Fallow Frequency Research Articles

Twenty-four years of contrasting cropping systems on a brown chernozem in Southern Alberta: crop yields, soil carbon, and subsoil salinity

Cropping systems with perennial forages and reduced fallow frequency generally increase soil organic carbon and thus subsequent soil health and crop yield. We evaluated the impact of prior cropping systems on subsequent yields and soil properties in a semiarid region by using crop yields as a bioassay of soil health following the termination of a 24-year crop rotation study in the Brown soil zone in Alberta. During 24 growing seasons from 1992 to 2015, the study included three fallow-containing rotations, two annual crop rotations that were cropped continuously, and perennial grass hay, each with two to six fertilizer treatments. During the bioassay period from 2016 through 2020, all plots in the study were uniformly cropped. Compared to unfertilized fallow wheat, soil organic C in the fall of 2015 was 54% higher after 24 years of fertilized grass and up to 14% higher following annual crops in rotations without fallow. The most notable impact of the previous cropping system on yield during the bioassay years was low yield following perennial grass in 2016 and 2018. Soil electrical conductivity measurements showed that subsoil salinity was elevated following perennial grass, demonstrating the importance of subsoil characteristics for healthy soils. Crop yields in the fifth year of the crop bioassay were 10%–20% greater due to reduced fallow frequency or increased crop diversity. The long-term impact of the cropping system on crop yield in this study depended on drought intensity due to counteracting changes in soil organic matter and subsoil salinity.

The effects of dryland cropping system intensity on soil function and associated changes in macrofauna communities

AbstractCrop production in water‐limited environments may be enhanced through improved soil function by facilitating precipitation capture and erosion control. Soil macrofauna are known to support improved soil structure and water dynamics through ecosystem engineering activities, and their populations can be influenced by management. We examined the effect of bare summer fallow frequency on soil macrofauna communities and soil physical properties in a long‐term (32‐yr) dryland no‐till agroecosystem experiment at two sites in eastern Colorado, USA. Treatments represented a gradient of fallow frequency and organic matter inputs, which included wheat (Triticum aestivum L.)–fallow, wheat–corn (Zea mays L.)–fallow, and continuously cropped with no planned summer fallow. The design also included a perennial grass treatment with minimal management consisting of six native grasses. We observed links between soil macrofauna and soil functional metrics, particularly related to soil aggregation and water infiltration. There was a trend toward higher macrofauna populations and soil function with increased cropping system intensity, and perennial grass outperformed the cropped treatments significantly for most soil health parameters. Multivariate analyses revealed that different treatments support relatively distinct macrofauna communities. Our results suggest that soil macrofauna populations may be important facilitators of soil structure and associated water dynamics in dryland no‐till agroecosystems and respond positively to reduced fallow and higher organic inputs.

A prospectus for sustainability of rainfed maize production systems in South Africa

AbstractThe rainfed maize (Zea mays L.) production systems of South Africa require an integrated approach to use the limited soil available water more efficiently, and to increase system productivity and sustainability. The soils across the major maize production regions are highly susceptible to wind and water erosion. Rigorous soil tillage, maize monoculture, and fallow periods are common, which depletes the soil from organic matter and nutrients. Despite the pressing need for transforming the highly degraded rainfed maize production systems, adoption of more sustainable management approaches has been limited, likely due to a shortage of local scientific field trials to evaluate current and alternative maize agronomic management practices. Erratic interseasonal rainfall patterns cause high variability in maize grain yields. Major challenges associated with no‐tillage are poor crop establishment, subsoil compaction, and high maize grain yield variability. The use of fallow in the maize–fallow production system leads to excessive runoff and soil erosion losses despite increased maize grain yields. Crop intensification and alternative crops are needed to increase rainfall water use efficiency and lower fallow frequency. The use of cover and forage crops may provide the opportunity to diversify and intensify maize production systems. Cover crop biomass could be beneficial in livestock‐integrated production systems providing livestock feed in either winter or summer. Research is drastically required to improve the understanding of current South African rainfed maize production systems and to facilitate the development of fitting sustainable agronomic management practices.

Climate Change Impacts on Yields and Soil Carbon in Row Crop Dryland Agriculture.

Dryland agroecosystems could be a sizable sink for atmospheric carbon (C) due to their spatial extent and level of degradation, providing climate change mitigation. We examined productivity and soil C dynamics under two climate change scenarios (moderate warming, representative concentration pathway [RCP] 4.5; and high warming, RCP 8.5), using long-term experimental data and the DayCent process-based model for three sites with varying climates and soil conditions in the US High Plains. Each site included a no-till cropping intensity gradient introduced in 1985, with treatments ranging from wheat-fallow ( L.) to continuous annual cropping and perennial grass. Simulations were extended to 2100 using data from 16 global circulation models to estimate uncertainty. Simulated yields declined for all crops (up to 50% for wheat), with small changes after 2050 under RCP 4.5 and continued losses to 2100 under RCP 8.5. Of the cropped systems, continuous cropping had the highest average productivity and soil C sequestration rates (78.1 kg C ha yr from 2015 to 2045 under RCP 4.5). Any increase in soil C for cropped rotations was realized by 2050, but grassland treatments increased soil C (up to 69%) through 2100, even under RCP 8.5. Our simulations indicate that reduced frequency of summer fallow can both increase annualized yields and store more soil C. As evapotranspiration is likely to increase, reducing fallow periods without live vegetation from dryland agricultural rotations may enhance the resilience of these systems to climate change while also increasing soil C storage and mitigating carbon dioxide emissions.

Wheat Yield and Yield Stability of Eight Dryland Crop Rotations

Core Ideas Wheat yields are greater following fallow than following crops.The most stable systems are WF(NT), WF(CT), and WMF.The least stable systems are WCMF, WM, and WCF.The probability of obtaining a yield less than 1500 kg ha‐1 is low for wheat after fallow.Risk‐averse farmers wishing to intensify a WF system should consider WMF. The winter wheat (Triticum aestivum L.)–fallow (WF) dryland production system employed in the Central Great Plains has evolved in the past 40 yr to include a diversity of other crops, with a reduction in fallow frequency. Wheat remains the base crop for essentially all cropping systems. Decisions to change a farming system benefit from information about average wheat yields, yield stability, and probabilities of obtaining a specified minimum wheat yield. The objective of this experiment was to quantify wheat yields, yield stability, and the probability of obtaining a specified minimum yield in eight dryland rotational systems varying in cropping intensity. The study was conducted over a 24‐yr period at Akron, CO. Yield stability was characterized with six stability measures. The probability of obtaining a yield less than 1500 kg ha−1 was also calculated for each rotation. Wheat yields were greatest in rotations where wheat followed a fallow period and least where wheat followed millet production. Rotations ranked from most stable to least stable wheat production (averaged over the six stability measures) were WF(NT), WF(CT), WMF, WCMP, WCM, WCMF, WM, and WCF. The probability of producing <1500 kg ha−1 was very low for rotations with wheat following fallow (about 0.03) and much higher for wheat following pea (0.35) or millet (0.48–0.58). The study results identified the WMF rotation as an intensified rotation with relatively high average wheat yields and yield stability.

Probabilities of having minimum amounts of available soil water at wheat planting

Winter wheat (Triticum aestivum L.)-fallow (WF) remains a prominent cropping system throughout the Central Great Plains despite documentation confirming the inefficiency of precipitation storage during the summer fallow period. Wheat yield is greatly influenced by available soil water at planting, and that quantity is influenced by cropping intensity, tillage intensity, crop grown prior to winter wheat planting, and length of the non-crop period prior to winter wheat planting. The objective of this study was to determine the effect of cropping system intensity, tillage, and crop prior to wheat planting on available soil water at planting and the probabilities of having certain minimum amounts of available soil water at wheat planting. Available soil water was measured at wheat planting for nine cropping systems varying in fallow frequency, tillage intensity, and crop prior to wheat over a 25-yr period at Akron, CO. Available soil water at wheat planting was found to be greatest (average 218 mm) for no-tillage (NT) and reduced-tillage (RT) systems in which a fallow period of 12–14 months preceded wheat planting. The lowest amounts of available soil water at wheat planting were found for the continuously cropped rotations (average 100 mm). The cumulative probability exceedance graphs of available soil water at planting fell into three groupings: 1) the five rotations that had a NT or RT fallow period prior to the next wheat crop; 2) the WF (conventional till) rotation; 3) the three rotations with either pea (Pisum sativum L.) or proso millet (Panicum miliaceum L.) prior to the next wheat crop. These graphs provide a valuable decision support tool for helping farmers assess risk in moving from a WF cropping system to a system of greater cropping intensity and diversity.

Long‐Term Crop Rotation Effects on Production, Grain Quality, Profitability, and Risk in the Northern Great Plains

Core Ideas Diversified rotations are more productive and profitable than cereal only rotations. Fallow rotations are less profitable than continuous cropping in the Northern Plains. Continuous cropping is riskier; however, it is preferred when averse to risk. Crop production in the semiarid Northern Great Plains has historically been limited to wheat (Triticum aestivum L.), with fallow every second or third year. In response to current prices and new production technologies, these cropping systems have been replaced with reduced frequency of fallowing and inclusion of oilseed and pulse crops in the rotation. This study examined the long‐term changes that producers can expect in their production levels and economic returns for five wheat‐based rotations with different fallow frequencies, use of an annual legume green manure to partially replace fallow, and a continuous diversified rotation of cereal–oilseed–cereal–pulse crops. The findings were based on the last 11 yr of a 28‐yr (1987–2014) crop rotation experiment performed at Swift Current, SK, Canada. Despite the higher grain yield on fallow versus stubble, total grain production increased as fallow frequency decreased. The continuous wheat rotation produced 21% more wheat than the rotations with fallow. Wheat protein was highest for the rotation containing the legume green manure. Since its establishment in 2003, a wheat–canola (Brassica napus L.)–wheat–dry pea (Pisum sativum L.) rotation was more profitable than the traditional wheat systems. Participation in a crop insurance program reduced the financial risk from low crop yields, particularly for continuous cropping. We concluded that under current economic conditions and production practices, producers can indeed enhance production levels and farm profitability with adoption of more intensive (reduced fallow) crop rotations, particularly those that also include oilseed and pulse crops.

Intensifying a semi-arid dryland crop rotation by replacing fallow with pea

Increasing dryland cropping system intensity in the semi-arid central Great Plains by reducing frequency of fallow can add diversity to cropping systems and decrease erosion potential. However elimination of the periodic fallow phase has been shown to reduce yields of subsequent crops in this region. The objective of this experiment was to determine how productivity of a 4-yr WCMF rotation [wheat (W, Triticum aestivum L.); corn (C, Zea mays L.); proso millet (M, Panicum miliaceum L.); fallow (F)] was affected when the fallow phase was replaced with pea (P, Pisum sativum L.). The effect of this intensification of the WCMF rotation on the available soil water content at planting, the water use, and the yield of each crop, and on total system productivity and net income was quantified by analyzing data over a 20-yr period from a long-term crop rotation experiment at Akron, CO. Large year-to-year variations were found for available soil water at planting, water use, and yield for all four crops. Pea water use resulted in significant reductions in available soil water at planting, water use, and yield for wheat and corn, but had little effect on those quantities in the millet crop. Total production on a seed mass basis was not different between the WCMF and WCMP rotations, but system net income for the WCMP rotation was 32% lower than for WCMF. Intensification of the WCMF rotation by replacing the fallow phase with pea production could be recommended as an alternative production method if pea seed costs and nitrogen fertilizer applied to the subsequent wheat crop can be reduced.

Evaluating Potential Dryland Cropping Systems Adapted to Climate Change in the Central Great Plains

Climate in the semiarid central Great Plains is expected to become warmer and drier in coming decades, with potentially greater variability in precipitation and temperature. Cropping systems that include forages and allow flexibility for determining if a crop should be planted and which crop to plant (based on available soil water at planting) may provide the opportunity to maintain economic viability in a changing climate environment. The objective of this study was to compare cropping system productivity and profitability of flexible rotations that incorporate forages against grain‐based cropping systems that are set rotational sequences. Yield and net returns for five set rotations and three flexible rotations were compared at Akron, CO, over 5 yr. Winter wheat (Triticum aestivum L.) yields were reduced by 57% when the fallow period prior to wheat production was replaced with crop production. Average net income was greatest for the continuously cropped all‐forage set 3‐yr rotation followed by the flexible 3‐yr rotations that included wheat and forage phases. The lowest net returns were seen for the set grain‐based rotations and the flexible wheat–grain crop rotation. Incorporating forage production as a phase in dryland wheat rotational systems can add profitability and sustainability to the production system in the face of climate variability.Core Ideas Including forages in semi‐arid dryland cropping systems increases profitability. Using flexible rotations based on soil water at planting can reduce fallow frequency. Continuously cropping with an all‐forage rotation maximizes net returns. Flexible rotations with forages may mitigate negative effects of climate variability.

Mapping farmland abandonment and recultivation across Europe using MODIS NDVI time series

Farmland abandonment is a widespread land-use change in temperate regions, due to increasing yields on productive lands, conservation policies, and the increasing imports of agricultural products from other regions. Assessing the environmental outcomes of abandonment and the potential for recultivation hinges on incomplete knowledge about the spatial patterns of fallow and abandoned farmland, especially at broad geographic scales. Our goals were to develop a methodology to map active and fallow land using MODIS Normalized Differenced Vegetation Index (NDVI) time series and to provide the first European-wide map of the extent of abandoned farmland (cropland and grassland) and recultivation. We used a geographically well-distributed training dataset to classify active and fallow farmland annually from 2001 to 2012 using a Random Forests classifier and validated the maps using independent observations from the field and from satellite images. The annual maps had an average overall accuracy of 90.1% (average user's accuracy of the fallow class was 73.9%), and we detected an average of 128.7 million hectares (Mha) of fallow land (24.4% of all farmland). Using the fallow/active time series, we mapped fallow frequency and hotspots of farmland abandonment and recultivation of unused farmland. We found a total of 46.1Mha of permanently fallow farmland, much of which may be linked to abandonment that occurred after the dissolution of the Eastern Bloc. Up to 7.6Mha of farmland was additionally abandoned from 2001 to 2012, mainly in Eastern Europe, Southern Scandinavia, and Europe's mountain regions. Yet, recultivation is widespread too (up to 11.2Mha) and occurred predominantly in Eastern Europe (e.g., European Russia, Poland, Belarus, Ukraine, and Lithuania) and in the Balkans. We also tested the robustness of our maps in relation to different abandonment and recultivation definitions, highlighting the usefulness of time series approaches to overcome problems when mapping transient land-use change. Our maps provide, to our knowledge, the first European-wide assessment of fallow, abandoned and recultivated farmland, thereby forming a basis for assessing the environmental outcomes of abandonment and recultivation and the potential of unused land for food production, bioenergy, and carbon storage.

Carbon storage and nitrous oxide emissions of cropping systems in eastern Washington: A simulation study

Conservation tillage is an agricultural strategy to mitigate atmospheric greenhouse gas (GHG) emissions. In eastern Washington, we evaluated the long-term effects of conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) on soil organic carbon (SOC) storage and nitrous oxide (N₂O) emissions at three dryland and one irrigated location using the cropping systems simulation model CropSyst. Conversion of CT to NT produced the largest relative increase in SOC storage (ΔSOC, average yearly change relative to CT) in the top 30 cm (11.8 in) of soil where ΔSOC ranged from 0.29 to 0.53 Mg CO₂e ha⁻¹ y⁻¹ (CO₂e is carbon dioxide [CO₂] equivalent of SOC; 0.13 to 0.24 tn CO₂e ac⁻¹ yr⁻¹). The ΔSOC were less with lower annual precipitation, greater fallow frequency, and when changing from CT to RT. Overall, ΔSOC decreased from the first to the third decade after conversion from CT to NT or RT. Simulations of ΔSOC for the conversion of CT to NT based on a 0 to 15 cm (0 to 5.9 in) soil depth were greater than the ΔSOC based on a 0 to 30 cm depth, primarily due to differences among tillage regimes in the depth-distribution of carbon (C) inputs and the resultant SOC distribution with depth. Soil erosion rates under CT in the study region are high, posing deleterious effects on soil quality, productivity, and aquatic systems. However, an analysis that includes deposition, burial, and sedimentation on terrestrial and aquatic systems of eroded SOC indicates that the substantial erosion reduction obtained with RT and NT may result only in minor additional SOC oxidation as compared to CT. Simulated N₂O emissions, expressed as CO₂ equivalent, were not very different under CT, RT, and NT. However, N₂O emissions were sufficiently high to offset gains in SOC from the conversion of CT to RT or NT. Thus, reducing tillage intensity can result in net C storage, but mitigation of GHG is limited unless it is coupled with nitrogen (N) fertilizer management to also reduce N₂O emission.

Carbon footprint of spring wheat in response to fallow frequency and soil carbon changes over 25 years on the semiarid Canadian prairie

Growing interest in environmental quality has provided a strong incentive to examine how farming practices affect agricultural products’ carbon footprints (CF), an environmental quality indicator. This study determined (i) the CF of spring wheat (Triticum aestivum L.) grown in different cropping systems over 25 years, and (ii) the effect of soil organic carbon (SOC) changes over years on wheat CF. Wheat was grown in four cropping systems: (a) fallow-wheat (FW), (b) fallow-wheat-wheat (FWW), (c) fallow-wheat-wheat-wheat-wheat-wheat (FWWWWW), and (d) continuous wheat (ContW), in replicated field plots in Saskatchewan, Canada. Wheat CF was calculated at a system level with measured variables coupled with modeling approaches. Over the 25-year period, the soil under the ContW system gained organic C of 1340kgCO2eqha−1 annually, or 38%, 55%, and 127% more than those gained in the FWWWWW, FWW, and FW systems, respectively. The SOC gain more than offset the greenhouse gas (GHG) emissions occurred during wheat production, leading to negative emission values at −742kgCO2eqha−1 annually for ContW, and −459, −404, and −191kgCO2eqha−1 for FWWWWW, FWW, and FW systems, respectively. Wheat in the ContW system produced the highest grain yield and gained highest SOC over the years, leading to the smallest (more negative) CF value at −0.441kgCO2eqkg−1 of grain, significantly lower than the CF values from the three other systems (−0.102 to −0.116kgCO2eqkg−1 of grain). Without considering the SOC gain in the calculation, wheat CF averaged 0.343kgCO2eqkg−1 of grain and which did not differ among cropping systems. Wheat is the largest agricultural commodity in Saskatchewan, and the way the crop is produced has significant impacts on environmental quality, reflected by its carbon footprint. Cropping systems with decreased fallow frequency was shown to significantly enhance soil carbon gains over the years, increase annualized crop yields, and effectively lower the carbon footprint of this important commodity.

Research achievements and adoption of no-till, dryland cropping in the semi-arid U.S. Great Plains

The Great Plains region of the United States is an area of widespread dryland crop production, with wheat being the dominant crop. Precipitation in the region ranges from 300 to 500mm annually, with the majority of precipitation falling during hot summer months. The prevailing cropping system is a two-year rotation of wheat and summer fallow. The adoption of no-till practices has resulted in greater precipitation storage and use efficiency, which has led to greater cropping intensity, higher productivity, more diverse crop rotations, and improvements in soil properties. In Colorado, for example, a no-till rotation of winter wheat–maize–fallow increased total annualized grain yield by 75% compared to winter wheat–summer fallow. Soil erosion was reduced to just 25% of that from a conventional tillage wheat–summer fallow system. The primary challenge with reducing fallow frequency is the increase in yield variability and risk of crop failure. Improved approaches for choosing crop or fallow are being developed based on soil water content and forecasted weather. Development of alternative crops, crop rotations, and integrated livestock systems that are sustainable from both economic and ecological perspectives is an on-going effort. Other research is addressing adaptation of cropping practices to climate change and the potential for dryland biomass crop production for the developing biofuel industry.

Cropping Intensity Impacts on Soil Aggregation and Carbon Sequestration in the Central Great Plains

The predominant cropping system in the Central Great Plains is conventional tillage (CT) winter wheat (Triticum aestivum L.)–summer fallow. We investigated the effect of 15 yr of cropping intensities, fallow frequencies, and tillage (CT and no‐till [NT]) practices on soil organic C (SOC) sequestration, particulate organic matter (POM), and wet aggregate‐size distribution. A crop rotation study was initiated in 1990 at Akron, CO, on a silt loam. In 2005, soil samples were collected from the 0‐ to 5‐ and 5‐ to 15‐cm depths in permanent grass, native prairie, and cropping intensities (CI) that included winter wheat, corn (Zea mays L.), proso millet (Panicum miliaceum L.), dry pea (Pisum sativum L.), and summer fallow. The native prairie was sampled to provide a reference point for changes in soil parameters. The most intensive crop rotation significantly increased C sequestration compared with the other CIs where fallow occurred once every 2 or 3 yr. Legume presence in the rotation did not improve SOC sequestration relative to summer fallow. Significant amounts of macroaggregates were associated with grass and intensive cropping compared with the rotations that included fallow. Reduced fallow frequency and continuous cropping significantly increased soil POM near the surface compared with NT wheat–fallow. Macroaggregates exhibited a significant positive relationship with SOC and POM. A significant negative correlation was observed between microaggregates and POM, especially at 0‐ to 5‐cm depth. Overall, a positive effect of continuous cropping and NT was observed on macroaggregate formation and stabilization as well as SOC and POM.

Accumulation of nitrate N in the soil profile and its implications for the environment under dryland agriculture in northern China: A review

Nitrate (NO3-) leaching and water contamination have become a worldwide concern. In this review, some examples are presented to show the extent and magnitude of NO3- accumulation in the soil profiles and its potential effects on contamination of ground water and surface water under dryland farming in northern China. Climatic and management factors affecting NO3- leaching are also discussed. In northern China, rainfall is relatively sparse, but the high intensity of precipitation and porous soils play an important role in the accumulation of NO3N in soil and its subsequent leaching in the soil profile. There is a risk of nitrate accumulation and leaching when high rates of fertilizer N are applied to improve crop yields, and it becomes even worse when conventional land use is changed from cereal crops to vegetable crops and fruit orchards. Under such conditions, shallow ground water might be polluted by NO3-. This suggests that more attention should be paid to prevent this problem by using best management practices, especially by controlling the amount of N fertilizer input, balanced fertilization, split N application, inclusion of crops with deep taproots in the rotation and minimizing summer fallow (especially tilled) frequency. Key words: Accumulation, contamination, dryland farming, ground water, leaching, nitrate, northern China

Nitrogen mineralization under summer fallow and continuous wheat in the semiarid Canadian prairie

The ability of soils to provide a portion of the N required by crops via N mineralization of organic matter is of economic and environmental importance. Over a 40-yr period (1967–2006), soil NO3-N and plant-N measurements were made under summer fallow and in systems cropped to spring wheat (Triticum aestivum L.), on a medium-textured Orthic Brown Chernozem (Aridic Haploboroll), at Swift Current, Saskatchewan. These values were used to estimate net N mineralization (Nmin). Each year, above-ground plant N was measured at harvest and soil NO3-N was measured before seeding, soon after harvest, and just prior to freeze-up in October. Also, in the first 18 yr of this study NO3-N and above-ground plant N were measured eight times between spring and fall in selected treatments; these data were used to make a more detailed estimate of Nmin. In a third experiment, conducted on the same soil at a nearby site in 1975, many small lysimeters were sampled six times between spring and harvest of spring wheat. We used this lysimeter study to assess the effect of N fertilizer rate and soilwater on net Nmin. Results from the more frequent sampling were more plausible than those from sampling at three different times per year. On average, net Nmin in the 20-mo summer fallow period was about 118 kg ha-1 (15 kg ha-1 between harvest and the first spring, 93 kg ha-1 between the first spring and second fall, and 10 kg ha-1 between the second fall and seeding). The average net Nmin under a wheat crop between spring and fall was between 53 and 63kg ha-1. Net Nmin increased with water, but excessive water appeared to reduce apparent net Nmin, probably due to leaching and denitrification losses of N, which were not assessed in our estimation of Nmin. Regression analysis was used to show a positive association between net Nmin and precipitation, between spring and fall, for most of the systems examined. There was evidence that tillage promotes N mineralization. At normal rates of N fertilizer (i.e., < 100 kg ha-1), fertilizer had no effect on Nmin. Net Nmin was directly proportional to fallow frequency, averaging 68, 83, and 90 kg ha-1 yr-1 for continuous wheat, fallow-wheat-wheat, and fallow-wheat rotations, respectively. Although our results may only be applicable to medium-textured soils of similar organic matter content in the Brown and Dark Brown Chernozemic soil zone, they provide data and information against which process-based models can be tested. They also provide useful first approximations of Nmin measured under field conditions where few long-term data currently exist. Key words: N mineralization, plant-N, fertilizer-N, crop rotation, irrigation, tillage

Quantifying soil water conservation in the semiarid region of Saskatchewan, Canada: Effect of fallow frequency and N fertilizer

Soil water is the most limiting factor influencing crop production in the semiarid prairies. The effects of fallow frequency and nitrogen (N) fertilization on soil water conservation were quantified for a 40-yr (1967–2006) field experiment conducted on a medium textured Orthic Brown Chernozem (aridic haploboroll) in semiarid southwestern Saskatchewan, in which soil water contents were measured each year in early spring (generally a week prior to seeding), shortly after harvest, and again just prior to freeze-up in the fall. The three treatments examined were continuous spring wheat (Triticum aestivum L.) (Cont W) and fallow-wheat (F-W), each receiving recommended rates of N and P fertilizer, and Cont W receiving only P. On average, 36% of the precipitation received during the fall and winter months for Cont W (N + P) was conserved in the soil. In the summer fallow system [F-W (N + P)] a greater proportion (42%) of the precipitation was conserved during the first fall and winter. Despite the fact that cumulative precipitation from spring to late fall during the fallow period averaged 243 mm, compared with 152 mm received during the previous fall and winter period, the amount (31 mm) and proportion (13%) of precipitation conserved was considerably less than that during the first overwinter period. These differences were attributed mainly to much higher summer evaporative losses. During the second overwinter period, only 6% of the precipitation received was conserved in the F-W (N + P) system compared with 44% in the first overwinter period. This poor conservation during the second winter was thought to be related to increased snow blowoff due to smaller amounts of standing crop residues, and to the freezing of a wet and bare soil surface, restricting water entry during snowmelt or spring thaw events. Physical based soil-crop models, which must be first improved for overwinter simulations, should be tested on the current data set to further interpret the observations and hypotheses. Compared with the 36% of fall and winter precipitation conserved in Cont W (N + P), inadequate N fertility [Cont W (+ P)] resulted in only 27% of the precipitation being conserved during this period. At harvest, F-W (N + P) and Cont W (N + P) had similar amounts of water in the soil, but Cont W (+ P) had significantly (P < 0.05) more because of reduced water use. However, by the following spring soil water recharge being proportional to crop residues produced resulted in F-W (N + P), Cont W (N + P) and Cont W (+ P) having 252, 209 and 204 mm/1.2 m soil, respectively. Equations were developed that will allow estimation of water conserved as a function of precipitation received between harvest and seeding for F-W (N + P) and Cont W (N + P) (R2 = 0.52*** in each case). Trends in grain yield were fairly closely correlated with growing season precipitation and potential evapotranspiration [squared semipartial correlation coefficients for Cont W (N + P) 0.32 and 0.17, respectively, and for F-W (N + P) 0.35 and 0.12]; soil water conservation played a minor role in determining final grain yields (squared semipartial correlation coefficient < 0.08). Key words: Soil water, spring wheat, precipitation deficit, yield trends, water conserved trends

Microbial communities and enzyme activities in soils under alternative crop rotations compared to wheat–fallow for the Central Great Plains

Winter wheat–fallow (W–F) rotation is the predominant cropping system in the Central Great Plains. However, other cropping systems are being suggested because reduced tillage and fallow can provide more residues that can increase soil organic carbon (SOC) content and other parameters related to soil quality and functioning. This study compared the microbial biomass and community composition and enzyme activities under native pasture and research plots under grass and different crop intensities (CI) established for 15 years in Akron, CO. The soil (Weld loam; fine, smectitic, mesic Aridic Paleustolls) was under alternative CI rotations (100 and 67%) of winter wheat ( Triticum aestivum L.) (W), corn ( Zea mays L.) (C), proso millet ( Panicum miliaceum L.) (M), and fallow (F) under no-tillage (nt) compared to the typical 50% CI rotation (W–F) under either conventional tillage (ct) and nt. Relative to F–Wct, the 100% (C–M–W) and 67% (C–F–W) CI rotations increased soil microbial biomass C (MBC) and N (MBN) but only at the 0–5 cm depth. Native pasture and 15 years of undisturbed grass plots showed higher soil MBC up to 2–5-fold and 1.4–3-fold when compared to the cropping systems at 0–5 cm, respectively. Similar trends were found for MBN and several enzyme activities. Enzyme activities of C (β-glucosaminidase, β-glucosidase, and α-galactosidase) and P cycling (alkaline phosphatase, acid phosphatase and phosphodiesterase) as a group separated the 100 and 67% CI rotations from the 50% CI rotation (W–Fct) at 0–5 and 5–15 cm of soil. Separation in these enzyme activities was observed for rotations sampled under a crop (W–C–F) compared to when sampled under fallow (F–W–C). Principal component analyses (PCA) of fatty acids methyl esters (FAME) suggested a shift in the microbial community structure with greater fungal populations in pasture, grass, and CI rotations of 100 and 67% compared to W–Fct. The sum of fungal indicators (18:2ω6c, 18:3ω6c, 18:1ω9c, 16:1ω5c) was significantly correlated ( r > 0.60; P < 0.05) to β-glucosaminidase, β-glucosidase, acid phosphatase and α-galactosidase activities. After 15 years, our results show that the combination of no-tillage and continuous cropping with reduced fallow frequency in two alternative (100 and 67% CI) rotations for the Central Great Plains have had a positive effect on soil quality parameters such as the microbial populations and community composition but only at 0–5 cm depth, and in several enzyme activities at both 0–5 and 5–15 cm.

Nitrate leaching in the semiarid prairie : Effect of cropping frequency, crop type, and fertilizer after 37 years

A high NO3 concentration in drinking water can be a health hazard. Further, leached N represents an economic loss to the producer. Although NO3 leaching to ground water would be minimal on the semiarid prairies, leaching can occur especially where frequent summer fallowing is practiced. We used a crop rotation study, initiated in 1967 on a medium-textured Orthic Brown Chernozem, at Swift Current, Saskatchewan, to determine the influences of fallow frequency, crop types, and fertilizer on nitrate leaching after 37 yr. Nitrate distribution was measured to 4.5 m depth by 0.3-m increments, in 10 cropping systems in fall 2003. We deduced that some NO3 leached beyond the rooting depth (1.2 m) of spring wheat (Triticum aetivium L.), especially under a fallow-wheat rotation receiving N and P fertilizer. The amounts of NO3 leached tended to be greater and to be located deeper in the soil profile as fallow frequency increased (e.g., fallow-wheat &gt; fallow-wheat-wheat &gt; continuous wheat, all receiving N and P fertilizer based on soil test). However, in this semiarid environment, NO3 leaching was not great, being highest under fallow-wheat (N + P) (180 kg N ha-1 leached in 37 yr). In fallow-containing systems inadequate fertilizer N or P resulted in reduced crop growth and N uptake leading to a tendency for greater leaching of the NO3 (about 145 kg N ha-1 in 37 yr) mineralized during the fallow period than when such a system received N and P based on soil tests (about 66 kg N ha-1 leached in 37 yr). In continuously cropped treatments there was little evidence of leaching. Replacing wheat grown on fallow with the shallow-rooted flax (Linum usitatissimum L.) in a fallowwheat-wheat (N + P) rotation resulted in greater NO3 leaching in the flax system (156 vs. 66 kg N ha-1 ) due to less N uptake by flax. In contrast, when the wheat grown on fallow was replaced with fall rye (Secale cereale L.) there was no leaching, perhaps because the fallow period was much shorter (12 mo compared with 20 mo for spring wheat) and also because the fall-seeded crop used soil NO3 in the fall and early spring reducing opportunities for leaching. Key words: Wheat, flax, fall rye, lentil, cropping frequency

Effect of fallow frequency, flexible rotations, legume green manure, and wheat class on the economics of wheat production in the Brown soil zone

Producers in the semiarid Brown soil zone of Saskatchewan have historically produced spring wheat (Triticum aestivum L.) in fallow-based rotations because these cropping systems are profitable and risk efficient; however, their use has also been most damaging to soil quality. New wheat types and management methods have been developed that may offer wheat producers opportunities to enhance economic returns, while improving environmental sustainability. This study compares the economic merits of reducing fallow (F) frequency, using an annual legume green manure (LGM) crop as a summer fallow replacement, adopting a flex-cropping approach based on available soil water reserves (if water) or the need to control problem weeds (if weeds), and the production of Canada Western Red Spring (CWRS) wheat (W) versus the higher yielding Canada Prairie Spring (CPS) wheat class (HY). The results are based on 15 yr of data from seven crop rotations included in an ongoing experiment being conducted on an Orthic Brown Chernozem at the Semiarid Prairie Agricultural Research Centre at Swift Current, Saskatchewan. The crop rotations included F-W-W, LGM-W-W, F-HY-HY, F-W-W-W, continuous W (Cont W), Cont W (if water), and Cont W (if weeds). Cropping systems were managed using conservation tillage practices. They were fertilized with recommended rates of N and P based on soil tests, and crop residue was maintained as tall as possible (usually &gt; 30 cm) to enhance snow trapping. The 1988–2002 study period was characterized by above normal growing season precipitation; thus, grain yields were also above average for this region. Results showed that producers will earn the highest net return with Cont W ($41 ha-1), despite this rotation having the highest production costs. Net returns ranked second highest for F-W-W-W, F-HYHY, and the flex-crop rotations (about $15 ha-1 less than Cont W), and ranked lowest for F-W-W and LGM-W-W (about $25 ha-1 less). However, since 1993, when the LGM was managed more effectively than in the first 6 yr, LGM-W-W was more profitable than F-W-W. On average, it was more profitable to produce CPS compared with CWRS wheat when the CPS/CWRS price ratio was greater than 0.8. Producers who are highly averse to risk would still choose cropping systems that included some summer fallow, while those with lower risk aversion would choose Cont W, but with all-risk crop insurance. In the absence of an all-risk crop insurance program, producers would typically choose Cont W (if water), F-W-W-W, or F-W-W. We concluded that area producers, who practice conservation tillage management and use tall stubble for snowtrapping, can enhance farm income by moving to more intensive cropping systems, and while doing so, they will foster improved environmental sustainability. Key words: Crop rotations, wheat, summer fallow, legume green manure, flex-cropping, production costs, net returns, income variability