Erosional effects on soil organic carbon stock in an on-farm study on Alfisols in west central Ohio

Soil erosion and depositional processes in relation to land use and soil management need to be quantified to better understand the soil organic carbon (SOC) dynamics. This study was undertaken on a Miamian soil (Oxyaquic Hapludalfs) under on-farm conditions in western Ohio with the objectives of evaluating the effects of degree of erosion on SOC stock under a range of tillage systems. Six farms selected for this study were under: no-till (NT) for 15, 10, 6 and 1.5 years; chisel till every alternate year with annual manure application (MCT); and annual chisel till (ACT). A nearby forest (F) site on the same soil was chosen as control. Using the depth of A horizon as an indicator of the degree of erosion, four erosion phases identified were: uneroded (flat fields under F, NT15, and on the summit of sloping fields under NT10, NT6, NT1.5 and MCT); deposition (NT10, NT6, NT1.5 and ACT); slight (NT10, MCT and ACT); and moderate erosion (NT10 and ACT). Core and bulk soil samples were collected in triplicate from four depths (i.e., 0–10, 10–20, 20–30 and 30–50 cm) for each erosional phase in each field for the determination of bulk density, and SOC concentrations and stocks. SOC concentration in NT fields increased at a rate of 5% year⁻¹ for 0–10 cm and 2.5% year⁻¹ for 10–20 cm layer with increasing duration under NT. High SOC concentration for NT15 is indicative of SOC-sequestration potential upon conversion from plow till to NT. SOC concentration declined by 19.0–14.5 g kg⁻¹ in MCT and 11.3–9.7 g kg⁻¹ in NT10 between uneroded and slight erosion, and 12.0–11.2 g kg⁻¹ between slight and moderate erosion in ACT. Overall SOC stock was greatest in the forest for each of the four depths. Total SOC stock for the 50 cm soil layer varied in the order F (71.99 Mg ha⁻¹) > NT15 (56.10 Mg ha⁻¹) > NT10 (37.89 Mg ha⁻¹) = NT6 (36.58 Mg ha⁻¹) for uneroded phase (P < 0.05). The lack of uneroded phase in ACT indicated high erosion risks of tillage, as also indicated by the high SOC stock for deposition phase from 0 to 50 cm soil layer (ACT (56.56 Mg ha⁻¹) > NT1.5 (42.70 Mg ha⁻¹) > NT10 (30.97 Mg ha⁻¹)). Tillage increased soil erosion and decreased SOC stock for top 10 cm layer for all erosional phases except deposition.     

Effects of mechanical energy inputs on soil respiration at the aggregate and field scales

Cultivation machinery applies large amounts of mechanical energy to the soil and often brings about a decrease in soil organic carbon (SOC). New experiments on the effects of mechanical energy inputs on soil respiration are reported and the results discussed. In the laboratory, a specific energy, K, of 150 J kg⁻¹, similar to that experienced during typical cultivation operations, was applied to soil aggregates using a falling weight. Respiration (carbon dioxide, CO₂ emission) of the samples was then measured by an electrical conductimetric method. Basal respiration (when K=0) measured on Chromic Luvisol aggregates, was found to increase with increasing SOC, from 1.88 μg CO₂ g⁻¹ h⁻¹ for a permanent fallow soil (SOC=11 g kg⁻¹) to 8.25 μg CO₂ g⁻¹ h⁻¹ for a permanent grassland soil (SOC=32 g kg⁻¹). Basal respiration of a Calcic Cambisol, more than doubled (2.0–5.2 μg CO₂ g⁻¹ h⁻¹) with increasing gravimetric soil water contents. Mechanical energy inputs caused an initial burst of increased respiration, which lasted up to 4 h. Over the following 4–24 h period, arable soils with lower SOC contents, (11–21 g kg⁻¹), respiration rates dropped back to a level, approximately 1.14 times higher than the basal value. However, grassland soils with higher SOC contents (28–32 g kg⁻¹), increases in this longer-term respiration rate following 150 J kg⁻¹ of energy, were negligible. A field experiment, in which CO₂ was measured by infra-red absorption, also showed that tillage stimulated increased levels of soil respiration for periods ranging from 12 h to more than one week. The highest respiration rates, 80 mg CO₂ m⁻² h⁻¹ were associated with high energy, powered tillage on clay soils. On the same soil, low energy draught tillage resulted in a respiration rate of approximately half this value. The results of these experiments are discussed in relation to equilibrium levels of soil organic matter. The application of known quantities of mechanical energy to soil aggregates under laboratory conditions, in order to simulate the effect of different cultivation practices, when combined with the subsequent measurement of soil respiration, can provide useful indication of the likely consequences of soil management on SOC.     

Effect of cropland management and slope position on soil organic carbon pool at the North Appalachian Experimental Watersheds

Soil organic matter is strongly related to soil type, landscape morphology, and soil and crop management practices. Therefore, long-term (15–36-years) effects of six cropland management systems on soil organic carbon (SOC) pool in 0–30 cm depth were studied for the period of 1939–1999 at the North Appalachian Experimental Watersheds (<3 ha, Dystric Cambisol, Haplic Luvisol, and Haplic Alisol) near Coshocton, OH, USA. Six management treatments were: (1) no tillage continuous corn with NPK (NC); (2) no tillage continuous corn with NPK and manure (NTC-M); (3) no tillage corn–soybean rotation (NTR); (4) chisel tillage corn–soybean rotation (CTR); (5) moldboard tillage with corn–wheat–meadow–meadow rotation with improved practices (MTR-I); (6) moldboard tillage with corn–wheat–meadow–meadow rotation with prevalent practices (MTR-P). The SOC pool ranged from 24.5 Mg ha⁻¹ in the 32-years moldboard tillage corn (Zea mays L.)–wheat (Triticum aestivum L.)–meadow–meadow rotation with straight row farming and annual application of fertilizer (N:P:K=5:9:17) of 56–112 kg ha⁻¹ and cattle (Bos taurus) manure of 9 Mg ha⁻¹ as the prevalent system (MTR-P) to 65.5 Mg ha⁻¹ in the 36-years no tillage continuous corn with contour row farming and annual application of 170–225 kg N ha⁻¹ and appropriate amounts of P and K, and 6–11 Mg ha⁻¹ of cattle manure as the improved system (NTC-M). The difference in SOC pool among management systems ranged from 2.4 to 41 Mg ha⁻¹ and was greater than 25 Mg ha⁻¹ between NTC-M and the other five management systems. The difference in the SOC pool of NTC-M and that of no tillage continuous corn (NTC) were 16–21 Mg ha⁻¹ higher at the lower slope position than at the middle and upper slope positions. The effect of slope positions on SOC pools of the other management systems was significantly less (<5 Mg ha⁻¹). The effects of manure application, tillage, crop rotation, fertilizer rate, and soil and water conservation farming on SOC pool were accumulative. The NTC-M treatment with application of NPK fertilizer, lime, and cattle manure is an effective cropland management system for SOC sequestration.     

Effect of the conversion of grassland to spring wheat field on the CO2 emission characteristics in Inner Mongolia, China

Chinese grasslands have undergone great changes in land use in recent decades. Approximately 18.2% of the present arable land in China originated from the cultivation of grassland, but its impact on the carbon cycle has not been fully understood. This study was conducted in situ for 3 years to assess the comprehensive effects of cultivation of temperate steppe on soil organic carbon (SOC) and soil respiration rates as well as ecosystem respiration. As compared with those in the Stipa baicalensis steppe, the SOC concentrations at depths of 0–10 and 10–20 cm in the spring wheat field were found to have decreased by 38.3 and 17.4% respectively from 29.5 and 21.9 g kg⁻¹ to 18.2 and 18.1 g kg⁻¹ after a cultivation period of 30 years. Accordingly, the total amounts of soil respiration through the growing season (from April to September) in 2002, 2003 and 2004 were 265.2, 282.2 and 237.4 g C m⁻² respectively in the spring wheat field, which were slightly lower than the values of 342.2, 412.0 and 312.1 g C m⁻² in the S. baicalensis steppe, while ecosystem respiration of 690.9, 991.2 and 569.6 g C m⁻² respectively in the spring wheat field were markedly higher than those of 447.0, 470.9 and 429.7 g C m⁻² in the steppe plot. Similar seasonal variations of ecosystem respiration and soil respiration existed in both sample sites. Respiration rates were higher and greater differences existed in both ecosystem respiration and soil respiration during the exuberant growth stage of plants (from mid-June to mid-August). However, in the slower-growth period of the growing season (before late May and after late August), the CO₂ effluxes of the two sample sites were similar and remained at a relatively low level. The results also showed that ecosystem respiration and soil respiration were under similar environmental controls in both sample sites. Soil water content at a depth of 0–10 cm and soil temperatures at 5 and 10 cm were the main factors affecting the variations in ecosystem respiration and soil respiration rates in droughty years of 2002 and 2004 and in the rainy 2003, respectively. This study suggests that the conversion of the grassland to the spring wheat field has increased the carbon loss of the whole ecosystem due to the change of vegetation cover type and significantly reduced the carbon storage of surface soil. In addition, the tillage of grassland had different effects on ecosystem respiration and soil respiration. The effects were also dissimilar in different growth stages, which should be fully considered when assessing and predicting the effects of cultivation on the net CO₂ balance of grassland ecosystems.     

Cover crop effect on soil carbon fractions under conservation tillage cotton

Cover crops may influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. We examined the influence of legume [crimson clover (Trifolium incarnatum L.)], nonlegume [rye (Secale cereale L.)], blend [a mixture of legumes containing balansa clover (Trifolium michelianum Savi), hairy vetch (Vicia villosa Roth), and crimson clover], and rye + blend mixture cover crops on soil C fractions at the 0–150 mm depth from 2001 to 2003. Active fractions of soil C included potential C mineralization (PCM) and microbial biomass C (MBC) and slow fraction as soil organic C (SOC). Experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) under dryland cotton (Gossypium hirsutum L.) in central Georgia and in Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under irrigated cotton in southern Georgia, USA. Both dryland and irrigated cotton were planted in strip tillage system where planting rows were tilled, thereby leaving the areas between rows untilled. Total aboveground cover crop and cotton C in dryland and irrigated conditions were 0.72–2.90 Mg C ha⁻¹ greater in rye + blend than in other cover crops in 2001 but was 1.15–2.24 Mg C ha⁻¹ greater in rye than in blend and rye + blend in 2002. In dryland cotton, PCM at 50–150 mm was greater in June 2001 and 2002 than in January 2003 but MBC at 0–150 mm was greater in January 2003 than in June 2001. In irrigated cotton, SOC at 0–150 mm was greater with rye + blend than with crimson clover and at 0–50 mm was greater in March than in December 2002. The PCM at 0–50 and 0–150 mm was greater with blend and crimson clover than with rye in April 2001 and was greater with crimson clover than with rye and rye + blend in March 2002. The MBC at 0–50 mm was greater with rye than with blend and crimson clover in April 2001 and was greater with rye, blend, and rye + blend than with crimson clover in March 2002. As a result, PCM decreased by 21–24 g CO₂–C ha⁻¹ d⁻¹ but MBC increased by 90–224 g CO₂–C ha⁻¹ d⁻¹ from June 2001 to January 2003 in dryland cotton. In irrigated cotton, SOC decreased by 0.1–1.1 kg C ha⁻¹ d⁻¹, and PCM decreased by 10 g CO₂–C ha⁻¹ d⁻¹ with rye to 79 g CO₂–C ha⁻¹ d⁻¹ with blend, but MBC increased by 13 g CO₂–C ha⁻¹ d⁻¹ with blend to 120 g CO₂–C ha⁻¹ d⁻¹ with crimson clover from April 2001 to December 2002. Soil active C fractions varied between seasons due to differences in temperature, water content, and substrate availability in dryland cotton, regardless of cover crops. In irrigated cotton, increase in crop C input with legume + nonlegume treatment increased soil C storage and microbial biomass but lower C/N ratio of legume cover crops increased C mineralization and microbial activities in the spring.     

Effects of reforestation and deforestation on soil properties in humid mountainous areas: a case study in Wolong Nature Reserve, Sichuan province, China

Abstract. Natural secondary succession, forest planting and agricultural practices after deforestation affect soil properties in many ways. During the last 50 years, land uses have greatly changed in the mountainous areas in southwestern China as the result of deforestation and cultivation. A study was initiated in Wolong Nature Reserve, Sichuan province to elucidate the complex relationships in a humid mountainous region. Soil properties under six typical land use types (natural forest, grassland, shrub, secondary forest, cultivated land and reforested land) were compared. Significant differences between land uses were found for soil bulk density (BD), total nitrogen (TN), soil organic carbon (SOC), available phosphorus (AP) and available potassium (AK). Cultivated land had the lowest levels for most soil properties compared to other land uses and shrubland had a higher SOC, TN and available nitrogen (AN) than other land uses. Soils under grassland and shrub contained the greatest carbon mass (TC). Further studies on reforested land indicated that soil properties could be changed by length of reforestation. The SOC and TN in particular showed a linear relationship with years since reforestation. The results suggested that in an area of China where the climate favours secondary succession, 'leave nature as it is' is a better choice than the policy 'change farmland to forest land ', especially for the mountainous regions where there is lack of labour and financial support.     

黄土高原半干旱区不同土地利用下的土壤有机碳、碳组分和土壤营养

Cropland (CP), native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L. ) (ST), and branchytamarisk (Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China. Total organic carbon (TOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), total N (TN), nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N), ammonium nitrogen (NH₄⁺-N), total P, and available P (AP) were measured. The results showed that SOC in NG, ST and BT were 12.7%, 27.7% and 34.8% higher than that of the cropland, respectively. LFOC, light fraction (LF) dry matter, ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland. Cropland had the highest TN, the sum of NO₃^--N and NO₂^--N, TP and AP due to the use of chemical fertilizers. TOC significantly correlated with LFOC, HFOC and C/N. LFOC significantly correlated with dry matter of the LF and C/N. TN, the sum of NO₃^--N and NO₂^--N and AP were significantly negatively correlated with TOC and LFOC. Therefore, land use conversion from cropland to shrub land, or maybe grassland, contributed to SOC sequestration and improved soil nutrients stabilization.     

Soil organic carbon changes after 12 years of no-tillage and tillage of Grantsburg soils in southern Illinois

Many factors including management history, soil type, climate, and soil landscape processes affect the dynamics of soil organic carbon (SOC). The primary objective of this research was to determine the effects of no-tillage and tillage systems on the SOC content after 12 years of controlled treatments. A tillage experiment with three treatments (no-till (NT), chisel plow (CP) and moldboard plow (MP)) was initiated in the spring of 1989 in southern Illinois. The plot area was previously in a tall fescue hayland for 15 years and had a 6% slope. Maize (Zea mays L.) and soybean (Glycine max L. Merr.) were grown in the plot area on a yearly rotation system starting with maize. Periodically, the SOC content of various soil layers, to a depth of either 30 or 75 cm, was measured and expressed on both a gravimetric and volumetric basis. After 12 years, the 0–15 cm surface soil layer of MP was significantly lower in SOC than the NT and CP plots. For all but 2 values, the significance of findings did not change with the form of expression (gravimetric versus volumetric). The surface layer (0–15 cm), subsoil (15–75 cm), and rooting zone (0–75 cm) of all treatments had reduction in SOC on a volumetric basis when compared to the pre-treatment values for sod. At the end of the 12-year study, the MP system had significantly less SOC in the surface layer, subsurface layer and rooting zone than the NT system at comparable depths. After 12 years of tillage under a maize–soybean rotation, the NT treatment sequestered or maintained more SOC stock (47.0 Mt ha⁻¹) than the CP (43.7 Mt ha⁻¹) and MP (37.7 Mt ha⁻¹) treatments. The annual rate of SOC stock build up in the root zone (0–75 cm), above the MP system base, was 0.71 Mt ha⁻¹ year⁻¹ for the NT system and 0.46 Mt ha⁻¹ year⁻¹ for the CP system. For land coming out of the Conservation Reserve Program and returning to row crop production, NT and CP systems would maintain more SOC stock than MP system and reduce CO₂ emissions to the atmosphere.     

Long-term effects of tillage systems and rotations on soil structural stability and organic carbon stratification in semiarid central Spain

Under semiarid Mediterranean climatic conditions, soils typically have low organic matter content and weak structure resulting in low infiltration rates. Aggregate stability is a quality indicator directly related to soil organic matter, which can be redistributed within soil by tillage. Long-term effects (1983–1996) of tillage systems on water stability of pre-wetted and air dried aggregates, soil organic carbon (SOC) stratification and crop production were studied in a Vertic Luvisol with a loam texture. Tillage treatments included conventional tillage (CT), minimum tillage (MT) and zero tillage (ZT) under winter wheat (Triticum aestivum L.) and vetch (Vicia sativa L.) rotation (W–V), and under continuous monoculture of winter wheat or winter barley (Hordeum vulgare L.) (CM). Aggregate stability of soil at a depth of 0–5 cm was much greater when 1–2 mm aggregates were vacuum wetted prior to sieving (83%) than when slaked (6%). However, slaking resulted in tillage effects that were consistent with changes in SOC. Aggregate stability of slaked aggregates was greater under ZT than under CT or MT in both crop rotations (i.e., 11% vs. 3%, respectively).

SOC under ZT tended to accumulate in the surface soil layer (0–5 and 5–10 cm) at the expense of deeper ones. At depths of 10–20 and 20–30 cm no differences in SOC were encountered among tillage systems, but CT exhibited the highest concentration at 30–40 cm depth. Nevertheless, when comparisons were made on mass basis (Mg ha⁻¹), significant differences in stocked SOC were observed at depths of 0–10 and 0–20 cm, where ZT had the highest SOC content in both rotations. The stock of SOC to a depth of 40 cm, averaged across crop rotations, was greater under ZT (43 Mg ha⁻¹) than under CT (41 Mg ha⁻¹) and MT (40 Mg ha⁻¹) although these figures were not significantly different. Likewise, no significant differences were encountered in the stock of SOC to a depth of 40 cm among crop rotations (i.e., 42 Mg ha⁻¹ for W–V vs. 40 Mg ha⁻¹ for CM).

Crop production with wheat–vetch and continuous cereal showed no differences among tillage systems. Yields were strongly limited by the environmental conditions, particularly the amount of rainfall received in the crop growth season and its distribution. Similar yield and improved soil properties under ZT suggests that it is a more sustainable system for the semiarid Mediterranean region of Spain.     

典型喀斯特峰丛洼地坡面土壤养分空间变异性研究

采用线形取样,利用地统计学方法研究了典型喀斯特峰丛洼地坡面土壤养分的空间变异特征.结果表明:有机碳、全氮、碱解氮和速效钾具有相似的空间变异结构,其变程变化在212～251 m之间,与坡面不同土地利用方式的空间范围相当.全磷和全钾的变异尺度较小,为141.2 m和120.6m.受部分耕地施用磷肥影响,速效磷的变异尺度最小,仅为85.1 m.除pH值外,土壤各养分均表现为强烈的空间相关性.有机碳、全氮、碱解氮等养分的空间分布表现出随着海拔高度增加而增大的特征,人类的耕作管理和峰丛洼地特殊的水文地质过程是影响土壤养分空间变异的主要因素.     

Changes in soil properties in southern Beijing Municipality following land reform

Following land reform in China in the early 1980s, farm management practices, such as the type of crops grown and their rotations, intensity of cropping and fertilizer and pesticide use, underwent drastic changes. To investigate how these changes affected soil properties and ultimately the sustainability of agricultural production, a case study was conducted in Daxing County (southern Beijing Municipality). Soil in the Daxing area was sampled in 1982 at the onset of land reform and again in 2000. Surface soil (0–20 cm) samples were collected and analyzed for organic matter (OM), total nitrogen (TN), and available N (AN), P (AP) and K (AK) contents. The soil OM, TN, AN, and AP all increased significantly while AK decreased slightly, but significantly, for the sampling area over the 18-year study period. Increased crop yield (higher biomass production) with increasing fertilizer application combined with soil conservation measures that have retained more crop residue on land, are responsible for the increases in soil OM, N and P concentrations. However, the slight decreases in AK reflect the increased cropping intensity and low AK supplying power of these coarse textured soils as well as the low K fertilizer input.     

桂西北典型环境移民迁入区土壤养分特征分析

在桂西北典型环境移民迁入区,分析了5种土地利用方式表层(0-20 cm)土壤有机质(SOM)、全量养分和速效养分的变化特征.结果表明,根据变异系数(Cv)大小,除速效磷(AP)为强变异外Cv＞1.0),其余土壤养分都为中等变异(0.1＜Cv＜1.0).整体而言,移民迁入区SOM、全氮(TN)含量处于较高水平,速效氮(AN)、速效磷(AP)含量处于中等水平,全磷(TP)、速效钾(AK)处于偏低水平,而全钾(TK)处于低水平.土地利用方式是影响土壤养分的主要因素.灌丛和荒草地的SOM,TN,AN处于较高水平,果园和旱地则处于中等水平;次生林SOM处于较高水平,TN处于中等水平,而AN处于偏低水平.除旱地和果园AP含量处于中等水平外,不同利用方式土壤的TP,TK,AP,AK含量处于低或偏低水平.由于采取了较好的水土保持措施,移民后较大规模的土地利用变化没有导致明显的土壤退化,但需要增加磷钾肥的施用量.     

Land configuration and soil nutrient management options for sustainable crop production on Alfisols and Vertisols of southern peninsular India

Land configuration in combination with nutrient management has the potential to improve the productivity of Alfisols and Vertisols in the semi-arid tropics. A four year (1989–1990 and 1992–1993) field experiment was conducted at Coimbatore, India on Alfisols (Chromic Cambisol) to compare the effect of land configuration and nutrient management practices on yield of rainfed sorghum (Sorghum bicolor (L.) Moench). The land configuration treatments were flat bed (FB, the traditional practice), open ridging (OR, ridges, 45 cm apart and 30 cm high) and tied ridging (TR, same as OR plus ridges were tied randomly). The manure and fertilisers were farm yard manure (FYM, livestock excreta plus litter at 5 Mg ha⁻¹) and coir dust (CD, by-product after the extraction of coir from the coconut (Cocos nucifera L.) husk at 12.5 Mg ha⁻¹) in combination with nitrogen (N) and phosphorus (P) fertiliser levels. Tied ridges stored 14% more soil water and produced 14% and 11% more grain and straw yields of sorghum, respectively, than did flat bed. However, crop yield in TR was comparable with OR. Application of CD at 12.5 Mg ha⁻¹ combined with 40 kg N ha⁻¹ and 9 kg P ha⁻¹ was beneficial for more soil water storage and increased yield of sorghum by 7% over FYM at 5 Mg ha⁻¹ + 40 kg N ha⁻¹ and 9 kg P ha⁻¹. In Vertisols (Vertic Cambisols), experiments were conducted for two years (1991–1992 and 1992–1993) to evaluate land configuration practices. The treatments were broad bed furrow (BBF, 120 cm wide bed with 30 cm wide and 15 cm deep furrows on both sides), compartmental bunding (CB, bunds of 15 cm height formed in all the four sides to form a check basin of 6 m × 5 m size), ridging (RD, ridges were formed for each and every row of the crop manually at four weeks after sowing) and FB under sorghum + pigeonpea (Cajanus cajan (L.) Millsp) and pearl millet (Pennisetum glacum (L.) Stuntz) + cowpea (Vigna unguiculata (L.) Walp) intercropping separately. Compartmental bunding stored 22% more soil moisture and increased the yield of sorghum + pigeonpea intercropping than did FB in a low rainfall year. In a high rainfall year, BBF produced 34% and 33% more grain yield of sorghum and pearl millet base crops, respectively, over FB. However, BBF and CB were comparable. Pigeonpea intercrop under sorghum followed the same trend as its base crop, whereas, yield of cowpea differed compared to the pearl millet base crop. Tied ridging and application of manures (CD or FYM) in combination with inorganic N and P fertiliser can increase the soil water storage and yield of crops compared to traditional flat bed cultivation in rainfed Alfisol and related soils of semi-arid tropics. Similarly BBF and CB land configuration practices could be adopted on Vertisols for better water conservation to increase the soil fertility and productivity of intercropping systems.     

Diesel and glyphosate price changes benefit the economics of conservation tillage versus traditional tillage

Recent increases in diesel price and decreases in glyphosate [N-(phosphonomethyl) glycine] price should favor the profitability and farmer acceptance of herbicide-intensive conservation tillage systems versus fuel-intensive traditional tillage (TT) systems. Profitability results from a long-term field experiment that compared TT, minimum tillage (MT), and delayed minimum tillage (DMT) systems for winter wheat–(Triticum aestivum L.)summer fallow in eastern Washington, USA were calculated using both 1998 and 2005 input prices. Net returns for the MT and DMT systems increased by US$ 6.37 and 6.30 (rotational ha)⁻¹, respectively, and net returns to the TT system decreased by US$ 2.36 (rotational ha)⁻¹ when 2005 versus 1998 prices were used. Here, rotational ha equals 0.5 ha fallow and 0.5 ha wheat. Focusing on the dominant crop of soft white winter wheat (SWWW), the 2005 price hikes pushed diesel costs up for all systems, from US$ 6.81 (rotational ha)⁻¹ for DMT to US$ 9.00 (rotational ha)⁻¹ for TT. The cost of diesel for the conservation tillage systems, relative to the cost for TT, decreased by US$ 1.50–2.20 (rotational ha)⁻¹. The conservation tillage systems accrue greater savings from the price reduction in glyphosate because they consume more of this herbicide. An unanticipated result was that relative cost savings from price changes in N fertilizer rivaled those from diesel and glyphosate because anhydrous NH₃–N was exclusively used in the experiment for TT and aqueous NH₃–N for MT and DMT. The price of anhydrous NH₃–N increased from US$ 0.55 kg⁻¹ in 1998 to 0.85 kg⁻¹ in 2005, a 56% increase. Aqueous NH₃–N only increased from $0.75 kg⁻¹ in 1998 to 0.85 kg⁻¹ in 2005, a 15% increase. The greater price increase for anhydrous NH₃–N penalized the TT system because of its use of this fertilizer. If the same source of N fertilizer were used on all three tillage systems, this fertilizer cost effect would disappear. Nonetheless, the conservation tillage systems still retained a statistically significant profitability advantage over TT even if the same fertilizer was used throughout. The sharp price increase for diesel and the concurrent price decrease for glyphosate herbicide favored the conservation tillage systems over TT in this study. Results provide strong evidence for the superior profitability of conservation tillage winter wheat–summer fallow under current economic conditions.     

Soil organic carbon accumulation and carbon costs related to tillage, cropping systems and nitrogen fertilization in a subtropical Acrisol

Conservation management systems can improve soil organic matter stocks and contribute to atmospheric C mitigation. This study was carried out in a 18-year long-term experiment conducted on a subtropical Acrisol in Southern Brazil to assess the potential of tillage systems [conventional tillage (CT) and no-till (NT)], cropping systems [oat/maize (O/M), vetch/maize (V/M) and oat + vetch/maize + cowpea (OV/MC)] and N fertilization [0 kg N ha⁻¹ year⁻¹ (0 N) and 180 kg N ha⁻¹ year⁻¹ (180 N)] for mitigating atmospheric C. For that, the soil organic carbon (SOC) accumulation and the C equivalent (CE) costs of the investigated management systems were taken into account in comparison to the CT O/M 0 N used as reference system. No-till is known to produce a less oxidative environment than CT and resulted in SOC accumulation, mainly in the 0–5 cm soil layer, at rates related to the addition of crop residues, which were increased by legume cover crops and N fertilization. Considering the reference treatment, the SOC accumulation rates in the 0–20 cm layer varied from 0.09 to 0.34 Mg ha⁻¹ year⁻¹ in CT and from 0.19 to 0.65 Mg ha⁻¹ year⁻¹ in NT. However, the SOC accumulation rates peaked during the first years (5th to 9th) after the adoption of the management practices and decreased exponentially over time, indicating that conservation soil management was a short-term strategy for atmospheric C mitigation. On the other hand, when the CE costs of tillage operations were taken into account, the benefits of NT to C mitigation compared to CT were enhanced. When CE costs related to N-based fertilizers were taken into account, the increases in SOC accumulation due to N did not necessarily improve atmospheric C mitigation, although this does not diminish the agricultural and economic importance of inorganic N fertilization.     

Soil fertility properties on Agave angustifolia Haw. plantations

This study examined the variations in soil physical, chemical and biological properties from Agave angustifolia fields in three sites with different topographic conditions (valley, hill and mountain), in Oaxaca, Mexico, associated with the tillage systems, disk ploughing (DP), animal drawn ploughing (ADP) and minimum tillage (MT), respectively. Plant ages were 1.5–3.5 years (class 1), 3.6–5.5 years (class 2) and 5.6–7.5 years (class 3). Soil samples were taken at two soil depths (0–20 and 21–40 cm) from plots of 4000 m² within each site and plant age classes, during the spring of 2005. The main changes in soil properties were found in the mountain site. Soil bulk density (2.0 g cm⁻³), cone penetration resistance (CPR) (3.96 MPa), 0.7 and 1.0 mm water stable aggregates (WSA) (28.3 g kg⁻¹ and 102.2 g kg⁻¹, respectively) were higher in the mountain site than in the hill and valley fields. This result is consistent with the rocky substrate beneath the shallow soil. Soil organic carbon (SOC) (23.9 g kg⁻¹), available N (23.1 mg kg⁻¹) and soil microbial biomass carbon (SMBC) (969.6 μg g⁻¹) at the mountain site showed the highest values, suggesting that MT practiced in this topographic condition favours the organic matter accumulation and biological activity. Soil microbial biomass carbon and SOC seem to be the soil properties that were mainly affected by the sites and soil management associated with them. For the three sites, SOC, P_Olsen, available N, exchangeable Na⁺ and SMBC were higher at 0–20 cm depth than at 21–40 cm depth within each site. Exchangeable Ca²⁺ and K⁺, P_Olsen and CPR increased with plant age. In contrast, available N decreased. Soil chemical properties were more affected by the age of the plant than physical and biological properties. Results reported here represent a reference of the fertility properties of soils cultivated with A. angustifolia, which could be used in further studies focused on management and tillage systems.     

The influence of organic matter in reducing the destabilization of soil by simulated tillage

Different agricultural practices can result in a decline in soil organic carbon (SOC) and a consequent reduction in soil structural stability. Experiments were conducted on soils with a range of SOC values, to quantify the destabilizing effects of increased tillage intensity. Different tillage intensity was simulated with the use of a falling weight, where specific energy levels, similar to those experienced during tillage, were reproduced. The level of destabilization was assessed by the quantity of mechanically dispersed clay (using a turbidimetric technique) and the quantity of water-stable aggregates (WSA) > 0.25 mm remaining after being shaken in water.

The quantity of clay dispersed increased with increasing water content, in the absence of any mechanical pretreatment, the rate of increase rising sharply with declining SOC. Following simulated tillage, and at water contents above the plastic limit, clay dispersion increased in proportion to the energy of disruption, and also increased with decreasing SOC levels. Below the plastic limit all the soils were relatively insensitive to mechanical disruption. A simple empirical model was derived to link clay dispersion to SOC, water content and energy of disruption.

The proportion of WSA declined sharply with decreasing SOC, and to a lesser extent following tillage. The quantity of WSA following simulated intensive tillage (300 J kg⁻¹) of grassland (SOC, 2.8–3.2 g (100 g)⁻¹) was greater than that present, prior to tillage from fallow, arable and arable/ley rotation treatments (SOC 1.1–2.5 g (100 g)⁻¹). Aggregate tensile strength was found to be relatively insensitive to differences in SOC. However, variations of strength within treatments, an indicator of soil friability, increased in proportion with SOC. A turbidity index was derived in which the turbidity of natural and remoulded aggregates was compared. Variation of this index with increasing mechanical energy is used as an indicator of the sensitivity of soils to damage during tillage. A visual representation is constructed to link the sensitivity of soils to damage during tillage with both SOC and water potential. These experiments illustrate that management practices, which lead to a long term reduction in SOC, are responsible for an increase in aggregate strength and reduction in stability plus an increase in sensitivity of soils to structural decline following subsequent tillage.     

Soil C, N and crop yields in Alabama's long-term ‘Old Rotation' cotton experiment

The Old Rotation cotton experiment at Auburn, Alabama, is the oldest, continuous cotton experiment in the world (cf. 1896). Long-term cropping systems provide a unique opportunity to observe the effects of 100 years of cropping on soil organic carbon (SOC). The objective of this paper was to summarize limited data on SOC and N cycling in this historic experiment. Soil organic C has been measured on the 13 plots (6 cropping systems) in 1988, 1992 and 1994. Long-term planting of winter legumes with no other source of N applied resulted in higher SOC (9.5 g C kg⁻¹) in the plow layer (0–20 cm depth) compared to continuous cotton with no winter cover crops (4.2 g C kg⁻¹). A 3-year rotation of cotton–winter legumes–corn–small grain–soybean resulted in 12.1 g C kg⁻¹. There was a significant (P<0.05), quadratic cotton yield response (R²=0.54) to increasing SOC. Winter legume cover crops supplied between 90 and 170 kg N ha⁻¹. Where no N has been applied in fertilizer or from a legume crop, annual N removal in the cotton crop is around 13 kg ha⁻¹, about the same as that fixed in precipitation.     

Crop management effects on soil carbon sequestration on selected farmers’ fields in northeastern Ohio

Soil organic carbon (SOC) pool is the largest among terrestrial pools. The restoration of SOC pool in arable lands represents a potential sink for atmospheric CO₂. Restorative management of SOC includes using organic manures, adopting legume-based crop rotations, and converting plow till to a conservation till system. A field study was conducted to analyze soil properties on two farms located in Geauga and Stark Counties in northeastern Ohio, USA. Soil bulk density decreased with increase in SOC pool for a wide range of management systems. In comparison with wooded control, agricultural fields had a lower SOC pool in the 0–30 cm depth. In Geauga County, the SOC pool decreased by 34% in alfalfa (Medicago sativa L.) grown in a complex rotation with manuring and 51% in unmanured continuous corn (Zea mays L.). In Stark County, the SOC pool decreased by 32% in a field systematically amended with poultry manure and 40% in the field receiving only chemical fertilizers. In comparison with continuous corn, the rate of SOC sequestration in Geauga County was 379 kg C ha⁻¹ year⁻¹ in no-till corn (2 years) previously in hay (12 years), 760 kg C ha⁻¹ year⁻¹ in a complex crop rotation receiving manure and chemical fertilizers, and 355 kg C ha⁻¹ year⁻¹ without manuring. The rate of SOC sequestration was 392 kg C ha⁻¹ year⁻¹ on manured field in Stark County.     

Rotation and tillage effects on soil organic carbon sequestration in a typic Hapludalf in Southern Ontario

Increased use of conservation tillage is being considered as a way to sequester atmospheric C in the soil. However, little information exists on the effect of rotation and its interaction with tillage on soil organic carbon (SOC). A research trial with combinations of rotations and tillage treatments was sampled 20 years after its establishment to assess the effects on SOC sequestration in a typic Hapludalf in southern Ontario, Canada. The cropping treatments included continuous corn (zea mays L.), six rotations comprised of 2 years of corn following 2 years of another crop or crop sequence, and continuous alfalfa (Medicago sativa L.). Each rotation was split into either fall moldboard plow (MP) or fall chisel plow (CP) treatments. Continuous alfalfa was plowed and replanted every 4 years. Soil samples were taken incrementally to a depth of 40 cm and SOC and bulk density determined. The average SOC concentration (0–40 cm) was greatest in continuous alfalfa (18.0 g C kg⁻¹). The treatments of soybean (Glycine max L.Merr.)+winterwheat (Triticum aestivum L.) or barley+barley (Trifolium pratense L.) (interseeded with red clover) followed by 2 years of corn had higher SOC concentrations (17.2–17.3 g C kg⁻¹) than continuous corn and the treatments of 2 years of corn following 2 years of alfalfa or soybean (16.4–16.5 g C kg⁻¹). The rotation of 2 years of barley followed by 2 years of corn had the lowest SOC concentrations (15.2 g C kg⁻¹). On an equivalent mass basis, the rotations of soybean+winterwheat or barley+barley (underseeded with red clover) followed by 2 years of corn, had 2–9 Mg ha⁻¹ more C than the other corn-based rotations. Including red clover in the winter wheat seemed to accelerate the rate of C mineralization compared to winter wheat without red clover; whereas interseeding red clover with barley increased SOC contents compared to excluding red clover in the barley rotation. More SOC was found in the top 10 cm and less in the 10–20 cm depth of the CP than in the MP soils. However, the CP did not increase the SOC content (0–20 cm) above that of MP indicating that this form of reduced tillage did not increase C sequestration in any of the rotations on this soil.