Westpac New Zealand has posted faster profit growth than its rivals in the second half of the financial year as it chose not to chase market share growth in the hyper-competitive mortgage market.Westpac reported cash earnings growth of 7.7 per cent between the first and second halves of the year as it increased its net interest margin by four basis points to 233 basis points. Cash earnings of NZ$475 million in the six months to September 30 were also up 9.9 per cent from the same half a year earlier.ANZ New Zealand grew its profit only one per cent over the same period, while National Australia Bank's BNZ reported its profit fell 3.1 per cent. Both ANZ and BNZ saw their net interest margins fall one basis point and four basis points respectively in the second half of the financial year as they chased volume and market share growth in the key Auckland housing market. Westpac NZ Chief Executive David McLean said the bank had grown its housing lending slower than the rest of the banking system and wanted to grow through better service and branding, rather than simply having a lower price."We're trying to be better at navigating the balance between volume and price through this year," McLean told Banking Day.Westpac had a naturally lower share of the Auckland market than the other banks, given its history of not having bought the former cooperative Trust bank in Auckland. Westpac bought the Trust bank network outside of Auckland and Taranaki in 1996, which meant its share of Auckland was lower than its rivals, although it was still a growth market for Westpac, McLean said.The dominant trust bank in Auckland was Auckland Savings Bank, which became ASB and was subsequently bought by Commonwealth Bank of Australia."We don't necessarily see price as the best way to do it," he said of Westpac's growth plans, referring to its drive to allow completely online mortgage applications and improving its branches in growth areas of Auckland."The trouble is price is not adding anything long term to the customer."McLean said Westpac also had a lower than natural share in agricultural lending and it was growing lending in that market, but it had yet to see a big drop in credit quality in the key dairy market, where milk prices have been at unprofitable levels for two years.He said Westpac was supporting its loss-making dairy farming customers while milk prices recovered and was being cautious not to pull the trigger with receiverships too quickly. It had worked with farmers on budget advice and had moved to interest only loans in some cases."We have committed to seeing them through it.  When the going gets tough, farmers have got long memories about how the bank reacted to them, and also to some guy down the road," McLean said.Westpac's farm lending grew to NZ$7.9 billion or 7.9 per cent of total loans by September 30 from 7.7 per cent a year earlier. The percentage of farm loans categorized as stressed