Abstract
Cassava is often grown in low-fertility soils and has a reputation for having modest nutrient requirements. The storage roots that are harvested, however, contain relatively large amounts of potassium (K). We carried out a field experiment in Laos to determine the growth response to K fertiliser and to examine the field’s K balance over the cropping season. Four different rates of K (0-40-80-120 kg K2O equivalents ha−1) were applied to cassava variety Rayong11. Harvests were done at 8 and 10 months after planting, when the crop was at early and full maturity respectively, to assess if any benefits for productivity or K balance could be achieved by early harvest. We found a positive effect of K fertiliser (up to 39% yield increase compared to no K fertiliser at early harvest, 21% at late harvest) and a positive effect of late harvest (on average a 35% increase compared to early harvest) on cassava root yield. Low-K crops benefited more from a late harvest. At 10 months, the harvested cassava contained 99–142 kg K ha−1, indicating that there was a net removal of K from the fields, even at high K fertilisation levels. This experiment was carried out in comparatively fertile soil with relatively high background K levels, yet, yield benefits of K fertilisation were observed and soil K reserves were depleted by the harvest. It can be concluded that K fertilisation of cassava is advisable for better yields and to avoid progressive depletion of the soil K capital.
Highlights
Cassava (Manihot esculenta Crantz) is a rainfed crop grown in tropical and subtropical countries of Latin America, Africa and Asia [1,2,3]
Cassava tuber yield has been observed to decline after continuous cropping without adequate fertiliser inputs, which has been attributed to the exhaustion of soil K along with other nutrients [12,22]
Tuber exports of K were observed to be much higher than K supplied (Figure 3)
Summary
Cassava (Manihot esculenta Crantz) is a rainfed crop grown in tropical and subtropical countries of Latin America, Africa and Asia [1,2,3]. It is reputed to grow in soils with low fertility and is drought and acid tolerant [2,4,5]. As the world’s third most important crop, it acts as a staple food for at least 500 million people worldwide; its tuberous roots are a main source of calories [4,5,6,7,8]. In Asia, elimination of soil constraints, such as low fertility, could increase cassava yields by 35% [9]. Smith et al [11] reported that less than
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