Need to revisit potassium soil test methods: ammonium acetate method does not correlate with tuber yield and potassium uptake in potato

• Published in: Journal of plant nutrition Vol. 47; no. 3; pp. 392 - 412
• Main Authors: Pandher, Lovedeep Kaur, Sekhon, Bharpoor Singh
• Format: Journal Article
• Language: English
• Published: Philadelphia Taylor & Francis 07-02-2024; Taylor & Francis Ltd
• Subjects: Acetic acid; Ammonium; Ammonium acetate; Bicarbonates; Correlation; Diethylenetriamine pentaacetic acid; Extractants; Fertilizers; illitic soils; multi-nutrient extractants; Nitric acid; Potassium; Potassium oxides; potato; Potatoes; segmented models; Soil surfaces; soil test K; Soil testing; Soils
• ISSN: 0190-4167; 1532-4087
• DOI: 10.1080/01904167.2023.2277393

The study was driven by concerns regarding lack of response to K applied as per existing soil test based fertilizer recommendations in case of the potato crop in northwest India. Geo-tagged surface soil (0-15 cm) samples 180 were collected from three (60 each) different fields (named A, B and C) followed by pot experiment involving potato planted to 30 different surface (0-15 cm) soils using two K levels (0 and 60 kg K
2
O ha
−1
). Cate-Nelson (CN) model, and non-linear segmented linear-plateau (LP) and quadratic-plateau (QP) models were used to compute critical K levels by relating relative yield with soil test K using five different methods: 1 M ammonium acetate (AA K), ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA), Mehlich-3, sodium tetraphenylboron (STPB) and 1 M boiling nitric acid. These were validated by conducting fertilizer response trials (six K fertilizer levels- 0, 15, 30, 45, 60 and 90 kg K
2
O ha
−1
) at four sites. AA K correlated with other soil K extractants in the order: AB-DTPA (r = 0.93**, 0.27* and 0.67**)> STPB K (r = 0.71**, 0.27* and 0.39**) whereas AA K generally did not show any correlation with HNO
3
K. AAK method was poorly correlated with yield and plant K uptake (r = 0.15, 0.24, respectively) in comparison to AB-DTPA (r = 0.75**, 0.64**), Mehlich-3 (r = 0.78**, 0.72**), STPB (0.58**, 0.76**) and nitric acid method (0.55**, 0.44*). Thus, multi-nutrient extractants like AB-DTPA and Mehlich-3 are better (than AAK) indices of plant available K.