Identifying indicators of C and N cycling in a clayey Ultisol under different tillage and uses in winter

Although tropical and subtropical environments permit two cropping cycles per year, maintaining adequate mulching on the soil surface remains a challenge. In some cases, leaving soils fallow during the winter as an agricultural practice to control pathogens contributes to reduce soil mulching. The aim of this study was to assess attributes associated with C and N cycling in a soil under conventional and no-tillage management, with contrasting uses in winter: black oats (Avena strigosa Schreb) as cover crop or fallow. No-tillage increased total C and N, irrespective the winter crop. Cropping black oats under no-tillage resulted in more microbial biomass C and N, and glutaminase activity (15.2%, 65.2%, and 24%, respectively) than no-tillage under fallow. Under conventional tillage, winter cropping did not affect the attributes under study. Available P was higher in the no-tillage system (9.2–12.3 mg kg⁻¹), especially when cropped with black oats, than in the conventional tillage system (4.8–6.6 mg kg⁻¹). A multivariate analysis showed strong relationships between soil microbiological and chemical attributes in the no-tillage system, especially when cropped with black oats. Soil pH, dehydrogenase and acid phosphatase activities were the most effective at separating the soil use in winter. Microbial N, total N, microbial to total N ratio, available P, metabolic quotient (qCO₂), and glutaminase activity were more effective at separating soil management regimes. The no-tillage system in association with winter oat cropping stimulated the soil microbial community, carbon and nutrient cycling, thereby helping to improve the sustainability of the cropping system.     

Soil tillage effects on monovalent cations (Na+ and K+) in vertisols soil solution

Potassium is an essential macronutrient for plants; it is characterized by increased photosynthetic activity by ensuring a better utilization of light energy, also acts as a regulator of cell osmotic pressure, decreasing transpiration and helping to maintain cell turgidity. However, the sodium is not an essential element for plants, although it is beneficial to certain crops, in some instances can replace the potassium and osmotic regulation making and turgidity of the cells, this effect is greatest when the supply of potassium is deficient (Wild, 1992). Both elements, in periods of aridity, delayed the wilting of plants to maintain cellular osmotic potential and in cold periods, they lower the freezing point of sap (Navarro and Navarro, 2000).This is an experiment to study the influence of soil management techniques on the monovalent cations in soil solutions at different depths. The cropping systems studied are conventional tillage, minimum tillage and direct drilling.Conventional tillage releases more Na⁺ and K⁺ to the soil solution than the conservative techniques. In the case of Na⁺, the conventional tillage soil solution has an average concentration of 0.563 meq/L compared to 0.303 meq/L of minimum tillage and 0.340 meq/L of direct drilling. As for the K⁺, the soil solution concentration of conventional tillage is 0.097 meq/L, compared to 0.079 meq/L of the solution of minimum tillage and 0.056 meq/L of direct drilling.The behavior for the two cations studied is distinct at different depths. The Na⁺ is more abundant in water samples of soil taken in depth. Therefore, the salinization risk may take place in the subsoil, especially in conventional tillage where the Bw₁ horizon values are three times higher than in the Ap horizon, while the K⁺ is more abundant in the surface horizon. Conventional tillage and minimum tillage techniques, in the Ap horizon have a similar pattern with a K⁺ concentration average of 0.15 meq/L and 0.14 meq/L, respectively, resulting in lower values for direct drilling.Studies on clay soils have not been performed previously because of the difficulty presented by these soils when soil solution extracted for analysis. We analyzed the monovalent cations (sodium and potassium) from soil solution; because the soil solution is the immediate source of sodium and potassium for plants.     

Influence of rotation and tillage on forage maize productivity,weed species,and soil quality of a fine sandy loam in the cool–humid climate of Atlantic Canada

Reduced tillage systems may be an option to allow rapid crop establishment in areas constrained by a short growing season, but such methods need to be adapted to soil tillage requirement and crop establishment needs. Rotation and tillage studies were conducted during a 6-year period on a fine sandy loam (Podzol) with silage maize (Zea mays L.) under the cool, humid climate, and relatively short growing season of Prince Edward Island, Atlantic Canada. The objective was to compare a continuous maize rotation with a maize–barley (Hordeum vulgare L.) rotation, using both no-tillage and conventional mouldboard ploughing for the maize, and to evaluate treatment effects on maize growth and productivity, weed populations, and soil quality. Plant population and maize yield were not consistently influenced by the tillage or rotation treatments. Mean maize yield ranged from 7.2 to 7.7 Mg ha⁻¹. An increasing density of weeds over the 6-year period, especially perennial species, was evident under no-tillage, compared to mouldboard ploughing. Except for slight changes in soil pH, spatial variation in extractable soil P, and a higher level of organic C and labile forms of C (microbial biomass and mineralizable C), soil chemical quality was similar among treatments. An apparent decline in soil physical quality, as indicated by a reduction in macro-porosity volume and increase in soil penetration resistance below the 8 cm soil depth, was evident under the no-tillage at the end of the 6-year period. However, macro-pore continuity was less affected by a reduction in tillage, while field measurements of soil hydraulic conductivity increased under no-tillage compared to ploughing. The latter result may be related to the observed increase in earthworm population where tillage was reduced. Use of rotational tillage resulted in an intermediate soil physical condition between continuous no-tillage and ploughing. Overall, no-tillage appears a promising strategy to facilitate a fast and early establishment of maize on sandy loam soils in Atlantic Canada, but some ongoing monitoring of the soil physical condition would be required.     

Effects of alternative management practices on the economics,energy and GHG emissions of a wheat–pea cropping system in the Canadian prairies

In recent years alternative farming practices have received considerable attention from Canadian producers as a means to improve their net return from grain and oilseed production. Enhancing the efficiency of nitrogen fertilizer use, including a pulse crop in the rotation, reducing tillage and pesticide use are seen as viable options to reduce reliance on fossil fuel, lower input costs and decrease the risk of soil, air and water degradation. The objective of this study was to determine the effects of 16 alternative management practices for a 2-year spring wheat (Triticum aestivum L.)–field pea (Pisum sativum L.) rotation on economic returns, non-renewable energy use efficiency, and greenhouse gas emissions. The alternative management methods for wheat consisted of a factorial combination of high vs. low soil disturbance one pass seeding, four nitrogen (N) fertilizer rates (20 kg N ha^?1, 40 kg N ha^?1, 60 kg N ha^?1 and 80 kg N ha^?1), and recommended vs. reduced rates of in-crop herbicide application. Alternative management practices for field pea were high vs. low soil disturbance one pass seeding. The resulting 16 cropping systems were evaluated at the whole farm level based on 4 years (two rotation cycles) of data from field experiments conducted on two Orthic Black Chernozem soils (clay loam and loam textures) in Manitoba, Canada. The highest net returns on the clay loam soil were for the high disturbance system with 60 kg N ha^?1 applied to wheat and the recommended rates of in-crop herbicides. The lowest application rate of N, together with low disturbance seeding, provided the highest economic returns on the loam soil. Energy use efficiency was highest for the lowest rate of N application for both tillage systems. The highest rate of N fertilizer and recommended rates of in-crop herbicide produced little additional yield response, lower net returns, and higher GHG emissions. An increase in N fertilizer application from 20 kg ha^?1 to 80 kg ha^?1 increased whole farm energy requirements by about 40%, while reducing herbicide rates had negligible effects on grain yields and total energy input. Overall, as N fertilizer rate increased, the associated GHG emissions were not offset by an increase in carbon retained in the above-ground crop biomass. Moderate to high soil test NO₃-N levels at experimental sites reduced the potential for positive yield responses to N fertilizer in this study, thus minimizing the economic benefits derived from N fertilizer application.     

Tillage and slurry over-fertilization affect oribatid mite communities in a semiarid Mediterranean environment

Fertilization with animal residues together with no-tillage is being widely used in dryland Mediterranean agriculture. The aim of this work is to assess the potential impacts of these combined management practices on oribatid mite species, and to evaluate their potential use as bioindicators of soil disturbances. From an experiment established ten years ago, eight fertilization treatments (including minerals or pig slurries), all combined with minimum tillage (MT) and no-tillage (NT), were studied. Four of these combinations were sampled three times during the winter cereal cropping season. The rest, and a neighbouring oak forest, were only sampled close to the end of the season (May). In total, 34 oribatid species and 4140 individuals were recovered. Oribatid abundance responded positively (p < 0.05) to the reduction of tillage intensity (NT) and marginally (p < 0.1) to slurry fertilization at sowing (close to maximum legislation allowed rate: <210 kg N ha⁻¹ yr⁻¹). At this slurry rate, Shannon index of diversity varied through the season, and was higher in May in MT than in NT plots. The Berger–Parker index of abundance signals plots without slurries as the most disturbed (compared with the forest). Nitrogen slurry over-fertilization reduced abundance of Oribatula (Zygoribatula) connexa connexa , but the impact on the most relevant species depended on the tillage system: Epilohmannia cylindrica cylindrica dominated in MT plots; under NT it was balanced by Tectocepheus velatus sarekensis and Passalozetes (Passalozetes) africanus. Scutovertex sculptus is also very negatively affected by tillage. Oribatida are a good target for the biological indication of soil disturbances associated to agricultural management.     

Modeling organic carbon dynamics under no-tillage and plowed systems in tropical soils of Brazil using CQESTR

CQESTR simulates the effect of management practices on soil organic carbon (SOC) stocks. The beta version of the model had been calibrated and validated for temperate regions. Our objective was to evaluate the CQESTR model performance for simulating carbon dynamics as affected by tillage practices in two tropical soils (Ultisol and Oxisol) in southeastern and northeastern Brazil. In the southeast (20.75 S 42.81 W), tillage systems consisted of no tillage (NT); reduced tillage (RT) (one disc plow and one harrow leveling [RT1] or one heavy disc harrow and one harrow leveling [RT2]); and conventional tillage (CT) (two heavy disc harrows followed by one disc plow and two harrow levelings). In the northeast (7.55 S 45.23 W), tillage systems consisted of NT, RT (one chisel plow and one harrow leveling), and CT (one disk plow, two heavy disk harrowings, and two harrow levelings). CQESTR underestimated SOC at both sites, especially under NT systems, indicating that adjustments (e.g., the inclusion of clay mineralogy factor) are necessary for more accurate simulation of SOC in the tropics. In spite of this, measured and simulated values of SOC in the 0–20 cm depth were well correlated (southeast, R² = 0.94, p < 0.01; northeast, R² = 0.88, p < 0.05). With respect to initial conditions (native forest), CQESTR estimated a decrease in SOC stocks in plowed and no-tillage systems. In 2006, in the southeast, SOC stocks were 28.8, 23.7, 23.2, and 22.0 Mg ha^?1 under NT, RT2, RT1, and CT, respectively; in the northeast, stocks were 36.0, 33.8, and 32.5 Mg ha^?1 under NT, RT, and CT, respectively. The model estimated carbon emissions varying from 0.36 (NT) to 1.05 Mg ha^?1 year^?1 (CT) in the southeast and from 0.30 (NT) to 0.82 (CT) Mg ha^?1 year^?1 in the northeast. CQESTR prediction of SOC dynamics illustrates acceptable performance for the two tropical soils of Brazil.     

Soil organic matter and water-stable aggregates under different tillage and residue conditions in a tropical dryland agroecosystem

Changes in the proportions of water-stable soil aggregates, organic C, total N and soil microbial biomass C and N, due to tillage reduction (conventional, minimum and zero tillage) and crop residue manipulation (retained or removed) conditions were studied in a tropical rice–barley dryland agroecosystem. The values of soil organic C and total N were the highest (11.1 and 1.33 g kg⁻¹ soil, respectively) in the minimum tillage and residue retained (MT+R) treatment and the lowest (7.8 and 0.87 g kg⁻¹, respectively) in conventional tillage and residue removed (CT−R) treatment. Tillage reduction from conventional to minimum and zero conditions along with residue retention (MT+R,ZT+R) increased the proportion of macroaggregates in soil (21–42% over control). The greatest increase was recorded in MT+R treatment and the smallest increase in conventional tillage and residue retained (CT+R) treatment. The lowest values of organic C and total N (7.0–8.9 and 0.82–0.88 g kg⁻¹ soil, respectively) in macro- and microaggregates were recorded in CT−R treatment. However, the highest values of organic C and total N (8.6–12.6 and 1.22–1.36 g kg⁻¹, respectively) were recorded in MT+R treatment. The per cent increase in the amount of organic C in macroaggregates was greater than in microaggregates. In all treatments, macroaggregates showed wider C/N ratio than in microaggregates. Soil microbial biomass C and N ranged from 235 to 427 and 23.9 to 49.7 mg kg⁻¹ in CT−R and MT+R treatments, respectively. Soil organic C, total N, and microbial biomass C and N were strongly correlated with soil macroaggregates. Residue retention in combination with tillage reduction (MT+R) resulted in the greatest increase in microbial biomass C and N (82–104% over control). These variables showed better correlations with macroaggregates than other soil parameters. Thus, it is suggested that the organic matter addition due to residue retention along with tillage reduction accelerates the formation of macroaggregates through an increase in the microbial biomass content in soil.     

Effects of tillage and nitrogen management on soil chemical and physical properties after 23 years of continuous sorghum

Long-term tillage and nitrogen (N) management practices can have a profound impact on soil properties and nutrient availability. A great deal of research evaluating tillage and N applications on soil chemical properties has been conducted with continuous corn (Zea Mays L.) throughout the Midwest, but not on continuous grain sorghum (Sorghum bicolor (L.) Moench). The objective of this experiment was to examine the long-term effects of tillage and nitrogen applications on soil physical and chemical properties at different depths after 23 years of continuous sorghum under no-till (NT) and conventional till (CT) (fall chisel-field cultivation prior to planting) systems. Ammonium nitrate (AN), urea, and a slow release form of urea were surface broadcast at rates of 34, 67, and 135 kg N ha⁻¹. Soil samples were taken to a depth of 15 cm and separated into 2.5 cm increments. As a result of lime applied to the soil surface, soil pH in the NT and CT plots decreased with depth, ranging from 6.9 to 5.7 in the NT plots and from 6.5 to 5.9 in the CT plots. Bray-1 extractable P and NH₄OAc extractable K was 20 and 49 mg kg⁻¹ higher, respectively, in the surface 2.5 cm of NT compared to CT. Extractable Ca was not greatly influenced by tillage but extractable Mg was higher for CT compared to NT below 2.5 cm. Organic carbon (OC) under NT was significantly higher in the surface 7.5 cm of soil compared to CT. Averaged across N rates, NT had 2.7 Mg ha⁻¹ more C than CT in the surface 7.5 cm of soil. Bulk density (Δ_b) of the CT was lower at 1.07 g cm⁻³ while Δ_b of NT plots was 1.13 g cm⁻³. This study demonstrated the effect tillage has on the distribution and concentration of certain chemical soil properties.     

Impact of reduced tillage on carbon and nitrogen storage of two Haplic Luvisols after 40 years

It is broadly accepted that reduced tillage increases soil organic carbon (C_org) and total nitrogen (N) concentrations in arable soils. However, the underlying processes of sequestration are not completely understood. Thus, our objectives were to investigate the impact of a minimum tillage (MT) system (to 5–8 cm depth) on aggregates, on particulate organic matter (POM), and on storage of C_org and N in two loamy Haplic Luvisols in contrast to conventional tillage (CT) (to 25 cm). Surface soils (0–5 cm) and subsoils (10–20 cm) of two experimental fields near Göttingen, Germany, were investigated. Each site (Garte-Süd and Hohes Feld) received both tillage treatments for 37 and 40 years, respectively. In the bulk soil of both sites C_org, N, microbial carbon (C_mic), and microbial N (N_mic) concentrations were elevated under MT in both depths. Likewise, water-stable macroaggregates (>0.25 mm) were on average 2.6 times more abundant under MT than under CT but differences in the subsoils were generally not significant. For surface soils under MT, all aggregate size classes <1 mm showed approx. 35% and 50% increased C_org concentrations at Garte-Süd and Hohes Feld, respectively. For greater macroaggregates (1–2, 2–10 mm), however, differences were inconsistent. Elevations of N concentrations were regular over all size classes reaching 61% and 52%, respectively. Density fractionation of the surface soils revealed that tillage system affected neither the yields of free POM nor occluded POM nor their C_org and N concentrations. Moreover, more C_org and N (15–238%) was associated within the mineral fractions investigated under MT in contrast to CT. Overall, similar to no-tillage, a long-term MT treatment of soil enhanced the stability of macroaggregates and thus was able to physically protect and to store more organic matter (OM) in the surface soil. The increased storage of C_org and N did not occur as POM, as reported for no-tillage, but as mineral-associated OM.     

Soil organic carbon and nitrogen in a Mollisol in central Ohio as affected by tillage and land use

Minimum tillage practices are known for increasing soil organic carbon (SOC). However, not all environmental situations may manifest this potential change. The SOC and N stocks were assessed on a Mollisol in central Ohio in an 8-year-old tillage experiment as well as under two relatively undisturbed land uses; a secondary forest and a pasture on the same soil type. Cropped systems had 51±4 (equiv. mass) Mg ha⁻¹ lower SOC and lower 3.5±0.3 (equiv. mass) Mg ha⁻¹ N in the top 30 cm soil layer than under forest. Being a secondary forest, the loss in SOC and N stocks by cultivation may have been even more than these reported herein. No differences among systems were detected below this depth. The SOC stock in the pasture treatment was 29±3 Mg ha⁻¹ greater in the top 10 cm layer than in cultivated soils, but was similar to those under forest and no-till (NT). Among tillage practices (plow, chisel and NT) only the 0–5 cm soil layer under NT exhibited higher SOC and N concentrations. An analysis of the literature of NT effect on SOC stocks, using meta-analysis, suggested that NT would have an overall positive effect on SOC sequestration rate but with a greater variability of what was previously reported. The average sequestration rate of NT was 330 kg SOC ha⁻¹ year⁻¹ with a 95% confidence interval ranging from 47 to 620 kg SOC ha⁻¹ year⁻¹. There was no effect of soil texture or crop rotation on the SOC sequestration rate that could explain this variability. The conversion factor for SOC stock changes from plow to NT was equal to 1.04. This suggests that the complex mechanisms and pathways of SOC accrual warrant a cautious approach when generalizing the beneficial changes of NT on SOC stocks.     

Effect of tillage on earthworms over short- and medium-term in conventional and organic farming

Earthworms play an important role in many soil functions and are affected by soil tillage in agricultural soils. However, effects of tillage on earthworms are often studied without considering species and their interactions with soil properties. Furthermore, many field studies are based on one-time samplings that do not allow for characterisation of temporal variation. The current study monitored the short (up to 53 days) and medium term (up to 4 years) effects of soil tillage on earthworms in conventional and organic farming. Earthworm abundances decreased one and three weeks after mouldboard ploughing in both conventional and organic farming, suggesting direct and indirect mechanisms. However, the medium-term study revealed that earthworm populations in mouldboard ploughing systems recovered by spring. The endogeic species Aporrectodea caliginosa strongly dominated the earthworm community (76%), whereas anecic species remained <1% of all earthworms in all tillage and farming systems over the entire study. In conventional farming, mean total earthworm abundance was not significantly different in reduced tillage (153 m⁻²) than mouldboard ploughing (MP; 130 m⁻²). However, reduced tillage in conventional farming significantly increased the epigeic species Lumbricus rubellus from 0.1 m⁻² in mouldboard ploughing to 9 m⁻² averaged over 4 years. Contrastingly, in organic farming mean total earthworm abundance was 45% lower in reduced tillage (297 m⁻²) than MP (430 m⁻²), across all sampling dates over the medium-term study (significant at 3 of 6 sampling dates). Reduced tillage in organic farming decreased A. caliginosa from 304 m⁻² in mouldboard ploughing to 169 m⁻² averaged over 4 years (significant at all sampling dates). Multivariate analysis revealed clear separation between farming and tillage systems. Earthworm species abundances, soil moisture, and soil organic matter were positively correlated, whereas earthworm abundances and penetration resistance where negatively correlated. Variability demonstrated between sampling dates highlights the importance of multiple samplings in time to ascertain management effects on earthworms. Findings indicate that a reduction in tillage intensity in conventional farming affects earthworms differently than in organic farming. Differing earthworm species or ecological group response to interactions between soil tillage, crop, and organic matter management in conventional and organic farming has implications for management to maximise soil ecosystem functions.     

Responses of soil nematode community structure to soil carbon changes due to different tillage and cover crop management practices over a nine-year period in Kanto,Japan

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100 kg N ha⁻¹ for upland rice, and 0 and 20 kg N ha⁻¹ for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure.     

Conservation farming strategies in East and Southern Africa: Yields and rain water productivity from on-farm action research

Improved agricultural productivity using conservation farming (CF) systems based on non-inversion tillage methods, have predominantly originated from farming systems in sub-humid to humid regions where water is not a key limiting factor for crop growth. This paper presents evidence of increased yields and improved water productivity using conservation farming in semi-arid and dry sub-humid locations in Ethiopia, Kenya, Tanzania and Zambia. Results are based on on-farm farmer and research managed experiments during the period 1999–2003. Grain yield of maize (Zea mays L.) and tef (Eragrostis Tef (Zucc)) from conventional (inversion) tillage are compared with CF with and without fertilizer. Rain water productivity (WP_rain) is assessed for the locations, treatments and seasons. Results indicate significantly higher yields (p < 0.05) for CF+ fertilizer treatments over conventional treatments in most locations, increasing from 1.2 to 2 t ha^?1 with 20–120% for maize. For tef in Ethiopian locations, the yield gains nearly doubled from 0.5–0.7 to 1.1 t ha^?1 for “best bet” CF+ fertilizer. WP_rain improved for CF+ fertilizer treatments with WP gains of 4500–6500 m³ rainwater per t maize grain yield in the lower yield range from 0 to 2.5 t ha^?1. This is explained by the large current unproductive water losses in the on-farm water balance. There was a tendency of improved WP_rain in drier locations, which can be explained by the water harvesting effect obtained in the CF treatments. The experiences from East and Southern Africa presented in this paper indicate that for smallholder farmers in savannah agro-ecosystems, conservation farming first and foremost constitutes a water harvesting strategy. It is thus a non-inversion tillage strategy for in situ moisture conservation, rather than solely aimed at minimum tillage with mulch cover. Challenges for the future adoption of CF in sub-Saharan Africa include how to improve farmer awareness of CF benefits, and how to efficiently incorporate green manure/cover crops and manage weeds.     

Tillage effects on soil properties and wheat cultivars traits

Information regarding the evaluation of tillage effects on soil properties and rainfed wheat (Triticum aestivum L.) cultivars of Iranian fields is not available. Therefore, this research was conducted in Sanandaj (west of Iran) using a randomized complete block design in a split-plot arrangement. Three types of tillage including conventional tillage (moldboard plow to soil depth of 30 cm plus disk harrow twice), minimum tillage (chisel plow to soil depth of 15 cm plus disk harrow once) and no-tillage are assigned to the main plots. Wheat cultivars (Sardari and Azar2) were randomly distributed within the subplots in each tillage system. Results showed that the greatest bulk density and cone index were found in the minimum tillage and no tillage systems. The highest rate of grain yield was obtained in the minimum tillage system. The grain yield of Sardari cultivar (1624.1 kg ha^?1) was significantly greater than that of Azar2 (1572 kg ha^?1). Minimum tillage improved soil physical properties and wheat growth compared with the other tillage systems. No tillage increased microbial biomass carbon and bacteria number in soil compared with the other tillage systems. We conclude that using minimum tillage for Sardari cultivar will be more effective compared with other treatments.     

Endogeic and anecic earthworm abundance in six Midwestern cropping systems

Endogeic and juvenile anecic earthworm abundance was measured in soil samples and anecic populations were studied by counting midden numbers at the sites of two long-term cropping systems trials in South-central Wisconsin. The three grain and three forage systems at each site were designed to reflect a range of Midwestern USA production strategies. The primary objectives of this work were to determine if the abundance of endogeic or anecic earthworms varied among cropping systems or crop phases within a cropping system and were there specific management practices that impacted endogeic or anecic earthworm numbers. The earthworms present in the surface soil were: Aporrectodea tuberculata (Eisen), A. caliginosa (Savigny), A. trapezoides (Dugés); and juvenile Lumbricus terrestris (L.). True endogeic abundance was greatest in rotationally grazed pasture [188 m^?2 at Arlington (ARL) and 299 m^?2 at Elkhorn (ELK)], and smallest in conventional continuous corn (27 m^?2 at ARL and 32 m^?2 at ELK). The only type of anecic earthworm found was L. terrestris L. There was an average of 1.2 middens per adult anecic earthworm and the population of anecics was greatest in the no-till cash grain system (28 middens m^?2 at ARL, 18 m^?2 at ELK) and smallest in the conventional continuous corn system (3 middens m^?2 at ARL, 1 m^?2 at ELK). Earthworm numbers in individual crop phases within a cropping system were too variable from year-to-year to recommend using a single phase to characterize a whole cropping system. Indices for five management factors (tillage, manure inputs, solid stand, pesticide use, and crop diversity) were examined, and manure use and tillage were the most important impacting earthworm numbers across the range of cropping systems. Manure use was the most important management factor affecting endogeic earthworm numbers; but no-tillage was the most important for the juvenile and adult anecic groups and had a significantly positive influence on endogeic earthworm counts as well. The pesticides used, which were among the most commonly applied pesticides in the Midwestern USA, and increasing crop diversity did not have a significant effect on either the endogeic or anecic earthworm groups in this study. Consequently, designing cropping systems that reduce tillage and include manure with less regard to omitting pesticides or increasing crop diversity should enhance earthworm populations and probably improve sustainability.     

Effects of tillage,organic resources and nitrogen fertiliser on soil carbon dynamics and crop nitrogen uptake in semi-arid West Africa

Tillage, organic resources and fertiliser effects on soil carbon (C) dynamics were investigated in 2000 and 2001 in Burkina Faso (West Africa). A split plot design with four replications was laid-out on a loamy-sand Ferric Lixisol with till and no-till as main treatments and fertiliser types as sub-treatments. Soil was fractionated physically into coarse (0.250–2 mm), medium (0.053–0.250 mm) and fine fractions (< 0.053 mm). Particulate organic carbon (POC) accounted for 47–53% of total soil organic carbon (SOC) concentration and particulate organic nitrogen (PON) for 30–37% of total soil nitrogen concentration. The POC decreased from 53% of total SOC in 2000 to 47% of total SOC in 2001. Tillage increased the contribution of POC to SOC. No-till led to the lowest loss in SOC in the fine fraction compared to tilled plots. Well-decomposed compost and single urea application in tilled as well as in no-till plots induced loss in POC. Crop N uptake was enhanced in tilled plots and may be up to 226 kg N ha⁻¹ against a maximum of 146 kg N ha⁻¹ in no-till plots. Combining crop residues and urea enhanced incorporation of new organic matter in the coarse fraction and the reduction of soil carbon mineralisation from the fine fraction. The PON and crop N uptake are strongly correlated in both till and no-till plots. Mineral-associated N is more correlated to N uptake by crop in tilled than in no-till plots. Combining recalcitrant organic resources and nitrogen fertiliser is the best option for sustaining crop production and reducing soil carbon decline in the more stabilised soil fraction in the semi-arid West Africa.     

Surface soil responses to silage cropping intensity on a Typic Kanhapludult in the piedmont of North Carolina

Although reduced tillage itself is beneficial to soil quality and farm economics, the amount of crop residues returned to the soil will likely alter the success of a particular conservation tillage system within a farm operation. We investigated the impact of three cropping systems (a gradient in silage cropping intensity) on selected soil physical, chemical, and biological properties in the Piedmont of North Carolina, USA. Cropping systems were: (1) maize (Zea mays L.) silage/barley (Hordeum vulgare L.) silage (high silage intensity), (2) maize silage/winter cover crop (medium silage intensity), and (3) maize silage/barley grain—summer cover crop/winter cover crop (low silage intensity). There was an inverse relationship between silage intensity and the quantity of surface residue C and N contents. With time, soil bulk density at a depth of 0–3 cm became lower and total and particulate C and N fractions, and stability of macroaggregates became higher with lower silage intensity as a result of greater crop residue returned to soil. Soil bulk density at 0–3 cm depth was initially 0.88 Mg m⁻³ and increased to 1.08 Mg m⁻³ at the end of 7 years under high silage intensity. Total organic C at 0–20 cm depth was initially 11.7 g kg⁻¹ and increased to 14.3 g kg⁻¹ at the end of 7 years under low silage intensity. Stability of macroaggregates at 0–3 cm depth at the end of 7 years was 99% under low silage intensity, 96% under medium silage intensity, and 89% under high silage intensity. Soil microbial biomass C at 0–3 cm depth at the end of 7 years was greater with low silage intensity (1910 mg kg⁻¹) than with high silage intensity (1172 mg kg⁻¹). Less intensive silage cropping (i.e., greater quantities of crop residue returned to soil) had a multitude of positive effects on soil properties, even in continuous no-tillage crop production systems. An optimum balance between short-term economic returns and longer-term investments in improved soil quality for more sustainable production can be achieved in no-tillage silage cropping systems.     

In-field management of corn cob and residue mix: Effect on soil greenhouse gas emissions

In-field management practices of corn cob and residue mix (CRM) as a feedstock source for ethanol production can have potential effects on soil greenhouse gas (GHG) emissions. The objective of this study was to investigate the effects of CRM piles, storage in-field, and subsequent removal on soil CO₂ and N₂O emissions. The study was conducted in 2010–2012 at the Iowa State University, Agronomy Research Farm located near Ames, Iowa (42.0°′N; 93.8°′W). The soil type at the site is Canisteo silty clay loam (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquolls). The treatments for CRM consisted of control (no CRM applied and no residue removed after harvest), early spring complete removal (CR) of CRM after application of 7.5 cm depth of CRM in the fall, 2.5 cm, and 7.5 cm depth of CRM over two tillage systems of no-till (NT) and conventional tillage (CT) and three N rates (0, 180, and 270 kg N ha⁻¹) of 32% liquid UAN (NH₄NO₃) in a randomized complete block design with split–split arrangements. The findings of the study suggest that soil CO₂ and N₂O emissions were affected by tillage, CRM treatments, and N rates. Most N₂O and CO₂ emissions peaks occurred as soil moisture or temperature increased with increase precipitation or air temperature. However, soil CO₂ emissions were increased as the CRM amount increased. On the other hand, soil N₂O emissions increased with high level of CRM as N rate increased. Also, it was observed that NT with 7.5 cm CRM produced higher CO₂ emissions in drought condition as compared to CT. Additionally, no differences in N₂O emissions were observed due to tillage system. In general, dry soil conditions caused a reduction in both CO₂ and N₂O emissions across all tillage, CRM treatments, and N rates.     

Soil losses due to cassava and sweet potato harvesting: A case study from low input traditional agriculture

Soil loss due to crop harvesting (SLCH) has been established as an important soil erosion process that has significantly contributed to soil degradation in highly mechanised agriculture. This has stimulated the need to investigate the importance of this process of erosion under low input agriculture where, until now, only water and tillage erosion are known as important phenomena causing soil degradation. This study was conducted in Eastern Uganda with the following objectives: (1) to assess the amount of soil lost due to the harvesting of cassava roots and sweet potato tubers under low input agriculture, (2) to look into the factors that influence variations in these soil losses, and (3) to estimate the amount of plant nutrients lost due to SLCH for cassava and sweet potato. Soil sticking to roots and tubers was washed and the soil suspension oven dried to estimate the amount of soil lost after harvesting. Mean annual soil loss for cassava was 3.4 tonnes ha⁻¹ and for sweet potato was 0.2 tonnes ha⁻¹. Ammonium acetate lactate extractable soil nutrient losses for cassava were N = 1.71 kg ha⁻¹ harvest⁻¹, P = 0.16 kg ha⁻¹ harvest⁻¹, K = 1.08 kg ha⁻¹ harvest⁻¹ and for sweet potato were N = 0.14, P = 0.01 kg ha⁻¹ harvest⁻¹, K = 0.15 kg ha⁻¹ harvest⁻¹. Difference in soil loss due to crop harvesting for cassava and sweet potato could be due to: (1) smaller yields of sweet potato leading to smaller soil losses on an area basis, (2) smoother skin and less kinked morphology of sweet potato that allowed less soil to adhere, and (3) the fact that sweet potato is planted in mounds which dry out faster compared to the soil under cassava. Soil moisture content at harvesting time and crop age were significant factors that explained the variations in the soil lost at cassava harvesting. Soil loss under cassava justifies the need to conduct further investigations on this process of soil erosion under low input agriculture.     

Cotton management in a compacted subsurface microirrigated coastal plain soil of the southeastern US

A loamy sand Acrisol (Aquic Hapludult) that had been microirrigated for 6 years became so severely compacted that it had root limiting values of soil cone index in the Ap horizon and a genetic hardpan below it. Deep and surface tillage systems were evaluated for their ability to alleviate compaction. Deep tillage included subsoiling or none. Both deep tillage treatments were also surface tilled by disking, chiseling, or not tilling. Subsoiling was located in row or between rows to avoid microirrigation tubes (laterals) that were buried under every other mid row or every row. Cotton (Gossypium hirsutum) was planted in 0.96-m wide rows. Cotton yield was improved by irrigation from 485 to 1022 kg ha⁻¹ because both 2001 and 2002 were dry years. Tillage loosened the soil by an average of 0.5–1.3 MPa; but compacted zones remained outside tilled areas. Subsoiling improved yield by 131 kg ha⁻¹ when performed in row where laterals were placed in the mid rows; but subsoiling did not improve yield when it was performed in mid rows. For subsurface irrigation management in these soils, the treatment with laterals buried under every other mid row was able to accommodate in-row subsoiling which improved yield; and this treatment was just as productive as and had been shown to be less expensive to install than burying laterals under every row.