Abstract
Nitrogen (N), phosphorus (P) and potassium (K) fertiliser application, was able to counteract growth reductions, in cassava cultivated on nutrient poor soils, under one water stress condition. It however remains to be seen, whether N, P and K fertiliser application, would produce similar results, across different water stress conditions. A study was therefore conducted to determine how N, P and K fertiliser application, would influence cassava growth on nutrient poor soils, under various water stress conditions. Effects on new leaf formation and leaf size were also investigated. The study was a 2×3×4 factorial pot experiment, in a randomised complete block design. It included: two cassava varieties, three water stress levels and four fertiliser treatments. The water stress levels kept some plants watered at field capacities of 30% (severe water stress), 60% (mild water stress) and 100% (zero water stress). The fertiliser treatments consisted of a control (no fertiliser), a sole K fertiliser treatment (25 mg K/kg), a moderate N, P and K fertiliser treatment (25 mg N + 5 mg P + 25 mg K/kg) and a high N, P and K fertiliser treatment (50 mg N + 13 mg P + 50 mg K/kg). All data were analysed using the analysis of variance. Cassava growth was assessed by monitoring changes in the dry shoot mass of cassava plants. High and moderate N, P and K fertiliser application, produced cassava plants with higher and similar dry shoot masses, under mild water stress (10.5 g/plant, SE = 0.6 and 9.0 g/plant, SE = 0.6, respectively). High N, P and K fertiliser application, however gave cassava the highest dry shoot mass, under severe water stress (7.9 g/plant, SE = 0.4). Relatively high cassava growth was consistently achieved with high N, P and K fertiliser application, across all water stress conditions.
Highlights
With climate change either reducing rainfall amounts or causing prolonged dry spells, in several parts of the world [1], the efficient use of the often limited available water, is becoming more and more critical, for lessening the negative impacts of low and erratic rainfall on crop growth and yields
The study was carried out as a pot experiment. It was conducted at Sokoine University of Agriculture (SUA) (S 65101300, E 373902600), in Morogoro district, in Tanzania
Since air-dry soil was used to fill the pots in the pot experiment, the amount of water needed to bring its oven-dry equivalent mass to 100% field capacity (FC), had to take into account the moisture already contained in the air-dry soil (18.67%–0.15% 1⁄4 18.52%) (Eq 1)
Summary
With climate change either reducing rainfall amounts or causing prolonged dry spells, in several parts of the world [1], the efficient use of the often limited available water, is becoming more and more critical, for lessening the negative impacts of low and erratic rainfall on crop growth and yields. Application of N, P and K fertilisers, was able to counteract reductions in the production of dry matter, in cassava cultivated on nutrient poor soils, under one water stress condition (level) [14]. Knowing how N, P and K fertiliser application, would affect cassava growth on nutrient poor soils, across different water stress conditions, is essential This knowledge would bring some understanding to how water stress affects the productivity of cassava, on soils with varied fertility. The hypothesis tested was that the application of N, P and K fertilisers, on nutrient poor soils, does not influence the dry shoot mass of cassava plants, under different water stress conditions. The second hypothesis tested was that the application of N, P and K fertilisers, on nutrient poor soils, does not influence new leaf formation and the leaf size of cassava plants, under different water stress conditions
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