Evaluating maize cultivars that were bred under nutrient-limited biodynamic-organic conditions. II. Field trials with farmers

Mandaamin Institute (MI) hybrids, developed under biodynamic-organic conditions with limited nutrient availability, are colonized by seed-borne, endophytic bacteria. These hybrids were tested in multiple soils and farm systems. The best adapted MI hybrid (17.461) had similar grain yields to conventional hybrid FOS8500. FOS8500 responded positively to manure but 17.461 did not. 17.461 outyielded the conventional hybrid when manure was not applied. It produced slightly lower grain yields (8% in 2019) but higher stover and biomass yields/ha. In two years, 17.461 produced 9.3 and 22.5% more total protein/ha. 17.461 was more effective at obtaining and mobilizing macro-minerals into stover and micronutrients into grain. Its grain had 12% and 20% more macro-minerals, 28% and 98% more micro-minerals. In 2020, its grain had 11% more lysine, 21% more methionine, and 13% more cysteine. Tissue mineral, grain %N, and δ ¹⁵ N and δ ¹³ C levels, found between hybrids and soils, indicated that accumulation by plants of microbial biomass-N was enhanced on poorer, arable soils. δ ¹⁵ N correlated strongly and positively with increased N and minerals in both stover and grain and with more methionine and lysine in grain. 17.461 had higher δ ¹⁵ N isotope signature in stover and roots, suggesting uptake of N derived from microbial biomass. δ ¹⁵ N levels in grain varied with N limitation. Contributions from microbial partners to the total N in the plant were estimated at 27% in the 2019 trials on N rich soils and 61% in 2020 with less manuring. Maize with endophytes can reduce fertilizers and increase nutrient density and silage yield.