Thursday 31 May 2012

Soil carbon and soil water: perspectives from Down Under

A couple of useful technical pieces from the Australian Grains Research and Development Corporation.

What is soil organic carbon? “Although determining the total amount of organic carbon in soil is important, it does not tell us anything about the type of organic carbon present. For example, is the organic carbon dominated by pieces of plant residue or more recalcitrant charcoal?

“Understanding the partitioning of soil carbon within these different forms will help define the vulnerability of the carbon to subsequent change and the contribution that soil carbon may make to soil productivity. Therefore determining both the amount and the composition of soil organic carbon will be required to understand the implications of management practices on soil carbon stocks and vulnerability to change and on soil productivity.” 

And an interesting piece on soil water use monitoring and crop management. “Practices available to farmers to improve transpiration and transpiration efficiency include selection of drought-tolerant species, manipulation of crop morphology, reduction of weeds, pests and diseases and the use of cultural practices such as sequences of different crops, time of sowing, intercropping, use of fertilisers, fallowing, reduced tillage, stubble retention and water harvesting.

“Tools available for farmers to monitor water supply and use include direct soil sampling techniques and indirect water monitoring sensors. Direct sampling is typically prohibitively expensive but various low-cost sensors suffer from a technology divide. Simulation modelling is now a well established technology to assist in crop management decision making, but this too suffers from a technology divide.”

Thursday 24 May 2012

Secret soil cracks linger, despite surface sealing

Here's an interesting story which is highly relevant to parts of the UK at the moment, where a prolonged drought has been followed by intense, heavy rainfall in the past few weeks.   Are those heavy soils really suddenly waterlogged, or is it just surface water sitting on top of a compacted soil layer which is hiding drought-induced cracks further down? reports that deep cracks in soil can remain open underground even after they have visibly sealed on the surface, a new study has found. The results could have important implications for agricultural management around the timing and intensity of water and pesticide applications.

Cracks in the soil, which open up when the soil is particularly dry, provide "preferential pathways" allowing water to flow much faster than it would through non-cracked soil, rapidly transporting nutrients and pesticides beyond the crops' root-zone. If the plants can't access the water it has effectively been wasted.

Studying this preferential flow, the researchers have found that surface appearances can be deceiving. "We showed that soil cracks that developed in dry periods remain open as preferential flow paths, even after the cracks are visually closed," said lead author Dr Anna-Katrin Greve, a postdoctoral fellow with UNSW's Connected Waters Initiative. She found, however, that lower water application / irrigation intensity will give soil cracks time to close and more frequent irrigations could prevent the soil cracks from reforming.

Read more here.

Friday 11 May 2012

Improved roots will boost crops

An article in Science Alert reports that University of Western Australia researchers say that the "next frontier" of agricultural science is understanding the root system and function of crop plants to significantly increase grain production, keep farms viable and help continue to feed the world despite the onset of increasing drought and climate change. Scientists at the university have experimented with lupin roots to try to improve the water use and nutrient uptake of narrow-leaf lupin varieties that account for half of all grain legumes produced in Australia - an industry worth more than $600 million a year.

The study, published in the international journal Plant and Soil, warned that Australian grain producers faced increasing threats from poor local soils, harsh growing conditions and declining, less-predictable rainfall due to climate change. To help address this, a team led by UWA-based Chief Investigators Winthrop Professor Zed Rengel and Winthrop Professor Kadambot Siddique used new screening techniques and advanced computer modelling to understand lupin root systems variability.

Tuesday 8 May 2012

Fertilizer Tree Systems enrich soils naturally

The Worldwatch 'Nourishing the Planet' blog reports on a simple but ingenious means of tackling poor and degrading soil quality in Africa.  The article quotes a report, “Agricultural success from Africa: the case of fertilizer tree systems in southern Africa (Malawi, Tanzania, Mozambique, Zambia and Zimbabwe),” from the International Journal of Agricultural Sustainability, which states that simple “Fertilizer Tree Systems” (FTS) can double maize production in soil that is low in nitrogen.   A type of agroforestry, FTS incorporate nitrogen-fixing trees and shrubs into agricultural fields, usually inter-planted with food crops.  These trees take in atmospheric nitrogen and return it to the soil, where it serves as a nutrient for plants.

The article goes on to say that soil analyses by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and others in the 1980s revealed nitrogen to be a limiting factor in many African soils.   In response, on-farm studies in the 1990s showed that FTS with the right species could increase crop yields with or without mineral fertilizers.   FTS are much cheaper for farmers to implement than buying fertilizer inputs, and represent a more holistic approach to soil management.   FTS scaling-up programs were broadly implemented about ten years ago, and in that time the number of small-holder farmers using these techniques has ballooned from a few hundred to more than 250,000 in Malawi, Tanzania, Mozambique, Zambia, and Zimbabwe.

Read the full article here.