Dryland Regions Research Articles

Conservation tillage increases soil bacterial diversity in the dryland of northern China

Agricultural practices change soil’s physical and chemical properties, therefore modifying soil microbial communities. Conservation tillage is widely used to improve the soil texture and nutrient status in the dryland regions of northern China. However, little is known about the influence of soil properties on microbes, in particular on the effect of conservation tillage on soil bacterial communities. Here, we studied the effect of a 5-year tillage treatment on soil properties and soil bacterial communities in the dryland regions of northern China using a high-throughput sequencing technology and quantitative PCR of 16S rRNA genes. We compared the changes in soil bacterial diversity, and composition was measured for conservation tillage, including zero plow or chisel plow, and for conventional tillage using plow. Our results show that conservation tillage increased the Simpson index by 378 % and exhibited significantly dissimilar polygenetic diversity, with r of 1, and taxonomic diversity, of r higher than 0.49, compared to conventional tillage. This finding demonstrates that conservation tillage modifies soil bacterial diversity. Chisel plow and zero tillage increase the abundance of the genus Bacillus, including 85 % of the phylum Firmicutes, and of Rhizobiales belonging to the Alphaproteobacteria. Overall conservation tillage increased the abundance of profitable functional bacteria species.

Afforestation and the impacts on soil and water conservation at decadal and regional scales in Northwest China

Massive afforestation has been conducted in dryland regions of Northwest China since 1978. With the impending effects of climate change, it is necessary to reconsider the effects of artificial vegetation on soil and water conservation at decadal and regional scales. Using long-term official and synthesized data, the vegetation's impacts on reducing water loss and their ecological water requirement were studied in four provinces (e.g., Inner Mongolia, Gansu, Qinghai, and Xinjiang). Results showed that vegetation of the four provinces was dominated by grass, while artificial forest had taken up 13% of the total forest area. At the plot scale, vegetation could reduce runoff and sediment by 44% and 83%, respectively. At the regional scale, soil erosion areas showed a decreasing trend, especially after the year 2000. In Inner Mongolia and Gansu, both runoff coefficients and water resource amounts showed decreasing trends. As such, future large-scale afforestation might be ecologically unsustainable in these two provinces. However, the runoff coefficients and water resource amounts of Qinghai and Xinjiang showed increases, mainly linked to climate change. This study helps elucidate the paradox of vegetation restoration in arid regions, and gives some suggestions for ecological restoration in other drylands of the world.

A potential role for overland dispersal in shaping aquatic invertebrate communities in arid regions

Summary Traditionally, dispersal of aquatic invertebrates has been thought to be very closely associated with river network structure, despite many species being capable of active or passive dispersal across the terrestrial matrix. However, recent studies of both population genetics and community structure from dryland regions indicate that aquatic species commonly disperse across catchments, implying that movement away from streams is more common than originally thought. This study investigated how aquatic invertebrate metacommunity structure in central Australia is influenced by interactions between species’ dispersal traits, dispersal routes and local environmental conditions. We sampled community composition in 16 perennial and long‐term inundated freshwater habitats in central Australia. Aquatic invertebrate taxa were allocated to one of four dispersal trait groups: obligate aquatic, passive aerial, weak flying and strong flying. We then used Mantel tests to examine correlations between trait group community dissimilarities, and four isolation models representing (i) local environmental conditions, (ii) geographical distances, (iii) landscape resistances restricted to river networks and (iv) landscape resistances incorporating overland dispersal ‘conduits’. We found that the community composition of aquatic invertebrates in three of four dispersal trait groups, and all traits combined, was influenced primarily by topographic connectivity via overland dispersal conduits. Our results suggest that rainfall events and their effect on the landscape as a whole, rather than river flow during these events, shape aquatic invertebrate metacommunity structure in central Australia. This study provides further support for the importance of overland dispersal conduits to aquatic invertebrates, particularly in arid environments with irregular rainfall.

Responses of soil fungi to 5-year conservation tillage treatments in the drylands of northern China

Soil fungi have many important ecological functions such as decomposition of soil organic matter and facilitation of nutrient turnover and availability in agricultural soils, which can be influenced by tillage treatments. Conservation tillage is widely used in the dryland regions of northern China. However, insights into the effect of conservation tillage on soil fungal community compositions and structures are considerably limited. This study aimed to investigate the effect of 5-year conservation tillage treatments, including chisel plow tillage (CPT), zero tillage (ZT), and plow tillage (PT) as convention tillage treatment, on soil fungal communities by using high-throughput sequencing technology and quantitative polymerase chain reaction. Conservation tillage significantly influenced soil fungal diversity and phylogenetic composition by altering soil organic carbon content and texture. The fungal diversity and composition structure were similar for treatments causing higher soil perturbation, i.e., CPT and PT; ZT, a less disruptive agriculture practice, preserved soil biological integrity. The most abundant phyla across all samples were Ascomycota and Basidiomycota, which are considered to be the main classical fungal decomposers in soils. These results suggested that conservation tillage can affect crop residue decomposition and the soil organic carbon content, leading to changes in soil fungal community distribution patterns. Our findings might form the basis for the application of conservation tillage to produce more stable and sustainable soil ecosystems in the drylands of northern China.

Cumulative drought and land‐use impacts on perennial vegetation across a North American dryland region

AbstractQuestionThe decline and loss of perennial vegetation in dryland ecosystems due to global change pressures can alter ecosystem properties and initiate land degradation processes. We tracked changes of perennial vegetation using remote sensing to address the question of how prolonged drought and land‐use intensification have affected perennial vegetation cover across a desert region in the early 21st century?LocationMojave Desert, southeastern California, southern Nevada, southwestern Utah and northwestern Arizona, USA.MethodsWe coupled the Moderate‐Resolution Imaging Spectroradiometer Enhanced Vegetation Index (MODIS‐EVI) with ground‐based measurements of perennial vegetation cover taken in about 2000 and about 2010. Using the difference between these years, we determined perennial vegetation changes in the early 21st century and related these shifts to climate, soil and landscape properties, and patterns of land use.ResultsWe found a good fit between MODIS‐EVI and perennial vegetation cover (2000: R2 = 0.83 and 2010: R2 = 0.74). The southwestern, far southeastern and central Mojave Desert had large declines in perennial vegetation cover in the early 21st century, while the northeastern and southeastern portions of the desert had increases. These changes were explained by 10‐yr precipitation anomalies, particularly in the cool season and during extreme dry or wet years. Areas heavily impacted by visitor use or wildfire lost perennial vegetation cover, and vegetation in protected areas increased to a greater degree than in unprotected areas.ConclusionsWe find that we can extrapolate previously documented declines of perennial plant cover to an entire desert, and demonstrate that prolonged water shortages coupled with land‐use intensification create identifiable patterns of vegetation change in dryland regions.

Plant Characteristics and Growth Parameters of Vegetable Pigeon Pea Cultivars

Pigeon pea (Cajanus cajan) is an important crop in dry land and semiarid regions and is a supplementary source of dietary protein for the economic resource-constrained farmers. The aim of this research was to evaluate growth parameters of 12 vegetable pigeon pea cultivars at two locations in eastern Kenya. The number of days from planting to flowering, plant height, primary and secondary branches, and pod length and width were quantified in experimental plots in a randomized complete block design with three replications. Significant differences (P < 0.01) in days to 50% and 70% flowering (DTF) and plant maturity (DTM), respectively, were recorded among cultivars at both locations. The average plant height was significantly (P < 0.05) greater at Kiboko than at Kambi ya Mawe. The number of DTF and DTM were also greater at Kiboko than at Kambi ya Mawe site, because of supplemental irrigation. Similarly, mean pod length and width at Kiboko location exceeded that at Kambi ya Mawe by 6% and 8%, respectively. Positive and significant (P < 0.05) correlation coefficients between grain yield and pods per plant were observed, indicating that pod number is a useful indicator of yield potential of vegetable pigeon pea. The cultivars ICEAP 00068, ICEAP 00540, ICEAP 00554, ICEAP 00902, KAT 60/8, and MZ 2/9 were identified for high-yield potential under rain-fed conditions, whereas ICEAP 00902, ICEAP 00068, ICEAP 00557, ICEAP 00554, KAT 60.8, and MTHAWAJUNI showed the greatest potential when supplemental water applications were made. The cultivars KAT 60/8, ICEAP 00068, ICEAP 00554, and ICEAP 00902 were suitable for production under both rain-fed conditions and additional water applications. Yield potential of pigeon pea in the dry regions can be greatly enhanced by using cultivars with good plant growth characteristics and shoot density.

Coping strategies for extreme weather in dryland agriculture

Dryland areas account for 48% of area under food crop and 52% under non-food crop cultivation and contribute about 42% of total food grain production in India. Drought is the predominant weather extreme influencing the socio-economic structure of not only dry land regions but also the entire country. Various drought monitoring techniques and mechanisms aim at mitigating the drought impacts at different spatial scales. They are discussed briefly here with strategies to cope up this weather anomaly at different time scales. Dry land districts that are prone to frequent hail episodes are identified and measures to minimize damage to agriculture are also discussed.

Revisiting trends in wetness and dryness in the presence of internal climate variability and water limitations over land

AbstractA theoretically expected consequence of the intensification of the hydrological cycle under global warming is that on average, wet regions get wetter and dry regions get drier (WWDD). Recent studies, however, have found significant discrepancies between the expected pattern of change and observed changes over land. We assess the WWDD theory in four climate models. We find that the reported discrepancy can be traced to two main issues: (1) unforced internal climate variability strongly affects local wetness and dryness trends and can obscure underlying agreement with WWDD, and (2) dry land regions are not constrained to become drier by enhanced moisture divergence since evaporation cannot exceed precipitation over multiannual time scales. Over land, where the available water does not limit evaporation, a “wet gets wetter” signal predominates. On seasonal time scales, where evaporation can exceed precipitation, trends in wet season becoming wetter and dry season becoming drier are also found.

The role of refuges in the persistence of Australian dryland mammals.

Irruptive population dynamics are characteristic of a wide range of fauna in the world's arid (dryland) regions. Recent evidence indicates that regional persistence of irruptive species, particularly small mammals, during the extensive dry periods of unpredictable length that occur between resource pulses in drylands occurs as a result of the presence of refuge habitats or refuge patches into which populations contract during dry (bust) periods. These small dry-period populations act as a source of animals when recolonisation of the surrounding habitat occurs during and after subsequent resource pulses (booms). The refuges used by irruptive dryland fauna differ in temporal and spatial scale from the refugia to which species contract in response to changing climate. Refuges of dryland fauna operate over timescales of months and years, whereas refugia operate on timescales of millennia over which evolutionary divergence may occur. Protection and management of refuge patches and refuge habitats should be a priority for the conservation of dryland-dwelling fauna. This urgency is driven by recognition that disturbance to refuges can lead to the extinction of local populations and, if disturbance is widespread, entire species. Despite the apparent significance of dryland refuges for conservation management, these sites remain poorly understood ecologically. Here, we synthesise available information on the refuges of dryland-dwelling fauna, using Australian mammals as a case study to provide focus, and document a research agenda for increasing this knowledge base. We develop a typology of refuges that recognises two main types of refuge: fixed and shifting. We outline a suite of models of fixed refuges on the basis of stability in occupancy between and within successive bust phases of population cycles. To illustrate the breadth of refuge types we provide case studies of refuge use in three species of dryland mammal: plains mouse (Pseudomys australis), central rock-rat (Zyzomys pedunculatus), and spinifex hopping-mouse (Notomys alexis). We suggest that future research should focus on understanding the species-specific nature of refuge use and the spatial ecology of refuges with a focus on connectivity and potential metapopulation dynamics. Assessing refuge quality and understanding the threats to high-quality refuge patches and habitat should also be a priority. To facilitate this understanding we develop a three-step methodology for determining species-specific refuge location and habitat attributes. This review is necessarily focussed on dryland mammals in continental Australia where most refuge-based research has been undertaken. The applicability of the refuge concept and the importance of refuges for dryland fauna conservation elsewhere in the world should be investigated. We predict that refuge-using mammals will be widespread particularly among dryland areas with unpredictable rainfall patterns.

Water Efficient Cropping Systems for Semi-Arid Regions in Pakistan

Abstract Water scarcity and land degradation are emerging threats to global food production. The dry land regions of world are affected by climate change to a greater extent and facing food insecurity. The current pattern of food production has been estimated to be inadequate to meet demands of growing population and required around 38% increase to meet world`s food demands by 2025. Food insecurity in erosion hit dry land regions of Pakistan also demands development of resource-efficient cropping systems to meet the food needs of population growing. The research studies involved different cropping patterns such as fallow-wheat, mungbean-wheat, sorghum-wheat, fallow-lentil, mungbean-lentil, sorghum-lentil, fallow-barley, mungbean-barley and sorghum-barley. The organic amendments involved farmyard manure, NPK, poultry manure, compost and inoculation by phosphorus solubilizing microbes. The effect of cropping systems and soil amendments were evaluated at field scale in terms of water use efficiency measured in terms of economic terms. The results of the studies revealed that double cropping (mungbean-lentil and mungbean-barley) was feasible option in the dryland regions of Pakistan if integrated with the use of poultry manure as alternate environmental-friendly strategy to cut down the use of mineral fertilizers and eliminate summer fallowing.

Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands

Reactive nitrogen species have a strong influence on atmospheric chemistry and climate, tightly coupling the Earth's nitrogen cycle with microbial activity in the biosphere. Their sources, however, are not well constrained, especially in dryland regions accounting for a major fraction of the global land surface. Here, we show that biological soil crusts (biocrusts) are emitters of nitric oxide (NO) and nitrous acid (HONO). Largest fluxes are obtained by dark cyanobacteria-dominated biocrusts, being ∼20 times higher than those of neighboring uncrusted soils. Based on laboratory, field, and satellite measurement data, we obtain a best estimate of ∼1.7 Tg per year for the global emission of reactive nitrogen from biocrusts (1.1 Tg a(-1) of NO-N and 0.6 Tg a(-1) of HONO-N), corresponding to ∼20% of global nitrogen oxide emissions from soils under natural vegetation. On continental scales, emissions are highest in Africa and South America and lowest in Europe. Our results suggest that dryland emissions of reactive nitrogen are largely driven by biocrusts rather than the underlying soil. They help to explain enigmatic discrepancies between measurement and modeling approaches of global reactive nitrogen emissions. As the emissions of biocrusts strongly depend on precipitation events, climate change affecting the distribution and frequency of precipitation may have a strong impact on terrestrial emissions of reactive nitrogen and related climate feedback effects. Because biocrusts also account for a large fraction of global terrestrial biological nitrogen fixation, their impacts should be further quantified and included in regional and global models of air chemistry, biogeochemistry, and climate.

Contribution of green manure legumes to nitrogen dynamics in traditional winter wheat cropping system in the Loess Plateau of China

Abstract Excessive application of N fertilizer in pursuit of higher yields is common due to poor soil fertility and low crop productivity. However, this practice causes serious soil depletion and N loss in the traditional wheat cropping system in the Loess Plateau of China. Growing summer legumes as the green manure (GM) crop is a viable solution because of its unique ability to fix atmospheric N 2 . Actually, little is known about the contribution of GM N to grain and N utilization in the subsequent crop. Therefore, we conducted a four-year field experiment with four winter wheat-based rotations (summer fallow-wheat, Huai bean–wheat, soybean–wheat, and mung bean–wheat) and four nitrogen fertilizer rates applied to wheat (0, 108, 135, and 162 kg N/ha) to investigate the fate of GM nitrogen via decomposition, utilization by wheat, and contribution to grain production and nitrogen economy through GM legumes. Here we showed that GM legumes accumulated 53–76 kg N/ha per year. After decomposing for approximately one year, more than 32 kg N/ha was released from GM legumes. The amount of nitrogen released via GM decomposition that was subsequently utilized by wheat was 7–27 kg N/ha. Incorporation of GM legumes effectively replaced 13–48% (average 31%) of the applied mineral nitrogen fertilizer. Additionally, the GM approach during the fallow period reduced the risk of nitrate-N leaching to depths of 0–100 cm and 100–200 cm by 4.8 and 19.6 kg N/ha, respectively. The soil nitrogen pool was effectively improved by incorporation of GM legumes at the times of wheat sowing. Cultivation of leguminous GM during summer is a better option than bare fallow to maintain the soil nitrogen pool, and decrease the rates required for N fertilization not only in the Loess Plateau of China but also in other similar dryland regions worldwide.

Towards a better understanding of landscape patterns and ecosystem processes of the Mongolian Plateau

The Mongolian Plateau has been well known to the world as the cradle of the Mongolian nomadic civilization. The plateau is located in the hinterland of temperate Asia, consisting primarily of two entities: the Inner Mongolia Autonomous Region of China (Inner Mongolia hereafter) and the entire territory of Mongolia (formerly the Republic of Mongolian). The Mongolian Plateau has a total area of 2.75 million km (1.18 km for Inner Mongolia and 1.57 million km for Mongolia) and a population of about 28 million (25 million for Inner Mongolia and 3 million for Mongolia in 2015). It has a hyper-continental climate, with most rainfall concentrated in summer and a long and cold winter. In the past millions of years, the plateau has changed from an ancient ocean to a forested region and then to a dryland region (Wu et al. 2015b). The plateau’s vegetation now is dominated by steppes and deserts which account for 44 and 34 % of the total land area, respectively, and also includes forests (14 %), cropland (5 %), and alpine vegetation (3 %) (Fig. 1; Zhao et al. 2014). The plateau is also dotted with numerous lakes, which have been disappearing or shrinking in size rapidly during the past three decades (Tao et al. 2015). Once ruled by the Great Mongol Empire founded by Genghis Khan, whose army and herds roamed across the Eurasian grassland region and beyond during the thirteenth century, the Mongolian Plateau has experienced increasingly rapid landscape transformations since the late Qing Dynasty due to both human and natural factors (Wu et al. 2015b). The most dramatic landscape and ecological changes occurred during the past several decades. In the past 30 years, human activities have become more intensive and extensive, with increasing human population (especially in Inner Mongolia), livestock overgrazing, coal and mineral mining, and rapid urbanization (Tao et al. 2015; Wu et al. 2015a, b). Meanwhile, the climate has become warmer and drier, with annual mean temperature increasing by 1.2 C and annual precipitation generally decreasing since the mid-1990s Zhao et al. J. Fang Y. Bai State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China

Energy partitioning and surface resistance of a poplar plantation in northern China

Abstract. Poplar (Populus sp.) plantations have been, on the one hand, broadly used in northern China for urban greening, combating desertification, as well as for paper and wood production. On the other hand, such plantations have been questioned occasionally for their possible negative impacts on water availability due to the higher water-use nature of poplar trees compared with other tree species in water-limited dryland regions. To further understand the acclimation of poplar species to semiarid environments and to evaluate the potential impacts of these plantations on the broader context of the region's water supply, we examine the variability of bulk resistance parameters and energy partitioning in a poplar (Populus euramericana cv. "74/76") plantation located in northern China over a 4-year period, encompassing both dry and wet conditions. The partitioning of available energy to latent heat flux (LE) decreased from 0.62 to 0.53 under mediated meteorological drought by irrigation applications. A concomitant increase in sensible heat flux (H) resulted in the increase of a Bowen ratio from 0.83 to 1.57. Partial correlation analysis indicated that surface resistance (Rs) normalized by leaf area index (LAI; Rs:LAI) increased by 50 % under drought conditions and was the dominant factor controlling the Bowen ratio. Furthermore, Rs was the main factor controlling LE during the growing season, even in wet years, as indicated by the decoupling coefficient (Ω = 0.45 and 0.39 in wet and dry years, respectively). Rs was also a major regulator of the LE / LEeq ratio, which decreased from 0.81 in wet years to 0.68 in dry years. All physiological and bioclimatological metrics indicated that the water demands of the poplar plantation were greater than the amount available through precipitation, highlighting the poor match of a water-intensive species like poplar for this water-limited region.

Spatiotemporal variation and trends in rainfall erosivity in China's dryland region during 1961–2012

This study evaluated rainfall erosivity and its changes in China's dryland region during 1961–2012, using a daily rainfall erosivity model, ArcGIS based spatial interpolation tools, and the Mann–Kendall and Sen's methods. It was found that mean rainfall erosivity was 2–4098MJmmha−1h−1a−1 in the region, with the regional average of 794MJmmha−1h−1a−1, showing a significant increase trend accordingly with an increase in rainfall from northwest to southeast. Rainfall erosivity varied annually with the CV of 32.4–491.3%, and varied seasonally with about three-quarter distributed in summer. During 1961–2012, a statistically significant increase/decrease trend in rainfall erosivity was detected only for 24/10 stations or about 4.6/0.4% of the region, and a non-significant increase/decrease trend was observed for 32/45 stations or 16.5/10.0% of the region at the 50 to 90% confidence level. No statistically confidential trend was found for other 126 stations or 68.5% of the region. At regional level, mean annual erosivity of the arid zone indicated an upward trend, while the sub-humid zone a downward, but the semi-arid zone generally had no evidential trend. Comparing the 26year's averages during 1987–2012 and 1961–1986, mean erosivity of the arid zone increased by 17.4%, the sub-humid zone decreased by 6.1%, and the semi-arid zone reduced slightly by 0.45%. The results suggest that change in the rainfall characteristics during the past half century had no significant influence on water erosion in the majority of the region, but it could probably induce an increase of water erosion risk in parts of the drier west and a slight decrease in parts of the wetter east including the Loess Plateau.

Fluvial–Eolian Interactions In Sediment Routing and Sedimentary Signal Buffering: An Example From the Indus Basin and Thar Desert

Abstract Sediment production and its subsequent preservation in the marine stratigraphic record offshore of large rivers are linked by complex sediment-transfer systems. To interpret the stratigraphic record it is critical to understand how environmental signals transfer from sedimentary source regions to depositional sinks, and in particular to understand the role of buffering in obscuring climatic or tectonic signals. In dryland regions, signal buffering can include sediment cycling through linked fluvial and eolian systems. We investigate sediment-routing connectivity between the Indus River and the Thar Desert, where fluvial and eolian systems exchanged sediment over large spatial scales (hundreds of kilometers). Summer monsoon winds recycle sediment from the lower Indus River and delta northeastward, i.e., downwind and upstream, into the desert. Far-field eolian recycling of Indus sediment is important enough to control sediment provenance at the downwind end of the desert substantially, although the proportion of Indus sediment of various ages varies regionally within the desert; dune sands in the northwestern Thar Desert resemble the late Holocene–Recent Indus delta, requiring short transport and reworking times. On smaller spatial scales (1–10 m) along fluvial channels in the northern Thar Desert, there is also stratigraphic evidence of fluvial and eolian sediment reworking from local rivers. In terms of sediment volume, we estimate that the Thar Desert could be a more substantial sedimentary store than all other known buffer regions in the Indus basin combined. Thus, since the mid-Holocene, when the desert expanded as the summer monsoon rainfall decreased, fluvial–eolian recycling has been an important but little recognized process buffering sediment flux to the ocean. Similar fluvial–eolian connectivity likely also affects sediment routing and signal transfer in other dryland regions globally.

A Water Yield‐Oriented Practical Approach for Multifunctional Forest Management and its Application in Dryland Regions of China

AbstractMountainous forest areas are vitally important for water supply in dryland regions which suffer from high erosion risk and severe water shortage. Massive afforestation, mainly for erosion control, may reduce the water yield and threaten local water supply security. Moreover, many over‐dense forests due to a strict logging ban policy have produced remarkably negative impacts for both forests (e.g., low timber quality, restricted natural regeneration, and high stand instability) and water yield. To satisfy the rapidly increasing demands on water supply and other services, a practical approach for managing forest stands in a multifunctional way, which particularly addresses water yielding, is urgently required. For this purpose, we integrated the existing knowledge and experience, designed an “ideal” stand structure to represent multifunctional forest (MFF) and determined its key parameters (a ground coverage of >0.7, a canopy density around 0.7, and an H/DBH ratio (tree height [m] to the diameter at breast height [cm]) of <0.7). Moreover, a decision process for MFF stand management was recommended as: (1) investigating the site quality; (2) identifying the site‐specific main forest functions; (3) quantifying the stand structure; (4) diagnosing the stand structure by comparing with the “ideal” one; and (5) arranging the functions/structure‐oriented management measures. In this way, the water‐yielding function can be improved and meanwhile other forest functions can be promoted.

Impact of tillage practices on nitrogen accumulation and translocation in wheat and soil nitrate-nitrogen leaching in drylands

Although the effects of tillage practices on soil properties and root growth is well studied, how they affect nitrogen accumulation and translocation in wheat in dryland regions is poorly understood. Here, the impact of different tillage practices, namely, strip rotary tillage (SR), strip rotary tillage after subsoiling (SRS), rotary tillage (R), and rotary tillage after subsoiling (RS), on nitrogen accumulation and translocation, grain yield, and economic benefit in wheat and soil nitrate-nitrogen leaching in drylands was studied over three wheat growing seasons from 2009 to 2012. The results showed that compared with R, nitrogen accumulation amount under SRS increased by 36.8% from jointing to maturity in 2009–2011 and by 12.9 and 16.4% from sowing to maturity in 2009–2010 and 2010–2011, respectively. Post-anthesis nitrogen accumulation, its contribution rate to grain and nitrogen accumulation in grains at maturity under SRS were 48.3, 31.3 and 12.7% higher, respectively, compared to that under R in 2009–2010. On the other hand, nitrate-nitrogen accumulation under SRS in 0–60cm soil layers was lower in comparison to that under SR and R, which suggested that SRS promoted absorption of nitrate-nitrogen in soil layers by wheat. However, no significant difference in nitrate-nitrogen accumulation in the 60–200cm soil layers was observed between SR and R. Average grain yield, nitrogen production efficiency and economic benefit were all the highest under SRS at 598.78gm−2, 39.9kgkg−1 and 8350.8 RMB¥ha−1, respectively, over the study period. Therefore, we propose that SRS is the optimal tillage practice for wheat production in this region.

Farmer risk-aversion limits closure of yield and profit gaps: A study of nitrogen management in the southern Australian wheatbelt

Nitrogen (N) is the most limiting nutrient in cereal crop production and is an important requirement in closing the gap between potential and achieved water limited yield. However, N fertiliser management in broadacre cereal cropping can be risky for farmers operating in dryland regions because of variability of rainfall and price. Farmers typically respond to this situation by making risk-averse decisions that are neither yield- nor profit-maximising. Here we use a set of case-study sites across the southern Australian wheatbelt to examine the risk-return profile of a range of N management options and show the extent to which the economics of N fertiliser decisions and the farmers' attitude to risk can determine N rates in a way that limits closure of yield gaps. Using a risk-return framework that incorporates crop simulation response to N application, probability theory, finance techniques, and risk-aversion analysis, we were able to better demonstrate how farmers might select N management practices that manage the trade-off between maximising economic net return and risk exposure using a risk-aversion analysis across four case-study sites.

Direct and Indirect Facilitation of Plants with Crassulacean Acid Metabolism (CAM)

Plants with crassulacean acid metabolism (CAM) are increasing their cover in many dryland regions around the world. Their increased dominance has been related to climate warming and atmospheric CO2 fertilization, while the effects of interspecies interactions and the role of CAM plant facilitation by trees and grasses remain poorly understood. Woody plants are known for their ability to directly facilitate CAM plants through amelioration of the abiotic environment. Mechanisms of indirect facilitation of trees on CAM plants in tree–grass–CAM associations, however, have received less attention. It is also unclear whether grasses might facilitate CAM plants in mixed tree–grass–CAM communities. For instance, the inclusion of grasses in tree–CAM associations could enhance hydraulic lift and facilitate CAM plants in their access to shallow soil moisture at the expenses of deep-rooted trees. If this effect outweighs the competitive effects of grasses on CAM plants, grasses could overall facilitate CAM plants through hydraulic lift. Here we develop a process-based ecohydrological model to investigate the direct and indirect facilitation in tree–CAM–grass associations; the model quantifies transpiration of CAM plants when isolated as well as in associations with trees and/or grasses. It is found that woody plants having a high root overlap with CAM plants indirectly facilitate CAM plants by significantly reducing grass transpiration in shaded conditions. For situations of a low-to-moderate root overlap, facilitation may occur both directly and indirectly. Conversely, grasses are unable to indirectly facilitate CAM plants through the mechanism of hydraulic lift because the competitive effects of grasses on CAM plants outweigh the facilitation induced by hydraulic lift.