J. Timsina

Crop residue management for nutrient cycling and improving soil productivity in rice-based cropping systems in the tropics

Publisher Summary Crop residues, usually considered a problem, when managed correctly can improve soil organic matter dynamics and nutrient cycling, thereby creating a rather favorable environment for plant growth. The intelligent management and utilization of crop residues is essential for the improvement of soil quality and crop productivity under rice-based cropping systems of the tropics. Viable option is to retain residue in the field; burning should be avoided. The major issue is adapting drills to sow into loose residues. Strategies include chopping and spreading of straw during or after combining or the use of disc-type trash drills. Residues rich in lignin and polyphenol contents experience the lowest decay. Decomposition of crop residues occurs at a rapid rate—about 80% of crop residue C is lost in the first year—under the warm and humid conditions of the tropics. Factors that control C decomposition also affect the N mineralization from the crop residues. Decomposition of poor-quality residues with low N contents, high C:N ratios, and high lignin and polyphenol contents generally results in microbial immobilization of soil and fertilizer N. Nutrient cycling in the soil–plant ecosystem is an essential component of sustainable productive agricultural enterprise. Although during the last three decades, fertilization practices have played a dominant role in the rice-based cropping systems, crop residues—the harvest remnants of the previous crop still play an essential role in the cycling of nutrients. Incorporation of crop residues alters the soil environment that in turn influences the microbial population and activity in the soil and subsequent nutrient transformations.

Productivity and Sustainability of the Rice–Wheat Cropping System in the Indo-Gangetic Plains of the Indian subcontinent: Problems, Opportunities, and Strategies

Abstract Rice and wheat are the staple foods for almost the entire Asian population and therefore they occupy a premium position among all food commodities. The era of the Green Revolution started during the early 1970s with wheat and rice and since then the rice–wheat cropping system of the Indo-Gangetic Plains has played a significant role in the food security of the region. However, recent years have witnessed a significant slowdown in the yield growth rate of this system and the sustainability of this important cropping system is at risk due to second-generation technology problems and mounting pressure on natural resources. Traditional cultivars and conventional agronomic practices are no longer able to even maintain the gains in productivity achieved during the past few decades. Demand for food is increasing with the increasing population and purchasing power of consumers. The rice–wheat cropping system is labor-, water-, and energy-intensive and it becomes less profitable as these resources become increasingly scarce and the problem is aggravated with deterioration of soil health, the emergence of new weeds, and emerging challenges of climate change. Therefore, a paradigm shift is required for enhancing the systems productivity and sustainability. Resource-conserving technologies involving zero- or minimum-tillage in wheat, dry direct seeding in rice, improved water- and nutrient-use efficiency, innovations in residue management to avoid straw burning, and crop diversification should assist in achieving sustainable productivity and allow farmers to reduce inputs, maximize yields, increase profitability, conserve the natural resource base, and reduce risk due to both environmental and economic factors. A number of technological innovation and diversification options have been suggested to overcome the systems sustainability problems but some of them have not been fully embraced by the farmers as these are expensive, knowledge-intensive, or do not fit into the system and have resulted in some other unforeseen problems. Different concerns and possible strategies needed to sustain the rice–wheat cropping system are discussed in this review on the basis of existing evidence and future challenges.

Water saving in rice-wheat systems

Abstract Water shortage is a major constraint to sustaining and increasing the productivity of rice-wheat systems. Saving water can be elusive in that reducing seepage, percolation and runoff losses from fields does not necessarily save water if it can be recaptured at some other temporal or spatial scale, for example by groundwater pumping. Many technologies appear to save substantial amounts of water through reducing irrigation water requirement, but whether these are true water savings is uncertain as components of the water balance have not been quantified. Such technologies include laser levelling, direct drilling, raised beds, non-ponded rice culture and irrigation scheduling. It is questionable whether puddling saves water. Reducing non-beneficial evaporation losses is a true water saving, and optimal planting time of rice to avoid the period of highest evaporative demand and changing to non-ponded rice culture can save significant amounts of water. However, moving away from puddled, ponded to more aerobic rice culture sometimes brings new production problems. Furthermore, farmers faced with unreliable water supplies need to store water on their fields as insurance, and puddling assists retention of water during the rice crop. Rehabilitation and improvement of canal and power systems in Asia, funded by charging according to use, are required to facilitate adoption of many water saving technologies. Australian farmers pay fixed plus volumetric charges for water to cover the cost of infrastructure and operation of irrigation systems, which are continuously being improved to provide water on demand and minimise losses. They are able to plan their plantings based on knowledge of the likely amount of irrigation water available each season and crop water use requirement, and thus avoid wasting water and financial loss by overplanting and crop failure. Such approaches have the potential to increase production and water productivity in Asia, however the challenge would be to apply them in an equitable way that benefits many millions of subsistence farmers.

Effect of nitrogen rates and weed control methods on weeds abundance and yield of direct-seeded rice

Field experiments were conducted at the Punjab Agricultural University, Ludhiana, India, during 2007–2008 to examine if nitrogen (N) rates and weed management practices using herbicides in combination with hand-weeding (HW) can improve crop competitiveness against weeds, and increase the yield, water productivity and profitability of direct-seeded rice (DSR). Increasing N application rate up to 150 kg ha−1 caused significant improvement in grain yield when the weeds were well controlled either by Pendimethalin + Bispyribac Na or by Pendimethalin + Bispyribac Na + 1 HW, respectively; however, under poor weed control condition (Pendimethalin + 1 HW), it resulted in a drastic reduction in yield. The highest net returns (

Effect of raised beds, irrigation and nitrogen management on growth, water use and yield of rice in south-eastern Australia

1083) and water productivity (0.60 kg m−3) were observed for N application of 150 kg ha−1 and weeds were controlled with Pendimethain + Bispyribac Na + 1 HW. We suggest that Pendimethalin + Bispyribac Na + 1 HW is the best integrated weed management strategy to control weeds, and to increase yield, water productivity, and profitability. We propose that the simulation modelling tool be utilized in future for evaluating options for improving sustainable N and weed management policies especially when crop, weeds, soil, weather and management data are available for calibration and validation of appropriate and existing simulation model of rice.

AGRONOMIC AND ECONOMIC EVALUATION OF PERMANENT RAISED BEDS, NO TILLAGE AND STRAW MULCHING FOR AN IRRIGATED MAIZE-WHEAT SYSTEM IN NORTHWEST INDIA

To remain economically and environmentally sustainable, Australian rice growers need to be able to readily respond to market opportunities and increase cropping system productivity and water productivity. Water availability is decreasing whereas its price is increasing. Alternative irrigation layouts and water management approaches could contribute to reduced water use and increased irrigation efficiency. This paper reports results for the first crop (rice) in a cropping system experiment to compare permanent raised bed and conventional layouts on a transitional red-brown earth at Coleambally, New South Wales. The performance of conventional ponded rice grown on a flat layout was compared with rice grown on 1.84-m wide, raised beds with furrow and subsurface drip irrigation. In addition, deep and shallow ponded water depth treatments (15 and 5 cm water depth over the beds) were imposed on the rice on beds during the reproductive period. A range of nitrogen (N) fertiliser rates (0–180 kg N/ha) was applied to all treatments. The traditional flat flooded treatment (Flat) achieved the highest grain yield of 12.7 t/ha, followed by the deep (Bed 15) and shallow (Bed 5) ponded beds (10.2 and 10.1 t/ha, respectively). The furrow (Furrow) irrigated bed treatment yielded 9.4 t/ha and the furrow/drip (Furr/Drip) treatment yielded the lowest grain yield (8.3 t/ha). Grain yield from all bed treatments was reduced owing to the wide furrows (0.8 m between edge rows on adjacent beds), which were not planted to rice. Rice crop water use was significantly different between the layout–irrigation treatments. The Flat, Bed 5 and Bed 15 treatments had similar input (irrigation + rainfall – surface drainage) water use (mean of 18.3 ML/ha). The water use for the Furrow treatment was 17.2 ML/ha and for the Furr/Drip treatment, 15.1 ML/ha. Input WP of the Flat treatment (0.68 t/ML) was higher than the raised bed treatments, which were all similar (mean 0.55 t/ML). This single season experiment shows that high yielding rice crops can be successfully grown on raised beds, but when beds are ponded after panicle initiation, there is no water saving compared with rice grown on a conventional flat layout. Preliminary recommendations for the growing of rice on raised beds are that the crop be grown as a flooded crop in a bankless channel layout. This assists with weed control and allows flooding for cold temperature protection, which is necessary with current varieties. Until we find effective herbicides and other methods of weed control and N application that do not require ponding, there is little scope for saving water while maintaining yield on suitable rice soil through the use of beds.

Performance and Water-use Efficiency of Rice Relative to Establishment Methods in Northwestern Indo-Gangetic Plains

SUMMARY No-tillage and raised beds are widely used for different crops in developed countries. A field experiment was conducted on an irrigated maize-wheat system to study the effect of field layout, tillage and straw mulch on crop performance, water use efficiency and economics for five years (2003–2008) in northwest India. Straw mulch reduced the maximum soil temperature at seed depth by about 3 ◦ Cc ompared to the no mulch. During the wheat emergence, raised beds recorded 1.3 ◦ C higher soil temperature compared to the flat treatments. Both maize and wheat yields were similar under different treatments during all the years. Maize and wheat planted on raised beds recorded about 7.8% and 22.7% higher water use efficiency than under flat layout, respectively. Straw mulch showed no effect on water use and water use efficiency in maize. The net returns from the maize-wheat system were more in no tillage and permanent raised beds than with conventional tillage. Bulk density and cumulative infiltration were more in no tillage compared with conventional tillage.

TILLAGE AND PLANTING METHODS EFFECTS ON YIELD, WATER USE EFFICIENCY AND PROFITABILITY OF SOYBEAN–WHEAT SYSTEM ON A LOAMY SAND SOIL

Gains or losses in grain yield and water-use efficiency of aerobic direct-seeded rice (Oryza sativa L.) must be considered before promoting this technology in areas where this is not common. In the northwestern Indo-Gangetic Plains (IGP) of South Asia, irrigation water for rice production is becoming scarce because of depleting surface and groundwater resources. The objective of this study was to compare the crop performance and water-use efficiency of 10 selected rice cultivars between aerobic direct-seeded rice (ADSR) and conventional puddled transplanted rice (CPTR) on a sandy loam soil in Punjab Agricultural University (PAU), Ludhiana, India. Grain yields were similar between ADSR and CPTR for cultivars PR-120, Punjab Mehak 1, Fang-ai-zan, and RH-664. Grain yields of the other cultivars decreased significantly in ADSR compared with CPTR. PAU-201, a medium-duration cultivar, had the highest grain yields in each crop establishment method, followed by PR-120. Water-use efficiency (WUE) values for Fang-ai-zan, RH-257 (hybrid), PAU-201, and PR-120 were significantly higher than the WUE of any other cultivar, and they also had high values for stress-tolerance index (STI). Averaged across cultivars, WUE was similar in ADSR and CPTR as yield reduction in ADSR overweighed the benefit of water saving. We recommend that for more economic water use in the northwestern part of IGP, growing cultivars such as Fang-ai-zan, RH-257, PR-120, and PAU-201 in ADSR because of their lower water requirement, yield maintenance, and relatively higher STI. Correlation coefficients between STIs revealed that STI, mean productivity (MP), and geometric mean productivity (GMP) were the best criteria for the selection of high-yielding cultivars under ADSR and CPTR.

Addressing sustainability of rice-wheat systems: analysis of long-term experimentation and simulation

Continuous rice–wheat (RW) cropping with intensive tillage has resulted in land degradation and inefficient use of water in Indo-Gangetic Plains (IGP) of South Asia. Replacement of rice with less water requiring crops such as soybean in RW system and identification of effective strategies for tillage management could result in sustainable cropping system in IGP. A field experiment was conducted for five years on an annual soybean–wheat (SW) rotation in the northwest IGP of India to evaluate effect of tillage, raised bed planting and straw mulch on yield, soil properties, water use efficiency (WUE) and profitability. In soybean, straw mulch reduced soil temperature at seeding depth by about 2.5 °C compared with no mulch. Straw mulch also resulted in slightly reduced water use and slightly higher WUE relative to their respective unmulched treatments. During wheat emergence, raised beds resulted in higher soil temperature by 1.6 °C compared with flat treatments. Bulk density and cumulative infiltration were greater in no-tillage compared with conventional tillage. Soil organic carbon in surface layer increased significantly after five years of experimentation. Soybean and wheat yields were similar under different treatments during all the years of experimentation. Soybean and wheat planted on raised beds recorded about 17% and 23% higher WUE, respectively, than in flat layout. The net returns from SW system were greater in no-tillage and permanent raised beds than with conventional tillage. Both no-tillage and permanent raised bed technologies can be adopted for sustainable crop production in SW rotation in northwest IGP. However, more studies are required representing different soil types and climate conditions for making recommendations for other regions of IGP.

Can Bangladesh produce enough cereals to meet future demand

The rice-wheat system dominant in the Indogangetic region of South Asia, is facing a number of complex problems, with severe implications on the sustainability of the system. Agronomic, soil, and historical weather data from a long-term experiment (LTE) at Pantnagar, India, were used for analysing yield trends, and in an attempt to explain sustainability related issues for the rice-wheat systems. Validated models (CERES-Rice and CERES-Wheat) were run in sequence using a Sequence Analysis Driver of DSSAT V3.0 for simulating long-term yields of rice and wheat for the LTE. Experimental data indicated that rice yields have declined, whereas wheat yields have increased during the same period. Long-term simulation indicated that, except for some outliers, the yield trends were similar to the trends obtained from the experiment. The Driver was then used in running the rice-wheat experiment for 20 years and 15 replications using generated weather data. The Sequential Analysis Program of DSSAT V3.0 was then used in analysing the trends of model outputs (yields, N, organic C) using percentiles and cumulative probability functions. Yield and soil fertility (total N, organic C) trends in context with sustainability of rice-wheat systems are explained using both long-term experimental and simulation results.