Wendy Vance

Field traffic has many beneficial effects of labour saving and timeliness, but little thought has been given to the potential deleterious consequences of soil compaction. The process of soil compaction reduces total porosity and increases bulk density, resulting in changes in soil physical properties. Excessive compaction in the seedbed may impede seedling emergence. Although greater soil compaction by heavier vehicle traffic has been reported worldwide, a lighter vehicle can cause soil compaction when used repeatedly. The spatial variability of soil physical properties from light farm machinery traffic with minimum tillage and or controlled traffic compared to conventional tillage are unknown. Hence, the objectives of the current study were: (i) to identify changes in soil physical properties as influenced by compaction during controlled traffic minimum tillage by a 2-wheel tractor and (ii) to determine the effect of soil physical properties on chickpea (Cicer arietinum) seedling emergence.

Controlled traffic and minimum tillage are expected over time to alleviate degraded soil structure, particularly in rice –based cropping soils that experience annual soil puddling and intensive tillage. However, minimum tillage over time may weaken the plough pan and in turn alter water balance in the rice-based systems. This implication of a change of water balance may be detrimental for rice but beneficial for following crops and for groundwater recharge. The aim of the current study is to determine how soil structure changes over time under continuous minimum tillage system and how changes in soil structure, particularly in the plough pan, affects water balance in rice-based cropping system. This paper reports the magnitude of water balance components in different tillage practices for the Boro rice period of the crop sequence.

Wide rows essentially ensure some temporal and spatial water availability in water-limiting crop environments, thus minimising the risk of water deficits at critical crop growth stages to ensure profitable yields (Whish et al., 2005). Presence of weeds will have a major impact on water availability to crops irrespective of planting geometries. Decreasing crop plant population and increasing row spacing decreases crop competitive ability against weeds, and generally wider row spacing will reduce crop competition for homogeneously distributed production factors, as postulated mathematically by Fischer and Miles, (1973). Hence good weed management becomes critical to the success of wide row systems, as failure to control water-using weeds defeats the purpose of wide row cropping where water conservation is the focus. With a perceived decline in rainfall in central and eastern wheat belt of Western Australia (WA), wide row cropping practices may prove more productive if weeds can be managed by appropriate herbicides and depriving weeds from applied nitrogen (N). We examined the effect of nitrogen and herbicide on the crop performance and weed control under normal and wide row spacing in a wheat – lupin– canola rotation at Cunderdin and wheat – chickpea rotation at Merredin, WA.

The development of 2-wheel tractors (2WT) with planters attached has given rise to one-pass seeding, and the possibility of minimum tillage and conservation agriculture suitable for smallholder agriculture. The main advantages of minimum tillage techniques include: soil water conservation, targeted placement of seed and fertiliser, lower rates of fertiliser and seed, less labour and fuel required, and less time required to sow a crop (Haque et al. 2010). Germination, emergence and early seedling growth of cool and dry (rabi) season crops (such as chickpea and lentil) grown on residual soil moisture can be limited in the silty clay soils of the High Barind Tract, Bangladesh due to rapid drying and hard-setting of the surface soil. One-pass seeding can minimise the time taken from rice harvest to sowing of the next crop and increases the probability that the surface soil retains sufficient moisture for crop establishment (Kumar et al. 2007). Minimum tillage is also a practice often used to conserve water in the soil profile and it has been reported that in conditions of less tillage there was greater soil water storage in the profile or greater soil water storage at depth in the profile later in the growing season (Barzegar et al. 2003). The objective of this work was to determine the effect of tillage type on: (i) seed-bed conditions and early chickpea establishment; and (ii) available water content and crop water use.

Crop residue retention is one of the core principles of conservation agriculture (CA). However, the level of retention and residue handling characteristics depend on household use of residue, crop type, residue type (loose or anchored), freshness (or weathering status), water content in residue, soil type, soil water content in the field, type of implements used to sow the next crop, disease of previous crops, height of residue, etc. Over the last decade, innovations made to a wide range of 2-wheel tractor (2WT) seeding implements now permit reliable seeding into minimally disturbed soil and moderate levels of crop residue. This provides a window of opportunity to develop CA cropping systems for small holder farmers in Asia and Africa, not only in terms of reduced soil disturbance but also with respect to biomass cover and crop rotation. The Versatile Multi-crop Planter (VMP) was designed as multi-functional and multi-crop 2WT-based planter for smallholders with capability for seed and fertilizer application in variable row spacing (Haque et al., 2011) but its capacity for residue handling using single-pass shallow-tillage (SPST), strip tillage (ST), zero tillage (ZT), bed planting (BP), and conventional tillage (CT) has not been systematically tested.

Proximity factors such as row spacing change the spatial distribution of crop plants and alters the intensity of crop-weed competition (Fischer and Miles 1973). Narrow row spacing is likely to facilitate crop plants with greater competitive ability than weeds, compared to wide row spacing (Hashem et al. 1998). In dry land conservation agriculture (CA), wide rows may ensure some temporal and spatial water availability at critical crop growth stages to ensure profitable yields. However, good weed management becomes critical to the success of wide row systems, as failure to control water-using weeds defeats the purpose of wide row cropping where water conservation is the focus. Management of nitrogen (N) also greatly affects the growth of weeds. While weeds may have easy access to applied N if top-dressed on the soil surface at sowing time, strategic N application technique may maximise the access of crop plants to N compared to weed plants such as annual ryegrass. This study was undertaken to examine the interaction of N rate (and N application technique) and weed control options under normal and wide row spacing in a wheat –lupin–canola rotation in CA.

The ACIAR-funded international collaborative project (2012-2016) on “Overcoming agronomic and mechanisation constraints to development and adoption of conservation agriculture in diversified rice-based cropping in Bangladesh (LWR/2010/080)” between Bangladesh and Australia, undertakes the majority of its research in Bangladesh in collaboration with a range of Bangladeshi institutional collaborators. Improving small scale machineries such as the Versatile Multi-Crop Planter (VMP), and the agronomy and weed management in conservation agriculture in Bangladesh are the major aims of the project.

Sowing of chickpea in the heavy textured soils of the High Barind Tract of Bangladesh with minimum tillage technology aims to increase the timely planting of large areas during a relatively short sowing window before soil water limits germination and emergence. However, the seedbed conditions into which chickpea is sown needs to be better quantified, so that limiting factors which affect germination and emergence can be identified. The soil physical characteristics of importance are soil water, strength and aeration. Growth cabinet studies have identified the fastest germination and emergence of chickpea to be in soils which have gravimetric water contents of 17 to 18 %, at soil water contents above and below this germination and emergence are delayed. Field experiments in Bangladesh have been monitored to determine in-field conditions at sowing. These field and laboratory experiments will be used to quantify the soil physical properties which limit the germination and emergence of chickpea in the HBT of Bangladesh.

Pulse crops in Bangladesh are mainly low-input rainfed crops with broadcast sowing. Since the 1990s, rotary tillage two-wheel tractors (2WT) have largely replaced animal draft for crop establishment. However, rotary tillage causes excessive evaporation from seedbeds in rapidly-drying soils. Therefore 2WT-based minimum tillage (MT) options were explored to optimize seedbed moisture for lentil and chickpea establishment. Two types of 2WT-mounted seeding units were manufactured, a strip tiller retaining rotary blades only in front of the tynes and a tyne seeder in which the rotary tiller shaft is removed. In some soil types, seedling emergence and grain yields of lentil and chickpea with these seeders matched those with broadcasting. In wet soils, the minimal soil disturbance with MT resulted in anaerobic conditions around seedling roots thereby limiting root growth and nodulation. In clay soils with rapid surface drying traction was inadequate for tyne tillage and strip tillage could not adequately penetrate rice paddy hardpans to allow adequate growth of seedling roots. Potential solutions to these limitations are under test so that 2WT-based MT can be adapted for more timely and economic sowing of crops, including pulses, in smallholder plots and to achieve the agronomic benefits of line sowing over broadcast sowing.

Siliceous sedimentary formations underlie much of Cambodia, consequently there is a propensity for sandy surface soils. Only the soils fringing the Tonle Sap lake, those of the alluvial plains along the major rivers (especially the Mekong), and soils developed on basalt deviate from the characteristic of sandy soils. Substantial areas of sandy, high permeability soils are used for lowland rainfed rice production. Due to their inherent high hydraulic conductivities, standing water in rice fields of the deep sandy soils drains rapidly after rainfall predisposing rice crops to drought and high rates of nutrient leaching. However, loss of soil water saturation may limit rice yield by inhibiting nutrient uptake more often than drought, per se. Prospects for growing field crops in sandy lowland soils are contingent on the amounts and reliability of early wet season rainfall or on amounts of stored water after harvesting rice. Apart from drought, waterlogging and inundation are significant water-related hazards that influence the growing of field crops in lowland soils. In addition, soil fertility constraints in the early wet season and dry season will likely differ from those encountered by rice due in part to the different soil water regime they encounter. In particular soil acidity, low nutrient status, hardsetting and shallow rooting depth have been identified as significant constraints for field crops. Vast areas of sandy upland soils occur in Cambodia but are only poorly described. Low soil fertility is likely to limit upland farming systems on the sandy uplands and erosion is a concern for their sustainable use. There is a need to hasten the pace of research and resource assessment of these uplands so that land suitability assessment and sustainable farming systems are available to guide the expansion of agriculture in these areas.