Plants influence soil nutrient dynamics and availability through rhizosphere enhanced decomposition of soil organic matter, symbiotic N₂ fixation, mobilization of nutrients by root exudates, and root uptake of plant nutrients.  Plant Root Simulator (PRS)™-probes are tools that integrate soil-microbe-rhizosphere interactions over time and aid in understanding soil nutrient bioavailability and uptake by plants. PRS™-probes were used to characterize the supply rates of anion and cation nutrients in a variety of soils as influenced by soybean (Glycine max L.) and sunflower (Helianthus annuus L.).  Rhizosphere effects (with and without plants) were studied in an organically farmed and an annual grassland Alfisol within a ¹³C-depleted, CO₂ controlled, growth chamber. 

Results/Conclusions

Fifty-seven days after planting, the PRS™-N supply rates were significantly reduced in the presence of plants due to increased plant N uptake in the organically farmed soil.  PRS™-probes were also used to monitor soil nutrient availability in relation to plant nutrient content.  Results showed that there was (1) a decrease in PRS™-N and K supply rates with increasing plant N and K update by plants (p<0.05); (2) an increase in PRS™-P, S, Fe, Cu, Mn, and Zn supply rates in the presence of plants (p<0.05); and (3) no effect of plants on nutrient supply rates of Ca, Mg, B, and Al (p>0.05) in the organically farmed soil.  These studies reveal that in the presence of plants, PRS™-probes adsorb nutrients that are present in the soil in excess of plant demand.  In the absence of plant roots, PRS™-probe nutrient supply rates reflect net mineralization of nutrients as affected by soil type and length of time the PRS™-probes are buried.  PRS™-probes measure soil nutrient dynamics resulting from soil-microbe-plant interactions.