For optimum production of crops sufficient amount of good quality water is required but, there is a severe shortage of water in Pakistan. So for sustainable production of crops scientists are trying to explore new techniques to combat this situation. Furrow-bed method of irrigation saves considerable quantity of water and permits more efficient use as compared to other surface irrigation systems. Application of irrigation water in furrows gave higher leaf area index (LAI), net assimilation rate (NAR), crop growth rate (CGR), and grain yield of maize than alternate or paired skip furrow irrigation. Irrigation by flooding water over the entire field results in leaching down the nitrates from the root zone causing loss of fertilizer. Over irrigation often leads to greater leaching loss of fertilizer and thereby reduces the final plant height, dry matter accumulation and grain yield of maize. Under the growing water scarce situation and decreasing crop productivities, there is a need to develop and evaluate improved planting methods with higher water use efficiencies and provide more water for crop production. Some early work in Pakistan on non-permanent beds and furrow irrigation produced yield increases of 20 % for wheat, and 48 % for cotton.
Pakistan is an agricultural country with the world’s largest contiguous irrigation system, the Indus basin irrigation system (IBIS). In IBIS, field crops are irrigated using the basin irrigation method. Application losses in fields are around 25-40% under flood and basin irrigation. Low application efficiencies reported in IBIS result from over irrigation, improper irrigation methods and timings, non-scientific irrigation scheduling and non leveled fields.
Per capita water availability in Pakistan has been decreasing at an alarming rate due to increase in population that puts Pakistan in the category of ‘high stress’ countries in terms of limited water resources. In 1951, per capita availability was 5300 cubic meters, which has now decreased to 1090 cubic meter just touching water scarcity level of 1000 cubic meter. Due to growing population pressures and extended periods of drought, it has been estimated that an additional 48 billion m3 water would be required to meet the growing demands of agriculture and the country’s economy by the year 2011 (Pakistan Economic Survey, 2009). Now a days, water shortage shifts attention from the traditional concept of crop yield-production per unit of land-to the productivity of water-production per unit of water. Whether this parameter is best increased through responsive, sophisticated irrigation scheduling or through predetermined schedules, providing limited water, has been a contentious issue for some years.
Mulching is one of the techniques to improve soil quality by increasing soil organic carbon. It decreases the evaporation rate, leaving greater moisture and there is less variation in soil temperature for a longer period of time. Appropriate soil moisture and temperature are important for metabolic activity of the soil microbes that recycle and release nutrients that are essential for growth. Besides moderating soil moisture and temperature, mulch residue affects the dynamics of soil organic matter (SOM).
Sustainable increases in agricultural productivity are necessary to secure food availability and livelihoods in the developing world over the coming decades. Such increases must come largely through better use of the water and land by adopting new techniques.
Friday, July 23, 2010
Co-innoculation of microbial ACC-deaminase on the growth of chickpea.
Chickpea (Cicer arietinum) is one of the most important dry land field crops. It is not only important in human diet, but also plays a vital role in improving the soil fertility by fixing atmospheric nitrogen into available form with the help of rhizobium species present in the nodules of its roots. However, under agro-ecological conditions of Pakistan, the nodulation of chickpea is poor, which is the major cause of its low yield. The N2-fixing bacteria of the genus rhizobium that form nodules on the roots of leguminous plants, such as chickpea, lentils etc. are called rhizobia. Mesorhizobium ciceri are well documented to be responsible for nodulation in chickpe.
It has been studied that soil-borne microbes interact with plant roots and soil constituents at the root–soil interface. The great array of root–microbe interactions results in the development of a dynamic environment known as the rhizosphere where microbial communities also interact. The differing physical, chemical, and biological properties of the root-associated soil, compared with those of the root-free bulk soil, are responsible for changes in microbial diversity and for increased numbers and activity of micro-organisms in the rhizosphere micro-environment. Microbial activity in the rhizosphere affects rooting patterns and the supply of available nutrients to plants, thereby modifying the quality and quantity of root exudates.
Microbes which interact with roots include both harmful and beneficial bacteria. Beneficial bacteria are generally referred to as plant growth-promoting rhizobacteria or PGPR, and are capable of promoting plant growth by associating with the plant roots. Plant Growth Promoting Rhizobacteria can be divided into two groups according to their relationship with the plants, symbiotic bacteria and free-living rhizobacteria. Generally, PGPR function in different ways, including, synthesizing particular compounds for the plants, facilitating the uptake of certain nutrients from the environment, and lessening or preventing the plants from diseases. Many plant-associated bacteria promote plant growth by synthesizing low molecular weight compounds or enzymes that can modulate plant growth and development. Microbial ACC-deaminase is the enzyme that is present in some of the PGPR along with some other enzymes and it facilitates plant growth and development by decreasing plant ethylene levels, especially following a variety of environmental stresses. When plants are exposed to stressful conditions, they often respond by producing high concentrations of ethylene which are, in general, inhibitory to root growth. Some of the ACC is exuded from seeds, roots or leaves along with other small molecules normally present in these exudates and may be taken up by the bacteria and subsequently cleaved by the enzyme, ACC-deaminase, to ammonia and α-ketobutyrate. The bacterium acts as a sink for plant ACC and as a result of lowering ACC in plant the amount of ethylene is also reduced. As a direct consequence of lowering plant ethylene levels, PGPR can reduce the extent of ethylene inhibition of plant growth following a wide range of stresses. Thus, plants grown in association with these bacteria should have better roots and shoots and be more resistant to growth inhibition by a variety of ethylene-inducing stresses. Ethylene in higher concentration has also been known as an inhibitor of nodulation in various legumes, including those which produce indeterminate nodules and those that produce determinate nodules. The PGPR are also known to participate in many important ecosystem processes, such as the biological control of plant pathogens, nutrient cycling, and/or seedling growth. Selected strains of PGPR are being used as seed inoculants. Many plant-associated bacteria promote plant growth by synthesizing low molecular weight compounds or enzymes that can modulate plant growth and development.
Co-inoculation improves plant growth by direct stimulation of rhizobial growth/survival in the soil, enlargement of the root system by hormone production for enhanced nutrient uptake and increase in the number of potential colonization sites by rhizobium, phosphate solubilization and pathogen suppression due to production of antibiotics. It has also been reported to increase the number of nodules, shoot dry weight and root dry weight in chickpea, soybean and pigeon pea.
The potential of microbial ACC-deaminase to enhance the Mesorhizobium ciceri efficiency in chickpea in a pot trial, thereby exploring the potential of Mesorhizobium-PGPR co-inoculation to enhance nodulation, growth and yield of chickpea.
It has been studied that soil-borne microbes interact with plant roots and soil constituents at the root–soil interface. The great array of root–microbe interactions results in the development of a dynamic environment known as the rhizosphere where microbial communities also interact. The differing physical, chemical, and biological properties of the root-associated soil, compared with those of the root-free bulk soil, are responsible for changes in microbial diversity and for increased numbers and activity of micro-organisms in the rhizosphere micro-environment. Microbial activity in the rhizosphere affects rooting patterns and the supply of available nutrients to plants, thereby modifying the quality and quantity of root exudates.
Microbes which interact with roots include both harmful and beneficial bacteria. Beneficial bacteria are generally referred to as plant growth-promoting rhizobacteria or PGPR, and are capable of promoting plant growth by associating with the plant roots. Plant Growth Promoting Rhizobacteria can be divided into two groups according to their relationship with the plants, symbiotic bacteria and free-living rhizobacteria. Generally, PGPR function in different ways, including, synthesizing particular compounds for the plants, facilitating the uptake of certain nutrients from the environment, and lessening or preventing the plants from diseases. Many plant-associated bacteria promote plant growth by synthesizing low molecular weight compounds or enzymes that can modulate plant growth and development. Microbial ACC-deaminase is the enzyme that is present in some of the PGPR along with some other enzymes and it facilitates plant growth and development by decreasing plant ethylene levels, especially following a variety of environmental stresses. When plants are exposed to stressful conditions, they often respond by producing high concentrations of ethylene which are, in general, inhibitory to root growth. Some of the ACC is exuded from seeds, roots or leaves along with other small molecules normally present in these exudates and may be taken up by the bacteria and subsequently cleaved by the enzyme, ACC-deaminase, to ammonia and α-ketobutyrate. The bacterium acts as a sink for plant ACC and as a result of lowering ACC in plant the amount of ethylene is also reduced. As a direct consequence of lowering plant ethylene levels, PGPR can reduce the extent of ethylene inhibition of plant growth following a wide range of stresses. Thus, plants grown in association with these bacteria should have better roots and shoots and be more resistant to growth inhibition by a variety of ethylene-inducing stresses. Ethylene in higher concentration has also been known as an inhibitor of nodulation in various legumes, including those which produce indeterminate nodules and those that produce determinate nodules. The PGPR are also known to participate in many important ecosystem processes, such as the biological control of plant pathogens, nutrient cycling, and/or seedling growth. Selected strains of PGPR are being used as seed inoculants. Many plant-associated bacteria promote plant growth by synthesizing low molecular weight compounds or enzymes that can modulate plant growth and development.
Co-inoculation improves plant growth by direct stimulation of rhizobial growth/survival in the soil, enlargement of the root system by hormone production for enhanced nutrient uptake and increase in the number of potential colonization sites by rhizobium, phosphate solubilization and pathogen suppression due to production of antibiotics. It has also been reported to increase the number of nodules, shoot dry weight and root dry weight in chickpea, soybean and pigeon pea.
The potential of microbial ACC-deaminase to enhance the Mesorhizobium ciceri efficiency in chickpea in a pot trial, thereby exploring the potential of Mesorhizobium-PGPR co-inoculation to enhance nodulation, growth and yield of chickpea.
A sustainable use of brackish water for cropping
Scarcity of sufficient amount of canal water for irrigation compelled the farmers to irrigate their crops with tube well water. The quality of ground water is deteriorating day by day due to rapid industrialization and urbanization. According to estimation about 70-75% of ground water that is being pumped out in Pakistan is brackish in nature. The continuous use of this water for irrigation leads to develop soil salinity which severely affects the physiological processes of plants. These adverse effects of salinity may be attributed to non-availability of water, disturbance in nutrient uptake causing deficiency and ion-toxicity to plants. Salinity and sodicity stresses are ever-present threats to crop yields, especially where tube well irrigation is an essential aid to agriculture.
It has been noticed that when the plant is under salinity stress then its ethylene (a growth hormone) production is increased. No doubt it is required for the optimal production of plant but up to certain limit. After that it has inhibitory effect on the plant growth and development. Ethylene is produced in plants from 1-aminocyclo propane-1-carboxylate(ACC), the immediate precursor of ethylene.
As plant has not any mechanism to stop this excessive ethylene production during salt stress and ultimately yield is reduced. But nature has gifted us certain soil microbes that have an enzyme ACC-deaminase which utilize the ACC (an immediate precursor of ethylene) as an energy source and cleavage it to NH3 and α-ketoglutaric acid. Treating of such microbes with crops jut prior to planting significantly reduced the salt stress in plants.
In an experiment on maize crop irrigated with brackish water [EC, 5dSm-1; SAR, 10 (mmol L-1)1/2] we have seen that plants treated with microbes having ACC-deaminase activity, increased the crop yield up to 30 % over untreated plant. Thus this is one of the promising techniques to use brackish water for sustainable crop production in agriculture.
It has been noticed that when the plant is under salinity stress then its ethylene (a growth hormone) production is increased. No doubt it is required for the optimal production of plant but up to certain limit. After that it has inhibitory effect on the plant growth and development. Ethylene is produced in plants from 1-aminocyclo propane-1-carboxylate(ACC), the immediate precursor of ethylene.
As plant has not any mechanism to stop this excessive ethylene production during salt stress and ultimately yield is reduced. But nature has gifted us certain soil microbes that have an enzyme ACC-deaminase which utilize the ACC (an immediate precursor of ethylene) as an energy source and cleavage it to NH3 and α-ketoglutaric acid. Treating of such microbes with crops jut prior to planting significantly reduced the salt stress in plants.
In an experiment on maize crop irrigated with brackish water [EC, 5dSm-1; SAR, 10 (mmol L-1)1/2] we have seen that plants treated with microbes having ACC-deaminase activity, increased the crop yield up to 30 % over untreated plant. Thus this is one of the promising techniques to use brackish water for sustainable crop production in agriculture.
MULCHING; A TECHNIQUE TO CONSERVE SOIL MOISTURE
Pakistan falls in the arid to semi-arid climatic region of the world. Potential evapo-transpiration is considerably higher as compared to rainfall received. High temperature promotes capillary movement of salts upwards causing deposition of salts on the soil surface. The country has one of the largest contiguous irrigation systems in the world, irrigating over about 17 million hectares (Mha), and accounting for 90 percent of the agricultural production in the country. Even then, the existing canal supplies are insufficient to meet the crop water requirements. Increased pressure of population has catalysed the need to bring more area under cultivation to fulfill the food and fiber demands. To bring more area under cultivation or increase in cropping intensity, some additional water is required, but under the existing situation one of the alternative is the exploitation of the groundwater reserves, the whole quantum of which cannot be used as such because of poor water quality characteristics. The poor quality water can be used for irrigation of salt tolerant crops/tree species by adopting appropriate techniques. Thus to tackle this problem in the present scenario a sustainable solution is required by adopting moisture conservation techniques.
For arable soils, the most effective conservation practices for reducing surface evaporation are those that provide some degree of surface cover for the soil. A cover can be best provided by mulches or by tillage practices that leave plant residues on the soil surface. Mulch is any material placed on a soil surface for the purpose of moisture conservation or controlling weeds. It act as barriers to movement of moisture out of the soil. They can be either natural (eg. straw, wood chips, peat) or man-made (eg. transparent or opaque plastic sheeting). Mulches can also enhance soil temperature, depending on the type of mulch being used. In addition to reducing evaporation, vegetative mulches can reduce the spread of soil borne diseases, prevent weed growth, reduce soil erosion, provide nutrients, and enhance organic matter status of soil and aid in infiltration. Mulches improve infiltration by protecting the soil surface from the impact of raindrops and eliminating soil crusting. Mulches can however, be expensive and labour intensive to obtain, transport and apply to the soil. Mulching is usually more practical for high value crops such as vegetables and berries. Specially prepared plastics can also control evaporative loss. These types of mulches are often applied by machinery and there are holes or slits present for plants to grow through. These mulches are commonly used for vegetable and small fruit crops. Thus mulching not only improve the soil physic-chemical properties of soil but also improve water use efficiency of crops
For arable soils, the most effective conservation practices for reducing surface evaporation are those that provide some degree of surface cover for the soil. A cover can be best provided by mulches or by tillage practices that leave plant residues on the soil surface. Mulch is any material placed on a soil surface for the purpose of moisture conservation or controlling weeds. It act as barriers to movement of moisture out of the soil. They can be either natural (eg. straw, wood chips, peat) or man-made (eg. transparent or opaque plastic sheeting). Mulches can also enhance soil temperature, depending on the type of mulch being used. In addition to reducing evaporation, vegetative mulches can reduce the spread of soil borne diseases, prevent weed growth, reduce soil erosion, provide nutrients, and enhance organic matter status of soil and aid in infiltration. Mulches improve infiltration by protecting the soil surface from the impact of raindrops and eliminating soil crusting. Mulches can however, be expensive and labour intensive to obtain, transport and apply to the soil. Mulching is usually more practical for high value crops such as vegetables and berries. Specially prepared plastics can also control evaporative loss. These types of mulches are often applied by machinery and there are holes or slits present for plants to grow through. These mulches are commonly used for vegetable and small fruit crops. Thus mulching not only improve the soil physic-chemical properties of soil but also improve water use efficiency of crops
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