Conventional Tillage Plot Research Articles

Impact of No-Tillage on Soil Invertebrate Communities in the Southern Forest Steppe of West Siberia: Preliminary Research

The aim of our study is to assess changes in soil macroinvertebrate biodiversity when conventional tillage (CT) is replaced by no-tillage (NT) in agroecosystems of the southern part of the West Siberian forest steppe. The research was conducted in the Novosibirsk region at the end of May 2017, May 2018, and in June 2018. The agricultural plots with CT and NT were located close to each other on identical soils, at a distance of about 200 m from the nearest forest shelterbelts. NT technology has been applied on the experimental plot since 2007. Sampling of invertebrates was conducted in two ways, namely soil sampling and pitfall trapping. The majority of basic physicochemical properties of soil were the same or similar between the CT and NT plots. However, depending on the type of tillage, different soil invertebrate communities had already developed in the control (CT) and experimental (NT) plots during this time. The community of the CT plot includes a large number of flying predatory Carabidae species typical of early successional stages (such as Bembidion properans and B. quadrimaculatum, Poecilus spp.) and phytophages, i.e., larvae of Elateridae. The NT plot has significantly higher density and species richness of earthworms (Eisenia nordenskioldi and synanthropic E. fetida in the NT plot versus one individual of E. nordenskioldi in the CT plot). The NT plot has a significantly richer and more abundant assemblage of spiders (especially in spring) and a poor assemblage of insect predators (except for the superdominant ground beetle Poecilus cupreus and the subdominant P. versicolor in summer 2018). Large numbers of larvae of some carabids (e.g., Amara consularis) were found in the NT soil, suggesting that they complete a full life cycle in this habitat.

The Yield and Weed Infestation of Winter Oilseed Rape (Brassica napus L. ssp. oleifera Metzg) in Two Tillage Systems

Results from a four-year field experiment were used to evaluate the effect of conventional tillage (CT) and no-tillage (NT) systems on the yield, selected yield and crop structure elements, weed infestation, and contents of fat and glucosinolates in the seeds of winter oilseed rape (Brassica napus L. ssp. oleifera Metzg). The study proved the beneficial effect of the NT system on the winter rape seed yield only during the precipitation shortage in the growing season. In the years with a sufficient sum of precipitation, a higher seed yield was produced in the CT than in the NT system. Considering the average values from the four-year study period, the seed yield and straw yield, plant density after emergence and before harvest, number of branches and main shoot length, and finally the 1000 seed weight were significantly higher in the CT compared with the NT system. In contrast, the NT system proved more beneficial regarding seed weight per silique and fat content of the seeds. The statistical analysis of the study results showed no effect of the tillage systems on the glucosinolate content of the seeds. In turn, a significantly higher number and air-dry weight of weeds as well as an increased density of Viola arvensis weeds were demonstrated in the NT plot compared with the CT plot of winter oilseed rape. Sonchus asper and Sonchus arvensis were identified in the NT plot but not in the CT plot. A significantly higher density of Chenopodium album and Euphorbia helioscopia weeds was detected in the CT system compared with the NT system. The statistical analysis of study results regarding weed community diversity showed similar values to the Shannon-Weinner diversity index (H’) in both tillage systems and a significantly higher value of the Simpson dominance index (SI) in the NT system compared with the CT system.

Adsorption and degradation of the herbicide nicosulfuron in a stagnic Luvisol and Vermic Umbrisol cultivated under conventional or conservation agriculture

The main goals of conservation agriculture are to enhance soil fertility and reduce soil degradation, especially through erosion. However, conservation agriculture practices can increase the risk of contamination by pesticides, mainly through vertical transfer via water flow. Better understanding of their sorption and degradation processes is thus needed in conservation agriculture as they control the amount of pesticide available for vertical transfer. The purpose of our study was to investigate the sorption and degradation processes of nicosulfuron in soil profiles (up to 90 cm deep) of a Vermic Umbrisol and a Stagnic Luvisol managed either in conventional or in conservation agriculture. Two laboratory sorption and incubation experiments were performed. Low sorption was observed regardless of the soil type, agricultural management or depth, with a maximum value of 1.3 ± 2.0 L kg-1. By the end of the experiment (91 days), nicosulfuron mineralisation in the Vermic Umbrisol was similar for the two types of agricultural management and rather depended on soil depth (29.0 ± 2.3% in the 0-60-cm layers against 7.5 ± 1.4% in the 60-90 cm). In the Stagnic Luvisol, nicosulfuron mineralisation reached similar value in every layer of the conservation agriculture plot (26.5% ± 0.7%). On the conventional tillage plot, mineralisation decreased in the deepest layer (25-60 cm) reaching only 18.4 ± 6.9% of the applied nicosulfuron. Regardless of the soil type or agricultural management, non-extractable residue formation was identified as the main dissipation process of nicosulfuron (45.1 ± 8.5% and 50.2 ± 7.0% under conventional and conservation agriculture respectively after 91 days). In our study, nicosulfuron behaved similarly in the Vermic Umbrisol regardless of the agricultural management, whereas the risk of transfer to groundwater seemed lower in the Stagnic Luvisol under conservation agriculture.

Long-term impact of reduced tillage on water and pesticide flow in a drained context

Influence of more than 20years (1988-2010) of reduced tillage (RT) practices on water and pesticide balances and dynamics is analyzed and compared to results from a conventional tillage plot (CT). The field study soils are described as silty clay stagnic luvisol, developed on a low permeable schist layer. A drainage network was set up according to French criteria (0.9m deep, 10m space) to avoid soil winter waterlogging. Climate is temperate oceanic and drainage generally occurs from November to March. Data were analyzed at yearly, weekly (pesticides) and hourly (water) time steps. Over the long term, cumulated drainage decreases significantly on RT (3999mm) compared to CT (5100mm). This differentiation becomes significant from 1999, 10years after plowing was stopped. Strikingly, hourly drainage peak flows are higher under RT, especially during the second period (2000-2010), associated with low or no base flow. These results suggest a strong influence of the macropore network under RT practice. In particular, drainage peaks are higher at the beginning of the drainage season (mid-October to December). Consistently, pesticides applied in late autumn, which are the most quantified on this site, are often significantly more exported under RT. For atrazine, applied in spring, fluxes are linked to cumulative flow and are de facto higher under CT. For others pesticides, losses appear to be heterogeneous, with generally low or null export rates for spring application. Generally speaking, higher concentrations are measured on RT plot and explain observed exportation rate differences. Finally, there is no clear evidence of correlation between pesticide losses and long-term impacts of RT on hydrodynamics, pointing the importance of studying the short-term effect of tillage on water and especially solute flow.

Spatial and temporal variability of soil gas diffusivity, its scaling and relevance for soil respiration under different tillage

Soils are an important source and sink for carbon. Soil management such as reduced or no-tillage management has been reported to increase soil organic matter budgets, probably due to a hampered microbial mineralization of organic components. While soil respiration is mainly controlled by temperature and soil moisture, it can be also limited by the soil pore system facilitating diffusive gas fluxes between the soil and the atmosphere. However, soil gas diffusivity as a controlling factor for soil respiration has not been assessed under different soil management. Moreover, no adequate methods have been developed yet that facilitate the description of spatial or temporal variations of the highly non-linear soil gas diffusivity functions. Therefore, the objectives of this study were to deduce and apply a scaling rule for gas diffusivity, and to observe and analyze spatio-temporal variations of soil respiration and gas diffusivity under conventional tillage (CT) and no-tillage (NT). We measured soil respiration rates and gas diffusivities along a transect on an arable field in Hollabrunn (Lower Austria) within the 2014 vegetation period. We also determined the soil hydraulic properties and gas diffusivities as a function of air-filled porosity. By adopting the similar media approach of Miller and Miller we facilitated scaling of spatially variable gas diffusivity model functions. The scaling performed well to derive representative mean parameters while preserving the spatial variability in the scaling factors. The comparison of scaling factors for soil water retention, hydraulic conductivity, and gas diffusivity revealed that flow pathways were not the same for water and gases. This finding was explained by the continuity of pores that are accessible for water or gas movement. Compared to NT, the CT plot was characterized by greater soil respiration rates, gas diffusivities, total porosities, and unsaturated hydraulic conductivities, while soil water retention, observed volumetric water contents, and the spatial variability of these properties were smaller. Soil respiration rates were mainly changing with time as a result of soil temperature and soil water content. However, we also found that the diffusive soil properties slightly influenced CO2 efflux rates.

Relationship between runoff and soil losses with rainfall characteristics and long-term soil management practices in a hilly vineyard (Piedmont, NW Italy)

Runoff and soil losses caused by natural rainfall events were monitored over a 10-year observation period in three experimental vineyard plots located in Alto Monferrato, a vine-growing area in Piedmont (NW Italy). The plots are characterized by a slope of about 15% and a soil classified as Typic Ustorthents, fine-loamy, mixed, calcareous, mesic. Each of them was managed with a different inter-row soil management practice: conventional tillage (CT), reduced tillage (RT) and controlled grass cover (GC), respectively. The rainfall characteristics, runoff discharge and concentration of soil in the water were measured. More than 150 rainfall events producing runoff and 63 erosive events were recorded. The data set was elaborated to investigate the relationships between runoff and soil losses with rainfall amount, duration and intensity, and to evaluate the effects of soil management methods. The amounts of water and soil that ran off the vineyard in the study period varied according to the season, rainfall characteristics and soil surface conditions. The highest soil losses were observed for tilled plots, with values of 111.5 and 207.7 Mg ha−1 in the CT and RT plots, and only 25.6 Mg ha−1 for GC treatment. The worst soil management practice was found to be the RT, whereas the GC was able to reduce soil lost from inter-rows in every season of the year, reaching the best effectiveness in summer (reduction greater than 90%). In addition, GC reduced runoff by 35% compared with the CT plot, showing a greater performance in summer and losing efficacy in autumn. A lower runoff reduction of 11% was observed in RT.

Soil respiration, N2O, and CH4 emissions from an Andisol under conventional-tillage and no-tillage cultivation for 4 years

No-tillage (NT) management is a promising method to sequester soil C and mitigate global warming caused by agricultural activities. Here, we report 4 years of continuous soil respiration rates and weekly nitrous oxide (N2O) and methane (CH4) emissions in NT and conventional-tillage (CT) plots in a typical Japanese volcanic soil. Overall, the soil respiration, N2O emission, and CH4 uptake decreased significantly in the NT plot. A difference in soil respiration and N2O emission between the two plots began after the tillage treatment and the incorporation of crop residues and fertilizers, whereas the CH4 uptake did not vary significantly during the fallow period after the treatments. The N2O emission was higher from the CT than from the NT plot during the fall. The overall lower CH4 uptake in the NT than in the CT plot likely resulted from a combination of decreased soil gas diffusivity and higher mineral N content at the soil surface. Higher soil respiration and N2O emission occurred in the NT plot in the summer of 2003 and were plausibly caused by an increase in the soil moisture content that resulted from lower temperatures during July and August; the higher soil moisture must have accelerated the decomposition of organic matter accumulated in the topsoil. These results indicate that NT management is generally effective for the mitigation of the total GWP by reducing soil respiration and N2O emission in temperate regions; however, NT management may increase rather than decrease these emissions when fields experience cool summers with frequent rainfall.

Impact of direct drilling and conventional tillage on seasonal changes of soil water content in Chromic Haploxerert (south-west Spain)

A continuous monitoring of spatial and temporal variability of soil water content was studied under two soil management systems: direct drilling (DD) and conventional tillage (CT), during four consecutive seasons. The soil water content was read at different soil depths using multisensor capacitance probes in each soil-management treatment. During the first season (2003–2004), soil water content dynamics for both treatments were similar during the rainy season, although the DD plot was able to retain more water in the soil profile, and during the maximum evapotranspirative period faster soil water depletion took place in the CT plot. The 2004–2005 season registered a high evapotranspiration rate (1741 mm) with low rainfall (228 mm), promoting a low soil water recharge for both treatments. The 2005–2006 season registered an increase in rainfall, promoting a greater recovery of the soil water reserve in DD than CC plot. Finally, during the 2006–2007 season with an evapotranspiration rate ET0 and rainfall of 1504 and 560 mm, respectively, DD retained more soil water content, mainly in the deeper zones, with progressive soil water depletion during the maximum evapotranspirative period in comparison to CT. Thus, DD was demonstrated to be a promising soil management technique for improving the soil water content.

Impact of three and seven years of no-tillage on the soil water storage, in the plant root zone, under a dry subhumid Tunisian climate

Conservation agriculture based on no-tillage (CA/NT) becomes a current tendency to enhance crop productivity by improving: (i) soil quality, (ii) water management and (iii) organic supply. In Tunisia, the applicability of CA was poorly documented. This study was carried out to evaluate changes in soil organic matter (SOM) and water properties generated by seven (NT7) and three (NT3) years of applying NT as compared to conventional tillage (CT). On three adjacent large plots, a field experiment was established since the growing season 2000/01 under rain-fed conditions on a clay loam soil in a dry subhumid zone of North Tunisia. In NT3 plot, a cultivation of wheat/fava bean sequence was investigated and residues biomass of 500kgha−1 and 450kgha−1 were left on the soil surface for wheat and fava bean, respectively. In NT7 plot, a cultivation of wheat/sulla sequence was investigated and residues biomass of 500kgha−1 and 700kgha−1 were left on the soil surface for wheat and sulla, respectively. However for the CT plot, a moldboard plowing at approximately 20cm depth was managed for continuous wheat production. The selected key parameters evaluated for a 0–30cm soil profile were SOM, bulk density (BD), total porosity (TP), macro-porosity (MP), micro-porosity (mP), soil water retention at field capacity (FC) and at permanent wilting point (PWP), available water content (AWC) and soil moisture content (SMC).NT7 have increased significantly (p<0.05) levels of SOM at the top 30cm soil layer, which in turn enhanced BD and TP of soil as compared to CT. However, improvement of these parameters was restricted to 0–10cm layer with NT3. Both NT3 and NT7 have increased considerably (p<0.05) mP at 0–30cm thereby increasing soil water content at FC and PWP, whereas MP was remarkably reduced by NT treatments as compared to CT but reduction was less important in NT7 plot. AWC was significantly (p<0.05) higher in NT7 across the 30cm profile while NT3 and CT have similar effect to each other. SMC was improved at different soil depths by NT system during the whole agricultural season and the highest content was found with NT3. Soil moisture values increased with increasing soil depth in both NT3 and NT7 indicating a good water infiltration induced by these treatments. Hence, water storage properties in rooting zone could be enhanced by NT7 and NT3 but water availability for plants was more important with NT7.

Effects of Strip Tillage on Soil Thermal and Moisture Conditions in a Drained Paddy Field for Dryland Crop Cultivation.

We investigated the effects of strip tillage, which tills the soil only at planting rows, on soil thermal and moisture conditions under a drained paddy field to evaluate its adaptability for dryland soybean cultivation. A drained Ando-soil paddy field, which had been used as a rice paddy in the previous cropping season, was pan-broken and tilled for a strip tillage plot (ST) and a conventional tillage plot (CT). The difference in daily mean soil temperature at a 13-14cm depth between ST and CT (ST – CT) ranged from –0.4 to +0.4ºC with a mean of 0.25ºC from sowing to June 31. Soil water content was higher at ST than at CT, but the soil matric potential was not significantly different between ST and CT. After 95mm of rainfall, which saturated the top 30cm of soil, the soil at ST drained as quickly as the soil at CT. We hypothesize that pan-breaking increased soil hydraulic conductivity, which resulted in this quick drainage. No significant differences in the growth and yield of soybean were observed between ST and CT. Therefore, with drainage methods such as pan-breaking, strip tillage can provide almost the same soil thermal and moisture conditions as conventional tillage at a drained Ando-soil paddy field for dryland crop cultivation.

Effects of conventional and conservation tillage on soil hydraulic properties of a silty-loamy soil

Infiltration into soils is strongly correlated with macroporosity. Under agricultural land use, the properties of the macropore network are governed by the applied management and tillage system. On an experimental site with a silt loam soil partly under conventional and conservation tillage, the methods of visual inventarization of stained and unstained macropores and infiltration measurements with an infiltrometer were applied to the macropore system. Dye tracer experiments with methylene blue as tracer agent yielded a penetration depth of 120 cm on the conservation tillage plot while a penetration depth of only 50 cm was recorded on the conventionally tilled plot. For both tillage treatments, infiltration rates were lower in the topsoil than in soil depths >30 cm. The conservation tillage plot showed higher infiltration rates at 50 and 90 cm soil depth than the conventional tilled plot. For both tillage systems, the visual recording of stained and unstained macropores ( d⩾1 mm) resulted in macropore densities ranging between 100 and 1,000 macropores/m 2, with the highest numbers in the topsoil and a gradual decrease with soil depth. At the conservation tillage plot, below 20 cm soil depth, macropore density was greater than at the conventionally tilled plot. Macroporosity obtained from the visual registering varied between 0.09% and 0.83% for the conventional tillage plot and between 0.08% and 0.6% for the conservation tillage plot. Macroporosity derived from tension infiltrometry, assuming a minimum macropore radius of 0.5 mm, range between 0.02% and 0.1%, about one order of magnitude lower than the figure obtained from visual inventarization. The results indicate a greater continuity and connectivity of the macropore system for silty soils with conservation tillage systems. Therefore, conservation tillage could possibly offer a means to reduce surface runoff and flood generation in agricultural landscapes dominated by silty-loamy soils.

Soil macropore dynamics affected by tillage and irrigation for a silty loam alluvial soil in southern Portugal

Soil tillage can have a significant effect on soil porosity and water infiltration. This study reports field measurements of near saturated hydraulic conductivity in an undisturbed soil under two tillage treatments, conventional tillage (CT) and minimum tillage (MT). The objective was to determine effective macro and mesoporosities, porosity dynamics during the irrigation season, and their contribution to water flow. Field observations were performed during the 1998 maize ( Zea mays L.) cropping season in an Eutric Fluvisol with a silty loam texture, located in the Sorraia River Watershed in the south of Portugal. Infiltration measurements were done with a tension infiltrometer. At each location an infiltration sequence was performed corresponding to water tensions ( φ) of 0, 3, 6 and 15 cm. Five sets of infiltration measurements were taken in both treatments in the top soil layer between May and September. One set of measurements was done at the depth of 30 cm at the bottom of the plowed layer in the CT plot. After 5 years of continuous tillage treatments the results show that regardless of the tillage treatment, saturated conductivity values K( φ 0) were several times larger than near saturation conductivity K( φ 3). This indicates that subsurface networks of water conducting soil pores can exist in both CT and MT maize production systems. In CT, the moldboard plow created macro and mesoporosity in the top soil layer while breaking pore continuity at 30 cm depth. This porosity was partially disrupted by the first irrigation, resulting in a significant decrease of 45% in the macropore contribution to flow. Later in the season, the irrigation effect was overlaid by the root development effect creating new channels or continuity between existing pores. In MT macroporosity contribution to flow did not show significant differences in time, representing 85% of the total flow. In both the treatments, macropores were the main contributing pores to the total flow, in spite of the very low macroporosity volumes.

Infiltration patterns into two soils under conventional and conservation tillage: influence of the spatial distribution of plant root structures and soil animal activity

The characteristics and properties of the soil macropore system may cause different infiltration behavior under different tillage practices. To evaluate the effect of a specific tillage system on infiltration and percolation with particular regard to the influence of crop structure and soil animal activity dye tracer irrigation experiments were conducted in a silty (Luvisol) as well as in a sandy loam soil (Podzolluvisol). The spatial distribution of water flow paths was experimentally examined at four square areas of 0.49 m 2, under conservation and conventional tillage. Natural rainstorms were simulated by irrigating the plots with 2.8×10 −3 M methylene blue solutions. For both soils the root crowns of the agricultural crop, wormcasts and stained soil sections as well as macroscopic conduits were traced on plastic sheets. The investigated soil depths were 0, 5, 10 and 20 cm for the both soils. For the Luvisol, the 30, 40, 50, 80 and 120 cm depths were also studied. For the Luvisol, the conservation tillage plot revealed pronounced vertical connectivity and continuity of the macropore network (maximum depth of stained pores=120 cm ), while at the conventional tillage plot, continuous macropores were observed to soil depths of 50 cm, but mainly restricted to the ploughed topsoil (0–30 cm soil depth). For the Podzolluvisol, at the conservation tillage site extensive mulch residues prevented water transport beneath 5 cm soil depth. In contrast, at the conventionally tilled site stained water reached a depth of 20 cm. For all investigated plots on both soil types, the location of the root crowns of agricultural crop and of wormcasts was not related to percolation patterns. The results suggest that conservation tillage on silty soils under agricultural landuse could induce an increased water retention capacity reducing the significance of fast runoff components.

Pea Leaf Weevil (Coleoptera: Curculionidae) Spatial Distribution in Peas

The effects of tillage, location within a plot, and date of sampling on the spatial distribution of adult Sitona lineatus (L.) in peas, Pisum sativum L., were evaluated using geostatistical analyses. The geostatistics procedure uses spatial variation to determine the degree and type of spatial association and dependence of spatially related data. These analyses showed that 88% of the locations sampled had aggregated spatial distribution for adult S. lineatus. The variation that was spatially dependent was only 11.5%. Of the 2 types of aggregated spatial distributions, the spherical spatial distribution was most common on the 1st sampling date under conventional tillage, whereas the check-mark spatial distribution was most common on the 2nd sampling date in the outside edge locations of the pea plots. The smoother soil surface and reduced plant residue of the conventional tillage plot may have increased weevil movement and facilitated aggregation development. The spatial dynamics of this insect changed over time and was probably affected by the physical environment, as represented by the 2 tillage regimes and location within the pea plots. The geostatistical analyses provided insights into the spatial distribution of this insect and potential relationship with agronomic practices.

Spatial variability of residual nitrate‐nitrogen under two tillage systems in central Iowa: A composite three‐dimensional resistant and exploratory approach

Soil nitrate‐nitrogen (NO3‐N) data arranged on a three‐dimensional grid were analyzed to compare tillage effect on the spatial distribution of residual NO3‐N in the soil profile of agricultural plots drained by subsurface tiles. A three‐dimensional median‐based resistant (to outlier(s)) approach was developed to polish the spatially located data on soil NO3‐N affected by directional trends (nonstationarity in the mean) in three major directions (row, column, and depth) and along the horizontal diagonal directions of the grid. Effect of preferential or nonpreferential path of transport of NO3‐N in the vertical direction defined as sample hole effect was also removed to make the data trend‐free across holes. Composite three‐dimensional semivariogram models (along horizontal and vertical directions) were used to describe the spatial structure of residual soil nitrate distribution. Two plots in the same field, one under each tillage system (conventional tillage and no tillage), were studied. In each plot, soil samples were collected at five depths (30, 60, 90, 120, and 150 cm) from 35 sites (holes) arranged on a 7×5 regular grid of 7.6×7.6 m. In the conventional tillage plot, residual NO3‐N concentrations decreased gradually to a depth of 90 cm and increased beyond this depth. The coefficient of variation, however, became gradually smaller, showing more uniform distribution for greater depths. In the no‐tillage plot, trends were similar to those in the conventional tillage system, but were spatially more stable across the profile. Structural analyses indicated that under conventional tillage, the semivariogram of residual soil nitrate distribution was linear in the horizontal and vertical directions. In contrast, the semivariograms for no‐tillage showed nugget‐type behavior, indicating a lack of spatial structure in the residual soil nitrate.

Penetration and Persistence of Commercially Formulated Beauveria bassiana Conidia in Soil of Two Tillage Systems

Penetration and persistence of commercially formulated conidia of Beauveria bassiana (Balsamo) Vuillimen in the profiles of long-term conventional and no-tillage plots were measured by recovery of colony-forming units (CFUs) at selected depths over 235 d after application of an aqueous spray of conidia to the soil. High percentages of fungal propagules recovered from the conventional and no-tillage plots remained in the upper 5 cm of the profiles of the Cecil sandy clay loam soil. The conidia (2–3 by 2.0–2.5 μm) apparently were filtered from the aqueous suspension by the soil matrix as the suspension passed through the soil profile. Penetration of small percentages of conidia to the depth of 10.1 to 15.0 cm in both tillage systems occurred before 8 h after application. Rate of penetration of propagules to these lower depths was faster in conventional plots than in no-tillage plots. Infiltration rates of water were consistent with the differential rate of penetration in the two systems. Although only 300 and 1,800 CFUs/cm3 of dry soil remained in the 10.1- to 15.0-cm depth of the conventional and no-tillage plots, respectively, after 12 d, 90 and 75% of Galleria mellonella (L.) larvae exposed to soil from this depth of the respective tillages were infected. Recovery of propagules from the 0- to 5-cm depth of the conventional and no-tillage plots decreased 95 and 86%, respectively, within 12 d of application of conidia. By day 235, the conventional tillage plot contained only 18 CFUs/cm3 of dry soil at this depth. A 10-fold decrease in the number of CFUs remaining in the no-tillage plots occurred by day 49 (4.8 × 104 CFUs/cm3 of dry soil) with no propagules detected by day 200. Persistence of granular and wettable powder formulations of B. bassiana in the Cecil series soil was compared in a separate study. A 10-fold decrease in viable CFUs in plots treated with aqueous suspensions of the wettable powder occurred by day 21. By day 202, no CFUs remained in those plots. The number of CFUs recovered from plots treated with the granular formulation was 10 times higher than the number recovered from plots treated with the aqueous spray. After 202 d, 111 viable CFUs/cm3 of dry soil remained in the plots treated with granular formulation.

不耕起栽培の評価 ＩＶ 土壌の変化と作物根系

We investigated the physical and chemical properties of soil, and the patterns of crop root growth from a serial experiments on successive no-tillage farming for seven years in this paper.1) The soil hardness of no-tillage plot (NT) was higher than that of conventional tillage plot (CT) in 5-20cm layer, the hardness of NT was almost equivalent to that of CT in 25-35cm layer and the hardness of NT was lower than that of CT in layer below 35cm. The soil hardening has already progressed since the second year of no-tillage farming.2) There was no difference between CT and NT in three phase of soil. The significant differences in both water content and bulk density for soil layers were observed in common with the two plots.3) The pH of NT was slightly lower than that of CT.4) In the analysis on various chemical properties of soil after six years of no-tillage farming, no clear difference between CT and NT was observed except for a few chemical components.5) Most of the crop root in NT concentrated on 0-10cm soil layer.

不耕起栽培の評価 ＩＩＩ 作物収量と投入エネルギー

We analysed the both direct and indirect energy input to the field with the data of fuel consumption and crop yield from a serial experiments on successive no-tillage farming for seven years.1) The average yield of dent corn in no-tillage plot(NT) was about 88% of that in conventional tillage plot(CT). The yield of turnip in NT was almost as same as that in CT. The both yield of barley and wheat in NT after six years were extreamly poorer then those in CT.2) From the yieid of dent corn, the duration of six years was thought as practical successive limits in no-tillage farming.3) The ratio of energy output/direct energy input was calculated with the yield obtained from our experiments for seven years. The average ratio for three crops in NT were 2-3 times as large as those in CT.4) As production energy of herbicide was generally large, energy input in NT was equivalent to 64% of that in CT for the processes before seeding, and 84% of that in CT for all processes, respectively.The difference of energy input between CT and NT including both direct and indirect energy was smaller than that including direct energy only.