Soybean can improve soil fertility and crop yield

SOYBEAN is an important legume crop that is widely cultivated and consumed around the world.
It has been introduced into Papua New Guinea but its uses and benefits have not been well realised, for decades.
Recent studies by the National Agriculture Research Institute (Nari) have shown that soybean can be used to address declining soil fertility and crop yield challenges in the Highlands.
After an initial natural resource management survey in 2014, further work was done over the next two years with the support of the Australian Centre for International Agricultural Research.
These studies assessed the potential of using locally available practices and resources such as legume crop rotations, fallow systems and organic wastes to manage soil fertility as well as pests and diseases.
It has been shown that the use of soybean rotation has many useful agricultural and socio-economic benefits for the smallholder farming sector.
Soybean is a crop that can grow on any type of soil up to 1,600 meters above sea level where temperatures range from 20 to 30 degrees celsius.
However, due to climate change, it has been observed to perform well even at higher altitudes in recent times.
This possibility offers smallholder farmers another good organic option for managing soil fertility to ensure improved yields.
Soybean rotation was observed to provide higher levels of useful nutrients into the soil to increase crop yield.
As a legume, soybean traps nitrogen and phosphorus from the atmosphere and stores them in its roots.
When the roots decompose, these nutrients are slowly released into the soil for the next crop to use.
From the studies, it has been observed that sweet potato yields obtained from soybean rotation plots were around 23 tonnes per hectare (t/h).
On average, this is higher compared to 21 t/ha outputs from other options such as peanut and back-to back sweet potato rotations.
These results can be improved by integrating different crop rotation options with organic fertilisers such as chicken manure and coffee pulp.

Generally, the practice of crop rotations is useful as it also interrupts the life cycles of pests and minimises the outbreak and spread of diseases.
Soybean rotation is an effective option for that.
Soybean has a certain chemical property which is helpful for discouraging insect pests from entering crop fields.
Therefore, farmers can grow soybeans as crop barriers among other crops either within or on the edges of gardens.
Another advantage of soybean is that it can serve as another important source of protein among many rural communities in PNG, apart from peanut.
Its inclusion in daily diets has the potential to address malnutrition, especially protein deficiency (kwashiorkor) among rural children and women.
Soybean has a high content of protein (40 per cent), carbohydrates (28 per cent) and fat (20 per cent) among other useful nutrients.
Importantly, soybean is very cheap compared to other protein sources like meat and milk products.
It can be easily accessed at very little or no cost at all.
This is of vital importance when considered in relation to current issues of food security and the need to adapt to the effects of climate change.
For example, during prolonged droughts; stored soybean grains can be soaked in cold or warm water for a few hours before being cooked for meals.
Furthermore, the grains can also be processed into alternate products such as soybean milk, soybean flour and baked beans.
These can be important sources of extra food and income security for households.
The storage life of soybean grains can be enhanced by drying for 4-5 days to bring moisture contents below 11 per cent.
Apart from human feed, soybean also provides a valuable source of protein for use in animal feeds.
Fish, poultry, cattle and pigs can grow well from soybean meal feed regimes.
This has a lot of potential in PNG highlands.
It can serve as a good, easy to prepare option.
This can help farmers to diversify their heavy reliance on sweet potato; a soybean meal is a dish comprising of boiled tubers mixed with cooked soybean.
Daily feeding of about a kilogram of soybean grains can supply sufficient amounts of protein for higher growth and weight gains in livestock such as pigs.
Soybean farming usually requires two good seeds being sown in hole of about 2-3cm depth.
This helps the seeds to absorb enough moisture to germinate.
For good results, farmers have to select a site with soil that has good moisture content levels to encourage healthy growths and yields.
The recommended plant and row spacing is 30cm by 40cm, respectively.
Variably, farmers can also use a 30cm by 30cm spacing option.
Soybean matures in four months but will take a little longer in cooler conditions.
Harvesting is done when the leaves and pods turn greenish-yellow to brown.
Nari is still continuing to undertake studies about locally available options of legumes and other organic soil management practices.
We hope to establish results and new ideas from these efforts to help make farming more fun and productive in the smallholder sector, going forward.

• Yapo Jeffery is a junior scientist in soil and water management based at Nari’s Aiyura Research Centre, Eastern Highlands