Influence of Soil Phosphate on Rhizobacterial Performance in Affecting Wheat Yield

As a primary nutrient in agricultural soils, phosphorus plays a crucial but growth-limiting role for plants due to its complex interactions with various soil elements. This often results in excessive phosphorus fertilizer application, posing concerns for the environment. Agri-research has therefore shifted focus to increase fertilizer-use efficiency and minimize environmental impact by leveraging plant growth-promoting rhizobacteria. This study aimed to evaluate the in-field incremental effect of inorganic phosphate concentration (up to 50 kg/ha/P) on the ability of two rhizobacterial isolates, Lysinibacillus sphaericus (T19), Paenibacillus alvei (T29), from the previous Breedt et al. (Ann Appl Biol 171:229-236, 2017) study on maize in enhancing the yield of commercially grown Duzi® cultivar wheat. Results obtained from three seasons of field trials revealed a significant relationship between soil phosphate concentration and the isolates' effectiveness in improving wheat yield. Rhizospheric samples collected at flowering during the third season, specifically to assess phosphatase enzyme activity at the different soil phosphate levels, demonstrated a significant decrease in soil phosphatase activity when the phosphorus rate reached 75% for both isolates. Furthermore, in vitro assessments of inorganic phosphate solubilization by both isolates at five increments of tricalcium phosphate-amended Pikovskaya media found that only isolate T19 was capable of solubilizing tricalcium at concentrations exceeding 3 mg/ml. The current study demonstrates the substantial influence of inorganic phosphate on the performance of individual rhizobacterial isolates, highlighting that this is an essential consideration when optimizing these isolates to increase wheat yield in commercial cultivation.

Plant-microbe-soil fertility interaction impacts performance of a Bacillus-containing bioproduct on bell pepper

Limited information is available on the performance of plant growth-promoting inoculants or bioproducts under different soil nutritional or fertility conditions. Consequently, the objective of this study was to evaluate the effects of a commercially available Bacillus-containing bioproduct, Microlife Abundance, at concentrations of 5.5 and 6.5 log cfu/ml on early growth, fertilizer use-efficiency, and fruit yield of bell pepper (Capsicum annuum L.) under two different soil fertility conditions (25% and 100% recommended N rates). Two pot experiments were conducted with bell pepper: (a) a 4-week-long early growth test with inoculant treatments applied once at transplanting; and (b) a 13-week-long yield test with inoculant treatments applied at transplanting and again at first blossom-set. Results from the early growth test indicated that at both N fertilization levels, applying Abundance once at transplanting at 6.5 log cfu/ml rather than 5.5 log cfu/ml significantly increased root dry weight, total root length, root volume, root surface area, and total length of very fine roots compared with the noninoculated control by 20%, 13%, 17%, 15%, and 12%, respectively. In contrast to the early growth, results from the yield test showed that only at the 100% recommended N rate, applying Abundance twice at both concentrations significantly enhanced N fertilizer use-efficiency and marketable yield of bell pepper over the noninoculated control by 34% (5.5 log cfu/ml) and 30% (6.5 log cfu/ml). Therefore, the efficacy of the Bacillus-containing bioproduct Abundance in enhancing fertilizer use-efficiency and marketable yield of bell pepper varied between soil nutritional conditions, but the early growth promotion effect of Abundance did not. Our results also demonstrate that selected microbial-based bioproducts, like Abundance, can be compatible with chemical fertilizers to enhance fertilizer use-efficiency and crop yields, but cannot be used as complete substitutes for chemical fertilizers.