NAB's BNZ has reported a 6.3 per cent rise in cash earnings, despite a five basis point fall in net interest margin, as it grew its farm lending market share and benefited from a drop in bad debt charges. BNZ's cash earnings rose NZ$47 million to NZ$788 million in the year to September, with most of that growth happening in the second half. Bad debt charges fell to NZ$43 million or 0.14 per cent of loans in the second half of the year from NZ$64 million or 0.22 per cent of loans in the same half a year earlier.BNZ CEO Andrew Thorburn said the bank held its mortgage market share through the year despite a surge of competition, particularly in the Auckland market where ASB and ANZ fought a battle for supremacy through late 2012 and early 2013. This has come at the cost of a slight fall in lending margins, particularly in the second half of the year. Meanwhile, BNZ increased its agribusiness market share by 29 basis points to 22 per cent, punching above its market share weight of around 16 per cent in the home mortgage market and 18.5 per cent in term deposits. BNZ gained share from ANZ, which merged with its rural-heavy National Bank arm during the year and had deliberately looked to reduce its over-exposure to the sector.BNZ's operating expenses rose 3.7 per cent or NZ$28 million as it geared up in the first year of a four to five year technology rollout expected to cost NZ$400 million. It also ramped up its marketing spending with a new "Be good with money" advertising campaign, which it said improved its brand consideration among non-customers by 25 per cent.