Fert co-op scoffs at humic substances

It says spending money on commercial preparations of humates for agricultural soil and plant health is like investing in the latest anti-wrinkle cream: the results probably won’t live up to expectations.

Independent research commissioned by Ballance Agri-Nutrients, which looked at the response of ryegrass to humic and fulvic acids, has discovered this, the co-op says.

Science manager Aaron Stafford says the most recent work has confirmed the co-operative’s position that applying humic substances, with or without nitrogen fertiliser, does no good in NZ soils.

“No doubt humates play an important role in soil moisture storage and nutrient retention and a lot of overseas work suggests adding more organic matter to soils might make a useful difference. 

“However NZ has soils rich in organic matter because of our largely pastoral agriculture systems and our climate. The relative lack of cultivation means organic matter decomposes relatively slowly, so it accumulates in the soil.  

“To a depth of 10cm a typical NZ pastoral soil can easily contain 5-10% organic matter.  That’s equivalent to approximately 50-100 t/ha organic matter , of which 75% is in the form of humus.  With such high organic matter content, there is already a lot of humic and fulvic acid released into the soil each year through organic matter turnover.  Because of this, Ballance has always held the view that humates and humic and fulvic acids are unlikely to provide much benefit to New Zealand farmers.

The Ballance research supports this thinking, says the co-op. This trial work involved perennial ryegrass and was done in pot trials so that the outcome was not influenced by other variables.

The soil used had an organic matter content of 8.5%, typical of a New Zealand agricultural soil. The pots were placed in simulated summer growing conditions. 

The soil surface was sprayed with liquid urea at two rates, 20kg N/ha and 40kg N/ha, with and without humic and fulvic acids at different concentrations. The effect of the treatments was determined by measuring the shoot dry weight of the ryegrass over several cuts.

“As you’d expect, the ryegrass responded well to the nitrogen application, but there was no significant additional response to the humic or fulvic acid, regardless of the rate of application.”

 Stafford says Ballance is all for supporting moves to improve soil and plant health and agricultural productivity. “But it is important that farmers know the dollar that goes in will come back in the returns they expect.”