February 2021

Phosphate is a key element for plant growth in New Zealand soils, but urgent change is required in how we use it to prevent environmental degradation before it’s too late, says Hamilton-based Soil Scientist Dr Gordon Rajendram (PhD). New Zealand soils and phosphate have a long history together, going back to World War Two when New Zealand soils were deficient and phosphate was imported as RPR and made into Superphosphate. “The issue with this is that the continuous use of Phosphate over the last 70 years will mean it is no longer deficient in most soils and can be detrimental to the other nutrients or lime being applied,” says Soil Scientist Dr Gordon Rajendram (PhD). The traditional method of farming was primarily focused on production. More grass, more protein, more milk and meat produced while environmental issues were not a concern. But farming has changed, he says. Now we want to produce as much as possible but also keep any phosphate applied to stay in the soil and not runoff as particulate P or leach into subsoils.  “Much of the loss is related to the soil type, climate, Anion storage capacity (ASC) or otherwise known as P retention, and overuse of soluble forms of P. P as a nutrient is one of the most expensive nutrients per kg,” advises Gordon. The scientific evidence is telling us not to use a highly water-soluble P fertiliser, as this type of fertiliser is far more likely to end up in waterways and particularly on low phosphate retentive soils.  “It is not nitrogen in waterways which is the issue, its P, only need small quantities to get into waterways to trigger eutrophication (algal blooms),” comments Gordon. It as Professor Walker once said, ‘Superphosphate has done more for NZ than any politician ever has’ this is true but we need to move on as this old technology”. About Dr. Gordon Rajendram – The Soil Scientist Dr. Gordon Rajendram worked at AgResearch, Ruakura Research Centre, Hamilton for 22 years.  He has developed two field calibrated soil tests ( N & S) which are used for agronomic advice in New Zealand.  He also quantified the leaching of cation & anions from pastoral systems and this has been included in the Overseer nutrient model. He now consults to farmers and fertiliser companies. Contact Dr. Gordon Rajendram – The Soil Scientist: Email: rajendram@xtra.co.nz Phone: 021 466 077 Facebook: https://www.facebook.com/GordonRajendramSoilScientist Website: http://dev.gordonrajendramsoilscientist.co.nz LinkedIn: https://www.linkedin.com/company/the-soil-scientist Instagram: https://www.instagram.com/thesoilscientistnz/ Contact MediaPA: Phone: 0274 587 724 Email: phillip@mediapa.co.nz Website: www.mediapa.co.nz Facebook: www.facebook.com/MediaPA YouTube: www.youtube.com/user/TheMediaPA

Phosphorus (P) is critical for healthy plants to grow in New Zealand’s naturally P deficient soil says Hamilton-based Soil Scientist Dr Gordon Rajendram (PhD). However, the shifting of P from farmland soils to local bodies of water has become a very serious environmental concern as too much P in waterways can cause the massive growth of aquatic plants and algal blooms. In a recent article by Warwick Catto on the subject off P loss, states that P loss comes from many sources but the contribution from fertiliser can be easiest to address. The two pathways of P loss have been identified as overland flow and by leaching through the soil profile. “P losses to the environment, from either of these sources can also affect farm profits, so it’s smart business sense to minimise them where you can,” says Soil Scientist Dr Gordon Rajendram (PhD). The article also recognised that reducing P loss within farm systems independent analysis identifies the use of low water-soluble fertilisers to be one of the least cost mitigations to achieve this. Rajendram’s own 2012 paper on P loss concluded that peat soils will lose more P than other soils. This is shown in my paper when I separate the 4 different soil types used for agronomic advice (ash, sedimentary, peat and pumice).  It only needs 0.1 kg of P in 1 hectare with 400 mm of drainage to cause eutrophication,” advises Gordon. Losses in an AgResearch study showed on two peat farms losses were 5 kg and 46 kg/ ha/year, and were directly related to P retention ability of the soils. There are other soil types around NZ with low phosphate retention ability which will be losing P readily. “The issue lies in the fact that highly soluble P fertilisers are still being sold to peat soils in Waikato and Hauraki Gulf.  And farmers are unaware of this issue,” advises Gordon. Using a lower water-soluble P fertiliser can reduce the loss of P into waterways. However, it is important to remember that fertiliser itself is only one facet of a good fertiliser management system. Ensuring that it is applied at the right time, place and rate is equally important. Dr. Gordon Rajendram – The Soil Scientist Dr. Gordon Rajendram worked at AgResearch, Ruakura Research Centre, Hamilton for 22 years.  He has developed two field calibrated soil tests ( N & S) which are used for agronomic advice in New Zealand.  He also quantified the leaching of cation & anions from pastoral systems and this has been included in the Overseer nutrient model. He now consults to farmers and fertiliser companies. Contact Dr. Gordon Rajendram – The Soil Scientist: Email: rajendram@xtra.co.nz Phone: 021 466 077 Facebook: https://www.facebook.com/GordonRajendramSoilScientist Website: http://dev.gordonrajendramsoilscientist.co.nz LinkedIn: https://www.linkedin.com/company/the-soil-scientist Instagram: https://www.instagram.com/thesoilscientistnz/ Contact MediaPA: Phone: 0274 587 724 Email: phillip@mediapa.co.nz Website: www.mediapa.co.nz Facebook: www.facebook.com/MediaPA YouTube: www.youtube.com/user/TheMediaPA