2017 ASHS Annual Conference

The understanding of crop potassium (K) accumulation and partitioning is essential to improve K use efficiency and reduce fertilizer cost. In tomato (Solanum lycopersicum L.) production, the largest K demand occurs during fruit development. Therefore, adequate K supply at that stage will be required to achieve optimum marketable yields. The objective of this study was to determine plant biomass, K uptake and use efficiency of drip-irrigated tomato with multiple K rates in a calcareous soil. The field experiment was conducted on a calcareous soil with 112 mg kg^-1 of Mehlich-3 extracted K (M3-K) during the winter season of 2014 in Homestead, FL. Potassium were applied at 0, 56, 93, 149, 186, and 223 kg ha^-1 of K and divided into pre-plant dry fertilizer and weekly drip fertigation. Plant samples were collected at 30, 60, and 95 days after transplanting (DAT) and the stem, leaf, root, and fruit were separated to measure dry-weight biomass, K concentration, and K uptake. Potassium use efficiency was calculated as apparent recovery efficiencies (ARE), partial factor productivity (PFP), and agronomic efficiency (AE). Total biomasses (stem, leaf, root, and fruit combined) and total K uptakes (TKU) were not significantly affected by K rates at 30 DAT. At 60 DAT, the TKU increased linearly with increasing K rates, but total biomasses were not significantly affected. Total biomass at 95 DAT increased quadratically with increasing K rate and reached a maximum at K rate of 187 kg ha^-1. The response of TKU at 95 DAT was predicted by linear-plateau model with critical rate of 192 kg ha^-1 and maximum TKU of 264 kg ha^-1. In the partitioning of total biomass and TKU at 95 DAT, the proportion of stem, leaf, root, and fruit ranged at 13-18%, 26-33%, 1.0-1.3%, and 51-60%, and 9-13%, 11-20%, 0.3-0.7%, and 66-80%, respectively. The ratio of fruit to TKU decreased with increasing K rates predicted by a linear-plateau model with critical rate of 187 kg ha^-1. The K rate of 56 kg ha^-1 resulted in a significantly higher ARE than other rates and the averaged ARE was 67% for K rates from 93 to 223 kg ha^-1. Increasing K rates from 56 to 223 kg ha^-1 quadratically reduced PFP and AE by 72% and 55%, respectively. Potassium rate of 192 kg ha^-1 was adequate to maximize TKU to 264 kg ha^-1 in calcareous soils with M3-K of 112 mg kg^-1 during tomato growing season.