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Overcoming constraints that poorly structured lowland rice-growing soils of the Lower Mekong River Basin present for growing non-rice crops during the dry season would have a significant positive impact on the livelihood of smallholder farmers. This study investigated whether the use of soil organic amendments, bed architecture (conventional, flat and narrow) and water application methods (sprinkler, furrow and over-bed irrigation) could improve plant water availability in typical rice-growing soils of Cambodia and Laos by either improving the movement of water into beds or the growth of the root system. Five experiments were conducted over two dry seasons on peanut and maize grown in a bed/furrow system. Organic amendments assessed were rice straw, cow/goat manure, biochar, manure plus rice straw and biochar plus manure. Results showed that compared with conventional bed/furrow design, narrowing beds increased soil moisture availability for peanut, whilst higher grain yield and water productivity were achieved with sprinkler irrigation than furrow irrigation. Placing a layer of sub-surface straw within beds did not consistently enhance soil moisture or improve root development. The study showed that maize grown on soil amended with biochar plus cow manure under a furrow irrigation system and on rice straw under sprinkler irrigation produced yields above the average yield that models have simulated for maize grown on these soils. These findings present opportunities to enhance maize production on lowland soils across Cambodia and Laos. The contrary was observed for peanut production, which indicates that factors other than water might be detrimentally affecting crop yields.

Incorporation of dry-season crops in the lowland production systems of the Lower Mekong Basin (LMB) may provide local smallholder farmers the opportunity to increase household cash income through diversification. However, water availability and lowland rice-growing soil characteristics often limit the yield potential of dry-season crops in rotation with wet-season rice. This work studied the effects of three frequencies of irrigation on the crop performance of dry-season furrow-irrigated maize (Zea mays Linnaeus) and peanut (Arachis hypogaea Linnaeus) grown on lowland rice-growing soils in terms of biomass, yield and water productivity (WP). In addition, the response of maize to two fertiliser rates was evaluated. The study was carried out in sites with typical lowland rice-growing soils located in Cambodia and Laos. Soil matric potential (&Psi, m) was monitored during the season at the centre of the beds and percentage of canopy cover, aboveground biomass (AGB), yield and WP were determined. The results showed that within the first weeks of furrow irrigation (~two weeks after emergence), &Psi, m dropped considerably (&lt, &minus, 200 kPa) after all treatments at both sites, suggesting that water movement from the furrows to the centre of the beds was limited. Shorter frequency of irrigation led to significantly (p &lt, 0.05) higher AGB and yield in maize but not in peanut. Fertiliser rates did not have a significant effect on maize. WP ranged from 0.84 kg m&minus, 3 to 1.42 kg m&minus, 3 for maize and from 0.27 kg m&minus, 3 to 0.49 kg m&minus, 3 for peanut with no significant differences among treatments. This work provides evidence of a lateral water movement limitation that is not well documented for the establishment of furrow-irrigated dry-season crop production in the lowlands of the LMB. Further research on methodologies that could help to overcome this limitation in these soils, such as the application of soil amendments or implementation of alternative irrigation systems, would be of great value.

Agricultural soils are a major source of nitrous oxide (N2O) emissions and an understanding of factors regulating such emissions across contrasting soil types is critical for improved estimation through modelling and mitigation of N2O. In this study we investigated the role of soil texture and its interaction with plants in regulating the N2O fluxes in agricultural systems. A measurement system that combined weighing lysimeters with automated chambers was used to directly compare continuously measured surface N2O fluxes, leaching losses of water and nitrogen and evapotranspiration in three contrasting soils types of the Riverine Plain, NSW, Australia. The soils comprised a deep sand, a loam and a clay loam with and without the presence of wheat plants. All soils were under the same fertilizer management and irrigation was applied according to plant water requirements. In fallow soils, texture significantly affected N2O emissions in the order clay loam > loam > sand. However, when planted, the difference in N2O emissions among the three soils types became less pronounced. Nitrous oxide emissions were 6.2 and 2.4 times higher from fallow clay loam and loam cores, respectively, compared with cores planted with wheat. This is considered to be due to plant uptake of water and nitrogen which resulted in reduced amounts of soil water and available nitrogen, and therefore less favourable soil conditions for denitrification. The effect of plants on N2O emissions was not apparent in the coarse textured sandy soil probably because of aerobic soil conditions, likely caused by low water holding capacity and rapid drainage irrespective of plant presence resulting in reduced denitrification activity. More than 90% of N2O emissions were derived from denitrification in the fine-textured clay loam-determined for a two week period using K15NO3 fertilizer. The proportion of N2O that was not derived from K15NO3 was higher in the coarse-textured sand and loam, which may have been derived from soil N through nitrification or denitrification of mineralized N. Water filled pore space was a poorer predictor of N2O emissions compared with volumetric water content because of variable bulk density among soil types. The data may better inform the calibration of greenhouse gas prediction models as soil texture is one of the primary factors that explain spatial variation in N2O emissions by regulating soil oxygen. Defining the significance of N2O emissions between planted and fallow soils may enable improved yield scaled N2O emission assessment, water and nitrogen scheduling in the pre-watering phase during early crop establishment and within rotations of irrigated arable cropping systems.

Practical solutions to optimise nitrogen use efficiency within modern surface irrigated cotton systems in Australia may be possible by regulating the frequency of water and reducing the N applied, compared with typical current practises. A two-year study examined the effect of irrigating at three different water deficits that applied a similar total irrigation volume: >−60 kPa (HF), between −80 and −100 kPa (IF) and between −100 and −120 kPa (LF) for a period from initial flowering throughout boll development, in combination with different nitrogen fertiliser rates on the growth, yield, nitrogen use efficiency and lint quality of cotton. It was hypothesised that shorter deficits would increase N uptake, and nitrogen use efficiency compared with longer deficits caused by consistently higher soil water potentials in the root zone. The major effects of irrigation treatment on growth was to increase plant height and number of bolls, delay crop maturity and decrease micronaire. The irrigation strategy according to yield was most consistently optimised over both seasons when soil matric potential was maintained between −80 and −100 kPa (IF treatment). Lint yield was reduced by 9–13% when the irrigation deficit was

Irrigated agriculture may contribute as much as two-thirds to future global food demand because of the high intensity of production that it offers. However, it also has relatively high fertilizer and water inputs and therefore, N 2 O emissions. This study examined how varying the volume of individual irrigation events could mitigate N 2 O emissions from irrigated grain sorghum in Australia. To maintain productivity, the applied water amount was kept constant over an entire growing season. Treatments included irrigation water applications of 120 mm (3 applications), 90 mm (4 applications), 60 mm (6 applications) and 30 mm (12 applications). A custom-designed automated chamber-weighing lysimeter system was used to measure soil N 2 O fluxes, leaching losses and evapotranspiration simultaneously. The cumulative seasonal N 2 O emissions (kg N 2 O-N ha −1 season −1 ) were greatest in the 120 mm (1.71 ± 0.70) and 90 mm (1.81 ± 0.39) treatments and least in the 30 mm (0.88 ± 0.21) treatment. Irrigation management had a significant ( p ≤ 0.001) effect on reducing N 2 O emissions by avoiding the high magnitude N 2 O pulses that are measured following larger irrigation applications. The losses of water through leaching decreased from 41 ± 1% in the 120 mm treatment to 12 ± 4% in the 30 mm treatment while mineral-N losses decreased from 20% in the 120 mm to 3% in the 30 mm treatment. Plant N uptake in the 30 mm and the 60 mm treatments was significantly ( p ≤ 0.05) higher than for the 120 mm treatment. The increase in plant N-uptake and decrease in leaching losses of N in frequent irrigations of ≤90 mm compared with 120 mm irrigations suggests improvements in crop nitrogen use efficiency and potential for productivity gains.

The contamination of drainage channels and creeks with pesticides used in the production of rice is of concern in south eastern Australia. Of major concern is the molinate that at times has been detected in over 25% of water samples from surface drains and creeks. The objective of this study was to evaluate the rice pesticide model RICEWQ version 1.7.2 for its applicability in simulating the fate of the pesticide molinate in paddy rice floodwater in south eastern Australia. The model was successfully calibrated using water depths and molinate concentrations obtained from a rice bay. By using the calibrated model, the effects of the different application methods and the rates of molinate on water quality were investigated. The molinate, which was applied directly onto ponded water, led to higher maximum concentrations in the ponded water than for application onto a dry bay, which was subsequently filled. However, the concentrations in water declined more rapidly for the application onto a ponded bay than those for the application onto a dry bay. The simulation results suggest that water and chemical management has great effects on chemical concentration in the runoff water. Overall, the RICEWQ model accurately predicted the molinate concentrations in floodwater and this model can be used to develop best management practices in rice farming.