Effects of a microbial-based soil conditioner on nitrate leaching.

The biological activity in soil is important to ensure plant growth and prevent leaching. However, soils that have been exposed to inorganic minerals and acidic chemicals have a depleted microbiome. Replacing this using specialised probiotics can reverse these problems. In this trial, lysimeters to collect ground water leachate were set up to measure the effect of microbial-based soil and plant products (MagnifyNZ Ltd) on nitrate leaching on a dairy farm in Canterbury (2.5 cows/ha). MagnifyNZ fermentation products establish an effective soil microbiome, creating opportunity for high output-low input agriculture/horticulture. The soils were stony shallow silt loams (400 mm deep), classified as Ruapuna and Darnley (medium and high leaching). Fertiliser was applied monthly to provide 190 kg of N/ha/yr. Two treatments were used (soil conditioner and plant biostimulant) in September 2022, January and August 2023 using Magni-Life (2 l/ha) and Magni-Grow (7 l/ha), with and without stored urine, to mimic cow N contributions (600 kg N/ha). The untreated control was Ruapuna soil using the same applications. Lysimeters generated 3-4 drainage collections monthly. Non-urine soil leaching averaged 0.77 mg NO3-N/l for the MagnifyNZ samples compared to 3.98 mg NO3-N/l (P<0.0001) for the control. There was no significant difference in drainage volumes between treatments, which was 325 mm from 901 mm rainfall plus irrigation over 12 months. Urine patch N lasted 40 d in MagnifyNZ soil versus 215 d for the control. Total nitrate loss was 1.18 and 15.04 mg NO3-N/l for the MagnifyNZ treatment and control, respectively (P<0.0001). For the year starting September 2022, estimated total leaching was 3.1 kg N/ha for the treated soils versus 48.99 kg N/ha for the control, compared to 17.15 kg N/ha for the calculated dicyandiamide (DCD) response (Di and Cameron, 2007). There was a 91% reduction in total nitrate leaching from the MagnifyNZ treatment, due to a more stable microbiome which affected absorption of available N by pasture and soil microbes. Modelling the results for DCD (Di and Cameron, 2007) using 600 kg N/ha urine, DCD’s would have given 20-65% reduction in leaching.