Search

The El Niño/Southern Oscillation phenomenon strongly influences rainfall distribution around the world. Using phases of the Southern Oscillation Index (SOI) allows a probabilistic forecast of future rainfall that can be useful to managers of agricultural systems. Using wheat as an example, we show in this study how the SOI phase system, when combined with a cropping systems simulation capability, can be used operationally to Improve tactical crop management and hence increase farm profits and/or decrease production risks. We show the validity of the approach for two contrasting locations, namely Dalby in Northern Australian and Piracicaba in Brazil At Dalby, highest median yields were achieved following a rapidly rising SOI phase in April/May and lowest median yields following a consistently negative phase. Conversely, highest median yields at Piracicaba followed a near zero April/May phase and lowest median yields when the phase was consistently positive. We show how tactical management options can range from crop or cultivar choice to nitrogen management and marketing of the future wheat crop. O fenômeno El Niño/Oscilação Sul influencia marcadamente a distribuição de chuvas no mundo. O uso de fases de índice de Oscilação Sul (IOS) permite uma previsão probabilística da precipitação pluvial futura, que pode ser útil para o manejo de sistemas agrícolas. Usando-se trigo como exemplo, foi demonstrado nesse estudo, como o sistema de fases IOS, quando combinado com modelos de simulação de sistemas de cultivo, pode ser usado para melhorar o manejo tático de culturas e assim aumentar os lucros e/ou diminuir os riscos da produção agrícola. A validade desse método é mostrada para dois locais diferentes, Dalby, na Austrália e Piracicaba, no Brasil. Em Dalby, os maiores rendimentos médios foram obtidos após um aumento rápido na fase IOS em abril/maio e os menores rendimentos médios após uma fase negativa consistente. Em Piracicaba, os maiores rendimentos médios foram alcançados após uma fase próxima a zero em abril/maio e os menores rendimentos médios, quando a fase foi consistentemente positiva. É mostrado como as opções de manejo tático podem variar da escolha de cultivares ao manejo de nitrogênio e de mercado da cultura de trigo.

Keywords: tropical Savannah, biochar, soil fertility, aerobic rice, grain yield, N2O emission Márcia Thaís de Melo Carvalho (2015). The impact of wood biochar as a soil amendment in aerobic rice systems of the Brazilian Savannah. PhD thesis, Wageningen University, The Netherlands, with summaries in English, Dutch and Portuguese, 160 pp. Rice is a staple food for 3 billion people in the world. In Brazil, rice is a traditional staple food mostly cultivated by smallholder farmers. Rice is better adapted to soil types and climate conditions of the Brazilian tropical Savannah than crops like corn and soybean. However, environmental and socio-economic constraints such as the variable rainfall and the limited access to mineral fertilization is a challenge for sustainable aerobic rice production in Brazil. Yields can vary from 1 to 5 Mg ha-1. In this context, the use of agronomic techniques able to improve soil properties seems a good option to increase quantity and stability of rice production. The use of biochar as a soil amendment represents one such option. Biochar is carbonized biomass, generally a by-product of bioenergy production from biomass. Its use in agricultural soils is inspired by the very fertile Terra Preta soils, which are a result of pre-Columbian human activity in the Amazon region. A key component of the fertility of Terra Preta soils is the high content of C, mostly present in form of pyrogenic C, result of carbonization of organic material. Pyrogenic C is also an important fraction of the soil organic matter present in the weathered soils of the Brazilian Savannah. These soils are mostly acidic, with low soil organic matter content, requiring liming and mineral fertilization if used for agriculture. The biochar tested in the current research is a by-product of charcoal production from eucalyptus wood via slow pyrolysis at 400-500 ○C. It is a porous material with a high C content and K, Ca and Mg availability, which make it a potentially suitable soil amendment for the low fertile soils of the Brazilian Savannah. We applied biochar in a sandy and a clay soil type of the Brazilian Central West region, where over 40% of the Brazilian total crop production is located. We investigated whether biochar amendment improves soil chemical and physical properties and how this in turn affects aerobic rice yields along four cropping seasons after a single biochar application. In both soil types, biochar decreased soil acidity up to 3.5 years after its application. On the clay soil, biochar application decreased the soil water retention capacity but increased the soil organic matter content. The effect of biochar on rice yields on the clay soil were either absent, negative or dependent on the amount of mineral N applied, as well as biochar-induced changes in soil properties, particularly soil water retention and soil organic matter. Most promising results were observed on the sandy soil, where biochar application increased the soil water retention capacity. On the sandy soil, first two seasons were drier than latter two seasons. Accordingly, effects of biochar on rice yields were divergent: the positive effects observed in the first two seasons were absent in subsequent seasons. During this study, weather conditions and rice blast infestations were factors that influenced the observed effects of biochar on rice yields. Further, biochar did not enhance N2O emissions on the clay soil. Based on these results wood biochar could be considered for use in farming systems of the Brazilian Savannah, particularly on sandy soils.

Keywords: Aerobic rice, water productivity, pre-flowering phenology, eco-efficiency, perceptions, transformational technology, food security, resource constraints, Punjab, Pakistan. Just like in many other parts of the world, diminishing resources of water, labour and energy threaten the sustainability of conventional flooded rice systems in Pakistan. Changing the current production system to non-flooded aerobic rice could considerably increase resource-use efficiencies. However, for subtropical conditions, such as those in South Asia, the non-conventional system is still very much in the development phase. The main objective of this study was to evaluate the aerobic rice system of the Punjab in Pakistan from a biophysical and socio-technological perspective. I employed a combined approach of experimentation and farmer surveys to contribute important information on aerobic rice crop performance, pre-flowering photothermal responses, and farmers’ perspective. Two seasons of field experiments (2009 and 2010) at the research station of the University of Agriculture, Faisalabad–Pakistan tested local (KSK133, IR6, RSP1) and exotic (Apo, IR74371-54-1-1) genotypes against different combinations of irrigation levels (high, moderate, low) and nitrogen rates (0, 170, 220 kg N ha−1). Under aerobic conditions, the water productivity (WPg; g grain kg–1 total water input) improved significantly, showing a potential water saving of about 20%. However, this improved water productivity was at the cost of declining land productivity, as the actual production per unit area decreased. Grain yield and total aboveground N uptake were mainly limited by irrigation and not by N. The results suggest significant losses of applied N, and indicate that improvements in N use efficiency might be expected if N application is better synchronised with the N-demand of the crop. Accurate knowledge on rice phenological development is an important feature when the aim is to better match supply and demand for further improvement in resource use efficiencies. A controlled-environment growth chamber study, aimed at estimating pre-flowering photothermal responses, gave a robust set of photoperiod-parameters and demonstrated that all four tested genotypes (KSK133, RSP1, Apo, IR74371-54-1-1) were strongly photoperiod-sensitive. The temperature range in the field experiments was too narrow to achieve convergence to a unique set of optimal temperature response parameters. Yet, sensitivity analysis clearly showed that commonly used standard cardinal temperatures (base, optimum, maximum: 8, 30, 42°C, respectively) overestimated the time to flowering. Data obtained under a wider range of temperatures should result in more accurate estimation of temperature response parameters. To supplement the basic biophysical research, I conducted farmer surveys (n=215) in three major cropping systems viz. rice-wheat, mixed-cropping and cotton-wheat to understand farmers’ perspective about the future prospects of aerobic rice system. Most of the farmers were unaware of aerobic rice technology but expressed their keen interest in experimenting. Farmers perceived aerobic rice as a system to improve resource use efficiency particularly for labour and water but they consider it a knowledge intensive system requiring careful and timely management practices especially for weeds. The unavailability of suitable fine grain aerobic basmati varieties was identified as a major constraint for large scale adoption. Understanding farmers’ perspective helped to develop guidelinesfor the emerging aerobic rice system. The aerobic rice system is a rational approach for improving WPg and eco-efficiencies of water, labour and energy. Associated risks of crop failure can be reduced by filling the identified knowledge and technological gaps through additional research and adequate training of farmers.

In Australia, the best use of limited national water resources continues to be a major political and scientific issue. Average water allocations for rice-cereal irrigation farmers in the Riverina region have been drastically reduced since 1998 as a consequence of high rainfall variability and prolonged periods of drought, together with political changes. This has severely impacted regional crop production during the last decade, threatening the livelihoods of many farmers and is in stark contrast to much of this region’s 100 year agricultural history, where water resources were available to farmers in steady abundance. The water ‘landscape’ has changed - bringing with it considerable social, economic and environmental consequences and forcing a rethink of how valuable water resources are best used under such variable, changed and changing conditions. This thesis presents details of investigations into on-farm adaptation options for rice-cereal farmers, using field experimentation, participatory engagement, and farming systems modelling as the major tools of research. Additionally, a major component of this work has been the development and testing of new modelling tools and decision-support structures. Well-tested cropping systems models that capture interactions between soil water and nutrient dynamics, crop growth, climate and management can assist in the evaluation of new agricultural practices. At the beginning of this research project, all available models were lacking in at least some major element required for simulation of rice-based cropping systems. The capacity to simulate C and N dynamics during transitions between aerobic and anaerobic soil environments was added into the APSIM model, to facilitate our need to model farming system scenarios which involved flooded rice in rotation with other crops and pastures. Thorough testing against international datasets was subsequently conducted. Photosynthetic aquatic biomass (PAB – algae) is a significant source of organic carbon (C) in rice-based cropping systems. A portion of PAB is capable of fixing nitrogen (N), and is hence also a source of N for crops. To account for this phenomenon in long term simulation studies of rice-based cropping systems, the APSIM model was modified to include new descriptions of biological and chemical processes responsible for loss and gain of C and N in rice floodwater. Using this improved APSIM model as a tool, together with participatory involvement of Riverina case-study farmers, it was demonstrated that the best on-farm cropping and irrigation strategies in years of high water availability were substantially different to those when water supplies were low. The strategies leading to greatest farm returns vary on a season-by-season basis, depending primarily on the water availability level. Significant improvements in average farm profits are possible by modifying irrigation strategies on a season-by-season basis. The opportunities for Riverina farmers to exploit their irrigation water resources also extend beyond the farm gate. Currently there is considerable confusion amongst farmers on how to evaluate and compare on-farm and off-farm water options. Direct selling of water seasonally on the open market and even permanent sale of irrigation water entitlements are possibilities. In response to this confusion, a new conceptual framework was developed that enables quantitative comparisons between various options. The framework is based on a method regularly employed in the financial world for share portfolio analysis. Simulation modelling provided risk-return characteristics for on-farm options, and helped to elucidate circumstances under which off-farm options were viable. A modified version of alternate wet-and-dry water management for Australian rice-growing conditions (delayed continuous flooding, DCF) was investigated via a 2 year field experiment – aimed at reducing irrigation water requirement and increasing water productivity (WP). We demonstrated up to a 17% increase in WP, and field data was generated on system performance for a range of discrete irrigation strategies. The APSIM model was then parameterized, calibrated and validated before being used to extrapolate findings from the two year experimental period to a much broader climatic record (55 years), allowing detailed investigation of optimal management strategies and a more realistic estimation of likely long-term gains in water productivity, and associated risks, from this new rice irrigation practice. Best practice guidelines were developed, and the potential impact of a changing climate on both optimal practice and likely benefits was assessed. This thesis concludes by synthesising the approaches taken - addressing the question of whether improved rice irrigation practices, seasonally-flexible cropping and irrigation strategies and off-farm exploitation options, can in combination address the challenges of reduced irrigation water allocations in Australia’s Riverina region. Evidence is presented that the answer is yes under certain circumstances, but that limits to change exist beyond which the investigated on-farm adaptations are not enough. The thesis also proposes that the concepts and methods developed during this project are globally applicable and useful in the design of farming system adaptation options. Keywords: irrigation, limited water resources, farming systems modelling, participatory engagement.