Using Mexican sunflower as an organic fertiliser in PNG

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YAPO JEFFERY from Nari discusses using locally available plant species to making compost and produce organic fertilisers.
Mexican sunflower is one of the options used to make compost and produce organic fertiliser

DECLINING soil fertility from unsustainable cultivation practices is a serious concern in the highlands of PNG.
This has affected the quality of yield of staples such as sweet potato, in recent years.
The National Agriculture Research Institute (Nari) has responded to this challenge through a study about the potential of using locally available plant species to making composts and produce organic fertilisers.
The project is undertaken with the support of the Australian Centre for International Agricultural Research (ACIAR) at Aiyura in Eastern Highlands.
Mexican sunflower is one of the options to emerge from this project.
Mexican sunflower is a soft shrub which commonly grows along roadsides and farm boundaries in the highlands.
It can be grown from seeds and 20 to 40cm stem cuttings immediately planted in moist soil.
It is not a legume but has great potential in extracting and storing up soil nutrients in its stem, branches, leaves and flowers.
The leaves are particularly rich in nitrogen, phosphorus and potassium concentrations.
Nitrogen and potassium are especially essential for improving crop growths and yields.
The upper parts or top biomass are, therefore, ideal for preparing composts to make organic fertilisers.
The top biomass includes the branches, leaves and flowers but does not include the hard stem.

Top: Combined compost of Mexican sunflower, tephrosia and wild piper leaves added into sweet potato mounds.

Results from the study show that cultivated Mexican sunflowers can produce up to 88.4 kilograms of fresh top biomass per hectare.
On average, this amount of fresh top biomass can produce about 2.7 kilograms of nitrogen, 0.8 kilograms phosphorus, and 1.6 kilograms of potassium.
It is possible to realise this output every two to three months as the harvested parts can regenerate at a very fast rate.
The harvested upper parts of the plant can be used to manage soil fertility in three main ways.
Firstly, the leaves and soft stems can used as mulch material to help stop moisture in the soil from being evaporated during periods of dry weather.
Secondly, decomposed parts can serve as a form of organic fertiliser that can used to replenish levels of potassium and nitrogen contents in the soil.
Thirdly, the roots have an important role in fixing the level of phosphorus in the soil for crops to take up. Therefore, it is useful to grow Mexican sunflower on exhausted farm lands during fallow periods.
Apart from a bit of manual labour in producing and transportation, Mexican sunflower is a very cost-effective option for smallholder farmers to improve levels of soil fertility and crop yields.
In comparison, chemical fertilisers could cost farmers lots of money, time and distances covered in order to source them.
Therefore, as a locally available natural or purposely reared resource; the plant offers opportunities for farmers to achieve very good return in terms of the quality yields produced and the amount of income earned from sales.
There are also environmental advantages.

Top: Mexican sunflower growing in the wild along garden borders.

Their lack of competency in using commercial fertilisers often pose serious threat and damage to the health of natural ecosystems when using high concentrations.
As such, the use of Mexican sunflower derived organic fertiliser is a very sustainable and environmentally friendly option.
Very encouraging results have emerged so far from the on-going studies.
Particularly, the applications of Mexican sunflower composts have generated impressive outputs in trials.
For example, plots of sweet potato administered with sunflower compost have yielded around 26 tonnes of marketable tubers per hectare.
Apart from Mexican sunflower, other local options of organic fertiliser such as fish-poison bean, wild piper and coffee pulp are also being explored in the on-going project.
These are undertaken both at on-station and on-farm trials.
The former is undertaken at Nari’s research centre at Aiyura.
The latter is done as collaboration with target farming communities in Asaro valley, outside Goroka.
Findings arising from the current project can be used to enhance levels of productivity of smallholder farmers throughout the country.
It is, therefore, essential that concerned public and private sector agencies should support efforts to sustain such initiatives into the future.

  • Yapo Jeffery is a Junior Scientist in Soil and Water Management based at Nari’s Aiyura Research Centre in Eastern Highlands.

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