Potassium Management for Improving Processing Tomato Yield and Quality in Xinjiang

A field trial and demonstration was conducted each year in Xinjiang, China, during 2014 to 2016. The objectives of this project were to: 1) evaluate the effect of different ratios of potassium chloride (KCl) application in fall on yield and quality of processing tomato and chloride (Cl^-) residue in soil profile; 2) determine input/output balance of Cl^- in plant soil systems; and 3) determine the right source and time of potassium (K) application.

The treatments included in the study were: 1) 50% recommended K as KCl in the fall and the remaining 50% applied as potassium sulfate (K₂SO₄) at flowering; 2) 50% recommended K as KCl in the fall and the remaining 50% by K₂SO₄ at fruiting; 3) 70% recommended K as KCl in fall and the remaining 30% by K₂SO₄ at flowering; 4) 70% recommended K as KCl in fall and the remaining 30% by K₂SO₄ at fruiting; 5) 50% recommended K as KCl at flowering and the remaining 50% by KCl at fruiting; 6) farmer practice of applying 50% recommended K as K₂SO₄ at flowering and the remaining 50% by K₂SO₄ at fruiting. All of the treatments received the same amount of N-P₂O₅-K₂O (360-210-120 kg/ha).

Results from the three years of study indicated that KCl application did not negatively affect fruit yield and quality indices, such as fruit pH, soluble solids, color difference, total acid, and lycopene content of processing tomato compared with farmer practice of K₂SO₄ alone. The full recommended dose of K applied as KCl resulted in a higher soil Cl^- content than the farmer practice of using K₂SO₄, but did not cause excessive Cl^- accumulation or a significant increase in the soluble salt content in the soil. Basal application of 70% recommended K as KCl at fall plus a topdressing of the remaining 30% as K₂SO₄ at fruiting had a beneficial effect on fruit yield, produced good economic benefit with no negative effects on paste quality, and can be recommended as the best K management practice for processing tomato production in Xinjiang. In an arid region like Xinjiang, the soil Cl^- content should be monitored when applying KCl to these low Cl^- content soils (<50 mg Cl^-/kg), and caution must also be taken to avoid Cl^- toxicity to tomato plants when applying KCl in high Cl^--containing soils (>300 mg Cl^-/kg).