On-farm soybean response to a field foliar applied humic biostimulant at differing cropping environments of Uruguay

Soybean (Glycine max (L.) Merr.) is an important crop in Uruguay with increasing production destined to exports that has been negatively affected by drought in the last years. Assessing the consistency of a biostimulant efficacy in field conditions involves multiyear replication across locations. The main objective of this study was to evaluate the effects of a single treatment with a humic biostimulant (HB) field foliar-applied at R3-R4 at dose of 4 L ha-1 on soybean crops grown during 8 yr (2014 to 2021) at 156 farm sites with different soil and water conditions on the main country cropping areas. The CONEAT index that measures soil quality and production capacity, and effective rainfall (eR) were assessed for each soybean farm site. The average grain yield varied from 8.83 (2018) to 19.93 g (2017) per untreated plants, and from 10.20 (2018) and 24.01 g (2017) per biostimulant-treated plants. The means for grain yield (g plant-1) by site were poorly related to the CONEAT and the eR indices. Similarly, the yield response to HB treatment ((%) was not related to the environmental indices which indicates a relatively constant and positive effect of the biostimulant independent of the environment, considering soil productivity and rainfall. Yield component analysis at the farm trials attributed the yield boosts by the humic largely to increased pod retention without affecting the grain weight. Overall, data analyses from all the farm trials across the years showed that the treatment significantly increased soybean yield by an average of 16.3% relative to the untreated plants. These results confirm that HB can be incorporated into the normal management plan for soybean production in Uruguay.