Uncovering the Interaction between Potassium, Magnesium and Sulfur on Cassava Growth and Root Yield

Abstract

wide range of yield limiting factors causes a large yield gap. Next to pests and diseases, nutrient deficiencies and imbalances are likely contributors to low yields. Cassava has a high potassium (K) demand, yet previous research shows that K application does not generally lead to increased yields. Potassium may have antagonistic effects on magne-sium (Mg) and cause relative deficiency of Mg. The objective of this study was to de-termine if interactions between K and Mg affect growth and root yield of cassava. A randomized complete block design with three replicates was used in a 18 × 2 factorial arrangement. Eighteen fertilizer treatments with 4 levels of K (0,90,180 and 270 kg ha-1), 3 levels of Mg (0,15.5 and 31 kg ha-1) were combined with exclusion of Mg treatments but addition of sulfur (S), to account for the S in the Mg source Kieserite, at 2 levels of S (20.5 and 41 kg ha-1), yet excluding Mg. The cassava varieties TME419 and TMS581 were used. Stem height, stem mass and total aboveground mass, storage root yield and starch content were evaluated. Stem height, fresh stem yield and fresh total above ground yield significantly increased with the application of K, K+Mg and K+S, compared with treatments not receiving K, emphasizing the importance of K and indicating that Mg is less important for shoot growth. Fresh and dry matter storage root yield did not respond to K application above 180 kg ha-1as KCl. The application of 270 kg ha-1 K with 41kg ha-1S attained the highest fresh and dry matter storage root yield, indicating that the lack of S had a stronger yield limiting effect than Mg availability. Starch content was highest (19.7%) with application of 0K:31Mg:41S (kg/ha) hig-hlighting the role of Mg and S in the synthesis and accumulation of starch in the roots. Thus, it appears that at high K application levels, K2SO4 is the better source of K espe-cially in S deficient soils.