N. R. Hulugalle

Soil properties, nutrient uptake and crop growth in an irrigated Vertisol after nine years of minimum tillage

The effects of three contrasting tillage / cropping combinations on soil properties, nutrient uptake, growth, and yield of cotton and cowpea during 1993–1994 were evaluated in a trial running since 1985 in a Typic Pellustert (Vertisol) of north-western New South Wales, Australia. The treatments from 1985 to 1993 were: (a) maximum tillage (disc-ploughing to 0.2 m depth, chisel ploughing to 0.3 m depth followed by ridging every year) sown with continuous cotton (Gossypium hirsutum L.); (b) minimum tillage (planting on ridges retained intact from previous years with soil disturbance being limited to deepening of the furrows with disc-hillers and shallow cultivation on ridge surfaces, if required) with continuous cotton; and (c) a cotton-winter wheat (Triticum aestivum L.)-summer (bare) fallow-cotton sequence where cotton was sown with minimum tillage and wheat was sown with no-tillage. Soil was sampled to a depth of 0.6 m in August 1993 and May–June 1994. Soil properties evaluated were organic matter fractions, dispersion index, soil resilience (a measure of the self-mulching ability of the soil), plastic limit, soil strength (as cone index), soil shrinkage indices derived from shrinkage curves, exchangeable Ca, Mg, K and Na, pH, nitrate-N and electrical conductivity. Profile water content and water extraction, nutrient uptake, crop vegetative growth, cotton lint yield and fibre quality were also quantified. In comparison with maximum tillage, values of exchangeable Na, ESP and dispersion index were lower with minimum tillage in 1993 and 1994, and nitrate-N, particulate and total organic matter were greater and pH lower in 1994. Soil compaction (evaluated from shrinkage indices) in ridges was in the order minimum tillage / cotton-wheat-fallow-cotton < minimum tillage / continuous cotton < maximum tillage / continuous cotton, whereas subsoil compaction in maximum tilied plots was less than that in minimum tilled plots. In comparison with published data, however, subsoil compaction was large in all treatments. Nonetheless, water extraction during extended drying cycles was deeper and more extensive with minimum tillage and suggests that “by-pass channels” may have played a significant role in determining water extraction patterns at this site. Nutrient concentrations in plant tissues were not significantly affected by tillage / crop combinations. In comparison with maximum tillage, vegetative growth of cotton and cowpea in January and February (the peak of the summer crop growing season), and cotton lint yield were higher, and cotton lint fibre quality was better with minimum tillage. The highest lint yield and value, and the best fibre quality occurred where minimum tillage / cotton-wheat-summer fallow-cotton had been sown in the past.

The impact of ant bioturbation and foraging activities on surrounding soil properties

Summary Nest building and foraging activities are two of the many ways that ants impact on the surrounding soil environment within and beyond the mound. These activities have both long- and short-term effects on the soil part of the ecosystem through structural alterations, nutrient accumulation and release, with possible enhancement of soil quality. This study illustrates the impact of ant foraging activities on the soil and the pattern of arrangement existing in soil properties in the mound soil environment. Eight active mounds of Iridomyrmex greensladei , greater than 50 cm in diameter, were randomly selected from four blocks in a vegetation remnant adjacent to the main Wee Waa highway, Narrabri, New South Wales. The soil volume, soil mass and slope for each mound was characterised. Soil samples were collected in the plots at 0–10 cm depth from the top of the mound, the mound perimeter, 5 m radius from the mound perimeter, the foraging tracks, and from other locations unaffected by ant activity. The soil samples were analysed for physical and chemical properties. The extent of pore distribution as cavities and galleries, was evaluated by taking photographs of a cross section of an ant mound after pouring in water miscible paint (1:8 paint to water suspension) into an open cut on the top of the mound. The paint moved through the pores, to a depth of about 150–200 cm from the surface through vertical and lateral galleries. In comparison to the surrounding soil, ant-impacted soils were lower in clay, higher in sand and silt, and lower in exchangeable Ca, Mg, K and Na. The top of the mound was higher in NO 3 , P and more compacted than soils not modified by ant mounds. Ant-impacted soils had low dispersion indices compared with unmodified soil. Ant bioturbation activities increased soil porosity in the mounds extending to about 200 cm down the soil profile. Ant bioturbation and foraging activities were found to affect soil properties beyond the perimeter of the mound and into the surrounding ecosystem.

A review of the changes in soil quality and profitability accomplished by sowing rotation crops after cotton in Australian Vertosols from 1970 to 2006

In agricultural systems, soil quality is thought of in terms of productive land that can maintain or increase farm profitability, as well as conserving soil resources so that future farming generations can make a living. Management practices which can modify soil quality include tillage systems and crop rotations. A major proportion of Australian cotton (Gossypium hirsutum L.) is grown on Vertosols (~75%), of which almost 80% is irrigated. These soils have high clay contents (40–80 g/100 g) and strong shrink–swell capacities, but are frequently sodic at depth and prone to deterioration in soil physical quality if incorrectly managed. Due to extensive yield losses caused by widespread deterioration of soil structure and declining fertility associated with tillage, trafficking, and picking under wet conditions during the middle and late 1970s, a major research program was initiated with the objective of developing soil management systems which could improve cotton yields while concurrently ameliorating and maintaining soil structure and fertility. An outcome of this research was the identification of cotton–winter crop sequences sown in a 1 : 1 rotation as being able to sustain lint yields while at the same time maintaining soil physical quality and minimising fertility decline. Consequently, today, a large proportion (~75%) of Australian cotton is grown in rotation with winter cereals such as wheat (Triticum aestivum L.), or legumes such as faba bean (Vicia faba L.). A second phase of research on cotton rotations in Vertosols was initiated during the early 1990s with the main objective of identifying sustainable cotton–rotation crop sequences; viz. crop sequences which maintained and improved soil quality, minimised disease incidence, facilitated soil organic carbon sequestration, and maximised economic returns and cotton water use efficiency in the major commercial cotton-growing regions of Australia. The objective of this review was to summarise the key findings of both these phases of Australian research with respect to soil quality and profitability, and identify future areas of for research. Wheat rotation crops under irrigated and dryland conditions and in a range of climates where cotton is grown can improve soil quality indicators such as subsoil structure, salinity, and sodicity under irrigated and dryland conditions, while leguminous crops can increase available nitrogen by fixing atmospheric nitrogen, and by reducing N volatilisation and leaching losses. Soil organic carbon in most locations has decreased with time, although the rate of decrease may be reduced by sowing crop sequences that return about 2 kg/m2.crop cycle of residues to the soil, minimising tillage and optimising N inputs. Although the beneficial effects of soil biodiversity on quality of soil are claimed to be many, except for a few studies on soil macrofauna such as ants, conclusive field-based evidence to demonstrate this has not been forthcoming with respect to cotton rotations. In general, lowest average lint yields per hectare were with cotton monoculture. The cotton–wheat systems generally returned higher average gross margins/ML irrigation water than cotton monoculture and other rotation crops. This indicates that where irrigation water, rather than land, is the limiting resource, cotton–wheat systems would be more profitable. Recently, the addition of vetch (Vicia villosa Roth.) to the cotton–wheat system has further improved average cotton yields and profitability. Profitability of cotton–wheat sequences varies with the relative price of cotton to wheat. In comparison with cotton monoculture, cotton–rotation crop sequences may be more resilient to price increases in fuel and fertiliser due to lower overall input costs. The profitability of cotton–rotation crop sequences such as cotton–wheat, where cotton is not sown in the same field every year, is more resilient to fluctuations in the price of cotton lint, fuel and nitrogen fertiliser. This review identified several issues with respect to cotton–rotation crop sequences where knowledge is lacking or very limited. These are: research into ‘new’ crop rotations; comparative soil quality effects of managing rotation crop stubble; machinery attachments for managing rotation crop stubble in situ in permanent bed systems; the minimum amount of crop stubble which needs to be returned per cropping cycle to increase SOC levels from present values; the relative efficacy of C3 and C4 rotation crops in relation to carbon sequestration; the interactions between soil biodiversity and soil physical and chemical quality indicators, and cotton yields; and the effects of sowing rotation crops after cotton on farm and cotton industry economic indicators such as the economic incentives for adopting new cotton rotations, farm level impacts of research and extension investments, and industry- and community/catchment-wide economic modelling of the impact of cotton research and extension activities.

Amelioration of soil physical properties by Mucuna after mechanized land clearing of a tropical rain forest

We studied the effect of mucuna (Mucuna utilis) cover on the physical properties of an Oxic paleustalf in western Nigeria, previously cleared by four different methods. The methods used were manual clearing and clearing with a shearblade, a tree-pusher, and a treepusher/root rake. The soil physical properties measured were total porosity, penetrometer resistance, infiltration, and soil water retention. In contrast to cropping, mucuna cover improved soil porosity, penetrometer resistance, and hydraulic properties in all treatments. Total porosity of the 0− to 100-mm depth increased with mucuna cover from 0.55 to 0.59, 0.54 to 0.57, and 0.57 to 0.59 m3 m−3 in the manual, shearblade, and treepusher clearing treatments, respectively. Porosity of the treepusher/root rake clearing method was unaffected by mucuna cover. Penetrometer resistance of the 50− to 70-mm depth decreased with mucuna from 426 to 409, 425 to 418, 436 to 398, and 412 to 403 kPa in the manual, shearblade, treepusher and treepusher/root rake methods, respectively. Cumulative infiltration amounts over 3 h of the plots sown to mucuna were 134.1, 55.2, 14.6, and 186.8% greater than the corresponding cropped plots for the manual, shearblade, treepusher, and treepusher/root rake treatments, respectively. Similar decreases were noted in soil water retention at a potential of 0 kPa. The beneficial effects of mucuna cover were greater in manually cleared and treepusher-cleared plots. It was indicated that where land clearing causes high soil compaction, mucuna cover for about 1 yr would be a useful practice to restore soil physical properties to favorable levels for arable farming.

Effects of no-tillage and alley cropping on soil properties and crop yields in a Typic Kandiudult of southern Cameroon

The effects of no-tillage and alley cropping withCassia spectabilis hedgerows on soil properties and crop yields in a Typic Kandiudult of the humid forest zone of Central Africa were studied over the period 1990–1992 in southern Cameroon. The experimental treatments were no-tillage and hand tillage, both of which were either alley cropped withC. spectabilis hedgerows at interhedgerow spacings of 6 m or not alley cropped (control). A maize + cassava intercrop was planted in all plots at the commencement of each growing season.No-tillage had no significant effects on soil physical properties except to decrease soil temperature. In comparison to hand tillage, no-tillage increased soil organic C and total N in both years and pH in 1991. Mean organic C and total N with no-tillage were 1.77% and 0.174%, respectively, whereas with hand tillage were 1.35% and 0.145%, respectively. Notillage also resulted in a greater proportion ofC. spectabilis roots occurring in the topsoil. Alley cropping caused significant reductions in dry season soil temperature, surface seal formation and cassava root growth, and increases in exchangeable Ca, effective CEC and water infiltration compared with non-alley cropped controls. Infiltration rate at 2 h after commencing measurements were greater by 75% with alley cropping. Lowest maize cob and cassava tuber yeilds were observed when no-tillage was combined with alley cropping whereas highest yields occurred with no-tillage alone.

Residual effects of tillage and crop rotation on soil properties, soil invertebrate numbers and nutrient uptake in an irrigated Vertisol sown to cotton

Abstract The residual effects of tillage and cropping sequence on soil physical and chemical properties, surface-active and soil invertebrate composition and abundance, nutrient uptake, growth and yield of cotton were evaluated from 1994 to 1996 in a compacted Typic Haplustert (Vertisol) of north-western New South Wales, Australia. The experimental treatments from 1985 to 1992 were intensive tillage (disc-ploughing to 200 mm, chisel ploughing to 300 mm followed by ridging every year) sown with continuous cotton (Gossypium hirsutum L.); minimum tillage (planting on ridges retained intact from previous years with soil disturbance being limited to deepening of the furrows with disc-hillers and shallow cultivation on ridge surfaces) sown with either continuous cotton or a cotton-winter wheat (Triticum aestivum L.)-fallow rotation where wheat was sown with no-tillage. The tillage treatments were repeated in May 1993, and the plots were either followed or cropped by sowing either cowpea (Vigna unguiculata Walp.) or cotton. Cotton was sown with minimum tillage in 1994 and 1995 in all plots. Soil was sampled from the 0–150 mm, 150–300 mm, 300–450 mm and 450–600 mm depths, and analyzed for organic carbon, dispersion index, soil resilience (a measure of the self-mulching ability of the soil), plastic limit, soil strength, pH, exchangeable Ca, Mg, K and Na, and nitrate-N. Profile water content, nutrient uptake, numbers of soil invertebrates, cotton growth and lint yield, and fibre quality were also quantified. Soil strength was lowest where intensively tilled continuous cotton had been sown, whereas in plots where minimum tillage and cotton-wheat-fallow rotation were combined soil fertility was best (indicated by lowest values of pH, exchangeable Na, exchangeable sodium percentage and dispersion, and highest values of organic C) and water extraction by cotton greatest during periods of reduced water availability. The latter was attributed to cotton utilizing stable pores with a high degree of pore-continuity created by the root systems of preceding crops or associated macrofauna as ‘by-pass channels’ to avoid the restrictions of the soil matrix, thereby facilitating rapid access to sub-soil water. Cotton growth reflected these differences such that vegetative and reproductive growth, nutrient uptake and lint yield were greater and fibre quality superior wherever minimum tillage had been imposed, and best in plots under minimum tilled cotton-wheat-fallow rotation. Composition and abundance of surface-active and soil invertebrates were determined primarily by soil microclimate and pesticide application regime rather than by tillage and cropping system. Ant numbers were lowest in intesively tilled plots whereas Collembola activity was limited to periods when the soil was moist.

SOIL PHYSICAL CHANGES AND CROP ROOT GROWTH FOLLOWING DIFFERENT METHODS OF LAND CLEARING IN WESTERN NIGERIA

We studied the effects of four different methods of land clearing in western Nigeria on soil physical properties of an Alfisol and on the root growth of the following crop. The methods used were manual clearing and clearing with a shearblade, a treepusher, and a treepusher/root rake. Soil physical properties measured were bulk density, saturated hydraulic conductivity, infiltration rate and cumulative infiltration, total porosity, pore size distribution, and soil water retention. Mechanical clearing increased bulk density and proportion of medium-sized pores (2 to 14.3-μm radius) and decreased infiltration rate, cumulative infiltration, saturated hydraulic conductivity, total porosity, and proportion of macropores (>14.3-μm radius). Soil water content at a potential of 0 kPa was significantly reduced, whereas that at potentials of –10 and –33 kPa was increased. In comparison with the forested control, the magnitude of changes in soil physical properties was in the order of manual clearing < treepusher < shearblade < treepusher/root rake. Although the differential effects of land clearing methods on the soil were reflected only in the initial pattern of maize root growth during the seedling stage, it was sufficient to affect grain yield. Root growth of mucuna and cowpea were not affected by the changes in soil physical properties.

Changes in some soil properties due to tillage practices in rainfed hardsetting Alfisols and irrigated Vertisols of eastern Australia

Changes in soil physical and chemical properties were evaluated in several on-farm studies located in rainfed, hardsetting red Alfisols (Ferric Luvisols) and in irrigated, self-mulching Vertisols (Chromic Vertisols) of eastern Australia. The objective of the studies was to evaluate changes in soil physical and chemical properties with time under commercial farming situations where changes had been made to previously used farming systems (native pasture to wheat (Triticum sp.) cultivation in the hardsetting Alfisols; intensively tilled cotton (Gossypium sp.) monoculture to minimum tilled cotton monoculture and cotton‐ wheat sequences in the irrigated Vertisols). The soil physical and chemical changes in the Alfisols were caused by changing land use from native pasture to intensively tilled wheat cultivation with long fallow and stubble burning, whereas those in the Vertisols were caused by changing from intensive to minimum tillage in cotton-based cropping systems. Indicators of soil physical (tensile strength, structural stability, dispersion) and chemical (pH, electrical conductivity, organic C, total N) quality evaluated in the Alfisols indicated that a significant deterioration in soil quality, which was characterized by an increase in hardsetting behaviour and acidity, and a decrease in organic C, total N and aggregate stability had occurred. These changes were due to inappropriate tillage practices causing soil inversion and the rapid breakdown of organic matter which occurs when intensive tillage practices are imposed in previously untilled soils. In the Vertisols, however, indicators of soil physical (specific volume of air-filled pores in oven-dried clods, plastic limit, soil resilience) and chemical (pH, electrical conductivity, exchangeable sodium percentage, and soil organic C) quality indicated that while deterioration in physical quality (i.e., characterized by an increase in compaction) had occurred, chemical quality had improved. The latter was characterized by an increase in soil organic C and a decrease in exchangeable sodium percentage. These changes were due to replacing intensive tillage with minimum tillage. # 1999 Elsevier Science B.V. All rights reserved.

Root growth of maize in a compacted gravelly tropical alfisol as affected by rotation with a woody perennial

Abstract The objective of this experiment was to evaluate the effects of growing a deep-rooting perennial on the root system development of a subsequent crop with low root penetrating ability. These effects were measured on a gravelly Alfisol with a compacted subsoil horizon for three tillage methods (zero tillage, conventional tillage and reduced tillage, consisting of chiseling in the row zone once a year) and two cropping sequences (pigeon pea-maize and continuous maize). The root development was related to changes in soil physical and chemical properties. At all times overall root growth was in the order of zero tillage > reduced tillage > conventional tillage. Among zero-tilled plots, maize root growth in plots sown to a pigeon pea-maize sequence was greater than in plots sown to continuous maize. Macroporosity of the gravel layer, measured as soil water content at 0 kPa in the 500–600 mm depth, was not affected by cropping sequence. Among tillage systems, soil water content at 0 kPa was 18.9, 11.8 and 13.9% on a volume basis for zero-tilled, reduced-tilled and conventionally-tilled plots, respectively. Soil physical properties above the gravel layer were improved in the order of zero tillage > reduced tillage > conventional tillage. Among zero-tilled plots, however, the pigeon pea-maize sequence improved soil physical properties more than continuous maize did. Mean seasonal soil temperature at 50 mm depth, measured at 1400 h during the major growing season, was 32.8 and 34.7°C in zero-tilled plots sown to a pigeon pea-maize sequence and continuous maize, respectively. At the same time mean seasonal temperature was 33.8, 35.5, and 39.7°C in zero-tilled, reduced-tilled and conventionally-tilled plots. In relation to continuous maize, sowing of pigeon pea prior to maize increased levels of organic carbon, exchangeable Ca, Mg and K and cation exchange capacity. Grain yield in plots sown to a pigeon pea-maize sequence was greater than in plots sown to continuous maize. Among tillage systems zero-tilled and reduced-tilled plots outyielded conventionally-tilled plots.

Effects of cassava-based cropping systems on physico-chemical properties of soil and earthworm casts in a tropical Alfisol

Abstract The effects of cassava-based intercropping systems and rotations on physical and chemical properties of earthworm casts and the adjacent soil were studied on an Oxic Paleustalf in south-western Nigeria. Earthworm activity was greater with intercropping although it was not significantly affected by the number of component crops in a mixture. The particle size distribution, bulk density, exchangeable cations, Bray-1-P, pH and effective cation exchange capacity (CEC) of soil and earthworm casts did not differ among the cassava-based cropping systems investigated. Greatest values of mean weight diameter, organic C and total N were observed in earthworm casts from three component crop mixtures, although the adjacent soil was not similarly affected. The results suggest that although the cropping system changed some physico-chemical properties of earthworm casts, similar changes did not occur in the adjacent soil. Water infiltration into the soil was, however, increased by intercropping and may be related to earthworm activity. Cropping system may, therefore, influence soil fertility indirectly by changing water infiltration characteristics and hence, nutrient losses in run-off and erosion. In relation to soil, earthworm casts had higher silt and clay contents, bulk density, mean weight diameter, pH, Bray-1-P, Organic C, total N, C:N ratio, exchangeable cations and effective CEC, and lower sand content.