Reduced Soil Organic Matter Research Articles

Conservation tillage production systems compared in San Joaquin Valley cotton

Tillage operations, including preplant soil preparation, in-season weed control and postharvest stalk management, can account for 25% or more of overall cotton production costs. These operations reduce soil organic matter and contribute to air pollution. Conservation tillage practices similar to those used successfully elsewhere in the Cotton Belt may be a viable means for increasing profitability and improving soil in San Joaquin Valley cotton fields. In a comparison of reduced-tillage production methods, conservation tillage planting and stalk-management systems had yields comparable to those of standard tillage practices in two back-to-back cotton crops in Riverdale, Calif. These reduced-till systems decreased the number of tractor operations by 41% to 53%, fuel use by 48% to 62%, and overall production costs by 14% to 18%.

Characterization of soil profiles in a landscape affected by long-term tillage

Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat ( Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha −1 year −1 were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing ∼19 g kg −1 of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha −1 year −1 exhibited thick sola with low inorganic carbon content (mean 3 g kg −1) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.

Nitrogen cycling at treeline: Latitudinal and elevational patterns across a boreal landscape

:We studied spatial and temporal patterns of nitrogen pools and fluxes in soils at treeline and forested sites within three mountain ranges across a 785-km transect in Alaska during 2001–2002. We measured pools of soil mineral (ammonium and nitrate) and organic (amino acid and microbial biomass) nitrogen, in situ rates of net mineralization, net nitrification, net amino acid production, and decomposition, as well as soil carbon turnover in a laboratory incubation experiment. Soils at treeline were mostly colder than forested soils, particularly during fall and over winter, and had reduced rates of nitrogen cycling and litter decomposition relative to forested stands. Treeline soils also had lower rates of potential respiration per unit carbon, suggesting reduced soil organic matter quality relative to forest soils. Therefore, effects of both colder temperatures and poorer substrate quality appeared to suppress rates of nitrogen turnover at treeline. Seasonal patterns of nitrogen turnover were similar across latitudes (i.e., mountain ranges). On average, 70% of total annual net nitrogen mineralization occurred from August through May, suggesting that fall and winter are critical periods for soil nitrogen transformations in both forested and treeline ecosystems. Among mountain ranges, pool sizes and fluxes of nitrogen were similar despite significant variation in growing season length and mean annual temperatures. Soil moisture and soil organic matter quality may have stronger effects on variation in nitrogen cycling than temperature at our sites.

Chemical and biochemical properties in a silty loam soil under conventional and organic management

To improve soil fertility, efforts need to be made to increase soil organic matter content. Conventional farming practice generally leads to a reduction of soil organic matter. This study compared inorganic and organic fertilisers in a crop rotation system over two cultivation cycles: first crop broad bean ( Vicia faba L.) and second crop mixed cropped melon-water melon ( Cucumis melo-Citrullus vulgaris) under semi-arid conditions. Total organic carbon (TOC), Kjeldahl-N, available-P, microbial biomass C (Cmic), and N (Nmic), soil respiration and enzymatic activities (protease, urease, and alkaline phosphatase) were determined in soils between the fourth and sixth year of management comparison. The metabolic quotient (qCO 2), the Cmic/Nmic ratio, and the Cmic/TOC ratio were also calculated. Organic management resulted in significant increases in TOC and Kjeldahl-N, available-P, soil respiration, microbial biomass, and enzymatic activities compared with those found under conventional management. Crop yield was greater from organic than conventional fertilizer. The qCO 2 showed a progressive increase for both treatments during the study, although qCO 2 was greater with conventional than organic fertilizer. In both treatments, an increase in the Cmic/Nmic ratio from first to second crop cycle was observed, indicating a change in the microbial populations. Biochemical properties were positively correlated ( p < 0.01) with TOC and nutrient content. These results indicated that organic management positively affected soil organic matter content, thus improving soil quality and productivity.

Soil Microbial, Chemical and Physical Properties in Continuous Cotton and Integrated Crop–Livestock Systems

Continuous monoculture systems can reduce soil organic matter because of low organic inputs and disturbance from tillage practices. Integrated cotton (Gossypium hirsutum) cropping and livestock production systems in West Texas may provide more sustainable alternatives to the traditional continuous cotton system and improve soil quality. Our study was conducted on a Pullman soil (Fine, mixed, thermic Torrertic Paleustolls) after 5 yr as a complete randomized block design (three replications) that compared continuous cotton and an integrated livestock‐crop system with a perennial warm‐season grass pasture (Bothriochloa bladhii) paddock and two paddocks (two stages) of a rotation (wheat [Triticum aestivum]‐fallow‐rye [Secale cereale]‐cotton). Total N (average: 1.0 g kg−1 soil) remained similar among systems and soil pH was &gt;8.1. Organic C was higher (13.5 g kg−1 soil) in perennial pasture compared with continuous cotton (9.0 g kg−1 soil) at 0 to 5 cm. A similar trend was found for the soil aggregate stability. Soil microbial biomass C (Cmic) was greater in perennial pasture (193 mg kg−1 soil) and the rotation under rye and cotton (237 mg kg−1 soil) compared with continuous cotton (124 mg kg−1 soil) at 0 to 5 cm, and in perennial pasture at 5 to 10 and 10 to 15 cm. Soil microbial biomass N (Nmic) showed similar trends. Soil enzyme activities were greater in perennial pasture and the rotation (under rye and cotton) than under continuous cotton at 0 to 5 cm. The integrated crop‐livestock system had higher protozoa (20:4ω6c = 1.98%) and fungi (18:3ω9c = 1.30%) than continuous cotton (20:4ω6c = 1.09%; 18:3ω9c = 0.76%). These findings suggest positive differences in soil function and sustainability of the integrated crop–livestock system compared with continuous cotton.

Declining soil quality in South Africa: effects of land use on soil organic matter and surface crusting

Soil conservation in South Africa has historically focussed on preventing soil erosion. Effective maintenance of the soil resource requires, in addition to erosion control, an understanding of how land use practices affect more subtle indicators of soil quality. This review outlines how land use in South Africa can rapidly result in a marked reduction in soil organic matter (SOM) content and a greater tendency of soils to crust. Removal of a cover of vegetation whether by ploughing, grazing or burning tends to reduce SOM due to reduced organic matter inputs and enhanced soil microbe activity. Loss of SOM, particularly from the top few centimetres of soil (named here the pedoderm) has a disproportionately large effect on soil infiltrability and nutrient supply. The mineralogy of the clay fraction also has great bearing on the response of soil to land use effects. The unexpected role of quartz in soil dispersion and crusting in South Africa has only recently been unveiled. Apart from SOM effects, land use can lead to subtle changes in soil chemistry. Plantation forestry has resulted in an increase in soil nitrate in many areas, possibly due to greater mineralisation under forests than grasslands. Annual burning in the Kruger National Park bushveld has been shown to increase clay dispersibility and crusting of the pedoderm, which was ascribed to a reduction in electrical conductivity and SOM as well as an increase in the exchangeable sodium percentage. Soil quality is a multifaceted concept. One aspect stands out, however, as critical and that is the conservation and replenishment of nitrogen which is all important for retaining humus and maintaining soil quality.

Characterization of Soil Amended with the By‐Product of Corn Stover Fermentation

Corn (Zea mays L.) stover is a potential biofuel; however, removing this stover from the land may increase the risk of erosion and reduce soil organic matter (SOM). Land application of corn stover fermentation by‐product, which is about 70% lignin, may reduce the environmental risk from biofuel harvest by helping to stabilize soil structure. A column study, with soil collected from a toeslope (noneroded, Svea; fine loamy, mixed, superactive, frigid Pachic Hapludoll) and a shoulder slope (severely eroded, Langhei; fine loamy, mixed, superactive, frigid Typic Eutrudepts) was conducted to evaluate the effect of fermentation by‐product on soil properties. Soil was either not amended (control) or amended with corn stover or by‐product at 0.75, 3.0, and 6.1 g kg−1 Soils were incubated for 123 d at ambient temperature in a laboratory, with an initial water‐filled pore space (WFPS) of 0.6 m3 m−3 and drying cycles to 0.35 m3 m−3 WFPS. Compared with the control, amending soil with 6.1 g by‐product kg−1 increased CO2 flux by 68% and increased soluble C and microbial biomass C by about 20%. In the severely eroded soil, humic acid concentration (r2 = 0.97, p = 0.009) and aggregate stability (r2 = 0.98, p = 0.005) increased linearly with increased by‐product concentration. Water‐holding capacity, bulk density, and aggregate distribution were not changed by soil amendments. Careful management of stover removal (avoiding eroded or erosion prone areas) and selective placement and rates of the by‐product will contribute to a sustainable use of corn stover for ethanol production.

Earthworm casts form stable aggregates in physically degraded soils

Topsoils affected by surface mining suffer severe physical degradation and lose most of their earthworm populations. After mining, replaced soils are planted to grassland and managed to improve soil structure. Earthworm inoculation into selected restored areas produced populations similar to those of undisturbed soils within 3 years. Soil properties in inoculated areas were compared with those of controls to evaluate the contribution of casts to bulk soil aggregation, and soil organic matter and root content responses to earthworm activity. Crumb porosity and coarse particle content were measured in water-stable macro-aggregates and earthworm casts to establish whether aggregates were formed by earthworms. Over a 5- to 6-year period, inoculation increased stable aggregation (>2 μm, >60 μm and >3 mm), even at 0- to 5-cm depth where it reduced soil organic matter content. Productivity and root content were also increased by inoculation; roots and organic matter were re-distributed to greater depth. Crumb porosity decreased with casts > aggregates (inoculated plots) > aggregates (control plots). Coarse particle content increased with casts < aggregates (inoculated plots) < aggregates (control plots). Coarse particle and porosity data were consistent with much of the newly aggregated soil being processed and formed by earthworms as casts. Whilst levels of soil organic matter were often closely associated with percentage stable aggregation, root content showed weaker associations. Aggregation percentage was most closely associated with abundance of Aporrectodea longa, although at particular depths significant correlations were also obtained for Aporrectodea caliginosa and Lumbricus terrestris. Results suggest that earthworms, rather than plant roots, initiate aggregation in severely degraded grassland soils.

Effects of deforestation on grass biomass and soil nutrient status in miombo woodland, Zambia

There is a growing concern in central and southern Africa about the negative effects of deforestation caused by shifting cultivation and charcoal production. In the absence of long-term studies that document and assess impacts of tropical deforestation, it is difficult to evaluate the relevance of current policy interventions that address the negative effects of deforestation. To contribute to the knowledge about impacts of tropical deforestation, the effects of clearing Brachystegia– Julbernardia (miombo) woodland on grass biomass and soil nutrient status were assessed at four sites over a 10-years period, from 1991 to 2000 in central Zambia. Woodland clearing increased grass biomass by 20–50% and although its impacts on topsoil organic matter and available phosphorus were apparent, these were not statistically significant. Site and year had the most significant effects on soil nutrient stocks, regardless of the woodland clearing treatment. Generally, fire did not affect grass production but reduced topsoil organic matter and nitrogen at three of the study sites. Deforestation followed by cultivation significantly reduced soil organic matter in the study area. Based on these results, it is recommended that local cultivation practices should incorporate measures that minimize loss of soil organic matter in order to sustain long-term soil fertility.

Modeling potential erosion due to the Cerro Grande Fire with a GIS-based implementation of the Revised Universal Soil Loss Equation

Erosional processes directly influenced by wildland fire include reduction or elimination of above- ground biomass, reduction of soil organic matter, and hydrophobicity. High fuel loads promoted by decades of fire suppression in the U.S. increase the duration and intensity of burning, amplifying these effects. The Cerro Grande fire (6–31 May 2000) consumed approximately 15 000 hectares around and within the town of Los Alamos, New Mexico, USA. Private and public infrastructure including Los Alamos National Laboratory are at continuing risk due to increased threats of upstream erosion. We use a geographic information system (GIS) based implementation of the Revised Universal Soil Loss Equation (RUSLE) to model pre- and post-fire soil loss conditions and aid erosion risk analysis. Pre- and post-fire vegetation cover data layers were generated from Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM) data. Based upon annual average rainfall amounts we estimate that subwatershed average pre-fire erosion rates range from 0.45 to 9.22 tonnes ha–1 yr–1 while post-fire erosion rates before watershed treatments range from 1.72 to 113.26 tonnes ha–1 yr–1. Rates are approximately 3.7 times larger for 50 year return interval rainfall amounts. It is estimated that watershed treatments including reseeding will decrease soil loss between 0.34 and 25.98% in the first year on treated subwatersheds. Immediately after the fire an interagency Burned Area Emergency Rehabilitation (BAER) team produced initial estimates of soil erosion. Our estimates of average erosion rates by subwatershed were in general larger than those initial estimates.

Corn Yield as Affected by Liming and Tillage System on an Acid Brazilian Oxisol

Tillage system affects many soil parameters that may influence plant growth. This study evaluated the effect of liming on corn (Zea mays L.) yield and chemical characteristics of a Humic Hapludox (clayey, kaolinitic, goethitic, termic) under both conventional tillage (CT) and no‐tillage (NT) systems. Rates of dolomitic lime, from 0 to 18 t ha−1, were plowed into the soil in 1992 in southern Brazil; our study was conducted from 1996 through 1999. Lime rate was allocated to subplots, and tillage systems to main plots, in a split‐plot design. Corn yield increased with liming in all years and was higher with CT than with NT in 2 of 3 yr. Averaged across years and systems, liming increased yield by 66%, which ranged from 4.4 to 7.8 t ha−1. The highest average yield (7.8 t ha−1) was obtained at pH 6.5; yields at pH 6.0 or 5.5 were 97 and 89% of the maximum, respectively. Liming reduced soil organic matter (SOM) in both systems, but nutrients (P, K, Ca, Mg, Fe, Cu, Zn, and Mn) remained above sufficiency on all treatments. Aluminum, pH, SOM, and other nutritional parameters did not differ between tillage systems, partly because limestone was initially incorporated in all plots and partly due to dilution effects in the plow layer because sampling was not stratified in small depths. Some soil restriction impaired by absence of plowing, probably increases in bulk density, offset the benefits of NT on plant growth and was responsible for the smaller yield in this tillage system compared with CT.

REGIONAL PATTERNS OF DECOMPOSITION AND PRIMARY PRODUCTION RATES IN THE U.S. GREAT PLAINS*

Warmer regions generally exhibit greater rates of soil respiration and organic matter decomposition than colder regions. In the Great Plains of the United States, soil organic matter declines from the northern part of the region to the south, suggesting greater decomposition rates in areas with warmer temperatures. Our study used a regional data set of aboveground net primary production, soil organic carbon, soil texture, and climate to evaluate the environmental controls over areal patterns in decomposition rates, (k; expressed as grams per year per gram of initial mass), throughout the U.S. Great Plains. We conducted multiple regression analyses of steady-state k with respect to mean annual temperature, mean annual precipitation, and percentage soil clay content to examine both the combined and individual effects of these independent variables on regional decomposition rates. Our results indicated that precipitation contributes more than either temperature or soil texture to areal patterns of decomposition rates in the U.S. Great Plains, explaining >30% of the areal variability in k. Decomposition rates increased with increasing precipitation and with decreasing soil clay content. Temperature explained <8% of the regional variability in k. Ancillary analyses that related temperature and aboveground net primary production in the region indicated that plant productivity declines with increasing temperatures. This suggests that the reduction in soil organic matter to the south in the U.S. Great Plains may be due to reduced plant inputs rather than to increases in decomposition rates. The response of decomposition to temperature is probably constrained by moisture in this water-limited region. Therefore, changes in decomposition rates resulting from temperature dynamics are likely to be minimal unless they are accompanied by sufficient changes in precipitation.

Corn Yield as Affected by Liming and Tillage System on an Acid Brazilian Oxisol

Tillage system affects many soil parameters that may influence plant growth. This study evaluated the effect of liming on corn (Zea mays L.) yield and chemical characteristics of a Humic Hapludox (clayey, kaolinitic, goethitic, termic) under both conventional tillage (CT) and no-tillage (NT) systems. Rates of dolomitic lime, from 0 to 18 t ha−1, were plowed into the soil in 1992 in southern Brazil; our study was conducted from 1996 through 1999. Lime rate was allocated to subplots, and tillage systems to main plots, in a split-plot design. Corn yield increased with liming in all years and was higher with CT than with NT in 2 of 3 yr. Averaged across years and systems, liming increased yield by 66%, which ranged from 4.4 to 7.8 t ha−1. The highest average yield (7.8 t ha−1) was obtained at pH 6.5; yields at pH 6.0 or 5.5 were 97 and 89% of the maximum, respectively. Liming reduced soil organic matter (SOM) in both systems, but nutrients (P, K, Ca, Mg, Fe, Cu, Zn, and Mn) remained above sufficiency on all treatments. Aluminum, pH, SOM, and other nutritional parameters did not differ between tillage systems, partly because limestone was initially incorporated in all plots and partly due to dilution effects in the plow layer because sampling was not stratified in small depths. Some soil restriction impaired by absence of plowing, probably increases in bulk density, offset the benefits of NT on plant growth and was responsible for the smaller yield in this tillage system compared with CT.

Apple and Peach Orchard Establishment Following Multi-year Use of Diuron, Simazine, and Terbacil

Combinations of diuron, simazine, and terbacil were applied every year over 15 and 16 years to the same plots. Apple (Malu×domestica Borkh.) and peach (Prunus persica L.) trees then were planted 1 and 2 years following the last herbicide application. In general, apple-tree growth was not affected, but peach tree growth was reduced by some herbicide treatments. Peach-tree growth was reduced in plots treated with terbacil and soil organic matter was lowest in these plots. Time of last herbicide treatment did not affect apple- or peach-tree growth. The results indicated that reduced fruit-tree growth was associated with reduced soil organic matter and that residual terbacil may have inhibited peach-tree growth. Chemical names used: N′-(3,4-dichlorphenyl)-N,N-dimethylurea (diuron); 6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine (simazine); 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione (terbacil).

Efeitos de métodos de controle de plantas daninhas na cultura do cafeeiro (Coffea arabica L.) sobre a qualidade física do solo

Estudaram-se os efeitos de diferentes métodos de controle de plantas daninhas na cultura do cafeeiro sobre alguns indicadores da qualidade física do solo. O experimento foi instalado, em 1977, na Fazenda Experimental da EPAMIG em São Sebastião do Paraíso (MG), em um Latossolo Roxo distrófico. Foi utilizado o cultivar "Catuaí Vermelho" LCH 2077-2-5-99, plantado no espaçamento 4 x 1 m. Roçadeira (RÇ), grade (GR), enxada rotativa (RT), herbicida de pós-emergência (HC), herbicida de pré-emergência (HR) e capina manual (CM) foram empregados no controle das plantas daninhas na entrelinha de plantio ("ruas"), em comparação com a área cultivada mantida sem capina (SC) e a condição original de mata (MT). Os seguintes indicadores da qualidade física do solo foram avaliados, entre 1978 e 1995, nas camadas de 0-15 e 15-30 cm: matéria orgânica, densidade do solo, volume total de poros e estabilidade de agregados em água. Após dezoito anos de avaliações, a qualidade física do solo mostrou-se diretamente correlacionada com o seu teor de matéria orgânica. A utilização contínua de herbicida de pré-emergência, além de reduzir o teor de matéria orgânica do solo, provocou o surgimento de encrostamento superficial do solo. Os usos da enxada rotativa e da roçadeira acarretaram o surgimento de camada subsuperficial compactada. O controle das plantas daninhas por meio de capinas manuais e herbicidas de pós-emergência mostraram-se eficientes na manutenção da qualidade física do solo.

MORPHOLOGICAL AND CHEMICAL PROPERTIES OF SOILS ALONG A VEGETATION GRADIENT AFFECTED BY FIRE IN HONG KONG

This work examined the effects of hill fire on the morphology and soil chemical properties of a vegetation gradient that transcends a newly burnt short grassland, tall grassland, mixed grassland/shrubland, and woodland vegetation. Distinct soil horizons were observed, and the thickness of the O (1.5-6 cm) and A (4.5-21 cm) horizons decreased with successive development of the vegetation. Similarly, the immediate effect of fire on soil properties was observed, although it is difficult to discriminate between the effects of fire and those of vegetation. However, the effect on soil chemical properties seemed to dissipate with time after the fire and successional development. The fire effect raised pH, mineral nitrogen (NH 4 + and NO 3 - ), exchangeable Ca 2+ , and base saturation of the soils, but reduced soil organic matter (SOM) and total Kjeldahl nitrogen (TKN) and had no effect on total phosphorus, exchangeable K + , Na + , and Mg 2+ . Many of these effects disappeared 1 year after the occurrence of fire. In the absence of fire, natural succession proceeds in the sequence of grassland, mixed grassland/shrubland and woodland, each accompanied by specific changes in soil properties. The disturbed soils have obviously accumulated sufficient nutrients to support development of the woodland six years after the occurrence of fire.

Potential for nitrate leaching from different land uses in the Pukekohe area

Nitrogen balances (inputs minus outputs) were calculated for 5 dairy farms, 5 orchards and a range of crops. All the balances were positive, i.e., surplus N was present and a proportion of this N will eventually reach the groundwater as nitrate. On a per ha basis, the greatest N surplus was from early potatoes &gt; winter cabbage, winter lettuce and squash &gt; dairying, kiwifruit, summer cabbage and summer lettuce &gt; pumpkins, onions and main crop potatoes &gt; dry stock farming. The area in each activity was multiplied by the surplus N factor to obtain the potential contribution of N to groundwater in the Pukekohe area. Early potatoes (217 t N), contribute much more than onions (105 t N), dairying (59 t N) or dry stock farming (57 t N). Other activities contributed &lt; 30 t N each. Winter crops had higher surplus N levels than the same crop grown in summer because winter crops had higher fertiliser N inputs and lower crop off-take of N. Management practices contributing to the N surpluses include high rates of N fertiliser used on some crops; a long history of cultivation, which has reduced soil organic matter contents and the ability of these soils to immobilise mineral N; and nil to intermittent use of cover crops to retain N in the topsoil. Keywords: aquifers, dairying, fertiliser, groundwater, land use, management, nitrate, nitrogen balance, nitrate leaching, vegetables.

Factors in conservation farming that reduce erosion

A medium-term (10 years) stubble x tillage field experiment was established in 1984 on a red-brown earth at Tarlee, 70 km north of Adelaide, to develop a suitable system for sustaining the soil resource. Measurements of infiltration capacity, soil detachment rate, and erosion were taken in summer, autumn, winter, and spring 1989-90. The rotation was wheat-barley-grain legume, and treatments included 3 levels of stubble retention (0.5, 3.0, 5.0 t/ha.year) and 4 types of tillage [no-tillage (NT), direct drill (DD), reduced tillage (RT), conventional cultivation (CC)]. NT was seeded with narrow points (30 mm) and the other tillage treatments with wide shares (150 mm). The Northfield rainfall simulator with an erosive rainfall of 100 mm/h and an energy of 28.6 J/ m2.mm was used to measure runoff and soil and nutrient loss. This paper reports on erosion from this experiment. The results show that runoff was reduced through farming practices such as the retention of adequate stubble residue (about 3-5 t/ha.year of cereals), NT, or a combination of these factors. Increasing the average - - - annual stubble retention decreased runoff and soil loss linearly. The greater the amount of stubble retained annually, the less the runoff and soil loss, whether or not the soil surface was protected. The significant sediment release and soil loss from bared soil is inversely related to soil stability measured by a reduction in soil organic matter. Crop type also influenced erosion; for example, soil was more vulnerable to erosion after peas than after cereal. The amount of stubble after harvest was usually greater with cereals than with grain legumes. Runoff as a percentage of applied rain, and soil loss, ranged from 26 to 60% and 0.52 to 1 .I t/ha for 0.5 t/ha. year stubble (means of all treatments) for April 1989 and August 1990, respectively, and from 5 to 35% and 0.03 to 0.8 t/ha for 5.0 t/ha.year stubble for the same simulation period. Runoff rates in the last 3 min of 18 min simulation ranged from 0.4 to 1.1 mm/min for 5.0 t/ha.year stubble and from 0.8 to 1.7 mm/min for 0.5 t/ha.year stubble. The runoff rates recorded at the 18th minute of simulation ranged from 0.5 to 1.2 mm/min for NT and 0.7 to 1.5 mm/min for CC.

Effect of long term cropping on availability of Cu, Mn and Zn in soil following clearing of a boreal forest

Temporal changes in labile soil Cu, Mn and Zn were measured for up to 23 years after conversion of a boreal forest to the following crop production systems: (i) continuous barley, (ii) continuous legume and (iii) continuous bromegrass for hay, and (iv) barley/legume-bromegrass hay rotation. Decreases in labile Mn and Zn were greater than can be accounted for by crop offtake except for the continuous grass treatment. Some Mn and Zn was probably converted to less labile forms due mostly to reduction in soil organic matter associated with soil cultivation and some cropping systems. Labile copper was increased slightly with time under agriculture.

The impact of 20 years' absence of earthworms and three levels of N fertilizer on a grassland soil environment

Replicated plots of a sward sown to perennial ryegrass ( Lolium perenne) growing at Hurley on a soil of the Griston series were given 188, 376 or 752 kg N fertilizer ha −1 year −1 for a period of 20 years. Half of each plot at the lowest and highest application rate of N fertilizer was treated frequently with the pesticide phorate, which kept those halves almost free of earthworms and other invertebrates. Measurements of several soil parameters were made during at the end of the 20-year period. The pesticide treatment, i.e. absence of earthworms, dramatically increased soil bulk density, shear strength, penetrability and depth of leaf litter, but greately reduced soil organic matter content, initial infiltration rate, pH and soil moisture content. Increasing the level of nitrogen fertilizer increased soil shear strength and penetrability, but had little or no significant effect on the other parameters measured. The soil profile was examined in detail to a depth of 1.5 m at the junction of a low-N-level pesticide-treated sub-plot and an untreated sub-plot. The main changes in the soil profile attributable to the pesticide treatment were confined to the topsoil. The leaf litter layer (F horizon) on the treated plot was pronounced and some 2–3 cm deep. The topsoil on treated plots had a more developed coarse angular blocky structure and was more brittle. There was no visible earthworm activity in the treated plot.