Reduced Tillage Systems Research Articles

On-farm study of reduced tillage on sandy soil: effects on soil organic carbon dynamic and earthworm abundance

Information about the long-term effects of reduced soil tillage on soil fertility of sandy soils under dry climatic conditions is scarce. Soil organic carbon and earthworm populations were evaluated as soil fertility indicators in an on-farm study between 1996 and 2008. The study comprised adjacent conventional and reduced tillage treatments, undertaken at field (74 ha) scale in Northeast Brandenburg, Germany, with a total of 42 plots on heterogeneous sandy loam. The soil is classified as a Luvisol. Organic carbon stocks at 0–30 cm depth increased between 1996 and 2008 in both tillage systems. This increase corresponded to predictions obtained with the humus balance method based on crop rotation and yields. Increases of organic carbon stocks were slightly more pronounced in plots under reduced tillage. Earthworm population numbers determined by handsorting at 42 plots, were higher in plots under reduced tillage compared to conventional tillage, mainly due to the occurrence of Lumbricus terrestris. The results indicate that reduced tillage systems provide a suitable crop production strategy for maintaining soil fertility on sandy soils under dry climatic conditions.

Agriculture and greenhouse gases, a common tragedy. A review

Increased atmospheric concentrations of greenhouse gases has led to global warming and associated climatic changes. The problem has been aggravated by the perception that the atmosphere is an infinite and toll-free resource. The well-known concept proposed by Garrett Hardin—“The Tragedy of the Commons”—highlights the misuse of common resources, which ultimately lead to their depletion. This article emphasizes the relevance of the same concept to the current climatic changes and highlights the impact of agriculture on the environment. The specific focus is on field crop production and livestock husbandry that have resulted in deteriorating environmental services and increased greenhouse gas emissions. Meanwhile, the total amount of energy consumed by these sectors is enormous, encompassing 11 exajoules (EJ) annually. In addition, the article highlights possible impacts of climate change on agricultural productivity. Considering the foreseen growth of the global human population, it is expected that additional pressures will aggravate natural environments. Adoption of recommended management practices is crucial to reverse the environmental footprint of agriculture and lessen its impact on climate change. Regarding croplands, these practices can include reduced tillage systems, crop residue management, improved management of nutrients and pests, cover cropping, agroforestry, biochar application as soil amendment, and utilization of precision agriculture technologies. In the livestock sector, recommended management practices include changes in animals’ diet and appropriate management of manure. Adoption of these practices is also expected to decrease the on-farm and off-farm energy use. To encourage the adoption of these practices, authorities should provide the farmers with incentives, such as payments for improving environmental services. Also, international regulations must be enforced to instigate a notable shift in human diets with the goal of reducing the environmental impact of food production. Judicious implementation of related policies would be crucial for promoting the required links between agricultural production and environmental sustainability.

Climate, duration, and N placement determine N2O emissions in reduced tillage systems: a meta‐analysis

No-tillage and reduced tillage (NT/RT) management practices are being promoted in agroecosystems to reduce erosion, sequester additional soil C and reduce production costs. The impact of NT/RT on N2 O emissions, however, has been variable with both increases and decreases in emissions reported. Herein, we quantitatively synthesize studies on the short- and long-term impact of NT/RT on N2 O emissions in humid and dry climatic zones with emissions expressed on both an area- and crop yield-scaled basis. A meta-analysis was conducted on 239 direct comparisons between conventional tillage (CT) and NT/RT. In contrast to earlier studies, averaged across all comparisons, NT/RT did not alter N2 O emissions compared with CT. However, NT/RT significantly reduced N2 O emissions in experiments >10years, especially in dry climates. No significant correlation was found between soil texture and the effect of NT/RT on N2 O emissions. When fertilizer-N was placed at ≥5cm depth, NT/RT significantly reduced area-scaled N2 O emissions, in particular under humid climatic conditions. Compared to CT under dry climatic conditions, yield-scaled N2 O increased significantly (57%) when NT/RT was implemented <10years, but decreased significantly (27%) after ≥10years of NT/RT. There was a significant decrease in yield-scaled N2 O emissions in humid climates when fertilizer-N was placed at ≥5cm depth. Therefore, in humid climates, deep placement of fertilizer-N is recommended when implementing NT/RT. In addition, NT/RT practices need to be sustained for a prolonged time, particularly in dry climates, to become an effective mitigation strategy for reducing N2 O emissions.

Soil roughness evolution in different tillage systems under simulated rainfall using a semivariogram-based index

Among the factors that contribute to greater changes in soil surface roughness are the tillage systems and rainfall conditions. This study evaluated the changes of surface roughness under different tillage systems and the application of artificial rain. The experiment was conducted in 2009 and 2010 for conventional tillage (CT), reduced tillage (RT) and no tillage (NT), in micro plots with 1m×1m size for each treatment. Simulated rainfall with intensity of 80mmh−1 was applied. Soil microrelief was measured with a portable laser scanner with a 1-cm horizontal resolution. The height readings were submitted to geostatistical analysis through the semivariogram method, and the index used to represent the roughness of the soil (RI) was extracted from the semivariograms. The RT and NT systems presented higher roughness in the first year, but in the second year, the greatest RI was observed in the NT system. The RI values in the same treatment differed between applied rainfalls only in NT for the second year. In CT, the RI did not differ between the applied rainfalls, but showed the same trend in the two years studied: initially an increase of roughness occurred until a maximum rain amount, then it decreased. Differences between the years studied occurred only in NT, which showed greater RI in the second year in comparison to the first one, CT and RT were similar and did not differ between the two years evaluated.

Role of earthworms in regenerating soil structure after compaction in reduced tillage systems

New non-tillage or reduced tillage agricultural practises are being increasingly adopted but generally result in higher soil compaction. Due to their recognised physical influence mainly through burrow creation, it is often claimed that earthworm activity could alleviate soil compaction in these systems. To put this assumption to the test, an experimental compaction event was carried out on one plot of arable land. The abundance and biomass of earthworms were evaluated in compacted (under wheel tracks) and non-compacted (between wheel tracks) zones, seven times over a two-year period. In addition, the functional consequences of earthworm activity, defined by burrow abundance assessed in 2D and 3D and water infiltration, were measured three times over the same period. The short-term (less than three months) effects of the compaction were clear: soil bulk density increased from 1.46 to 1.57 g cm−3, the abundance and biomass of earthworms were greatly reduced (−40% and −70% respectively) and the number and continuity of macroporosity were lower under wheel tracks at least until a depth of 30 cm. After these initial detrimental effects, we observed a rapid recovery of earthworm populations with no statistical difference between compacted and control zones more than three months after the compaction. However, the recovery of soil functional properties linked to earthworm activity, macroporosity and water infiltration, was much slower and took between 12 and 24 months. Despite these modifications, there were no significant changes in soil bulk density with time during the two-year period. This study demonstrates that earthworms are important actors in the regeneration of compacted soil. Although the complete regeneration of compacted soil by earthworms is a slow process, agricultural practises that promote earthworm density and activity should be encouraged in reduced or minimum tillage systems.

Wepp as a tool for enabling a more comprehensive analysis of the environmental impacts of soil erosion

Cropland area in Uruguay, mostly soybeans, increased 300% during the last decade due to expansion to new areas. Although no-tillage practices are generalized among farmers, soil erosion is still a major environmental and economic issue. A predictive tool as the Water Erosion Prediction Model Project (WEPP), based on soil processes, has never been used in Uruguay. The objective of this research was to evaluate the soil erosion impact of various managements of intensive agriculture on Mollisols of Uruguay, applying the WEPP erosion model. The model was first adjusted and validated for annual erosion estimates of an Abruptic Argiudoll (Nash Sutcliffe (NS)= 0.81 and R2 = 0.89) and a Vertic Argiudoll (NS= 0.86 and R2= 0.90), and later applied to evaluate three Mollisols and one Vertisol with different soil managements. Treatments combined no tillage (NT) and reduced tillage (RT) with different crop rotations. Crop rotations were: continuous soybean (CS), soybean-wheat (SW), soybean-winter cover crop (S-Cover crop), cornsoybean- wheat-3/4 yr pasture (CSW-PPP/PPPP), and corn-soybean-wheat-soybean-wheat-3/4 yr pasture (CSWSWPPP/ PPPP). Soil erosion under RT system or CS was always above 7Mg.ha-1 (T value). Pastures inclusion under NT showed values below 7 Mg.ha-1.WEPP simulated an average erosion rate below T for SW rotation with NT (100m; 3% slope) in three of the four soils studied. However, by varying the slope and the length of the hillslope, the range for which the average annual erosion remains below this level is limited (only 3% - 4%). Moreover, for those hillslopes whose average annual erosion does not exceed the T value, there is still approximately a 25% probability that this may occur any given year. Our work highlights the potential of using WEPP in the development of criteria for assessing sustainability of soil management, alternative to T value of average annual erosion units, including risk analysis.

Using a morphological approach to evaluate the effect of traffic and weather conditions on the structure of a loamy soil in reduced tillage

A morphological approach and soil porosity have been used to evaluate the effect of compaction and climate on the soil structure of a loamy soil in a reduced tillage system. The study was carried out between 2000 and 2006 as part of the long-term “cropping systems and soil structure” experiment conducted in Estrées-Mons in northern France. Soil hydraulic, mechanical and pore morphological properties were also measured to characterise the effects on soil structure dynamics. A complementary characterisation of the soil structure was conducted on a microscale.The method for morphological description of the soil macrostructure was well suited to studying soil structure dynamics in reduced tillage systems. Results showed that the soil structure in the layer without tillage depended in the first instance on compaction intensity. Structural porosity was partly preserved in the cropping system with little compaction. In contrast just one operation, such as the harvest of sugar beet (Beta vulgaris L.), was sufficient to reduce structural porosity for 5 years even though no further compaction occurred during this period. Morphological analysis revealed the evolution of highly compacted zones under the effects of weather conditions. Platy soil structures were systematically observed in the upper part of the highly compacted zones under the tilled layers, with cracking slowly penetrating deeper into the soil with time. The structure types observed corresponded to specific soil properties resulting from the transformation of the soil structure over time. A micro-morphological assessment was performed to get detailed information about the network of cracks. The morphological characterisation showed that a visual morphological approach was insufficient for revealing the entire network of cracks.

Reduced tillage, mulching and rotational effects on maize (Zea mays L.), cowpea (Vigna unguiculata (Walp) L.) and sorghum (Sorghum bicolor L. (Moench)) yields under semi-arid conditions

Proponents of conservation agriculture (CA) argue that the CA approach offers the greatest opportunity to increase the productivity in smallholder agro-ecosystems. This study was designed to assess (1) first year maize, cowpea and sorghum yield responses to a combination of reduced tillage and mulching and (2) maize yield responses to rotation with cowpea and sorghum in reduced tillage systems. Two conservation tillage methods (ripping and planting basins) combined factorially with seven mulch levels (0, 0.5, 1, 2, 4, 8 and 10tha−1) were compared with conventional mouldboard ploughing. The experiment was run for four consecutive growing seasons allowing for a rotation of maize, cowpea, sorghum and maize in some fields used in the study. Crop yields were determined across all tillage and mulch combinations in each year.Tillage system had no significant effect on maize yield while maize grain yield increased with increase in mulch cover in seasons that had below average rainfall. Mulching at 2–4tha−1 gave optimum yields in seasons with below average rainfall. Tillage system and mulching had no significant effect on cowpea yield when soil moisture was not limiting. However, the ripper and basin systems had 142 and 102% more cowpea grain than the conventional system in 2006/2007 because of differences in planting dates used in three systems and poor rainfall distribution. The conventional and ripper systems gave 26 and 38% more sorghum grain than the basin system. Rotating maize with cowpea and sorghum resulted in 114, 123 and 9% more grain than first year maize, maize–maize monocrop and maize–cowpea–maize in the conventional system. In the ripper system, maize–cowpea–sorghum–maize rotation gave 98, 153 and 39% more grain than first year maize, maize–maize monocrop and maize–cowpea–maize rotation. In the basin system, maize–cowpea–sorghum–maize rotation gave 274, 240 and 43% more grain than first year maize, maize–maize monocrop and maize–cowpea–maize rotation. However, long term studies under different soil, climatic and socio-economic conditions still need to be conducted to substantiate the observations made in the reported study.

A comparison of GHG emissions from UK field crop production under selected arable systems with reference to disease control

Crop disease not only threatens global food security by reducing crop production at a time of growing demand, but also contributes to greenhouse gas (GHG) emissions by reducing efficiency of N fertiliser use and farm operations and by driving land use change. GHG emissions associated with adoption of reduced tillage, organic and integrated systems of field crop production across the UK and selected regions are compared with emissions from conventional arable farming to assess their potential for climate change mitigation. The reduced tillage system demonstrated a modest (<20%) reduction in emissions in all cases, although in practice it may not be suitable for all soils and it is likely to cause problems with control of diseases spread on crop debris. There were substantial increases in GHG emissions associated with the organic and integrated systems at national level, principally due to soil organic carbon losses from land use change. At a regional level the integrated system shows the potential to deliver significant emission reductions. These results indicate that the conventional crop production system, coupled to reduced tillage cultivation where appropriate, is generally the best for producing high yields to minimise greenhouse gas emissions and contribute to global food security, although there may be scope for use of the integrated system on a regional basis. The control of crop disease will continue to have an essential role in both maintaining productivity and decreasing GHG emissions.

Quality and dynamics of soil organic matter in a typical Chernozem of Ukraine under different long-term tillage systems

Kravchenko, Y., Rogovska, N., Petrenko, L., Zhang, X., Song, C. and Chen, Y. 2012. Quality and dynamics of soil organic matter in a typical Chernozem of Ukraine under different long-term tillage systems. Can. J. Soil Sci. 92: 429–438. Tillage has been reported to induce changes in soil organic matter (SOM) concentrations and quality. Conversion of plow-tillage to minimum till and no-till (NT) farming enhances the SOM pool. Enrichment of the SOM pool is essential for maintaining fertility of Chernozems, advancing food security, and improving the environment. The main objective of this study was to examine the effect of different tillage systems on the SOM concentration, its quality and dynamics including CO2assimilation by heterotrophic bacteria and humus characteristics – the carbon (C) concentration in humic substances and the labile soil organic C fraction (SOCL) extracted with 0.1 N NaOH – as well as the molecular masses, spectroscopic parameters and physiological effects of humic acids on germinating pea (Pisum sativum L.) seeds. Our study was conducted on a long-term experimental site on a Haplick Chernozem in the Poltava region of Ukraine over a 10-yr period from 1996 to 2006. Results indicate that conversion from conventional to reduced soil tillage systems increased SOM concentrations in 0- to 10-cm soil layer and led to the accumulation of C in fulvic acids and humins. No significant differences in SOM storage in the 0- to 100-cm layer were observed among tillage systems. However, reduced tillage systems had a higher proportion of SOCL, a lower ratio of C in humic acids/C in fulvic acids and more humic acids with molecular masses from 110 to 2000 kDa. Our study demonstrated that the quality and dynamics of SOM are closely related to soil tillage practices.

The after-effect of long-term reduced tillage systems on the biodiversity of weeds in spring crops

A strictly controlled field experiment on traditional and reduced tillage systems as well as herbicide treatment was conducted at the Agricultural Experimental Station of Uhrusk in the years 2007-2011. In the last year of the experiment, the effect of different tillage systems on the level of weed infestation and biodiversity of weeds was determined in all the plots for the crop of common spring wheat &lt;i&gt;Triticum aestivum&lt;/i&gt; L., spring durum wheat &lt;i&gt;Triticum durum&lt;/i&gt; Desf., and oat &lt;i&gt;Avena sativa&lt;/i&gt; L. at two growth stages: tillering (23/24 on BBCH scale) and dough stage (83/85). A higher number and higher air-dry weight of weeds were determined at tillering than at the dough stage. Long-term reduced tillage increased the number of weeds per 1m&lt;sup&gt;2&lt;/sup&gt; at the tillering stage, contrary to herbicide treatment. At the dough stage, a higher number of weeds was observed in the herbicide treatment and reduced tillage plots compared to traditional tillage. The air-dry weight of weeds at the tillering and dough stages of cereals was significantly higher in the case of herbicide treatment than under the traditional and reduced tillage systems. Weed communities in spring wheat, durum wheat and oat included mostly annual weeds. A higher number of weed species was determined in the plot with long-term herbicide treatment than in the plots with reduced and traditional tillage systems.

New pests threat to agricultural plants

Changes in cultivation technologies such as growing plants in monoculture, reduced tillage system, no-tillage system and climate changes, caused an increase of importance of some pests of agricultural crops. The following insect species: the bird cherry-oat aphid, the chloropid gout fly, the wheat ground beetle and the European corn borer, occurring previously in a small number and on limited areas, recently have became the major pests of agricultural plants. Cultivation of maize in monoculture is the main factor influencing the expansion of the western corn rootworm (an invasive pest) in Poland.

Transporte de Atrazina e Diuron no Perfil de um Argissolo

The transport of atrazine and diuron in an argisol profile was observed by using three lysimeters assembled in the laboratory, filled with undisturbed soil. The soil samples were obtained from an area of corn produced in a reduced tillage system. In each lysimeter, 31.95 L of water were applied representing 650.85 mm of rain. The water volumes collected in lysimeters corresponded to 72.57 ± 8.40% of total applied. The hydrodynamic behavior in the three lysimeters was not uniform. On the 5th day the herbicides diuron and atrazine were applied in doses equivalent to 2.5 and 2.4 kg per hectare of active ingredient, respectively. High concentrations of herbicides were recorded at the depth of 5 cm, with a rainfall of 15 mm applied. Pesticides remained in the soil for a period of about 100 days. The amount of diuron recovered was 1.36% of total applied and the atrazine was 4.03%. From the total mass of atrazine recovered, 78% occurred within the first 19 days

Wepp as a tool for enabling a more comprehensive analysis of the environmental impacts of soil erosion

Cropland area in Uruguay, mostly soybeans, increased 300% during the last decade due to expansion to new areas. Although no-tillage practices are generalized among farmers, soil erosion is still a major environmental and economic issue. A predictive tool as the Water Erosion Prediction Model Project (WEPP), based on soil processes, has never been used in Uruguay. The objective of this research was to evaluate the soil erosion impact of various managements of intensive agriculture on Mollisols of Uruguay, applying the WEPP erosion model. The model was first adjusted and validated for annual erosion estimates of an Abruptic Argiudoll (Nash Sutcliffe (NS)= 0.81 and R2 = 0.89) and a Vertic Argiudoll (NS= 0.86 and R2= 0.90), and later applied to evaluate three Mollisols and one Vertisol with different soil managements. Treatments combined no tillage (NT) and reduced tillage (RT) with different crop rotations. Crop rotations were: continuous soybean (CS), soybean-wheat (SW), soybean-winter cover crop (S-Cover crop), cornsoybean- wheat-3/4 yr pasture (CSW-PPP/PPPP), and corn-soybean-wheat-soybean-wheat-3/4 yr pasture (CSWSWPPP/ PPPP). Soil erosion under RT system or CS was always above 7Mg.ha-1 (T value). Pastures inclusion under NT showed values below 7 Mg.ha-1.WEPP simulated an average erosion rate below T for SW rotation with NT (100m; 3% slope) in three of the four soils studied. However, by varying the slope and the length of the hillslope, the range for which the average annual erosion remains below this level is limited (only 3% - 4%). Moreover, for those hillslopes whose average annual erosion does not exceed the T value, there is still approximately a 25% probability that this may occur any given year. Our work highlights the potential of using WEPP in the development of criteria for assessing sustainability of soil management, alternative to T value of average annual erosion units, including risk analysis.

Phosphorus Determination after Mehlich 3 Extraction and Anion Exchange Resin in an Agricultural Soil of Northwestern Spain

Differences in soil phosphorus (P) contents measured by various techniques may have implications for agronomic and environmental testing. Reduced-tillage systems combined with surface manure application increase the potential risk of nutrient losses by surface runoff. A field trial was conducted to evaluate the effect of livestock slurry on nutrient accumulation at the surface layer of an acidic soil rich in organic matter with excess P levels and loamy texture. Two reduced-tillage systems, no tillage (NT) and minimum tillage (MT), and four different fertilizer treatments were assessed. The amounts of P extracted by anion-exchange resin (AER) and by Mehlich 3 (M3) were compared; in addition, differences between two determination methods of P contents extracted by Mehlich 3, namely molybdic acid colorimetric standard procedure (M3-COL) and inductively coupled plasma–mass spectroscopy (M3-ICP), were evaluated. Ninety-six soil samples were taken from the 0- to 5-cm surface layer in three successive dates after increasing manure addition. Colorimetric Mehlich 3 P ranged from 49 to 431 mg dm–3. The ranks of mean extractable soil P concentrations were AER < M3-COL < M3-ICP. The linear correlation coefficient between M3-COL and M3-ICP was highly significant (R2 = 0.89; P < 0.01), but a two-straight-lines model or a quadratic relationship were more adequate for describing the dependence between the two determination procedures after M3 extraction. Relative and absolute differences between M3-COL and M3-ICP showed a tendency to increase as organic carbon content increased. Phosphorus content extracted by AER and M3-COL or M3-ICP reported a significant but much less predictable relationship with R2 values of 0.27 and 0.21 (n = 96), respectively. The P in the surface layer accumulated more under NT than under MT.

MUNGBEAN RESPONSE TO TILLAGE SYSTEMS AND PHOSPHORUS MANAGEMENT UNDER MOISTURE STRESS CONDITION

A field experiment on the response of mungbean (Vigna radiata L. Wilczek) to tillage systems (reduced and conventional) and phosphorus management under rainfed condition was conducted at New Developmental Farm of NWFP Agricultural University, Peshawar during summer 2005. Combined analysis of the data indicated that reduced tillage produced higher number of branches (3.8), pods plant−1 (17), number of grains pod−1 (9.0), 1000 grain weight (47.34 g), while higher plants m−2 (31), biological yield (2992 kg ha−1) and grain yields (663 kg ha−1) and number of plants at harvest (281200 ha−1) were obtained from conventional tillage system. Phosphorus applied at the rate of 40 kg P2O5 ha−1 significantly increased plant heights (57 cm), number of branches (4.1) and pods plant−1 (19), number of grains pod−1 (10), 1000 grain weight (48.42 g), biological (3197 kg ha−1) and grain yields (684 kg ha−1). Placement application method of phosphorus had significantly greater number of branches plant−1 (3.8), number of pods plant−1 (17), and number of grains pod−1 (9.0), 1000 grain weight (47.39 g), biological (2797 kg ha−1) and grain yield (610 kg ha−1), respectively. The interaction between tillage (T) and method of application (M) showed that highest number of pods plant−1 (18), and number of branches plant−1 (3.9) were recorded in plots of reduced tillage system in which placement method of P2O5 application was used. The interaction between methods of application (M) and P levels showed that greater number of pods (20), biological (3368 kg ha−1), and grain yield (718 kg ha−1) were obtained when 40 kg P2O5 ha−1 was applied by placement application method.

Development of reduced tillage systems in organic farming in Europe

AbstractNo-tillage and reduced tillage are considered sustainable options of conservation tillage. While US organic farming researchers have focused on no-tillage, European organic farming researchers have concentrated on reduced tillage through the reduction of tillage depth or the application of noninversion tillage practices. Combinations of these two approaches have been implemented by the use of the two-layer plow or the layer cultivator. These innovations often came from farmers, aiming at reducing off-farm inputs such as fuel, and saving costs and labor, while at the same time building up soil fertility. Systematic, documented research on reduced tillage systems in Europe started only 1–2 decades ago, with experiments in Germany, Switzerland and France. While most experiments mimic stockless farms, other experiments include fodder crops such as grass–clover ley and applications of manure and slurry as is typical for mixed farms with animals and crops. Soil organic carbon, microbial activity and soil structure are often improved in the upper soil layer under reduced tillage compared with plowed soils. However, these positive findings were confounded by lower yields in some cases and enhanced weed pressure, except for the two-layer plow. Often it was not possible to determine whether and to what extent yield reduction was due to weed competition or to nitrogen shortage, because of retarded nitrogen mineralization in spring in reduced tillage systems. In systems with manure use, also higher soil fertility measures concomitant with increased yields were reported under reduced tillage. Indeed, it is difficult to gain an overview on research activities dealing with reduced tillage in organic farming in Europe due to dispersed experimental infrastructures and the scarcity of peer-reviewed published literature. To close this knowledge gap a European Network is being established aiming at further developing reduced tillage systems in organic farming, addressing the issue of carbon sequestration and N2O emissions, as well as weed and nutrient management.

Estimation of decay constants for crop residues measured over 15 years in conventional and reduced tillage systems in a coarse-textured soil in southern Ontario

Beyaert, R. P. and Voroney, R. P. 2011. Estimation of decay constants for crops residues measured over 15 years in conventional and reduced tillage systems in a coarse-textured soil in southern Ontario. Can. J. Soil Sci. 91: 985–995. Crop residues are the primary means of sustaining soil organic matter levels in agricultural soils. This study was undertaken to determine the effects of tillage practices on the rate of decomposition of crop residues over a 15-yr period under field conditions in southern Ontario. Microplots were amended with14C-labelled above-ground residues of five annual agricultural crops: corn (Zea mays L.), soybean (Glycine max L.), winter wheat (Triticum aestivum L.), winter rye (Secale cereale L.) and tobacco (Nicotiana tobaccum L.). The crop residues were added to the soil immediately following harvest during the 1990 growing season using a simulated conventional mouldboard plough–disc management (CT) or conservation tillage management (RT), and the amounts of crop residues remaining were measured periodically. The rate of decomposition of the labile C was positively correlated to the levels of hot-water soluble C and N content and negatively correlated to the C:N ratio and hemicellulose concentration of the residues. Decomposition of the residue C was greater under CT during the initial phase of decomposition, indicating that the incorporated residues were exposed to a more favourable environment for microbial activity compared with surface-applied residues. Kinetic analysis of residue decomposition showed that residues managed under CT had a larger labile component and faster rate of decomposition and a smaller resistant component with a slower decomposition rate than RT. Comparisons of models describing the decomposition of combined crops/tillage practices did not describe the decomposition process as well as models for individual crop/tillage combinations.

Long‐Term Influence of Tillage and Fertilization on Net Carbon Dioxide Exchange Rate on Two Soils with Different Textures

The importance of agricultural practices to greenhouse gas mitigation is examined worldwide. However, there is no consensus on soil organic carbon (SOC) content and CO emissions as affected by soil management practices and their relationships with soil texture. No-till (NT) agriculture often results in soil C gain, though, not always. Soil net CO exchange rate (NCER) and environmental factors (SOC, soil temperature [T], and water content [W]), as affected by soil type (loam and sandy loam), tillage (conventional, reduced, and NT), and fertilization, were quantified in long-term field experiments in Lithuania. Soil tillage and fertilization affected total CO flux (heterotrophic and autotrophic) through effect on soil SOC sequestration, water, and temperature regime. After 11 yr of different tillage and fertilization management, SOC content was 23% more in loam than in sandy loam. Long-term NT contributed to 7 to 27% more SOC sequestration on loam and to 29 to 33% more on sandy loam compared with reduced tillage (RT) or conventional tillage (CT). Soil water content in loam was 7% more than in sandy loam. Soil gravimetric water content, averaged across measurement dates and fertilization treatments, was significantly less in NT than CT and RT in both soils. Soil organic carbon content and water storage capacity of the loam and sandy loam soils exerted different influences on NCER. The NCER from the sandy loam soil was 13% greater than that from the loam. In addition, NCER was 4 to 9% less with NT than with CT and RT systems on both loam and sandy loam soils. Application of mineral NPK fertilizers promoted significantly greater NCER from loam but suppressed NCER by 15% from sandy loam.

EFFECT OF REDUCED TILLAGE AND MINERAL FERTILIZER APPLICATION ON MAIZE AND SOYBEAN PRODUCTIVITY

SUMMARYReduced tillage is said to be one of the potential ways to reverse land degradation and ultimately increase the productivity of degrading soils of Africa. We hypothesised that crop yield following a modest application of 2 t ha−1 of crop residue in a reduced tillage system is similar to the yield obtained from a conventional tillage system, and that incorporation of legumes in a cropping system leads to greater economic benefits as opposed to a cropping system involving continuous maize. Three cropping systems (continuous maize monocropping, legume/maize intercropping and rotation) under different tillage and residue management systems were tested in sub-humid western Kenya over 10 seasons. While soybean performed equally well in both tillage systems throughout, maize yield was lower in reduced than conventional tillage during the first five seasons but no significant differences were observed after season 6. Likewise, with crop residue application, yields in conventional and reduced tillage systems are comparable after season 6. Nitrogen and phosphorus increased yield by up to 100% compared with control. Gross margins were not significantly different among the cropping systems being only 6 to 39% more in the legume–cereal systems relative to similar treatments in continuous cereal monocropping system. After 10 seasons of reduced tillage production, the economic benefits for our cropping systems are still not attractive for a switch from the conventional to reduced tillage.