Agricultural systems models worldwide are increasingly being used to explore options and solutions for the food security, climate change adaptation and mitigation and carbon trading problem domains. APSIM (Agricultural Production Systems sIMulator) is one such model that continues to be applied and adapted to this challenging research agenda. From its inception twenty years ago, APSIM has evolved into a framework containing many of the key models required to explore changes in agricultural landscapes with capability ranging from simulation of gene expression through to multi-field farms and beyond.Keating et?al. (2003) described many of the fundamental attributes of APSIM in detail. Much has changed in the last decade, and the APSIM community has been exploring novel scientific domains and utilising software developments in social media, web and mobile applications to provide simulation tools adapted to new demands.This paper updates the earlier work by Keating et?al. (2003) and chronicles the changing external challenges and opportunities being placed on APSIM during the last decade. It also explores and discusses how APSIM has been evolving to a "next generation" framework with improved features and capabilities that allow its use in many diverse topics. APSIM is an agricultural modelling framework used extensively worldwide.It can simulate a wide range of agricultural systems.It begins its third decade evolving into an agro-ecosystem framework.

APSIM - Evolution towards a new generation of agricultural systems simulation

Soil fertility depletion in smallholder farms is the fundamental biophysical root cause for declining per-capita food production in Africa, and soil fertility replenishment should be considered as an investment in natural resource capital. An average of 660 kg N ha-1, 75kg P ha-1, and 450 kg K ha-1 has been lost during the last 30 years from about 200 million ha of cultivated land in 37 African countries. The consequences are felt at the farm, watershed, national, and global levels. There is an exact congruence between the concepts of capital stocks and service flows in economics and that of nutrient pools and fluxes in soil science. Phosphorus-replenishment strategies are mainly fertilizerbased with biological supplementation, while N replenishment strategies are mainly biological with chemical supplementation. Africa has ample phosphate rock deposits that could be used directly or as superphosphates to reverse P depletion. Decomposing organic inputs produce organic acids that help solubilize phosphate rocks. Agroforestry trees and herbaceous leguminous green manures play a major role in N capture and internal cycling. Accompanying technologies, such as soil conservation are needed to make recapitalization operational. Policy improvements are needed to provide the appropriate fertilizers at a reasonable cost and at the right time; better infrastructure; access to micro credit; timely access to markets; adaptive research and extension education. Soil fertility replenishment was found to be profitable at the farm level in three contrasting case studies, but resource poor farmers lack the capital and access to credit to make the initial investment. The issue of who should pay for this recapitalization is based on the principle that those who benefit from a course of action should incur the costs of its implementation. Progress to date on soil fertility initiatives throughout Africa will be summarized.

Soil Fertility Replenishment in Africa: An Investment in Natural Resource Capital

Strigolactones (SLs) were originally isolated from plant root exudates as germination stimulants for root parasitic plants of the family Orobanchaceae, including witchweeds (Striga spp.), broomrapes (Orobanche and Phelipanche spp.), and Alectra spp., and so were regarded as detrimental to the producing plants. Their role as indispensable chemical signals for root colonization by symbiotic arbuscular mycorrhizal fungi was subsequently unveiled, and SLs then became recognized as beneficial plant metabolites. In addition to these functions in the rhizosphere, it has been recently shown that SLs or their metabolites are a novel class of plant hormones that inhibit shoot branching. Furthermore, SLs are suggested to have other biological functions in rhizosphere communications and in plant growth and development.

The Strigolactone Story

Concern about potential increases in weed populations without the use of herbicides has limited the uptake of organic farming. However, as both public demands for organic produce and the profile of organic farming have increased in recent years, so too has the range of weed control options. Progress in cultural methods of weed control has included the use of novel weed-suppressing cover crops, and the identification of specific crop traits for weed suppression. Direct weed control has also seen developments, with new implements appearing on the market that could benefit in the future from sophisticated machine guidance and weed detection technology. Advances in novel techniques such as steaming have also been made. Many weed control operations in organic systems present the grower with conflicts, and both these and many of the most recent developments in organic weed control are reviewed. An increase in our understanding of weed biology and population dynamics underpins long-term improvements in sustainable weed control. The outcome of these studies will benefit conventional and organic growers alike. Emphasis is given to the need for flexibility and a combination of weed biology knowledge, cultural methods and direct weed control to maintain weed populations at manageable levels.

Non‐chemical weed management in organic farming systems

Species of Orobanche and Striga are among the most damaging parasitic weed species worldwide, but there are few reliable statistics on the full extent of the economic losses they cause. The distribution, host range and economic importance of the major species of Orobanche and Striga are briefly summarised. A review of literature over the period since 1991 suggests that many million hectares are infested and that the losses amount to $ US billions annually. Unfortunately there are almost no fully reliable figures on which to base these figures precisely. Meanwhile, there is little evidence of any significant change in intensity, range or losses caused over this period. Any reduction in the importance of these damaging weeds is sporadic, and alleviation of the problems is mostly localised. Furthermore, while the importance of Orobanche species may be broadly static, Striga species on cereals continue to become more serious in many countries owing to continued loss of soil fertility. It is suggested that new techniques may be needed for measurement of the extent of losses caused by these genera and their economic impact. There is continued urgency to develop control measures appropriate to the farming systems involved, and to reduce the risk of spread of both groups of parasite to new areas.

Observations on the current status of Orobanche and Striga problems worldwide

Biology and Management of Weedy Root Parasites

Ethnobotanical study of medicinal plants utilised by Hani ethnicity in Naban River Watershed National Nature Reserve, Yunnan, China

Population growth increases the demand for food and thus leads to expansion of cultivated land and intensification of agricultural production. There is a definite limit to both of these options for food security and their multiple negative effects on the environment undermine the aim for sustainability. Presently the impact of the Green Revolution on crop production is levelling off at high yields attained and even the potential of large scale irrigation programmes and transgenic crops seem to be limited in view of the expected increase in demand for food. Moreover, climate change threatens to affect agricultural production across the globe. Skyfarming represents a promising approach for food production that is largely environment independent and therefore immune to climate change. Optimal growing conditions, shielded from weather extremes and pests are aimed at raising plant production towards the physiological potential. Selecting rice as a pioneer crop for Skyfarming will not only provide a staple for a large part of the global population, but also significantly reduce the greenhouse gas emission caused by paddy cultivation. Multiplication of the benefits could be achieved by stacking production floors vertically. In Skyfarming the crop, with its requirements for optimal growth, development and production, determines the system’s design. Accordingly, the initial development must focus on the growing environment, lighting, temperature, humidity regulation and plant protection strategies as well as on the overall energy supply. For each of these areas potentially suitable technologies are presented and discussed.

Joachim Sauerborn

Papers

Biology and Management of Weedy Root Parasites

Ethnobotanical study of medicinal plants utilised by Hani ethnicity in Naban River Watershed National Nature Reserve, Yunnan, China

Skyfarming an ecological innovation to enhance global food security

Intercropping controls Striga in maize based farming systems

The role of biological control in managing parasitic weeds