consultant. "Obtaining professional advice for an average farm is likely to be about $200 per year, including soil testing costs. The potential savings from using the most cost effective fertilisers for the individual requirements of each farm could be considerable in many cases".