INTEGRATED PLANT NUTRIENT MANAGEMENT SYSTEM (IPNMS)
Integrated plant nutrient management system (IPNMS) pertains to the combined use of organic and inorganic fertilizers in proper proportion accompanied by sound cultural management practices in crop production. Such cultural practices include the use of appropriate varieties, good water management, pest control (including weeds) and crop rotation (Rice Production Manual, 1991). According to Singh (1994), the basic concept of IPNMS is to limit the unfavorable exploitation of soil fertility and plant nutrients.
The maintenance and improvement of soil fertility and plant nutrition at an optimum level to sustain the desired crop productivity through optimization of the benefits from all possible sources of plant nutrients in an integrated manner is the main concern of IPNMS. The combination of organic and inorganic fertilizer seem to be more practical than the use of organic fertilizer alone. The importance of IPNMS is recognized mainly because of the growing consumption of inorganic fertilizers and the unavailability of nutrients at low cost. Another reason is that, many researches revealed that neither inorganic fertilizers nor organic sources alone can achieve a sustainable productivity of soils as well as crops under highly intensive cropping systems (Singh, et. al., 1994).
There are many factors that should be considered in the adoption of IPNMS and should include the farmer’s socio-economic and cultural conditions. There are varying approaches in the utilization of organic materials in different localities. In Central Luzon, one common practice of the farmer is the dumping and burning of rice hull in the field prior to planting. This burned rice hull is the farmer’s way of controlling pest especially weeds and diseases (Aganon, et. al, 1999).
IPNMS also considers the water resource in the area. In upland farming where water is usually limiting, the application of organic matter is encouraged to increase the soil water holding capacity and provide more available water to the plants.
In the mid-1960s, when projections of global starvation were common, no one questioned the role of mineral fertilizer in increasing food production, particularly in the food-deficit countries. On the contrary, fertilizer use was an integral part of the “Green Revolution” technological package of improved varieties of rice and wheat, irrigation, and fertilizer that helped many densely populated countries to achieve food self-sufficiency in the short span of 20 to 25 years.
In the early 1990s, however, fertilizer became the target of criticism, mainly because of heavy use in the developed countries, where it was suspected of having an adverse impact on the environment through nitrate leaching, eutrophication, greenhouse gas emissions and heavy metal uptakes by plants. Consequently, fertilizer use per se was mistakenly identified as harmful to the environment. But, if for any reason fertilizer use were discontinued today, world food output would drop by an estimated 40 per cent with all its disastrous consequences. While fertilizer misuse can contribute to environmental contamination, it is often an indispensable source of the nutrients required for plant growth and food production.
Unless all the soil nutrients removed with the harvested crops are replaced in proper amounts from both organic and inorganic sources, crop production cannot be sustained: soil fertility will decline. If in the past, the emphasis was on increased use of fertilizer; the current approach should focus on educating farmers to optimize use of organic, inorganic, and biological fertilizer in an integrated way. Plant nutrition in future will require the judicious and integrated management of all sources of nutrients for sustainable agriculture.
Need for change
To promote this integrated approach in a more systematic and scientific manner, FAO pioneered the development of new technologies such as Integrated Pest Management (IPM) and IPNS. The basic concept underlying IPNS is the maintenance and possible increase of soil fertility for sustaining increased crop productivity through the optimization of all possible sources, organic and inorganic, of plant nutrients required for crop growth and quality in an integrated manner appropriate to each cropping system and farming situation within the given ecological, social and economic boundaries.
Integrated nutrient management differs from conventional nutrient management in that it more explicitly considers nutrients from different sources, notably organic materials, nutrients carried over from previous cropping seasons, the dynamics and transformation of nutrients in soil, interaction between nutrients, and the availability of nutrients in space (the rooting zone) and time (the growing season), in relation to the nutrient demand by the crop. In addition, it integrates the objectives of production with ecology and environment, that is, optimum crop nutrition, optimum functioning of the biosphere (soil health), and minimum nutrient losses or other adverse effects on the environment.
Integrated Nutrient Management (INM) has to be considered an integral part of any sustainable agricultural system. Attempts made in several countries of South and South-East Asia to complement the use of mineral with organic sources of plant nutrients have generated useful, though limited, information on the complementary and synergistic effects of these materials on the yield of crops. Because organic sources of nitrogen are also improving soil structure and soil bioactivity which are not directly improved by mineral sources of N, the productivity of the crop for each kg of N may be better with organic sources of N than with only mineral sources of N. If the objective of IPNS is the balanced and effective use of various sources of plant nutrients than the strategy should be the mobilization of all available, accessible and affordable plant nutrient sources in order to optimize the environmentally benign productivity of the whole cropping system and to increase the monetary return to the farmer.
Thus, there is need for more information on (i) integrated nutrient recommendations for cropping systems as a whole taking into account the complementary and the synergistic effects of combined use of both mineral and organic/ biological sources for sustained crop production, (ii) recommendations for different agro-ecological situations taking into account available organic/ biological resources, (iii) and finally, transfer of this technology for the benefit of small farmers through the national agricultural extension services.
Components and technology of IPNS
Soils supply all the 16 essential plant nutrients. Nutrients are mostly found in organic and/or fixed mineral form. Plants can meet much of their nutritional requirement from this source, if managed properly, mainly through mineralization of soil organic matter. But due to continuous and intensive cultivation, the nutrient supplying capacity of soils has decreased considerably.
Therefore, under any intensive agriculture system, special emphasis should be given to raising Soil Organic Matter (SOM) to maintain soil nutrient and to reduce soil degradation. To enhance soil nutrient supply it is necessary to adopt appropriate soil management practices, such as improvement of soil physical conditions and addition of appropriate quantities of nutrients including micronutrients through mineral fertilizer, organic and biological sources.
Various types and grades of fertilizer are available throughout Asia supplying major nutrients such as N, P and K. The fertilizer use levels differ widely between various countries and nutrient use is mostly imbalanced, favouring lopsided use of nitrogen. Balanced fertilization is known to improve fertilizer use efficiency (FUE) and at the same time profitability for the farmer. Using ever higher rates of nitrogen (urea mostly) alone with improved better varieties, the resulting higher yields also remove ever larger amounts of soil nutrients if not replenished and the FUE declines further resulting in stagnating and even declining yields. This leads to the paradox situation where statistics report the continuing increase in fertilizer use but the expected crop production increases are not taking place.
Apart from N, P and K, sulphur (S) and micronutrients such as zinc (Zn), iron (Fe) manganese (Mn) and boron (B) have also gained in importance in recent years. The secondary nutrient sulphur (S) has become deficient over wide areas especially since the intensive use of high analysis fertilizer, urea, instead of sulphate of ammonia and TSP or DAP instead of single superphosphate or NPK compounds. The major effect of these and several other factors is the gradual decline in crop yields and fertilizer use efficiency.
Organic fertilizer sources
The sustainability of highly intensive cropping systems and the associated heavy mineral fertilizer use without organic manures is widely questioned. This has brought the almost forgotten farmyard manures (FYM) and composts back to the forefront. Regular applications of such organic manures not only supply all the various secondary and micronutrients, though in small quantities, but also improve the physical and biological properties of the soil.
Furthermore, return to the farm is the best way to take care of the large amounts of animal waste produced in the commercial dairy, pig and poultry farms, instead of dumping and degrading the environment.
Farmyard manure (FYM) traditionally does not receive the attention it deserves, as most farmers store their most valuable asset, their cattle/ buffalo manure not in a systematic, but in a rather haphazard way. Storage of FYM in rural households in the region is in heaps exposed to sun, wind and rain, which accounts for substantial nutrient losses. FYM preparation needs improvement, adhering to strict and prompt coverage for shading and prevention of drying out by hot wind or washing out of nutrients with heavy rains (pollution hazard). In the Indian subcontinent the widespread practice of using dried cattle and buffalo dung for burning (cooking) as firewood substitute should be discouraged and for the farmer affordable alternatives provided to the farmers e.g. use of biogas.
Unlike FYM, compost is not a by-product of common farm activities, but has to be specially prepared for its own sake. The quality of the ripe compost after undergoing a heating process reaching at least 60oC to destroy harmful pathogens and weed seeds will depend on the raw material used and the attention given to proper composting by the farmer. The C:N ratio needs to be lowered to 20-15 and good quality compost should have no more than 30 per cent moisture, as no farmer wants to carry excess water to the field. Practically all 16 known plant nutrients are contained in compost, but unfortunately, only in very small quantities. Composting is a labour and time-consuming process, which takes 3-6 months. To speed up the process in several countries, rapid composting technologies have been developed. With the use of Trichoderma harzianium (Philippines), a fungal activator, decomposition of rice straw and other organic material with high C:N ratio, combined with animal manure is enhanced to 25 days.
In Thailand, the Department of Land Development of the Ministry of Agriculture uses a mixture of bacterial and fungal microorganisms to inoculate raw rice straw compost for rapid decomposition. More than 100,000 packages of compost activator or inoculants are prepared per year for free distribution to farmers. Each package of 150 g is sufficient for rapid composting of one ton straw or other organic material together with 200 kg of animal manure plus 2 kg of urea. Commercially prepared composts marketed as organic fertilizer are available in most countries in the region and used mainly for high quality vegetable production and horticultural use.
Other freely available sources of organic matter that are available on-farm in large quantities are wheat and rice straws, maize stalks, and stovers of legumes and various pulses. Most of the crop residues are not collected for composting and nutrient recycling, but are used as animal feed (straws/stovers), burnt or left in the field for natural decomposition (fallen leaves and stubble). Crop residues in the long run also increase the OM content in the soil. Mulching with fresh straw or leaves is another good agronomic practice for conserving moisture, reducing soil erosion and for recycling of nutrients, if the partly decomposed mulching material is ploughed under for the following crop. Direct seeding of maize or soybean into mulch cover would be another good agronomic practice. Burning of straw which is still widely practised by farmers as the fastest and least labour requiring method of disposal should be discouraged or, if possible, banned as in most developed countries, mainly because of its air polluting effect.
Green manure crops such as Sesbania aculeata ploughed into the soil after 45-60 days, as practiced by Indian, Nepali and Pakistani farmers may contribute about 30-40 kg per hectare nitrogen for the following crop. However, it seems to be increasingly difficult to find a niche in the traditional farming calendar and cropping system to successfully grow a green manure crop, which occupies the land for several months and needs water and fertilizer, except N- just to plough it back into the soil.
Wherever possible and feasible the growing of grain legumes such as groundnuts, soybeans, chickpeas, cowpeas or mungbean as cash crops, which maintain soil fertility and provide farmers with extra income and fodder from crop residues should be encouraged. Leguminous green manures, when incorporated, certainly add the nutrients present in their biomass including the bulk of nitrogen they have captured (fixed) from the air, but other nutrients have to be absorbed from the soil.
Green manuring apart from making net nitrogen addition, basically recycles other nutrients back in the soil. Furthermore, effective nitrogen fixation requires an adequate phosphorus status in soils which is usually lacking. It is a common misconception that using green manures to provide nitrogen would be less damaging to the environment than using mineral fertilizer, but far from it, the opposite is often the case. When the legume plants die at the end of the growing season or after harvest and there is no crop growth in the field to take up all the nitrate which is released from the rapidly decaying rhizobium nodules and plant residue, there is a great danger of nitrate leaching, especially under hot, humid and high rainfall climatic condition in the tropics.
Biogas plants in rural areas produce digested slurry as an end product, which could be applied directly in cultivated fields. Such slurry contains about 1.5-2.0 per cent nitrogen, 1.0 per cent phosphorus and a little over 1 per cent potassium. It is also a valuable source of micronutrients. Moreover, due to the heated digestion processes, biogas slurry is virtually free from weed seeds and pathogens.
Industrial waste materials
Most industrial waste materials as are valuable resources and should be properly managed and utilized. The large number of sugar cane processing factories in the region produce substantial quantities of organic by-products such as bagasse, pith and press-mud. Even though some of the bagasse and cane residues are used for cardboard production, most of them are burnt as fuel in the sugar industry. So far only a small portion is mixed with press-mud, composted and recycled as organic fertilizer.
Agro-industries, such as fruit and vegetable processing, cotton ginneries, oil mills, breweries and distilleries, also produce large quantities of organic waste materials which need to be properly managed and utilized for nutrient recycling instead of dumping and polluting the environment. An excellent example for organic waste recycling is the practice of Malaysia’s oil palm industry to effectively utilize the vast quantities of palm oil milling effluent
City refuse (garbage, sewage sludge)
Increasing population and even faster growth of urban population will consequently lead to increasing amounts of urban waste, which would create enormous disposal problems if not properly recycled as a source of crop nutrients. Processed, composted solid organic wastes and sewage sludge provide both organic matter and valuable plant nutrients to crops. The transport from urban composting plants to the farming areas constitutes a major part of the cost of processed organic wastes for farmers.
Marketing studies and advertising campaigns, attractive comparative prices together with a subsidy scheme to encourage the large-scale acceptance by farmers of urban compost should be considered. Subsidies, grants and credit should concentrate on transport and handling cost of such bulky products, which could nevertheless result in considerable savings in mineral fertilizer, for the farmers. As a rule of thumb the price per kg of nutrient in composted city refuse for the farmer should be at par or not considerably higher than the cost per kg nutrient in commonly used mineral fertilizer. The other not so easily quantifiable benefits of using organic fertilizer materials, such as increasing SOM, better water holding capacity, and better soil health, are to be accounted for by the cost of extra labour for spreading and incorporation in the field.
Enriched city compost
City compost produced at mechanical composting plants throughout the Asia and the Pacific region (India, Nepal, Pakistan, Philippines, Indonesia, and Thailand) is generally low in plant nutrients and therefore its acceptability by farmers has been limited. To improve the quality and nutrient content of city compost, low-grade rock phosphate and phosphate solubilising azotobacter spp. and the nitrogen fixing bacteria, such as azotobactor spp. or pseudomonas spp., are being used as inoculants.
Microbial inoculation and application of 1 to 5 per cent rock phosphate increased the nitrogen content of city compost by 24 to 30 per cent and more favourable C:N ratios have been obtained. Available P2O5 content of compost was increased by 60 to 114 per cent where rock phosphate was applied and inoculated with aspergillus awamori. Preparation of compost from enriched city garbage or otherwise is promising, provided that financial support from government is available.
However, heavy metals in sewage sludge when continuously applied in excessive quantities to farmland as organic manure could lead to problems. Monitoring for Cd, Zn, Pb, As, and Cu contents in compost is recommended.
Biofertilizers have an important role to play in rainfed areas in improving the nutrient content of crops. Although rhizobium is the most researched and well known among the biofertilizers, there are a number of microbial inoculants with potential practical application in IPNS. Such inoculates could contribute to increasing crop productivity through increased biological nitrogen fixation (BNF), increased availability or uptake of nutrients through phosphate solubilization, or increased absorption, stimulation of plant growth (hormones), or by rapid decomposition of organic residues (rapid composting technology).
The nitrogen fixed by rhizobia benefits legume crop production in two ways: (i) by meeting most of the legume crops nitrogen needs and (ii) by enriching the soil for the benefit of subsequent crops. Rhizobium inoculation should be considered in all legume green manure crops to gain maximum benefit from nitrogen fixation in the shortest possible time. Azospirillum, azotobacter and pseudomonas inoculations on upland grain crops are still in their infancy and field trial results are inconclusive, although good responses to azospirillum and azotobacter inoculation of wheat, rice and sugar cane have been recorded. Further research is needed to find agronomic practices that may help the inoculated bacteria to multiply profusely in the rhizosphere.
Biofertilizers for flooded rice: Azolla and BGA
Most important biofertilizers for wetland rice are the water fern azolla and the blue green algae (BGA), also known as floating nitrogen fertilizer factories. Both can grow alongside paddy. Azolla can also be used for green manuring which could contribute from 20 to 60 kg per hectare N. Phosphorus is a key element and its deficiency results in poor growth and reduced N fixation (addition of 1 kg P results in fixation of 5 to 10 kg N). Azolla is considered an efficient scavenger for potassium and serves as a source of K for rice crops. Azolla biofertilizer technology is labour intensive. Irrigation water, phosphate fertilizer and pest control measures are necessary inputs. Nitrogen fixed by azolla or BGA becomes available to the rice crop only after its decomposition. Numerous field experiments indicated that only up to one third of the fixed N is absorbed by the following rice crop, while two-thirds remained in the soil as residual N or is lost to the atmosphere.
Phosphate solubilizing microorganisms
A number of microorganisms known to have the ability to solubilize and transform inorganic P from normally insoluble sources through excretion of various organic acids have been isolated. These are bacteria of the bacillus and pseudomonas spp and fungi, such as aspergillus, penicillium and trichoderma spp. In addition to P-solubilization these microorganisms can also mineralize locked up organic P into soluble, plant available forms. As these reactions take place in the rhizosphere and the microorganisms bring more P into solution than they can absorb for their own growth, the surplus is available for plants to absorb. The effectiveness of these microorganisms depends on the availability of sufficient energy source, carbon in the soil, P concentration, particle size of rock phosphate as well as temperature and moisture.
Constraints to biofertilizer use
It is difficult to predict the performance biofertilizers, which is influenced by many factors, only some of which could be attributed to farm management. Essentially, the survival/ multiplication rate of the introduced strains needs to be improved. There are several constraints to the use of biofertilizer. For example, inoculum transportation and storage should be ideal. There would be a rapid decline in number of cultured bacteria if transported and stored at 45oC and above. Poor survival is also related to high temperature in the soil during summer months.
Growth and survival of rhizobium and other free-living N2-fixing bacteria is also influenced by competition and antagonism from other organisms, soil salinity, water logging and pesticides application. So far biofertilizer use is below potential, but could increase if GMO technologies presently being explored become successful. Intensive extension activities through widespread field demonstration programmes and wide publicity through mass media could help in creating awareness among farmers on the benefits of biofertilizer use.