Semi-arid Agricultural Systems Research Articles

Winter cover crops and irrigation alter soil microbial community composition in an arid cropping system

Cover cropping is a well-established strategy to improve soil health, especially in arid and semi-arid agricultural systems. Benefits to soil health are often mediated via effects of cover crops on soil microbial community structure, function and diversity, crucial for regulating soil biogeochemical cycles, eventually promoting agricultural sustainability. However, limited water availability is a major constraint for both cover crop growth and soil microbial activity. This study sought to characterize and elucidate the shifts in soil microbial community structure in response to different cover crops and differential irrigation treatments using phospholipid fatty acid (PLFA) profiling in southern New Mexico. We tested five cover crop treatments: Pisum sativum (Australian winter pea), Hordeum vulgare cv. Stockford (barley), Brassica juncea cv. Caliente 199 (brown mustard), a three-way mix, and a fallow control — in combination with irrigation treatments of one, two, or three irrigation applications — in a split-plot design over two years. Zea mays (sweet corn) was grown as the summer cash crop. We collected soil samples just after cover crop planting in the fall of 2018, following second year cover crop termination but during Z. mays growth in June 2020, and after the second season of Z. mays growth in October 2020. Differential irrigation treatments did not lead to consistent patterns of change under any cover crop or irrigation treatment. However, PLFA parameters in cover cropped compared to winter fallow plots tended to decrease under one and three irrigations but increased with two irrigations. Changes were more common for bacterial than for fungal PLFA biomarkers, and more common in B. juncea and H. vulgare cover crops than in P. sativa or the mix. It is important to note that, while cover crop effects were inconsistent, cover cropping did lead to some shifts in PLFA biomarkers, even in the short two-year period of cover cropping.

Irrigation effects on the formation of soil organic matter from aboveground plant litter inputs in semiarid agricultural systems

In semiarid agricultural systems, irrigation may increase soil organic matter (SOM) due to higher biomass production. However, aboveground production tends to increase more than belowground biomass, and in no-till systems SOM responses to irrigation would strongly depend on the fate of crop residues left on the soil surface. Litter decomposition and SOM formation can also be affected by irrigation due to changes in water dynamics, but little is known about the impacts of irrigation on the pathways of SOM formation. We used dual 13C and 15N labeled maize litter to quantify the effect of irrigation on the contribution of aboveground crop residues to SOM formation in semiarid, no-till agricultural systems. We incubated the litter in a continuous maize cropping system with two treatments, dryland and irrigated, and measured litter decomposition and its contribution to different SOM pools. Irrigation had a larger effect on litter C and N losses than on the formation of new SOM. After 13 months the C and N losses from the litter layer were 24% higher under irrigation, but there were no treatment differences in the litter-derived C and N recovered in SOM. Most of the litter-derived organic matter (OM) was found in the mineral associated OM pool (MAOM), but irrigation did not affect the amount of litter-derived OM found as MAOM or as particulate organic matter. Irrigation increased the amount of litter-derived OM found in macroaggregates, and this observation was more related to a higher aggregation than to aggregate enrichment in the irrigated treatment. Our results suggest that a smaller proportion of aboveground crop residues will form SOM in irrigated systems compared to dryland conditions and may help to partially explain why irrigation has a stronger relative effect on crop productivity and C inputs than on SOC stocks in semiarid agricultural systems.

On-farm evaluation of regenerative land-use practices in a semi-arid pasture agroecosystem in West Texas, USA

ABSTRACT Continually rising scarcity in water and nutrient resources, especially in semi-arid agricultural systems, combined with increased frequency of extreme weather events such as drought, contribute to a growing need for resilient and regenerative agricultural ecosystems. However, evaluating a myriad of combinations of producer-led sustainable management practices in on-farm research remains challenging. Few studies have elucidated spatial variability in measured soil properties across the study area due to logistical and economic constraints. As such, this study aimed to: 1) establish [...]

Integrated nutrient management to improve some soil characteristics and biomass production of saffron

Due to its profitability as well as low-water and -nutrient requirements, saffron (Crocus sativus L.) has been vastly promoted and recommended as an alternative plant in arid and semi-arid agricultural systems. Soil fertility guarantees sustainable nutrient availability for plants and biomass production. Accordingly, this study aimed to investigate the interaction effects between organic and chemical fertilizers and mycorrhizal inoculation on some soil characteristics, plant nutrient composition, and biomass production of saffron. To this purpose, we compare the experimental results of two growing seasons (2015–2016 and 2016–2017) obtained under semi-arid conditions. The experiment consisted of different nutrient management approaches: control (non-amended soil), compost (COM), compost + biochar (COM + B), and chemical fertilizers (CF), which were either inoculated or non-inoculated with arbuscular mycorrhizal (AM) fungus (Glomus mosseae). The results indicated that CF fertilization significantly increased the total biomass, nutrient uptake, and nutrient use efficiency of saffron when inoculated with AM. Findings also showed that applying merely organic amendments not only led to a significantly higher soil pH, available phosphorus (P), soil organic carbon (SOC), cation exchange capacity, and lower bulk density but also had positive effects on total biomass, nutrient uptake, and nutrient use efficiency in AM-inoculated plots. We also found that inoculation of organically-amended plots with AM increased the soil-available P by raising SOC decomposition during the growing season of 2015–2016, which was accompanied by higher P uptake and P use efficiency, especially over the season of 2016–2017. Further, lower nitrogen uptake (NU), lower nitrogen use efficiency (NUE), as well as lower soil N content were recorded in COM + B and non-amended soils. This decline can be attributed to higher C: N ratios, meaning that C: N ratio was negatively correlated with N acquisition parameters. However, AM-inoculation significantly increased N content and subsequently N acquisition in COM-amended soil. Based on the results of this study, it is safe to say that applying chemical fertilizers inoculated by AM can be considered as an approach to enhance nutrient acquisition and biomass production of saffron. Moreover, we managed to improve soil characteristics and saffron nutrient composition through integrated application of AM and compost, which can be another helpful approach to maintain soil fertility and enhance yield potential of saffron fields in semi-arid regions.

Comparison Quality of Interpolation Methods to Estimate Spatial Distribution of Soil Moisture Content

ABSTRACT Determining and predicting both the spatial and temporal variability of soil moisture content is a critical factor in crop production in semi-arid agricultural systems. The objective of this research was to predict the spatial distribution of soil moisture content using ordinary kriging (OK), regression kriging (RK) and cokriging (CK) models. For that purpose, the soil moisture was monitored in the wet period (March, April and May) and dry period (August, September and October) in Kadınhanı district of Konya Province, Turkey. In each monthly sampling period of the study, a total of 278 samples were collected from locations within an area of 29,608.6 ha. The coefficients of variation (CV) of the soil moisture in dry and wet soil conditions were 0.39 and 0.20, respectively. Soil texture, bulk density (BD) and land use were the most important factors influencing soil moisture. In addition, dry soil generally had a smaller nugget effect than wet soil. Overall, CK was able to better estimate the soil moisture content than OK and RK, as evidenced by the smaller mean absolute error (MAE) and mean square error (MSE). RK estimation is more vulnerable to error than CK and OK estimations because the low coefficients of determination in the regression equation lead to increased error and lower confidence in the estimates. The insights generated by the modeling utilized in this study can assist land use planners, land managers and farmers to more efficiently predict, manage and utilize soil moisture content and hence produce larger crops more sustainably.

Using stable water isotopes to assess the influence of irrigation structural configurations on evaporation losses in semiarid agricultural systems

The arid areas east of the Cascade Mountains in the Pacific Northwest have high irrigation water use and changing the elevation of sprinkler nozzles in these systems has been proposed as a strategy to reduce evaporative losses in order to diminish the total irrigation water demand. Validation of any structural modifications requires techniques able to identify water losses from these systems that were non-productive, particularly soil evaporation. In this study, we quantified evaporation losses from soils under Mid Elevation Spray Application (MESA) and Low Elevation Spray Application (LESA) irrigation systems by using stable isotope tracers to estimate the fraction of non-productive water losses (i.e. the ratio of soil water evaporation to irrigation water applied, E/I). During mid-summer 2017 in eastern Oregon and southeast Washington, we collected soil samples at multiple positions and depths around the central irrigation tower from four different agricultural fields, each with both LESA and MESA configurations. We measured the hydrogen and oxygen stable isotope ratio of soil water at MESA and LESA field locations using H2O liquid – H2O vapor equilibration laser spectroscopy. Though soil moisture contents were similar, the average isotope ratio of soil water under LESA irrigation (δD = −114.5‰, δ18O = −14.5‰) had lower values than under MESA irrigation (δD = −108.2‰, δ18O = −13.1‰). Calculated E/I values demonstrated higher sprinkler and soil water evaporation occurring at the MESA irrigated locations (E/I = 16.1%) compared to the LESA irrigated locations (E/I = 9.0%). We find that LESA systems have lower non-productive water losses than MESA systems and are thereby more efficient users of applied water. Our results suggest that stable water isotopes provide a technique for improving the management of water resources through the assessment of irrigation efficiency.

Morphological Features and Biomass Partitioning of Lucerne Plants (Medicago sativa L.) Subjected to Water Stress

Drought is one of the major abiotic stresses affecting the morphological, physiological, and metabolic processes of plants, and hence their growth and production on a global scale. Lucerne (Medicago sativa L.) is one of the most popular pasture species in semi-arid regions and plays a critical role in sustaining agricultural systems in many areas of the world. In order to evaluate the effect of water deficits on the growth and biomass distribution in different tissues of lucerne, plant height, leaf dry weight, leaf number and area, root dry weight, taproot length and lateral root number, and stem dry weight were measured at four stages from the seedling to flowering stages under three water regimes: (i) adequate water supply (minimum soil water content 85% pot capacity (PC)), (ii) moderate water stress (65% PC), and (iii) severe water stress (45% PC), imposed under a rainout shelter. With limited water supply, plant height, leaf number, leaf area and dry weight, taproot length, and total biomass were reduced, while lateral root numbers increased. The number of smaller leaves and root dry weight increased under moderate water stress, whereas severe water stress reduced them. Leaf, stem, and total dry weight were all reduced by the water deficits, but leaf dry weight was reduced the most and root dry weight the least, so there was a redistribution of biomass towards the roots, increasing the root–shoot ratio. These results help us to understand the response of lucerce to water stress and assist in developing a foundation for the sustainable use of lucerne in semi-arid agricultural systems.

Improving the sustainability of farming systems under semi-arid conditions by enhancing crop management

Under semi-arid conditions, water is the most limiting factor for ensuring the sustainability of Mediterranean agriculture. Proper management of practices such as irrigation, fertilization, and changes in sowing date and sowing density can contribute decisively to efficient water management in these agricultural systems. Thus, the aim of this study was to assess the effect in terms of yield and profit of combining those agricultural practices, and subsequently to define strategies for the sustainable intensification of semi-arid agricultural systems in southern Spain. The study focused on sunflower as a representative crop.Sustainable intensification practices were evaluated through a series of experiments, revealing the prominent role played by water availability in their performance. Thus, high sowing density provided much more satisfactory yield results compared to the traditional sowing density, and it was observed that this yield increase was related to water availability: higher yield increases (around 27%) were obtained with deficit irrigation strategies than under severe deficit irrigation or rainfed conditions (around 16%). Other intensification strategies such as support irrigation and early sowing date also generated satisfactory yield increases (around 45% and 30%, respectively). Finally, interactions between irrigation and fertilization indicated that under limited water availability, very low N-fertilization rates were required. All these results led to the conclusion that the combination of high sowing densities, early sowing date, deficit irrigation and limited fertilization constitutes an innovative intensification strategy for sunflower under semi-arid conditions.An economic analysis of the proposed agricultural practices also revealed a clear connection between water availability and optimized management of sowing density, sowing date and fertilization. These results confirmed that technical advisory services provided to farmers should focus on integrated site-specific crop management, especially under semi-arid conditions with severely limited water availability.

Intercropping potato (Solanum tuberosum L.) with hairy vetch (Vicia villosa) increases water use efficiency in dry conditions

Protection from soil erosion and efficient use of water are vital to sustainable dryland potato production in semi-arid regions. Introducing legumes into semi-arid agricultural systems as intercrops improves soil quality due to biological nitrogen fixation and reduced wind erosion as a result of better soil cover, but the consequences of introducing legumes for the water use efficiency of the crop system are less predictable. Here we carried out field experiments from 2014 to 2017 in Inner Mongolia, China. We compared a rotational intercropping system of potato (Solanum tuberosum L.) and hairy vetch (Vicia villosa) with monocultures of potato and hairy vetch and quantified crop yield, water use efficiency and land productivity. While the relative density (the ratio of plant density in intercrop and the density in sole stand) of both crops in the intercropping was 0.5, the average relative yield of the potato over four years was 0.43, but that of the vetch was 0.87, indicating dominance of the vetch in the intercropping system. Land and water equivalent ratios, defined as the area of land or amount of water that would be needed in single cropping to achieve the same yield as in intercropping, averaged to 1.30 and 1.29 over the years, respectively, indicating high relative land and water productivity of potato/hairy vetch intercropping compared to monocultures. Vetch was a stronger competitor for water than potato with a partial water equivalent ratio of 0.83. We conclude that the potato/vetch intercropping system improves land productivity and system level water use efficiency under the rain-fed semi-arid conditions of the study site. These results are useful to optimize cropping systems for regional sustainability with consideration of both arable crop production (potato) and provision of fodder for animal husbandry (vetch).

The Impact of Green Water Management Strategies on Household-Level Agricultural Water Productivity in a Semi-Arid Region: A Survey-based Assessment

This study evaluates the effect of policies that encourage farmers to shift to crops with higher water productivity (CWP) on the farm-level CWP of agricultural systems in a semi-arid region of western China. We combine survey results of farmers’ historical cropping decisions from a 2010 survey with estimates of CWP from agronomic experiments analogous to actual cultivation practices in the region to model CWP at the farm level and understand changes driven by shifting crops. Policies designed to replace subsistence agricultural systems with two cash crops; potatoes and maize; resulted in an increase in the CWP of semi-arid agricultural systems of approximately 30% between the years 1990–2010. This change was driven by shifting to crops that have a peak water demand that occurs in the portions of the growing season with the highest rainfall. The results of this article illustrate the potential of shifts in cropping patterns to increase the CWP of agricultural systems in semi-arid regions.

Crop diversification as a smallholder livelihood strategy within semi-arid agricultural systems near Mount Kenya

Crop diversification is one strategy that smallholder farmers may employ to reduce their vulnerability in the face of global environmental change. Diversification not only expands the number of potential crop types for market, it also improves agroecosystem functioning by building redundancy into the agricultural system and allowing for innovation in areas exhibiting impacts of climate variability. While the driving forces behind and impacts of crop diversification have been extensively investigated, there are particular issues for the prospects of crop diversification to reduce household vulnerability within semi-arid agricultural systems. The decision to diversify crops is a particularly challenging one for farmers in semi-arid systems. Semi-arid systems can exhibit greater variability in annual precipitation in areas that are marginal for agricultural production. Changes to the timing of the growing season (onset of rains) and mid-season dry periods in particular pose significant challenges to farmers in semi-arid ecosystems. This paper examines the spatial diversification of crop types across an upland-lowland gradient on Mount Kenya's northwestern slopes. We perform regression analyses using household-level survey data collected during the summer of 2012 to investigate the factors contributing to varying levels of crop diversification and implications for crop production in a semi-arid irrigated agricultural system. We hypothesize that the study area locations at higher elevations will be able to grow a greater variety of crops due to climate suitability. Our analysis demonstrates that household-level income, field size, exposure to agricultural extension officers, and suitability of environmental conditions are related to the likelihood of smallholder crop diversification. More favorable growing conditions appear to outweigh limitations posed by inaccessibility and financial constraints, which has implications for adaptation to climate change in semi-arid ecosystems. We discuss the results in the context of challenges posed by global environmental change.

Dry Soil Reduces Fertilizer Phosphorus and Zinc Diffusion but Not Bioavailability

Dry sowing is a practice used in many semiarid agricultural systems where crops are planted early into dry soil to hasten crop emergence following the first rains of the season. This practice increases water use efficiency by promoting rapid canopy development early in the growing season when soils are warm. The question that arises from this practice is whether the efficacy of fertilizers, which are usually simultaneously placed below the seed at planting, is influenced by being in contact with the dry soil for a period of time before seed germination and crop emergence. Commercial granular and liquid monoammonium phosphate fertilizers enriched with Zn were incubated under dry and wet conditions to test the effects of dry sowing on fertilizer diffusion, lability, and subsequent availability to wheat (Triticum aestivum L. ‘Axe’) plants in the growth chamber using isotopic techniques. Fertilizer incubated in dry soil tended to have a much greater lability than in wet soil, but diffusion was limited. The restricted diffusion during the incubation did not negatively impact nutrient availability to plants subsequently grown in the growth chamber, however, and simulated dry sowing was not shown to have a detrimental effect on fertilizer efficiency.

Dynamics of soil microbial biomass C and soil fertility in cropland mulched with plastic film in a semiarid agro-ecosystem

Microbial biomass C (MBC) is one of the soil properties used as an indicator for the fertility status of a soil. A study was conducted on a semi-arid Loess Plateau in China. The field was planted with spring wheat and mulched with plastic film for various lengths of time. Our primary objectives were to (i) explore the influence of film mulching on soil MBC and soil fertility, and (ii) seek an effective approach of maintaining and improving sustainability of cropland mulched with plastic film in two growing seasons. Four treatments were tested, non-mulching (M0), mulching for 30 days after sowing (M30), mulching for 60 DAS (M60) and mulching for the whole growing period (Mw). An increasing air temperature with time within the growing season promoted soil MBC in the two growing seasons, but a severe drought led to a lower MBC in 2000 compared with the wet year of 1999. Film mulching promoted MBC significantly in the 2 years, but decreased soil organic carbon (SOC). SOC is very low in the experimental soil, accounting for the higher MBC/SOC ratio compared with ratios reported by others. The SOC is greatly reduced in the non-mulched and the Mw treatments compared to the M30 and M60 treatments. In conclusion, the benefits of film mulching in semi-arid agricultural systems are enormous but realizing their full potential depends on how long the mulching material is maintained during the growing season. In the system tested, it is desirable to mulch the plots for 30–60 DAS in order to enhance microbial biomass and cycling of nutrients and also to provide a more stable soil micro-environment that generates more residues in the rhizosphere.

Akkadian Empire Where to Look?

With regard to the Research News article “Sea-floor dust shows drought felled Akkadian empire” by Richard A. Kerr (16 Jan., [p. 325][1]), the sediment core described by Heidi Cullen and Peter deMenocal provides compelling data for the idea of atmospheric drying and an increasingly dust-laden atmosphere for the period 2200 to 1900 B.C. For the Gulf of Oman, this amplifies the data presented by Sirocko ([1][2]), which demonstrates increased arrival of dust in sea floor sediments during periods of decreased strength of the southwest monsoon. However, to explain this dust, rather than look at northern Syria, where trends in atmospheric moisture change may have been opposite to those of the monsoonal area ([2][3]), we should first look at Arabia, where a well-attested moist period terminated around 5000 years ago, or after. The Yemen highlands and the Arabian desert both show significant drying toward the end of the mid-Holocene and could have contributed increased atmospheric dust to the atmosphere. In the later third millennium B.C., abandonment of settlements and terraced fields ([3][4]) may have been related to atmospheric drying resulting from increased southerly penetration of summer northwesterly winds during a period of decreased ocean upwelling and reduced monsoonal strength. In the north, although there was a dramatic decline in settlement in the Rhabur basin in Syria, climatically marginal towns like Tell Brak continued to be occupied in the post-Akkadian period, albeit perhaps with reduced populations. Further west in the Lake Tabqa area, where probably 250 to 300 millimeters of rainfall supported primarily rain-fed agriculture, we see in the final quarter of the third millennium B.C. an increase in settlement numbers and the growth of a town at Tell Sweyhat. In moister areas near Kurban Hoyuk in southern Turkey, growth in rural sedentary settlements was at the expense of towns. As Frank Hole states (“Wheat domestication,” Letters, 16 Jan., [p. 303][5]), something was going on at this time, but whether it was culturally or climatically driven, or a combination of both, is unclear ([4][6]). A case for increased atmospheric moisture in the mid-Holocene can be made from lake sediments and alluvial sediments ([5][7]). The former record suggests that there was dwindling but fluctuating moisture toward the end of the third millennium B.C., followed by greater drying in the later second millennium B.C., when settlement in northern Mesopotamia did indeed decline, but did not disappear. Although I, too, accept a role for climate, especially in these fragile, highly stressed semiarid agricultural systems, archaeological evidence suggests that not only was settlement decline in one part of this zone counteracted by increases in other areas, but also that there were adjustments within both pastoral and sedentary communities that could absorb some of the stress of climatic shocks. 1. [↵][8]1. F. Sirocko , Paleoecol. Africa 24, 65 (1996). [OpenUrl][9] 2. [↵][10]1. H. E. Wright 2. et al. 1. N. Roberts, 2. H. E. Wright , in Global Climates Since the Last Glacial Maximum, H. E. Wright et al., Ed. (Univ. of Minnesota Press, Minneapolis, MN, 1993), pp. 194-220. 3. [↵][11]1. T. J. Wilkinson , Geoarchaeology 12, 853 (1997). [OpenUrl][12] 4. [↵][13]1. H. N. Dalfes, 2. G. Kukla, 3. H. Weiss 1. K. Butzer , in Third Millennium B.C. Climate Change and Old World Collapse, H. N. Dalfes, G. Kukla, H. Weiss, Eds. (NATO ASI Series, Springer, Berlin, 1997), pp. 245-296. 5. [↵][14]1. G. Lemcke, 2. M. Sturm , ibid. 653-678; 1. A. M. Rosen , Geoarchaeology 12, 395 (1997). 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