11 10 Sources of potassium and nitrogen By Peter Anderson Northern Sales Agronomist, Haifa Australia HARVESTING and shipping fruit and vegetables results in mineral removal from the field. Potassium and nitrogen are exported with the crop and ideally should be replaced. Potassium nitrate supplies two x plant nutrients – the cation, potassium, as K+ and the anion, nitrogen, as NO3- (nitrate). Nitrogen Plants require nitrogen for synthesising amino acids and proteins, and N is a part of the chlorophyl molecule. Nitrogen is assimilated by plants in leaves and in roots. N can exist in different forms. The most common nitrogen fertilisers are Urea and salts of ammonia (NH4+) and nitrate (NO3-). Plants can absorb N as either NH4+ (ammonium) or NO3- (nitrate). While plants can absorb Urea directly, most N uptake derived from Urea is after it has been converted by soil bacteria into the NH4+ or NO3- form. Urea absorbed directly is not available for nutrition within the plant until it has been converted by urease into ammonium. While NH4+ is toxic to cells, it is quickly converted into amino acids and so neutralised in the roots and leaves by combination with sugars that have come from leaves as products of photosynthesis. Ammonium absorbed by roots is quickly metabolised to amino acids within the roots, using sugars that have been transported from leaves via phloem flow. These same sugars are required not only for ammonium metabolism, but also as fuel for respiration within the root cells. Nitrogen in leaves has been transported from roots in xylem flow as nitrates and it is converted to ammonium. This ammonium is quickly de-toxified by combination with nearby sugars to produce amino acids. These sugars are photosynthetic products abundant in leaf cells. Soil Urea in soil needs to be converted to NH4+ (ammonification) by an enzyme in the soil (urease) to be useful for plants. At this stage, N can be lost through volatilisation of ammonia (NH3) gas if there is no clay to bind it. Fertilising with urea and ammonium fertilisers, ie, sulphate of ammonia (SOA), is usually more efficient when soils contain high organic matter and clay, because these soil particles bind the NH4+, and some stays in the soil solution. In light soils, some N applied as Urea Potassium is very easily taken up by plant roots, but more slowly cycled between the sinks and the rate of mobilisation of K cannot match the rate of K uptake by plants, requiring application of K fertilisers. WHILE fertiliser prices have retreated significantly, global supply issues continue to pressure the market for horticulture customers. Haifa Australia Managing Director Trevor Dennis told the Lindsay Rural team at its recent Coffs Harbour conference in New South Wales that shipping costs were around half of what they were during their peak in 2021-22, while the cost of raw materials also had reduced. However, he said supply was the biggest immediate concern, with difficulty in shipping from Europe, while potassium could not be shipped in fertiliser products by Chinese exporters. “There is less than 20 per cent on the water of what there would be every other year,”Trevor said. LINDSAY Rural is on a strong growth curve and at its recent company conference it also recognised the role of its strategic supplier partners as part of the journey. A member of the Lindsay Australia group, the business has had a growth spurt of about 70 per cent since 2019 and recently added the WB Hunter chain of merchandise stores through Victoria and New South Wales to its stable. “We have been a strong services provider to the horticulture market and that will remain our core focus, and ensuring we resource the business accordingly with the suitable skillsets,” said General Manager Chris Kerton, who joined Lindsay Rural late last year. “We are a true independent with the firepower of a multi-national because of our wider business scale, and we want to keep that independence and provide great value to growers. “The breadth of our business means we can provide different areas with the right product offerings.’’ Chris said Lindsay Rural had consolidated and become more aligned with many of its strategic partners and it was looking to grow with more partners that placed a strong focus around innovation and sustainability. He said Haifa had been one of the company’s standout long-term partners. “This year Lindsay is celebrating 70 years for transport and 40 years for rural and Haifa has been a special part of that. It’s a big testament to the success of our longterm relationship together.’’ “Haifa provides high quality and fantastic support to our business, including with marketing and events. I have met the Haifa Australia team only recently in my short time with the business and I have been blown away by their support. Lindsay Rural General Manager Chris Kerton during a visit to a leading blueberry and raspberry growing operation near Coffs Harbour in New South Wales as part of its recent company conference. Haifa recognised in Lindsay Rural growth “There has also been very strong collaboration with Haifa in key product development and associated support for our customers. “We don’t have a transactional relationship with Haifa and that has been a very big aspect for us,’’ Chris said. Fertiliser prices dive, but supply concerns remain
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