RESEARCH
True cost of soil-borne disease By Tony Benny
Research conducted by AgResearch, shows soil-borne pathogens cause extensive losses to agricultural production.
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oil-borne plant pathogens could be costing some dairy farmers more than 200 kilograms of milksolids per hectare a year in lost production, a potential loss of $909 per hectare, according to a recently published paper by AgResearch. A research team from Ruakura research centre took samples from 30 dairy farm sites in Waikato, Canterbury and Southland and compared the growth of clover, ryegrass and plantain sown on untreated soils and samples that had been microwave pasteurised. The paper states that “Before sampling, no obvious root disease had been reported on any of the farm sites selected”. But the scientists found a variety of soil-borne fungal and oomycete pathogens and plant parasitic nematodes that were affecting pasture growth, particularly of clover and ryegrass. “Soil-borne plant pathogens cause extensive losses to agricultural production globally. These pathogens cause diseases such as root rots, damping-off and wilts that have a
A sample showing a healthy, unaffected clover plant against one being affected by pathogens in the soil.
DAIRY FARMER
March 2022
direct cost to plant growth and survival, and reduce the efficiency of water and nutrient uptake,” the paper states. Each sample taken was split in half. One half was pasteurised and the other half left untreated, and then seed was sown on all samples under laboratory conditions. “Ten seeds were sown onto the surface of each pot (one plant species per pot) and covered with 5g of the respective soil. Pots were adjusted to and maintained at 75% of the soil’s MWHC (maximum water holding capacity) by watering to weight with ‘Thrive AllPurpose Soluble Plant Food’ fertiliser every three days, to ensure that nutrient was not limited for plant growth,” it says. Aboveground plant material was harvested at six weeks and dry matter (DM) yields per plant recorded. White clover yields increased significantly on pasteurised soils (i.e those where pathogens had been eliminated) on six samples from Waikato and one from Southland and a similar effect was found for ryegrass on soils from Waikato, Southland and Canterbury. “The statistically significant increases in DM yield with soil pasteurisation ranged between 26% and 74% for white clover and 8% and 38% for ryegrass at individual farm sites,” the scientists found, it says. The results were less clear for plantain. The effects of soil-borne pathogens were greatest in Waikato overall, but samples from some individual sites in Southland did show white clover production increased by 52% following pasteurisation and on one site in Canterbury by 22% for ryegrass. The economic cost of soil-borne root pathogens to white clover production was determined to range from $700/ ha/year in Canterbury and Southland to $1500/ha/year in Waikato. On individual
Soil-borne pathogens greatly affect growth in clovers. Researchers found white clover yields increased significantly on pasteurised soil where pathogens had been removed.
farm sites, clover root diseases were found to reduce potential pasture DM production by more than 60%. “Collectively, our findings suggest that soil-borne disease constraints impose substantial costs on pasture production in New Zealand dairy systems. These are most prevalent in the Waikato region, although still present and potentially damaging at individual sites in Canterbury and Southland.” The scientists say given the scale of these costs, targeted management of soil-borne disease could present an economically viable approach to improving the resilience of the multiplant, multi-pathogen ecosystems. n
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