H. B. So

The effect of soil puddling on the soil, physical properties and the growth of rice and post-rice crops

Changes in soil physical properties due to traditional methods of puddling for lowland rice (Oryza sativa L.) production and post-rice legumes was investigated in field experiments conducted on three sites in Indonesia and two in the Philippines over a 3-year period. Puddling treatments used in the field were, in increasing order of puddling intensity, dry cultivation prior to submergence, one and two plowing and harrowing treatments using a draught animal and associated implements, and two cultivations using a mechanical roto tiller. Rice was followed by mungbean (Vigna radiata (L.) Wilzek) on all five sites, and in addition soybean (Glycine max L. Merr.) at Ngale and peanut (Aracis hypogaea L.) at Jambegede were also grown. All puddling treatments were followed by post-rice treatments of surface drainage (with and without surface drains) for the Indonesian sites and sowing technique (zero-till-dibble versus plough-broadcast-harrow) for the Philippine sites. Rice yields were highest under the traditional puddling techniques using draught animal traction. Results suggested that puddling with a roto tiller reduced yield because of insufficient depth of puddling, while dry cultivation may have reduced yield due to increased soil strength of the puddled layer; both are thought to limit root development. Puddling had no significant effect on post-rice mungbean and peanut production. However, results showed that increasing puddling intensity tended to reduce soybean yield. Dry cultivation of lighter textured, well drained soils such as at Manaoag, tended to require more intensive weed control in both rice and dryseason crops compared to higher puddled treatments. Weed infestation was thought to be the largest contributing factor for reduced mungbean yield at Manaoag. Increasing soil puddling intensity at Ngale and Jambegede appeared to reduce root growth. Soil water depletion tended to be smaller in the plough layer that was cultivated under wet conditions compared to pre-rice dry land preparation. Soil water extraction was small and root proliferation was upto 40 cm depth under wet conditions where plant water requirements were met from seasonal rainfall. Root proliferation was deeper and soil water use greater under dry climatological conditions. Small amounts of subsoil water use resulted in substantial yield increases ranging from 3-24 kg mm of soil water used, reinforcing the important role of subsoil water storage and use by the dry season crop in this farming system

Estimation of erosion model erodibility parameters from media properties

The aim of this research was to enable erodibility values for hillslope-scale erosion prediction models to be determined from easily measured media properties. Simulated rainfall and overland flow experiments were carried out on 34 soils and overburdens from 15 Queensland open-cut coal mines at The University of Queensland Erosion Processes Laboratory. Properties of the 34 media determined included aggregate stability, Atterberg limits, bulk density, cation exchange capacity, dispersion ratios, electrical conductivity, exchangeable sodium percentage, organic carbon content, pH, texture, and water content at field capacity and wilting point. Correlation and stepwise multiple regression procedures were used to determine those media properties that could best be used to predict rill and interill erodibility. Correlations between media properties and sediment delivery at each of 5, 10, 15, 20, and 30% slope revealed that different media properties were correlated with erosion rates at different slopes. A media property could show a strong correlation with erodibility at 30% slope, and a low correlation at 5% slope. Splitting the data set into soils only, and overburdens only, showed that properties that were positively correlated with erosion rates for one group could be negatively correlated for the other group. Therefore, in this study, erodibility could not be explicitly linked to one set of media properties for all medium types and erosive conditions. It was concluded that a single regression equation could not be used to predict erodibility under all conditions. Instead, 4 equations were developed to predict rill and interill erodibility, for soils and overburdens separately. The need for separate regression equations was attributed to the presence of different erosive sub-processes for specific combinations of medium type and slope gradient.

Use of laboratory-scale rill and interill erodibility measurements for the prediction of hillslope-scale erosion on rehabilitated coal mine soils and overburdens

Prediction of hillslope-scale soil erosion traditionally involves extensive data collection from field plots under natural rainfall, or from field rainfall simulation programs. Recognising the high costs and inconvenience associated with field-based studies, a method was developed and tested for predicting hillslope-scale soil erosion from laboratory-scale measurements of erodibility. A laboratory tilting flume and rainfall simulator were used to determine rill and interill erodibility coefficients for 32 soils and overburdens from Queensland open-cut coal mines. Predicted sediment delivery rates based on laboratory determinations of erodibility were tested against field measurements of erosion from 12-m-long plots under simulated rainfall at 100 mm/h on slopes ranging from 5% to 30%. Regression analysis demonstrated a strong relationship between predicted and measured sediment delivery rates, giving an r2 value of up to 0.74, depending on the particular modeling approach used. These results demonstrate that soil losses due to the combined processes of rill and interill erosion at the hillslope scale can successfully be predicted from laboratory-scale measurements of erodibility, provided a suitable methodology and modelling approach is adopted. The success of this approach will greatly reduce the cost and effort required for prediction of hillslope scale soil erosion.

Structural degradation of two Vertisols under continuous cultivation

Abstract Changes in soil physico-chemical properties as a result of continuous cereal cropping for up to 64 years of two southern Queensland Vertisols were investigated. The soils were the Waco black earth and the Langlands grey clay. For both soils, cultivation increased bulk densities relative to those of respective virgin soils, but soil density varied little among cultivated sites. The size and strength of dry seedbed aggregates decreased owing to cultivation, but remained suitable for wheat establishement. The stability of wet aggregates decreased with cultivation as indicated by dispersion and slaking measurements. The increased dispersion was associated with decreases in hydraulic conductivity which may limit infiltration and storage of soil water during the summer fallow, thereby reducing crop yields. Organic carbon contents decreased with cultivation while exchangeable sodium percentage (ESP) and pH values increased. Increased dispersibility was correlated with increased sodicity, although ESP values remained below accepted critical values. The relationship was strongest when both dispersibility and exchangeable sodium were expressed on an oven-dry soil basis rather than as the relative parameters, dispersion ratio and ESP. Organic carbon content accounted for less than 40% of the temporal variation in aggregate stability. The changes in physical and chemical properties with cultivation were consistent with exposure of subsurface material following soil erosion at rates typical for the region. We concluded that erosion control would limit further changes in levels of exchangeable sodium and thus soil dispersibility and hydraulic conductivities. The rate of loss of organic carbon would also be reduced and soil physical properties and chemical fertility would be maintained.

The response of sorghum and sunflower to short-term waterlogging

Sunflower and sorghum were waterlogged for nine days at the vegetative, budsvisible/initiation or anthesis stage of development under glasshouse conditions to document the changes which occurred in the soil environment. These changes were also monitored in the absence of plants. At all three stages, there was a rapid reduction in oxygen concentration followed by denitrification. The loss of nitrate was much greater in the presence of sunflower and sorghum. Other components of the redox system, manganese and iron, exhibited a slow increase in concentration as the duration of waterlogging was extended. However, increases were more marked at the later growth stages. Ethylene could be detected at all stages of water-logging although the highest levels were recorded during the first twenty-four hours at the vegetative stage under sunflower and sorghum. Toxins such as nitrite, volatile fatty acids and carbon dioxide appeared unimportant in this experiment. Similarly, observations on a range of cations suggested that nutrient availability was not a factor in causing waterlogging damage. The above changes in the soil environment are discussed in relation to observed effects on plant growth.

The effect of soil strength on the growth of pigeonpea radicles and seedlings

The effect of soil strength on the growth of pigeonpea radicles and seedlings was investigated in cores of three clay soils prepared at different water contents and bulk densities in the laboratory.Radicle elongation directly into soil cores was reduced from 50–70 mm d-1 at strengths less than 0.5 MPa to 0 mm d-1 at 3.5–3.7 MPa. The response to soil strength was affected by the water content of the soil, presumably as a result of reduced oxygen availability in wetter soil. This effect was apparent in soils wet to air-filled porosities less than 0.15 m3 m-3.Radicles were more sensitive to high soil strength (>1.5 MPa) than were seedling roots which encountered the same conditions at 60 mm in the profile. Radicle growth ceased at 3.5 MPa which reduced seedling root growth by only 60%.Despite a 60% reduction in root length in the high strength zone, seedling roots compensated in zones of loose soil above and below the compacted layer, and total root length and shoot growth were unaffected. There was no evidence of a ‘root signal’ response which results in reduced shoot growth in some species in response to high soil strength.The proliferation of roots in surface layers and the delayed penetration of the root system to depth in compacted soil are likely to expose seedlings to a greater risk of water-deficit in the field, particularly under dryland conditions where plants rely on stored subsoil water for growth.

Crop establishment of legumes in rainfed lowland rice-based cropping systems.

Poor crop establishment is one of the major limitations to the production of grain legumes after rice (Oryza sativa L.) in rainfed lowland lice-based cropping systems. The success of germination and emergence of mungbean (Vigna radiata (L.) Wilzek), soybean (Glycine max (L.) Merr) and peanut (Arachis hypogaea L.) planted in zero tilled (ZT), zero tilled combined with mulch application (ZTM) and tilled soils (T) were investigated in a crop establishment trial as a function of sowing delay. Sowing delay was used as a surrogate for soil-water content. This experiment was conducted under a rain-shelter to ensure continuous and progressive drying conditions. A dibbling trial using the same legumes was conducted concurrently and subjected to the: prevailing climatic conditions. Germination and emergence success rate of the traditional dibbling method was compared to dibbling incorporating depth control and seed cover. Both experiments were conducted towards the end of the 1994 rainy season in a Vertisol soil at Ngale and an Andosol soil at Jambegede, in East Java, Indonesia where the season gradually changes from wet to dry season. Mungbean emergence was 93-94% at Ngale and soybean emergence was 83-95% at Jambegede, both in the presence and absence of rain. Peanut emergence was low (50-69%) at both sites. In all three species at both sites, the percentage of seeds that failed to germinate was greater than seeds that failed to emerge, indicating that germination rather than emergence was limiting. Seed rot caused by fungal attack and poor imbibition associated with poor seed-soil contact (observed as intact seeds) were the main constraints for the success of germination of mungbean, soybean and peanut. Thr failure to emerge was mainly caused by seedling rot and the failure of hypocotyl and radicle to penetrate the hard soil, observed as a culling of the hypocotyl, Cultivation at Ngale on a Vertisol resulted in excessively cloddy soil, which in turn resulted in a significant decrease in germination and emergence. The application of straw mulch had little effect on the emergence of legumes on this soil, The use of depth control and application of seed-soil cover did not have a significant effect. Hence the traditional dibbling method where depth of planting ranged from 4 to 7 cm without seed cover was found to be appropriate for planting mungbean and soybean. Germination and emergence of peanut was improved with the application of soil cover and the dibbling stick had a spike added to the tip to assist the root to penetrate the hard compacted soil

Management of clay soils for rainfed lowland rice-based cropping systems: an overview

The problem of concern in this project is that in the dry season following a lowland rice (Oryza sativa L.) crop, yields of post-rice crops are generally low, despite adequate water commonly bring available in the soil profile to grow a potentially high yielding dry season (DS) crop without irrigation. Maize (Zea mays L.) yields are as low as 1 Mg ha(-1) or less, soybean (Glycine max L. Merr.) and cowpea (Vigna unguiculata L.) at 0.3 to 0.8 Mg ha(-1) in Indonesia and mungbean (Vigna radiata (L,) Wilzek) around 0.5 Mg ha(-1) in the Philippines. These are all very much below the yield potential of these soils. For example, mungbean yields of 2.2 Mg ha(-1) have been achieved by IRRI in the Philippines on these soils without irrigation or additional fertilisers. The causes of low yields of DS crops after rice are mainly poor crop establishment and poor root growth duc to soil physical constraints. These result from the breakdown of soil structure during wet cultivation (puddling) for rice. Yields are also limited by biological and chemical constraints. As a result of these low yields, farmers are reluctant to invest in post-rice crops. Therefore, land after lowland rice (at least 51 million ha in Asia according to Huke [Huke, R.E., 1982. Rice Area by Type of Culture: South, Southeast, and East Asia. International Rice Research Institute, Los Banos, Philippines, 32 pp.]) represents an underutilised resource that can be used to meet the food requirement of the ever increasing population of the developing world. To increase the utilisation of these soils, improved management practices are required to enable dry season crops to use the stored water in the soil profile after the rice crop. This paper outlines a project which was established with the general objective of developing soundly based soil management technologies that can overcome soil physical limitations to DS crop production after lowland rice. The specific objectives of the program were 1. to test a range of soil management and agronomic practices that have the potential to overcome adverse soil physical conditions fur DS crops after lice, across a range of soil and climates; 2. to evaluate these practices by 2.1. measuring the changes in soil physical conditions throughout the complete cropping cycle from rice to DS crops; 2.2. determining the performance of the DS crop (establishment and growth) and its ability to extract soil water. 3. to determine the mechanisms involved in dispersion due to puddling and in flocculation and structural development as the soil dries after. draining surface water from rice fields. Relevant outcomes from this project are described in the following papers in this issue

The effect of compaction on the growth of pigeonpea on clay soils. I. Mechanisms of crop response and seasonal effects on a vertisol in a sub-humid environment

Abstract Field experiments were conducted on a vertisol at Dalby, southeast Queensland to investigate the effect of soil compaction on the growth and seed yield of pigeonpea ( Cajanus cajan ). Deep ripping and roller compaction were used to establish three compaction treatments which represented the range of conditions observed in commercial fields. Trials were conducted with and without irrigation over two growing seasons (1984/1985 and 1987/1988). Growth restrictions resulting from compaction were primarily related to reduced water uptake resulting from decreased infiltration and storage of water, and restricted root growth. Seasonal conditions, in particular the distribution of rainfall, exerted a strong influence on plant response. Yield reductions resulting from compaction varied from 100% in a very dry season to 0% in a wetter season. The reduced impact of compaction in the wetter season was associated with reduced levels of soil strength during early root growth and a decreased reliance on stored subsoil water for growth. The effects of seasonal conditions on plant response make it difficult to predict the yield reduction likely to result from compaction and to identify a critical level of compaction when ameliorative measures are required. A modelling approach is required to assist in the prediction of yield reductions resulting from compaction and to identify seasonal conditions under which yield losses are likely to be most severe.

Low input tillage/cropping systems for limited resource areas

Agriculture in limited resource areas is characterized by small farms which an generally too small to adequately support the needs of an average farm family. The farming operation can be described as a low input cropping system with the main energy source being manual labor, draught animals and in some areas hand tractors. These farming systems are the most important contributor to the national economy of many developing countries. The role of tillage is similar in dryland agricultural systems in both the high input (HICS) and low input cropping systems (LICS), however, wet cultivation or puddling is unique to lowland rice-based systems in low input cropping systems. Evidence suggest that tillage may result in marginal increases in crop yield in the short term, however, in the longer term it may be neutral or give rise to yield decreases associated with soil structural degradation. On marginal soils, tillage may be required to prepare suitable seedbeds or to release adequate Nitrogen through mineralization, but in the longer term, however, tillage reduces soil organic matter content, increases soil erodibility and the emission of greenhouse gases. Tillage in low input cropping systems involves a very large proportion of the population and any changes: in current practices such as increased mechanization will have a large social impact such as increased unemployment and increasing feminization of poverty, as mechanization may actually reduce jobs for women. Rapid mechanization is likely to result in failures, but slower change, accompanied by measures to provide alternative rural employment, might be beneficial. Agriculture in limited resource areas must produce the food and fiber needs of their community, and its future depends on the development of sustainable tillage/cropping systems that are suitable for the soil and climatic conditions. These should be based on sound biophysical principles and meet the needs of and he acceptable to the farming communities. Some of the principle requirements for a sustainable system includes the maintenance of soil health, an increase in the rain water use efficiency of the system, increased use of fertilizer and the prevention of erosion. The maintenance of crop residues on the surface is paramount for meeting these requirements, and the competing use of crop residues must be met from other sources. These requirements can be met within a zonal tillage system combined with suitable agroforestry, which will reduce the need for crop residues. It is, however, essential that farmers participate in the development of any new technologies to ensure adoption of the new system