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

Abstract Changes in soil physical and chemical properties were evaluated in several on-farm studies located in rainfed, hardsetting red Al®sols (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 Al®sols; 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 Al®sols 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 Al®sols indicated that a signi®cant 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 (speci®c volume of air-®lled 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.

Water use and grain yield response of rainfed soybean to tillage-mulch practices in southeastern Nigeria

Despite the agronomic, economic and food values of soybean (Glycine max L. Merrill), there is still dearth of information on the tillage need and the implications of surface mulch for the crop in the eastern part of the forest-savanna transition zone of Nigeria. This study was therefore carried out on a sandy loam Ultisol at Nsukka with a sub-humid climate, during 2006 and 2007 cropping seasons. Our objective was to devise an appropriate tillage method for the crop from evaluated effects of no-till (NT), conventional tillage (CT) and mulch on selected key agronomic indices. Each of the NT and the CT was either unmulched (U) or mulched (M) in a split-plot, giving four treatments/tillage methods (NTU, NTM, CTU and CTM) randomized in four blocks. Rainfall was more favorable in the first than in the second season. The mean seasonal soil water storage (range, 99-109 mm) within 0.5-m soil layer differed among the treatments (NTU < CTU < NTM = CTM). However, for the first and second seasons, both water use (582-616 and 667-709 mm respectively) and grain yield (0.71-0.81 and 1.22-1.91 Mg ha-1 respectively) were not different. Mulch lowered the crop water use but had no influence on grain yield. Water use efficiency was enhanced with mulch only in the second season. Although either of the two mulch treatments (NTM/CTM) would be suitable for growing soybean especially in years of unfavorably distributed rainfall, NTM is a more rational choice than CTM. Rainfall adequacy at the critical reproductive stage of the crop showed to be a more important yield factor than the tested tillage methods

Biophysical interactions in tropical agroforestry systems

sequential systems, simultaneous systems Abstract. The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interac-tions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offse

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

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

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

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 NO₃, 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