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Abstract
Growers employ nutrient-sufficiency ranges (NSRs) after plant tissue analyses to ensure balanced nutrition, which is critical in soils of the Southeastern USA that are highly weathered with poor native fertility. A common NSR is the sufficiency range system by the Southern Cooperative Series Bulletin (SCSB), established from survey studies conducted across multiple locations, necessitating the need to test its validity in a controlled experiment. The timing of nutrient application is another important factor for row crops because of the potential to synchronize nutrient application with crop demand to ensure high yield and increase nutrient use efficiency (NUE). Nutrient availability for plant uptake is dependent on soil moisture, making the amount of soil water available, essential for crop growth and productivity. Thus, dry soils can reduce nutrient uptake due to the limited availability of water resulting from water stress. A controlled experiment was conducted across three years to validate the lower threshold of the NSRs for corn established by the SCSB. Varying nutritional levels were induced through different nutrient application rates. Validity depended on samples within the same replication having similar relative biomass if all its nutrient elements satisfied the NSRs. The results showed that the NSRs of the SCSB was not valid under the conditions tested. 47.6% of the samples satisfied the lower threshold of the NSRs, with 25.4% of those samples having relative biomass <50%. Another experiment investigated the benefits of secondary nutrient (SN) and micronutrient (MN) applications to the growth and development of corn. The results demonstrated that SN and MN were indeed limiting corn growth and that a yield of 12.5 Mg ha-1 can be achieved with lower PN rates than currently recommended. An experiment to evaluate the impact of Early-season nutrient stress (E-stress) revealed that corn could not recover from early-season nutrient stress due to the reduction in biomass, nutrient uptake, and yield by the E-stress treatment. A similar study on cotton revealed that cotton can recover from E-stress with a marginal yield reduction because cotton exhibits plasticity in its growth.