Effects of Foliar-Applied Mixed Mineral Fertilizers and Organic Biostimulants on the Growth and Hybrid Seed Production of a Male-Sterile Inbred Maize Line

Plants of inbred maize lines are characterized by low vigor due to their high rates of homozygosity and may, therefore, benefit from additional nutrients and biostimulants supplied via foliar spraying. The present study innovatively investigated the effects of foliar treatment with three commercial organic-mineral fertilizers/biostimulants on a male-sterile inbred line of maize at the five-leaf stage. The three fertilizers were characterized by their following content: (i) NPK + hydrolyzed animal epithelium + micronutrients (named 'NPK + Hae + micro'), (ii) NK + humified peat (named 'NK + Hp'), and (iii) PK + Ascophyllum nodosum extracts (named 'PK + An'). The resulting shoot and root growth and seed yield and quality were compared to a control (C). Both NPK + Hae + micro and PK + An treatments enhanced root growth in the top 20 cm soil layer at the ten-leaf stage: root dry biomass increased by 80 and 24%, respectively, and the volumetric root length density by 61 and 17%. The two treatments also allowed for a larger number of commercial seeds to be produced (on average +16 bags per gross hectare vs. C) owing to a better seed caliber, which consequently reduced rates of seed disposal (-11 and -20% for PK + An and NPK + Hae + micro, respectively) and, in the case of NPK + Hae + micro, due to an increment in the number of kernels per ear (+5% vs. C). These effects were not associated with any significant changes in shoot growth, height, or leaf net CO2 assimilation. In this preliminary trial, peak commercial benefit was obtained with the use of hydrolyzed epithelium together with macro- and micronutrients. Further investigation into application timing and dose, and the means by which these products alleviate the effects of low vigor and stress conditions observed particularly under mechanical emasculation is, however, necessary for their full exploitation in the production of hybrid maize seeds.