Humic acid (HA) is a relatively stable product of organic matter decomposition and thus accumulates in environmental systems. Humic acid might benefit plant growth by chelating unavailable nutrients and buffering pH. We examined the effect of HA on growth and micronutrient uptake in wheat (Triticum aestivum L.) grown hydroponically. Four root-zone treatments were compared: (i) 25 micromoles synthetic chelate N-(4-hydroxyethyl)ethylenediaminetriacetic acid (C10H18N2O7) (HEDTA at 0.25 mM C); (ii) 25 micromoles synthetic chelate with 4-morpholineethanesulfonic acid (C6H13N4S) (MES at 5 mM C) pH buffer; (iii) HA at 1 mM C without synthetic chelate or buffer; and (iv) no synthetic chelate or buffer. Ample inorganic Fe (35 micromoles Fe3+) was supplied in all treatments. There was no statistically significant difference in total biomass or seed yield among treatments, but HA was effective at ameliorating the leaf interveinal chlorosis that occurred during early growth of the nonchelated treatment. Leaf-tissue Cu and Zn concentrations were lower in the HEDTA treatment relative to no chelate (NC), indicating HEDTA strongly complexed these nutrients, thus reducing their free ion activities and hence, bioavailability. Humic acid did not complex Zn as strongly and chemical equilibrium modeling supported these results. Titration tests indicated that HA was not an effective pH buffer at 1 mM C, and higher levels resulted in HA-Ca and HA-Mg flocculation in the nutrient solution.

Grasslands in warm‐climate regions are often based on grass monocultures, increasing their dependence on N fertilizers. Integrating perennial legumes into grass pastures is a logical option. The objective of this 2‐yr study was to assess seven rhizoma peanut (Arachis glabrata Benth) cultivars: Arbrook, Arblick, Ecoturf, Florigraze, Latitude 34, UF Peace, and UF Tito. Above‐ and belowground responses included biomass, in vitro organic matter disappearance (IVOMD), N concentration, N content, δ15N, proportion of N derived from atmosphere (%Ndfa), and biological N2 fixation (BNF). Arbrook was more productive than Florigraze in both years (P ≤ 0.05) but produced similar biomass to other varieties in 2014. In 2015, Arbrook also was more productive than Arblick and Latitude 34. Herbage N concentration ranged from 19.2 to 36.3 g kg−1. Arbrook tended to be less digestible than other rhizoma peanut cultivars. The BNF represented >80% of herbage N and averaged 200 kg N ha−1 yr−1, with values ranging from 123 to 280 kg N ha−1 yr−1. Root and rhizome biomass varied among cultivars, with Ecoturf (26.9 Mg organic matter [OM] ha−1) and Latitude 34 (27.8 Mg OM ha−1) presenting greater root and rhizome mass than Florigraze (10.5 Mg OM ha−1) but similar to other varieties. Roots and rhizomes represented a significant portion of the total biomass and N pool, and further studies are needed to assess turnover of these tissues as well as their N contribution in grazing systems using grass–rhizoma peanut mixtures.

Novel approaches are needed for overcoming barriers to successful association of herbaceous legumes with grasses in warm‐climate pastures and to identify low‐cost, long‐term solutions to the problem of N limitation in low‐input systems. The objective of this experiment was to evaluate defoliation management options during the year of establishment when rhizoma peanut (RP) (Arachis glabrata Benth.) was strip planted into existing bahiagrass (Paspalum notatum Flüggé). Treatments were four defoliation strategies: (i) Control (no defoliation of the planted RP strip and adjacent bahiagrass harvested for hay), (ii) Hay Production (RP strip and adjacent bahiagrass harvested for hay every 28 d), (iii) Simulated Continuous Stocking (pastures grazed weekly), and (iv) Rotational Stocking (pastures grazed every 28 d). Simulated Continuous and Rotational Stocking reduced RP canopy cover and frequency of occurrence. Greatest RP cover during the establishment year was achieved in August with 32 and 29% for the Control and Hay Production treatments compared to 5 and 4% for Simulated Continuous and Rotational Stocking, respectively. Spread of RP was least in Simulated Continuous Stocking. Light penetration to the level of RP in the canopy was not a primary driver of RP response because it was greatest for grazed plots where RP performed poorest. Results show that defoliation management during the establishment year is critical and if pastures are defoliated, hay production is the recommended option.

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