SOIL MANAGEMENT OPTIONS FOR COTTON-BASED FARMING SYSTEMS IN SWELLING AND NON-SWELLING SOILS

Abstract                                                                         Back to Table of contents

The yield of cotton lint in Australia has increased greatly over the last 15 years.  This improvement is due partly to the development of soil management systems that are based on the objective measurement of soil structure in individual fields.  Average yields now exceed those of other major producers elsewhere in the world.  Grey swelling clays (Vertisols) dominate, but hard-setting red duplex soils with non-swelling surfaces (Alfisols) are also important for cotton in some areas.  On these soils mechanical compaction and instability in water are soil structural problems that can cause major yield declines if managed incorrectly.  Most Australian cotton is grown on ridges and is furrow irrigated.

Available methods for overcoming natural and man-induced soil structural problems include shrinkage crack formation (created by drought-stressed rotation crops; particularly useful for Vertisols), biopore formation and organic matter accumulation (due to decomposing roots, and soil fauna such as earthworms and ants; particularly useful for the topsoil of Alfisols), low draft deep tillage, and the use of gypsum and lime.  Extra water and nitrogen fertiliser can be used to obtain high yields on degraded soils, but such an approach tends to be inefficient and may cause off-site pollution.  Where the soil has favourable conditions for cotton root growth and water movement, ‘controlled traffic – reduced tillage’ systems are recommended to minimise costs.

In the future it is necessary to provide soil structure assessment procedures that are more objective and many of the procedures for improving and living with degraded soils need to be refined. Also, better farm machinery should be developed for controlled traffic systems under cotton; vital are engineering and soil mechanics inputs to optimise axle loadings, and tyre and tool dimensions and configurations, on soils with different water contents and pre-stress conditions.

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THE OPTIMISATION OF SOIL STRUCTURE FOR COTTON PRODUCTION

Abstract                                                                         Back to Table of contents

In cropping soils, optimising soil structure means minimising soil structure degradation and emphasising natural processes of structure formation.  Man-made soil structure degradation (compaction and shear stresses) has been shown to reduce green boll numbers in cotton up to 50% and cotton lint by 35%.

The Australian Cotton Industry is now, actively minimising the problem of soil structure degradation and providing the basis for optimising soil structure with the adoption of “retained-bed” systems.  In this form of controlled traffic, tractor and equipment wheels are restricted to specific furrows and the beds are only lightly cultivated.  Beds have been retained for up to seven years, which differs dramatically from practices of the 1960s and 1970s where beds were removed after harvest, the soil cultivated and the beds reformed for the next season.

Heavy, cracking clays (Vertisols) account for 84% of the irrigated cotton area.  The nature of these soils ensures that a retained bed system minimises structure degradation and allows natural processes of structure formation to be optimised.  The high water holding capacity of these soils causes them to remain in a plastic (mouldable) state for long periods of time.  However, the presence of swell-shrink clay minerals ensures cracking on drying, and with repeated wet/dry cycles the maintenance or re-formation of suitable soil structure for cropping.  Non-cracking soils (Alfisols) can also benefit with the retained bed system. Reducing mechanical disturbance increases organic matter (from break crops) and increases biological activity, leading to less surface crusting and an increase in the number of continuous macropores from the surface to depth.

Monitoring physical improvements in soil structure under cotton continues at the field, glasshouse and laboratory levels.  Measures include aeration, shrinkage, strength, water infiltration and image analysis. Studies cover several cotton regions and different bed systems and soils.  In new research the potential risk of structure degradation in cropping soils and the potential of these soils for self repair are being investigated.  These classifications will be based on the soil’s plastic limit, inherent properties that affect workability and repair potential (cations, clay content, etc.) and the dynamic forces of irrigation and weather.

Conclusions

Almost two decades ago soil structure degradation was recognised as a significant potential threat to the productivity of Australian cotton.  The problem has been intensively researched, leading to practical management strategies to not only prevent and control structure degradation but also to optimise the soil physical environment for reduced-cost cotton production.  Retained beds and minimum tillage of dry soil together with rotation crops will ensure optimum soil structure conditions that maximise natural structure formation and maintenance with minimum effort.  Structure degradation can not be eradicated, but current practices ensure its control and prevents it from being a problem.

Future research will continue to emphasise the optimisation of natural structure formation. However, research currently underway in the Department of Primary Industries (Queensland), is aiming to forecast the potential risk of structure degradation in soils and their potential for self repair.  It is important to know if some soils are more prone to degradation than others, so they can be managed with maximum care.  Alternatively, soils with a high self-repair potential can be cropped more frequently as structure regeneration will be achieved through wet/dry cycles especially with rotation crops.  Additionally, determination of the inherent physical/chemical properties that lead to greater strength or resilience may lead to the use of soil ameliorants, akin to fertiliser inputs to optimise chemical response.

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COMPACTION IN COTTON BEDS – MEASUREMENTS, MODELLING AND MANAGEMENT

Abstract                                                                         Back to Table of contents

We used field measurements and computer modelling of soil compaction to investigate management options for trafficking cotton beds.

In the field, we measured the influence of vehicles on vertical stresses in the soil and the consequent changes in soil physical properties. These effects were investigated for several different vehicles and also for different furrow and bed layouts. The impact of vehicles on soil deformation were modelled using computer simulations (finite element models). The models were tested by simulating the known soil behaviour measured in the field. The models furthered our understanding of compaction processes.

The information from the field and the models, run on “what if” scenarios, were then used to investigate compaction management options such as: wider versus narrower tyres in furrows; different furrow shapes; influence of bed width; influence of repeated wheelings; influence of initial soil moisture content.

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FOLIAR APPLICATION FOR YIELD AND QUALITY OF COTTON GROWN ON KAMPANG SAEN SOIL IN THAILAND

Abstract                                                                         Back to Table of contents

A comparative study on conventional fertilizer application and foliar fertilizer application of cotton grown on Kampaeng Saen soils (Udic Haplustalffs) was conducted for five years during 1986-1990. The results revealed that fertilizers applied at the recommended rate (37.5-37.5-37.5 kg/ha of N-P205-K20) in the first and second year could increase cotton growth, yield and quality over the unfertilized control and had residual effects on the third, fourth and fifth year. Cotton growth and yield of combined applications of conventional and foliar application were not different from conventional.

Foliar applications of the four grades of foliar fertilizer 16-48-0 (DAP), 30-20-10, 16-32-6 and 16-5-5 could increase cotton yield and quality over the unfertilized control.  The most economical foliar fertilizer was 16-48-0 (DAP).

Conclusions 

  1. Foliar fertilizer application integrated with soil fertilizer application was not necessary because the growth and the quality of cotton was not significantly different to soil application alone.
  2. It was possible to use foliar fertilizer application with cotton. Foliar fertilizer application increased plant growth and cotton quality. In term of economics, using foliar fertilizer application would take less risk than the other methods.
  3. Soil fertilizer application or conventional fertilization was the suitable method and it was cheap for the farmers in the long term. The study indicated that soil fertilizer application for two in five years is not adequate for nutriont replenishment but it returned a good income and also had residual affects for subsequent crops compared with other treatments.
  4. Soil properties: pH, organic matter, available P and exchangeable K were variable, but all showed a trend to be reduced after five years of cotton cropping.

 

Future Considerations

The study indicated that foliar fertilizer application could be used with cotton and recommended to farmers.

Future research should concentrate on the fertilizers that are not expensive and are found easily in the market, such as urea and DAP. The rate of fertilizer, time of application and the number of times of application should be studied on fertile and infertile soils.

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IMPROVEMENTS IN WATER USE EFFICIENCY IN IRRIGATED COTTON: CHOICES IN SYSTEMS AND MANAGEMENT

Abstract                                                                         Back to Table of contents

Major factors (crop, soil, topography, labor and management availability and skill, environmental concerns, regulatory controls, economic) influencing irrigation efficiency, water use efficiency and the choice of appropriate irrigation systems and management for cotton are reviewed and discussed.  One field experiment in the San Joaquin Valley of California which identifies the high yield potential, relatively low water use, and high water use efficiency possible under subsurface drip irrigation is described in detail.  Three different field experiments and grower experiences in evaluating different irrigation systems (furrow versus subsurface drip in all three, center pivots included in one grower evaluation)in terms of water requirements, water use efficiency and potential for minimizing deep percolation are reviewed in the context of options for improving water use efficiency in fully-irrigated cotton under conditions in the western United States.  Drip irrigation is discussed in detail but remains only one of the choices for changes in irrigation systems and management that are available to improve irrigation efficiency and water use efficiency while maintaining a favorable net economic return.

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MANAGEMENT OF LABLAB PURPUREUS L. RESIDUES IN COTTON-BASED FARMING SYSTEMS AND CONSEQUENT EFFECTS ON PROPERTIES OF A TYPIC PELLUSTERT

Abstract                                                                         Back to Table of contents

The effects of mulching or incorporating residues of dolichos (Lablab purpureus L.), sown in rotation with cotton (Gossypium hirsutum L.), in broad (1.5 m wide) beds on soil properties of a Vertisol was studied in Northern New South Wales, Australia. Soil was sampled from the 0-0.10 m (bed surface) and 0.20-0.30 m (below bed) depths of edges and centres of broad beds during January 1993. Soil properties monitored were particulate, mineralized and total organic matter, dispersion index, plastic limit, geometric mean diameter (GMD) of soil aggregates formed after puddling and drying at 40˚C (soil reactivity), soil aggregate density, exchangeable cations, nitrate-N and electrical conductivity of 1:5 soil:water suspension. Residue management had no significant effect on soil organic matter fractions, although coarse (2 mm – 212 µm), fine (212-53 µm) and total soil organic matter contents on bed surfaces were greater than that below beds, and coarse particulate organic matter at the edges of beds was greater than that at the centres. Compared with mulching, incorporating dolichos residues resulted in a significantly lower dispersion index. Mulching also resulted in higher values of dispersion index below beds when compared with bed surfaces. Plastic limit at the centres of beds, was significantly lower than that in the edges. Smallest GMD of soil aggregates occurred in the centre of mulched beds. Greatest values of soil aggregate density occurred at soil water contents ≤ 0.10 kg kg-1 below beds when dolichos residues were mulched. Where dolichos residues were incorporated, at soil water contents ≤ 0.10 kg kg-1 aggregate densities in the soil surface were lower in bed centres when compared with those at the edges of beds. Greatest exchangeable K, and lowest exchangeable Na and exchangeable sodium percentage (ESP) occurred where dolichos residues were incorporated. In comparison with mulching, exchangeable Mg was higher and exchangeable Ca lower below beds with residue incorporation. Nitrate-N on bed surfaces was higher than that below beds with mulching. Mulching improved only friability of surface soil in bed centres, whereas surface and sub-surface indices of soil physical and chemical fertility were improved by incorporating dolichos residues.

Conclusions

Soil reactivity in the of centre bed surfaces was the only soil property to be improved by mulching of dolichos residues whereas incorporating dolichos residues improved indices of soil quality such as aggregate stability, exchangeable cations and ESP (Doran et al., 1994) in the surface and at 0.2-0.3 m. Good soil quality can, therefore, be maintained at this site by incorporating residues of dolichos sown in rotation with cotton.

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THE PRINCIPLES OF COTTON WATER RELATIONS AND THEIR APPLICATION IN MANAGEMENT

Abstract                                                                         Back to Table of contents

The keys to understanding the principles of water relations that are specific to cotton are found in: (i) the ecology of the wild ancestors of cotton  (xerophytic shrubs), (ii) the basic pattern of development (the orderly and regular production of mainstem nodes, lateral fruiting branches and fruiting sites, and the progression at each fruiting site from floral bud through to open boll or shed fruiting form), (iii) relative sensitivity of these developmental processes, and the growth physiological processes, to water stress. The biological and agronomic responses to variation in water supply are reviewed and interpreted in light of this understanding.  Cotton is well adapted physiologically for both rain grown and irrigated production, and economically for both production on plantations and small holdings.  The relative importance of rain grown and irrigated cotton on a global scale are considered.  The management requirements of each in respect to optimising use of water discussed.  Effects of excess water (water logging) are as important as water deficits.

Technological developments relevant to water relations can be broadly classified as software (rules of thumb, indices, plant mapping, osmotic adaptation, computer models and decision support systems) and hardware (neutron probes, pressure chambers, infra-red thermometry, drip irrigation, lateral shift and centre pivot irrigation). Their use in management and research applications is discussed.  Management should aim to optimise the use of limited water resources, be it rainfall or irrigation supply, by maximising returns per unit input and minimising environmental impact.  Management decisions have to be made at policy, strategic and tactical levels and appropriate software and hardware selected. There are specific important challenges and opportunities: management of limited irrigation water supplies; environmental impact of irrigation on salinity, and pesticide and nutrient pollution; the use of urban domestic wastes and saline drainage water; interaction of water with other factors; and risk analysis.

Conclusions

Modern cultivated cotton species have inherited from their wild relatives attributes that enable them to survive long periods of drought and develop rapidly when water is available, enabling the crop to make full use of variable rainfall or respond well to irrigation.  These attributes are the indeterminate habit and the relative sensitivity of physiological processes to water deficits.  The former confers a flexible morphological and reproductive development and the latter determines priorities for assimilates.  Ancestral sensitivity to the putative wet and dry “signals” from the environment imposes special constraints on management of the cotton crop in relation to water.  Research is needed to see if signals from roots in drying soils found in other crops occur in cotton, and to determine their role in the response of the crop to water deficits, particularly boll shedding, priorities for growth, and the balance of vegetative and reproductive growth.

In order to maximise returns from limited rainfall and irrigation water supplies, research and management should concentrate on improving WUE in its various aspects.  Opportunities exist to improve WUE with:

  • new irrigation technology, or better use of existing technology, in order to reduce application, conveyancing and drainage losses and reduce the E component of ET;
  • use of hardware and software to monitor crop progress for tactical optimisation of irrigation scheduling;
  • identify by using simulation software, and then adopt, robust management strategies for irrigated and rainfed crops that will minimise risk and use maximise return from limited irrigation supplies and rainfall;
  • soil surface management technology to retain rainfall and reduce runoff and soil evaporation;
  • pursuit of genetic improvement of agronomic WUE by improved gas exchange and/or partition of assimilates.

If we are successful in raising WUE we will reap the benefits of higher returns from a limiting resource, with the added potential to reduce contamination of rivers and groundwater and reduce the risk of salinisation.

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PROBLEMS ASSOCIATED WITH SOIL STRUCTURAL ASSESSMENT ON VERTISOLS USED FOR IRRIGATED COTTON PRODUCTION

Abstract                                                                         Back to Table of contents

Techniques for assessing the severity of soil compaction were evaluated, mostly under commercial conditions, at twelve sites with contrasting degrees of damage.  The soils at each site are Vertisols used to produce irrigated cotton.  The reference technique for soil structural assessment was clod shrinkage analysis.  This procedure is prone to sampling bias, but until recently it was widely regarded to be the best available method.  We combined a number of the shrinkage parameters to provide a soil structural index (SSI).  A broad range of mostly cheaper soil structural and plant measurements were regressed against the SSI.  There was no single technique that accounted for more than 49% of the variation in the SSI.  Groups of alternative structural form measurements accounted for substantially more of the variation, but their routine use by cotton managers was considered to be impractical.  There was a lack of correlation between cotton lint yield and SSI when all the data were considered together.  Sites with poor soil structure frequently had high yielding crops, due to high nitrogen application rates and frequent irrigations, which appear largely to have compensated for the adverse effects of soil compaction on crop growth and yield.  However, such an approach to farming is inefficient, and may lead to off-site pollution, so the search for adequate procedures to measure the degree of compaction must continue.  Associated research carried out since our study was undertaken has demonstrated the potential of image analysis procedures, and of an improved version of the SOILpak scoring system.

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THE PHYSIOLOGY OF COTTON WATER USE EFFICIENCY

Abstract                                                                         Back to Table of contents

Availability of water causes major variation in cotton yield. Water use efficiency confers meanings of water conservation (i.e., savings of water and/or costs of water application) and transpiration efficiency (i.e., increasing productivity per unit of water transpired).  Because of the commonality in the pathways shared between transpiration and CO2 assimilation, there is a strong link between crop growth and transpiration.  This paper briefly reviews the circumstances leading to water use efficiency of cotton through water conservation, but fully explores our knowledge and water use as it relates to the transpiration efficiency and productivity of the cotton plant.  Emphasis is placed on our understanding of carbon isotope discrimination as it relates to transpiration efficiency and productivity.

Conclusion

Relatively little progress has been made in increasing productivity of cotton or other major crops per unit of water or solar radiation, even though dryland and irrigated yields have increased.  These yield increases have arisen mainly from changes in carbohydrate partitioning favoring fruit production (Gifford et al., 1984), although recent work suggest that genetic advances in yield of Pima cotton varieties (G. barbadense L.) resulted, in part, from selection of plants with higher stomatal conductance and photosynthesis (Cornish et al., 1991).  Nevertheless, selection for photosynthesis and stomatal conductance, per se,  has not been used in improving yield of cotton and other field crops.  Measurements of photosynthesis and stomatal conductance with conventional gas exchange techniques are too variable, measuring plant performance over a brief period time. Integrated over the season small changes in leaf gas exchange can result in large differences in total carbon uptake or water use.  Errors associated with direct gas exchange measurements may be too large to detect small gains in gas exchange efficiency.  In contrast, ∆ appears to be more effective than conventional gas exchange measurements in detecting genotypic differences in transpiration efficiency and productivity for several important crops (Hall et al., 1992).

The crucial role of water in production of cotton will not change.  Industrial, municipal, environmental, and recreational demands for water will intensify. Cotton farmers must continually examine and adopt sound water conservation practices. At the same time scientists must continue to improve our understanding of  crop water use and productivity.  We believe carbon isotope discrimination provides us with a new tool to improve the transpiration efficiency and productivity of field crops. Whether carbon isotope discrimination can be use to improve water use efficiency of cotton remains to be answered.

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EFFECTS OF SOAKING ON THE GERMINATION CHARACTERISTICS AND MINERAL LEAKAGE OF COTTON (GOSSYPIUM HIRSUTUM L.) SEED

Abstract                                                                         Back to Table of contents

Cotton seed (Gossypium hirsutum  L.) was tested to identify germination, seedling characteristics and growth as well as mineral leakage caused by soaking the seeds for different periods. Four cotton cultivars (BL. 644, Ç. 1518, DP. 299 and Sayar 314) were used with five different soaking periods (0, 4, 8, 16 and 24 hours).  Germination and seedling characteristics were tested in a growth cabinet at 25 ˚C.  The highest germination percentages were observed in all cotton cultivars with four and eight hours soaking, while the greatest abnormal seedlings were noted with 24 hours soaking.  Coleoptile and mesocotyl elongation and length were decreased with 24 hour treatments.  Vigour indices were decreased also with 24 hour soaking in all cultivars.  The leakage of K, P, Mn, Ca, Cu, Fe, and Zn mineral ions was increased significantly with 24 hour treatments.  The leakage of K+ and Ca++ ions was significantly correlated with the seed germination.  Zn++ was leaked less than other ions but the leakage of Zn++ was stable during other soaking periods.  Variation in seed mineral leakage was observed among the four cotton cultivars.

Conclusions

 These results indicate that soaking treatments of 4 to 6h in distilled water was helpful for better germination of cotton seeds and seedling establishment. Increasing soaking periods reduced germination. Soaked cotton seeds had leakages of K+ and Ca2+ cations, as well as Mn2+, Fe2+ and Cu2+. Similar conclusions were reported by Woodstock and Grabe (1967), Anderson et al. (1964), Cantrell, et al. (1972) and Woodstock et al. (1985).

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