- RB Cronje, IM Ratlapane, and PG Mostert
- 2021
- Volume: 24
- Pg 40-47
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In litchi, bearing branches for the new cropping season are produced after harvest and therefore are the basis for a productive tree. Fertilisation to support strong postharvest shoot growth is thus of high importance and does not only include adequate fertiliser amount but also, in particular, application time. Since limited information is available on the optimum application time to support strong litchi postharvest flushes in South Africa, trials were conducted in both early (Malalane) and mid-season (Nelspruit) production areas on ‘Mauritius’ litchi trees between 2014 and 2017 to determine the effect of various application times, specifically of nitrogen (N), before and after harvest. In the early area, N applications were applied as follows: a) single application at the start of harvest, b) single application after harvest, c) split application at the start of harvest and at hardening of the first postharvest flush to strengthen the second flush, d) no postharvest application (all N applied before flowering; control 1) and e) farm practice (control 2). Treatments for the mid-season area were the same except that the split application (c) was applied before and after harvest (3-4 weeks apart) as there is generally only one postharvest flush in this region. Four years of results showed that areas with two or more postharvest flushes benefit more from N fertilisers applied as a split application with 30% of the annual N at the start of harvest, 20% of the annual N after hardening of the first postharvest flush and the remaining 50% during flowering (30%) and at fruit set (20%). In areas with one postharvest flush, N fertilisers can be applied as a single application with 50% of the annual N at the start of harvest and the remaining 50% during flowering (30%) and at fruit set (20%) to support strong shoot growth.
Summary:
Research Objective: Evaluated optimal timing of postharvest nitrogen (N) fertilizer applications on ‘Mauritius’ litchi trees to promote strong bearing branch development, carbohydrate (starch) accumulation during dormancy, and support for the next season’s crop without stimulating excessive vegetative flush that could disrupt flowering.
Experimental Setup: Conducted on mature trees in a South African production area; treatments included N applications at different intervals post-harvest (e.g., immediately after harvest, delayed timings during autumn dormancy period); measured branch strength (diameter/girth), starch reserves in wood, flush control, and subsequent flowering/yield impacts.
Key Findings on Timing: Early postharvest N (within 2-4 weeks) enhanced vegetative growth and branch thickening but risked flush during critical dormancy; mid-autumn applications (e.g., 6-8 weeks post-harvest) balanced branch support with starch buildup; late applications (pre-induction) minimized flush while strengthening bearing wood.
Physiological Benefits: Strategic timing increased starch reserves in branches (up to 20-30% higher in optimal windows), improved structural integrity for heavy fruit loads, and correlated with higher panicle density and yield in the following season without compromising dormancy.
Practical Recommendations: Recommend split N applications starting 4-6 weeks post-harvest, guided by soil/leaf analysis, combined with ethephon for flush control; avoids over-fertilization risks like weak branches or poor flowering, optimizing resource use for sustainable production.