Food production the world over relies on fertile soil, but the UN warns that a significant proportion of soils are facing exhaustion and depletion.
One place where the issue of soil fertility is coming to the fore is PNG, particularly in the Highlands Region.
ACIAR’s Research Program Manager for Soil and Land Management, Dr Robert Edis, explains that it is a critical issue.
‘So much of PNG’s non-oil and gas wealth comes from agriculture. The whole food web and the health of the soil is essential to people’s income security and the nation’s social stability. If soil fertility is allowed to decline, the potential problems for PNG could be enormous,’ says Dr Edis.
‘This is why soil fertility is an issue that is touched upon in many ACIAR projects. We recognise that soil health is an essential component of the country’s long term prosperity.’
While the population of PNG has tripled in the last three decades, the area used for agricultural production in the Highlands Region has remained relatively stable. Land use has intensified to keep up with demand for food and this is affecting the health of the soil.
Finding a way to sustainably intensify food production systems in PNG so that a rapidly growing population can be fed without degrading the soil is a challenge currently being tackled by ACIAR and researchers from the University of Queensland.
PNG’s main source of carbohydrates is sweetpotato. As demand for product has increased, the production system has changed. In the Highlands Region, block sizes are smaller and the fallow periods between crops have shortened dramatically. Combined with high rainfall that produces nutrient leaching, this leads to declining soil fertility.
A compounding issue is that as soil fertility declines so too does the quality of the sweetpotatoes harvested. Dr Edis says, ‘As the nutrients are taken from the soil over time, not only do yields go down but the nutritional profile of the product also declines, both in terms of protein content and micronutrients. Given that sweetpotato is a staple food crop, this is a potential threat to nutrition security at a bulk level.’
To improve the livelihoods of rural communities in the Highlands Region and protect the productive capacity of the land, developing a system of sustainable intensification of the sweetpotato cropping system is critical.
With low rates of farmer commercialisation— less than 20%—using synthetic fertiliser to replace soil nutrients isn’t a viable option in much of PNG. Instead, better land management techniques are required to improve crop yields and manage soil health.
These techniques include improved fallows— resting the land from cultivation—and planting species of leguminous trees and shrubs that rapidly replenish soil fertility. Another technique is to incorporate non-leguminous, nutrient accumulator plant species into the system.
Dr Edis says, ‘PNG is in a state of transformation as the population grows and traditional agricultural practices are abandoned to keep up with the demand for food. Protecting the country’s soil fertility through sustainable intensification of agriculture systems will be very important for long-term food security.’