Benefits of combining inorganic fertilisers with organic soil amendments

As the world's population continues to increase so too does the demand for food and the need for fertiliser to produce it, whilst the area of arable land is decreasing due to urban expansion and the impact of climate change. In response to this, the remaining productive land needs to produce more food with fewer finite inputs such as mined phosphorus (P). This project tests the hypothesis that conventional synthetic and organic fertilisers could be used together to maintain or increase yield, whilst reducing demands on conventional, mined, synthetic P supplies. This was done using a glasshouse experiment growing barley (Hordeum vulgare); and a field trial using baby corn (Zea mays L.). Both experiments were comprised of treatments of singular additions or combinations of compost and synthetic fertiliser. Leaf dry matter yield (DMY) increased significantly at rate of 0.05g DMY (± 0.012g) per application equivalent to an additional 1 kg P/ha, with the remainder of the 20kg P/ha application as mono-ammonium phosphate (MAP). A significant increase in leaf P of 15.2 mg P/kg leaf (± 6.7) with an increase in compost equivalent to one additional kilogram of P per hectare, with the remainder of the 20kg P/ha application as MAP, was also found. In the field trial, however, yield was smaller in the treatments which had a partial substitution of synthetic fertiliser with compost, based on current local rates, because application of compost was not sufficient to meet nutritional requirements of the plant. A residual effect was seen in the glasshouse experiment and suggests that benefits for future crops could exist following the application of compost to a paddock. Therefore, it has been shown that the use of composts, together with synthetic fertilisers, make it possible to reduce the quantities of synthetic fertilisers required and prolong the availability of mined resourcessuch as P without compromising yield. The potential for increasing yield is also present.