Effect of aggregate size and soil water content on emergence of soybean (Glycine max, L. Merr.) and maize (Zea mays, L.)

Rapid wetting of irrigated soils often leads to slaking and slumping, and on drying a surface crust and hard-set conditions may occur. This results in reduced crop emergence unless the surface is kept moist. The effect of aggregate size and water content on the emergence of soybean and maize from an Entic chromustert (heavy cracking clay) was determined using pots of sieved aggregates with size ranges less than 1, 1–2, 2–5 and 5–15 mm at soil water contents of 15, 20 and 25 g (100 g)⁻¹. Unsieved soil was used as a control. Greatest emergence tended to occur from fine (1–2 mm) seedbeds compared with coarse (5–15 mm) seedbeds for both crops. A covered treatment, simulating a stubble mulch, resulted in greater emergence than an uncovered treatment for all water contents and aggregate sizes. Earlier emergence occurred from finer (less than 1 mm and 1–2 mm) seedbeds than from coarse (5–15 mm) seedbeds, and at the greatest water content used. Soil strength, measured with a shear vane, decreased with increasing water content and tended to be less on fine (1–2 mm) seedbeds compared with very fine (less than 1 mm) or coarse (5–15 mm) seedbeds. It is recommended that, for good emergence from this Entic chromustert, seedbeds be brought to a water content of 25 g (100 g)⁻¹ by capillary wetting to prevent hardsetting and consist of 1–2 or 2–5 mm aggregates for soybean and maize, respectively, and have a stubble mulch on the surface. This corresponds to an equivalent depth of water of 15 mm and 9 mm for soybean and maize, respectively, in the top 50 mm of the profile.     

Traffic and residue management systems: effects on fate of fertilizer N in corn

Soil compaction has been recognized as a problem limiting crop production, especially in the Southern Coastal Plain of the USA. Development of tillage and residue management systems is needed to alleviate soil compaction problems in these soils. Fertilizer nitrogen (N) management is also an important factor in these management systems. In 1988, a study was initiated with a wide-frame (6.3 m) vehicle to determine the interactive effects of traffic, deep tillage, and surface residue management on the fate of fertilizer N applied to corn (Zea mays L.) grown on a Norfork loamy sand (fine-loamy, siliceous, Thermic, Typic Kandiudults). Corn was planted into a winter cover crop of ‘Tibbee’ crimson clover (Trifolium incarnatum L.). Treatments included: traffic (conventional equipment or no traffic); deep tillage (no deep tillage, annual in-row subsoiling, or one-time only complete disruption); residue management (no surface tillage or disk and field cultivation). The one-time only complete disruption was accomplished by subsoiling at a depth of 43 cm on 25 cm centers in spring 1988. In 1990–1991, fertilizer applications were made as ¹⁵N-depleted NH₄NO₃ to microplots inside each treatment plot. The 1990 and 1991 data are reported here. In 1990 an extreme drought resulted in an average grain yield of 1.8 Mg grain ha⁻¹, whereas abundant rainfall in 1991 resulted in 9.4 Mg grain ha⁻¹. Deep tillage increased corn dry matter production in both years. In 1991, grain yields indicated that corn was susceptible to recompaction of soil owing to traffic when residues were incorporated with surface tillage. In the dry year, plant N uptake was increased 27% with deep tillage and decreased 10% with traffic. In the wet year, a surface tillage × deep tillage × traffic interaction was observed for total N uptake, fertilizer N uptake, and total fertilizer N recovery in the plant-soil system. When combined with traffic, plant N uptake was reduced with the highest intensity tillage treatment (135 kg N ha⁻¹) because of rootrestricting soil compaction, and with the lowest intensity tillage treatment (129 kg N ha⁻¹) because of increased N losses. In these soils, leaving residues on the soil surface can reduce the detrimental effect of traffic on corn production, but if no surface tillage is performed, deep tillage is needed.     

Some tools for parsimonious modelling and interpretation of within-field variation of soil and crop systems

Parsimony is a guiding principle in scientific investigation which goes back to the medieval schools. It is proposed in this paper that, in different guises, the principle of parsimony (using no more complex a model or representation of reality than absolutely necessary) is essential for agricultural research at the scale of the field or larger regions. Two examples of the principle are given, illustrated with examples from research on precision agriculture:

1. The spatio-temporal variability of a sequence of yield maps is considerable, and often defeats simple approaches to interpretation and analysis. Reducing the variability to a small number of basic temporal patterns with spatial expression allows useful information to be extracted. The normalised fuzzy partition entropy is a parsimonious criterion appropriate for identifying the number of distinct patterns in the data. It is shown in a case study how this can aid interpretation of a complex data set.

2. Models of the joint effect of different factors on crop yield can take various forms. A simple assumption is that the different factors are additive, the most complex models describe interactions. Justus von Liebig’s ‘Law of the minimum’ is a model of little complexity and may often be a parsimonious and powerful tool for modelling crop responses. A comparison of these models on some crop response data, using the Akaike information criterion to measure the parsimony of the different models, is given.

     

Comparison of options for sugarcane (Saccharum officinarum L.) stool destruction

Sugarcane (Saccharum officinarum L.) production is customarily from a plant crop followed by two or more ratoon crops, which are grown from the underground stubble called the sugarcane stool. Frequently, the stool has to be ploughed out when the yield of a ratoon crop falls below acceptable levels, or as a control measure for sugarcane diseases. Sugarcane stool destruction with conventional land preparation equipment has proved to be ineffective, especially in high-rainfall areas. Methods for killing the stools have either been too expensive or keep the land unproductive for an uneconomical period of time. More efficient and cheaper mechanical systems for stool destruction are therefore needed. This study was a comparison of four methods that could be used for stool destruction. The soils on the experimental site were a combination of Dystric Cambisols and Humic Acrisols in the petroferric phase. Three of the methods compared have traditionally been used at a leading sugarcane estate in Kenya, whereas the fourth utilizes a new implement that was developed with the objective of improving efficiency of the operation. Factors thought likely to influence individual methods are discussed. It is concluded that the new implement has potential as a device for sugarcane stool destruction under conditions of rainfed production. It is suggested that the shortest time period allowed between stool destruction and subsequent land preparation operations should be between 4 and 5 weeks.     

Development and application of landform segmentation procedures

Landscape-scale approaches to research in soil science are explicitly focused on transfers of components within and between landscapes. Despite wide-spread recognition of the importance of these transfers, the application of landscape-scale approaches has been hindered by the lack of clear, reproducible research designs. Landform segmentation is used to divide natural and human-influenced landscapes into functionally distinct units. A specific type of landform segmentation, landform element classification, was used in a comparative mensurative design to compare the effects of cultivation on soil distribution and soil organic carbon (SOC) storage and in a manipulative design to determine the relationship between N₂O emissions and fertilizer rate in a hummocky till geomorphic surface in southern Saskatchewan. Significant transfers of SOC and surface soil from convex shoulder units to lower slope positions occurred over the past 90 years, resulting in a change in the type of soils that occupy these positions at two research sites. The observed pattern is consistent with a tillage translocation dominated surface. The dominant control on N₂O emissions in the landscape are spatial differences in water-filled pore space (WFPS) that are strongly controlled by water redistribution. Emissions from drier, shoulder landform element complexes are consistently low throughout the year, whereas a strong positive relationship between N fertilizer rate and N₂O emissions occur in the wettest, level depressional elements.     

Identification of pre-existing cracks on soil fracture surfaces using dye

A significant strength-controlling property of aggregated soils is structural porosity such as cracks. A technique is presented to identify structural porosity on fracture surfaces using methylene blue dye. Soil aggregates were immersed in the stain, returned to their original water content, and equilibrated. They were then fractured under a dynamic load using an impact rig. The fragments were collected and sieved to selected size ranges. The proportion of the fragment surface that was stained from each size range was measured using a colour image analyser adapted for this experiment.

The first set of samples examined was formed by compacting aggregate beds to selected macroporosities to obtain samples with a statistically homogeneous macrostructure. Natural soil aggregates, collected from zero and conventional traffic treatments, were also tested. Results obtained illustrate that compaction reduces both structural porosity and fragmentation. An increase in the impact energy resulted in a decrease in the proportion of the fracture surface that was stained, showing that more ‘new’ surface area was being produced.     

Conservation tillage systems, fungal complexes and disease development in soybean and barley rhizospheres in Prince Edward Island

A potential for reduced soil macroporosity (below 12% soil volume) under direct drilling, with a concomitant increase in soil relative saturation, is associated with an increase in crown and root rots in Prince Edward Island field crops. Four long-term tillage systems (moldboard plowing, paraplowing-direct drilling, rotary cultivation and direct drilling) were compared in relation to the pathogenic fungal complexes formed in a two crop rotation in spring barley (Hordeum vulgare L.) and soybean (Glycine max L. Merrill) over a 3 year period in a cool humid region of eastern Canada. The principal phytopathogenic fungal complex of Rhizoctonia solani Kühn, Fusarium avenaceum (Fr.) Sacc. and F. oxysporum Schl. remained constant over the treatments. Tillage practice did not affect the number of colony forming units of R. solani in the rhizosphere. The recovery of R. solani from root tissues tended to be lower following conservation tillage and was attributed to antagonism associated with elevated numbers of saprophytic trash microflora concentrated at the soil surface. Disease levels in potato (Solanum tuberosum L.) plantlet bioassays were not influenced significantly by soil source or tillage regime. However, plantlet growth tended to be depressed following transplantation into soil from soybean plots in 1993. Under optimum soil physical conditions conservation tillage did not appear to influence disease levels in barley and soybean rotations.     

Soil properties, and cotton growth, yield and fibre quality in three cotton-based cropping systems

The effects of three cotton-based cropping systems on soil properties, black root rot severity, and growth of cotton in a Vertisol were evaluated after a series of floods in eastern Australia. The experimental treatments, which had been imposed since 1985, were conventionally and minimum-tilled continuous cotton, and minimum-tilled cotton–wheat rotation. Frequent rainfall and flooding during the winter of 1998 resulted in near saturated soil at spring sowing in October. Although conventional tillage operations were completed before flooding, minimum tillage operations were not possible due to excessive moisture and cotton was sown onto the old beds with no-tillage. Soil specific volume (electrical conductivity of a 1:5 soil:water suspension) EC_1:5, exchangeable Na content, pH and organic C were determined for the top 0.6 m of the profile in summer 1998 and again in 1999. Organic C in the surface 0.10 m was also evaluated during 1998–2000. Black root rot severity and mycorrhizal fungal colonisation were evaluated at 6 weeks after sowing. Tissue nutrient concentrations were measured in mature cotton plants. Cotton lint yield and fibre quality were evaluated after picking and ginning.

In comparison with either minimum- or conventionally tilled continuous cotton, minimum-tilled cotton–wheat rotation had the lowest exchangeable Na content and severity of bacterial black root rot, best surface structure and the highest crop growth, nutrient uptake and lint yields. Subsoil structure was the best with conventionally tilled continuous cotton. The 1998 floods appear to have decreased exchangeable Na and increased soil pH in all treatments. Surface organic C also decreased between 1998 and 2000. Soil structural damage was minimised by avoiding tillage and trafficking in wet conditions. Compared with 1998, average yield decreases in 1999 were of the order of 43%. Cotton lint fibre quality was also poorer in 1999.     

Effects of soil management practices and tillage systems on surface soil water conservation and crust formation on a sandy loam in semi-arid Kenya

The effect of different soil management practices on crust strength and thickness, soil water conservation and crop performance was investigated on a ferric lixisol in a semi-arid environment of eastern Kenya.

The study proved that manure and mulching with minimum tillage have a greater effect on the water balance of crusted soils and maize emergence. There was increase in steady infiltration rates, amount of soil water stored in the soil and better drainage. The physical effect of mulch was less important in the rehabilitation of crusted soils in the study site when it was incorporated into the soil. Manure and surface mulch with minimum tillage should therefore be taken into account in land management and water conservation in the semi-arid areas of Kenya. The response of crops to the improved water availability due to manure with minimum and with conventional tillage and surface mulch was very clear. These management practices should be recommended when considering the effectiveness of soil and water management techniques in the study area.     

Mitochondrial COII sequences indicate that the parthenogenetic earthworm Octolasion tyrtaeum (Savigny 1826) constitutes of two lineages differing in body size and genotype

Adult individuals of the parthenogenetic earthworm Octolasion tyrtaeum (Savigny 1826) differ considerably in body size. The length of adult specimens reaches 10–14 cm in some habitats, in others just 5–8 cm. In some habitats, individuals of both size classes coexist. Until now, size differences in O. tyrtaeum were ascribed to environmental rather than genetic factors. We used DNA-sequences of the mitochondrial gene for cytochrome oxidase II (COII) to measure genetic distances between O. tyrtaeum specimens of different size classes. Individuals of different geographical sites (including five sites in Germany and one site in Canada) were analysed. There was a strong correlation between the size of the earthworms and the COII sequences; large specimens separated clearly from small specimens. While sequences of large specimens were almost identical, those of small specimens were more diverse. This indicates that O. tyrtaeum consists of two morphologically and genetically different lineages.     

Earthworm channels in cultivated clayey and loamy Norwegian soils

Studies of earthworm species and their activity, expressed as channels, on cultivated loamy (Humic Cryaquept) and clayey soils (Typic Endoaqualf and Typic Cryaquept) were conducted in southern and central Norway before conversion from conventional to organic cropping systems. At all the three study areas: Landvik (Grimstad), Voll (Ås) and Kvithamar (Stjørdal), the earthworm species Aporrectodea caliginosa, Aporrectodea rosea, Allolobophora chlorotica and Lumbricus rubellus were found. At Landvik, where the deep-burrowing species Aporrectodea longa, A. caliginosa and Lumbricus terrestris dominated, medium (4–6 mm) and coarse (>6 mm) earthworm channels were most numerous below the plough layer. Almost no coarse pores were found at Voll and Kvithamar. The volume of earthworm channels below the plough layer was 0.6–0.8% of total soil volume at Landvik and Voll and 0.3–0.4% at Kvithamar. Earthworm channels >6 mm below the plough layer were useful to identify present and previous activity of deep-burrowing earthworms such as L. terrestris. Below the plough layer, roots were almost entirely restricted to earthworm channels and interaggregate spaces.     

Soil criteria for assessing the maximum permissible ground pressure of agricultural vehicles on Chernozem soils

The maximum permissible ground pressure of agricultural vehicles to permit satisfactory crop production on heavy loamy Chernozem soil was estimated from six criteria: (1) changes in soil water-physical properties; (2) crumbling characteristics; (3) depth of compaction; (4) rut depth; (5) soil strength potential; (6) self-loosening characteristics. Using these criteria it was possible to obtain reliable data for the maximum permissible ground pressure which was found to be correlated with the soil water content at the time of tillage.

At a water content equal to or somewhat lower than the water content at optimal soil crumbling (0.16–0.24 kg kg⁻¹), the permissible ground pressure was found to be within the range 80–120 kPa. At soil water contents slightly above the optimum soil crumbling (0.26–0.28 kg kg⁻¹), the permissible ground pressure was within the range 30–60 kPa.     

Multi-scale system approaches in agronomic research at the landscape level

Spatial multi-scale analyses of actual land use system performance as determined by spatial yield variability reveals the need for landscape research in agronomy. Main ‘drivers’ of spatial yield variability for five different crops in Honduras, Costa Rica and Ecuador were identified. It is demonstrated how they vary with spatial scales and that landscape-related factors often play a large and significant role in when the variability in yield is determined. These results indicate that landscape experiments in agronomy are relevant. Apart from empirical analysis, spatial–temporal explicit modeling of landscape process dynamics such as water and soil redistribution within a landscape can give insight in the performance of agronomic systems within a dynamic landscape context. For a case study in the South of Spain it is demonstrated how within a landscape this type of research can determine the on- and off-site effects of water and soil redistribution in agro-ecosystems. Only after a spatially explicit multi-scale system analysis and explorative landscape process modeling is completed, relevant agronomic landscape experiments can be designed.     

Effect of tillage and contour diking on sorghum establishment and yield on sandy clay soil in Sudan

Sandy clay soils locally known as gardud are less arable despite their better production potential than other infertile and exhausted sand soil in western Sudan due to surface physical constraints such as low infiltration and workability. Field experiments were, therefore, conducted on these soils to determine effect of two relatively new tillage systems to the area and two widely practised systems on soil bulk density, porosity, water storage and sorghum (Sorghum bicolor L.) plant growth and yield. Contour diking at specified spacings was superimposed on the four tillage treatments for impounding surface runoff. These systems were (1) chisel ploughing, (2) broadbed and furrow, (3) ridge-furrow, and (4) traditional no-till (control). Distances of the contour diking were at four levels: zero, 5, 10 and 20 m. Soil bulk density, porosity and water content were significantly affected by the different tillage systems and contour diking. Combined analysis of three successful seasons out of five seasons showed that plant establishment and growth were highly significant. Yield component data (percent of plants reaching physiological maturity, grain and straw) indicated significant differences among treatments tested for the three seasons of the experiment. The 3-year mean grain yield for chisel plowing pooled over the four contour diking distances produced 1448 kg/ha which was greater by 72%, 107% and 384% than broadbed and furrow, ridge-furrow and no-till, respectively. Similarly, the 10-m contour-diking-distance mean grain production (917 kg/ha) over the tillage systems was 16%, 5% and 30% for more than zero, 5-m and 20-m distances, respectively. These results indicate that chisel and 10-m contour diking are appropriate and suitable for gently sloping compacted sandy clay soils of western Sudan, and superior to widely practised ridge-furrow and no-till surface configuration.     

Problems and prospects in the utilization of animal traction in semi-arid west Africa: evidence from Niger

The use of animal draft power for soil tillage has long been a major theme of agricultural development programmes in semi-arid West Africa. The rationale for animal traction utilization ranges from increasing agricultural productivity and income to relieving the drudgery in farm work. Yet, its adoption remains low and localized. Previous research has identified the conditions which favour the adoption of animal traction, but evidence on the potential benefits realizable from its use is mixed. The issue of how to improve the adoption and profitable utilization of animal traction in semi-arid West Africa remains an important topic given that mechanization of agriculture is inevitable. This paper uses data collected from villages in two different agroclimatic zones of Niger to demonstrate the regional variability of potential gains from animal traction. Production functions were estimated to determine the impact of animal traction use on area cultivated, labour input and aggregate yield. Multi-year partial budget streams were also estimated to evaluate the profitability of animal traction at each location. The results show that the use of animal traction did not have any significant impact on area cultivated, but increased the yields of sorghum (Sorghum bicolor (L.) Moench) and maize (Zea mays L.) by 12–15%. It increased labour input by 15 man-hha⁻¹ (man hours per hectare) in the dry agroclimatic zone, but reduced it by 50 man-h ha⁻¹ in the wet zone. Rates of return on animal traction investment ranged from −4 to 18% in the dry zone and from 14 to 58% in the wet zone. These results suggest that the impact of animal traction on agricultural production varies by region and depends on a broad set of agroecological and economic conditions. The absence of these conditions in marginal areas strictly limits potential utilization and profitability. On efficiency grounds, it is recommended that animal traction should be promoted only in areas where the climate, soil and economic conditions permit its intensive and profitable utilization.     

Incorporation of tracers and dazomet by rotary tillers and a spading machine

Soil fumigant efficacy in forest-tree and ornamental nurseries depends on the tillage tool used for incorporation. Maximum depth and uniformity of incorporation of surface applied materials by three rotary tillers and a spading machine were compared in a loamy sand nursery using ceramic-sphere tracers (1–3 mm diameter) and dazomet (tetrahydro-3,5,dimethyl-2H-1,3,5-thiadiazone-2-thione) micro-granules. Depth of incorporation in the top 30 cm of soil was evaluated by (1) recovery of incorporated spheres in 2 cm increments, (2) biocidal activity in 6 cm increments, and (3) cone resistance by 1.5 cm increments to 45 cm. Uniformity of incorporation was evaluated by sphere recovery and biocidal activity. Depths above which more than 95% of the spheres were recovered for the four implements were: 12.5 cm, Kuhn and Fobro rotary tillers; 17 cm, Northwest rotary tiller; 21 cm, Gramegna spading machine. The spading machine produced a distribution of spheres through the soil profile closest to a uniform distribution compared with that produced by the three rotary tillers. Lettuce seed (Lactuca sativa L.) germination was inhibited in the upper 12 cm in low and high dazomet rate treatments, indicating that all four implements effectively incorporated dazomet into that zone. Maximum depth (24 cm) for total inhibition of germination was observed for the spading machine regardless of chemical rate. Cone index values showed the following maximum penetration: 14 cm, Fobro rotary tiller; 22 cm, Kuhn and Northwest rotary tillers; 27 cm, spading machine. All three measures of depth show a distinct superiority of the spading machine when the chemical fumigant must reach depths greater than 18 cm. Within transects across the width of the implement, variations of sphere counts among 5 cm³ volumes were much larger for the rotary tillers than for the spade machine.