12 July 1985 Orchardists warned against rushing into fertigation systems

Orchardists are warned against moving into fertigation systems for apple trees before having their orchard soils properly tested, by the Reader in Soil Science, Dr Kuan M. Goh, in the Department of Soil Science at Lincoln College.

Dr Goh said that fertigation that is supplying fertiliser nutrients through trickle irrigation systems had been used in New Zealand for only about three years, but last season had become very popular with growers.

His concern also was that some orchardists, developing new orchards in Canterbury, were not getting the best advice about fertilisers, he said.

"Many people are sampling orchard soils for soil testing using the same methods as for pastures, but the approach could be quite wrong," Dr Goh said.

"Some orchardists and advisers are using soil-testing procedures, such as random sampling to a depth of only 0-75 mm.

"This doesn't take into account that apple trees behave and grow very differently from ryegrass and white clover in pastures.

"Apple trees root very much deeper than 75 mm, so soils should be sampled down to at least a depth of 200 mm, and in new orchards an additional 200- 400 mm should be sampled."

Dr Goh said that in new orchards soils should be tested before planting, and if there were more than one soil type each should be sampled and kept separately for soil tests.

"Ideally, a combination of soil tests and leaf analyses should be used for fertiliser recommendations," he said.

"For leaf sampling, several mid-shoot leaves of current-season growth should be taken in the spring for chemical analysis."

Dr Goh said little research had been done in New Zealand on soil testing for fertiliser recommendations for apple trees.

Some work had been done around Auckland on soil testing in kiwifruit orchards, but there had not been work for other horticultural crops.

Nutrient surveys of apple orchards in Canterbury, with soil testing and leaf analysis, had been carried out by the college soil science department in the last two-and-half years.

Although data were still being processed, preliminary indications were that large discrepancies existed between soil-test values and leaf-nutrient status.

"A lot of effort is being put in by fertiliser companies to sell unproved fertiliser formulations to apple growers,'' Dr Goh said.

"But fertilising apple trees can have a profound effect, not only on the yield of the crop, but also on fruit quality."

Dr Goh said orchardists should sample the soil in their orchards from both the herbicide strips and the grass alleys at the same time.

"The samples should kept quite separate for sending away for testing,". He said.

"Soil tests used in New Zealand do not test for nitrogen, yet nitrogenous fertilisers are the most commonly used in orchards."

Dr Goh said excessive nitrogen on apple trees produce leafy, good looking trees, but the trees have low yields of fruit with poor colour and low keeping quality.

Further information from Dr·Kuan Goh, Department of Soil Science, Lincoln University College of Agriculture 8150