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Despite growing up in city life in Wellington, Brett Petersen had always been drawn to the countryside and spent many school holidays working on farms. His first attempt at studying agriculture failed dismally, but he didn’t give up. He went on to complete four years of study, resulting in diplomas in horticulture, agriculture, and later valuation and farm management. It was during his early years in the agricultural sector in the 1960s and 1970s that Petersen realised everything had a commercial or corporate angle, with each company promoting its own fertiliser. “Within a few years of working, I’d burned my study notes about how agricultural land was supposed to be managed,” Petersen said. Soil health “I spent 11 years working in the land division of Māori Affairs, followed by 12 years supervising Māori Trusts in a private capacity,” Petersen said. “Since 2008, I have focused on enhancing soil fertility and economic viability for farmers and growers.” Most farms followed the traditional NPK fertiliser system. Soil tests were routinely carried out, but there was little real expertise in interpreting individual results, so farmers tended to apply the same inputs year after year. “There was no one to discuss soil health with in those days,” he said. “During a course near Brisbane on soil fertility, lots of pennies dropped for me.” During his time as a farm supervisor, Petersen explored products and methods from six different companies in order to identify the best options. “Correctly balancing the soil should be the goal of any soil fertility programme, and we need to move away from the more harmful products, which are often the cheapest.” Kinsey Agricultural Services produced manuals showing how to calculate nutrient requirements from soil samples using specific formulae. These were based on the work of Dr William Albrecht, who authored more than 400 papers on soil fertility and developed the Albrecht System of Soil Fertility – an approach focused on feeding the soil and letting the soil feed the plants. These manuals and papers form the foundation of Petersen’s soil management approach. High-quality crop yields tend to share similar soil chemistry: calcium at 60-70%, magnesium at 10-15%, potassium at 5%, sodium at 1.5%, with defined levels of nitrogen, phosphate, sulphur and trace elements. Ripening bananas and a banana flower. Photo / Catherine Fry “The Lincoln University Dairy Farm [LUDF] achieved a best return on investment [ROI] of 4.5%,” he said. “On one of the Māori Trust properties I supervised, our worst ROI was 4.6%, and our average was 8.5%, using only 10% of the nitrogen applied at LUDF.” Tending land In 1980, Petersen purchased 4ha on Ohakana Island in Ōhiwa Harbour, where he built a home and grew tamarillos and passionfruit, quickly gaining organic certification for the land. He continued advising on soil health and sharing his knowledge through agricultural publications, including writing a column for Coast & Country News for several years. Brett Petersen in his banana plantation. Photo / Catherine Fry Now semi-retired, Petersen continues to advise several farms. He has lived on a 5.5ha property near Awakeri since 1991, where he has established a banana plantation. Bay bananas “For the first two years, I grew canna lilies as a cash crop,” he said. “I planted my first bananas 30 years ago. They were an inedible variety, but they didn’t seem to mind the climate.” Today, Petersen has a 30m by 50m area planted with edible banana varieties introduced in 2023, including Misi Luki, Dwarf Cavendish, Mons Mari and Goldfinger. He said they prefer free-draining soil. “I don’t look at what the plant wants – I look at what the microbiome beneath the plant wants. “Base saturation percentages are the key to getting things right.” Petersen aimed for a soil structure that maximises drainage, consisting of 50% pore space (for air and water), 45% mineral content and 5% organic matter. Banana plants have a pseudostem mad...
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