The integrated nutrient supply and management will lead to sustainable high yield crop production


Aug 18 - 24
, 2003 




One of the biggest challenges facing the world today is feeding its ever increasing burgeoning population. For this world that cannot sufficiently feed over 6 billion population today, the picture appears to be somewhat gloomy and bleak. In many developing countries including Pakistan the high population growth has a dual effect on food balance. It increases food demand and at the same time it degrades the agricultural lands. It has been seriously thought that in the mid-1960s, when projections of global starvation were very common, no one questioned the role of mineral inorganic fertilizers in increasing food production particularly in the food deficit countries of the world. On the contrary, fertilizer use was an integral part of the "Green Revolution" technological package of improved and certified varieties of rice and wheat, irrigation, fertilizer, use of insecticides etc. that helped mainly densely populated countries to achieve food self-sufficiency in the short span of about 30 years.

In the past, the employees has been on increased use of fertilizer, the approach nor must shift to educating farmers to use organic, inorganic and biological fertilizer optimally. Plant nutrition in future will required the judicious and integrated management of all sources of nutrients in agricultural fields. Prevention of erosion is equally import for maintenance of soil fertility and environmental protection.

The global necessity to increase agricultural production from a steadily decreasing and degrading land resource base places considerable strain on the fragile ecosystem. Land must be cultivated more intensely, water and labour be utilized more optimally and fertilizer and other purchased inputs used more efficiently. While the use of mineral fertilizers is the quickest and surest way of boosting crop production, their cost and other constraints frequently, deter farmers from using them in recommended quantities and in balanced proportions. Organic residues both of plant and animal origin are by-products of agricultural activities and thus virtually a source of plant nutrients. Organic manure, though bulky in nature and with low nutrient content, have the property of improving soil physical and microbial conditions, and thus enhance fertilizer use efficiency when applied in conjunction with mineral fertilizers.

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 and time in relation to the nutrient demand by the crop. Integrated nutrient management is to be considered an integral part of any sustainable agricultural system.

The role of organic sources of nutrient along with mineral fertilizers is also important from the sustainable point of view. Agricultural research contains to add to the knowledge of the components and technologies governing principles of crop production including the complex issues of plant nutrition. Soil supply all the 16 essential plant nutrient, which are well-known. Mostly, nutrients are found in organic and/or fixed mineral form. Plants can meet much of its nutritional requirement from this source, if managed properly, mainly through mineralization of organic matter. But, due to continuous and intensive cultivation the nutrient supplying capacity of soils has considerably corresponding to general decline in organic matter content of agricultural fields.

Therefore, under any intensive agriculture system, special emphasis has to be give to maintaining nutrient status of the soils and reducing of soil degradation. The soils of Pakistan are generally low in organic matter and thus in N, poor in P but have satisfactory to adequate levels of K. All soil types, except the organic soils are low in organic matter, therefore, practically all agricultural lands would benefit from liberal annual loss of organic matter. To enhance soil nutrient supply it is necessary to adopt appropriate soil management practices much as improvement of soil physical condition of appropriate quantities of nutrients through mineral fertilizer organic and biological sources. Salinity/alkalinity problems need amelioration through regular application of gypsum.

In Pakistan, today various types of fertilizer are available supplying major nutrients N, P, and K however, the N:P ratio of 3.8 to 1 is considered still too wide for agronomic requirements. Total potash quantity is almost negligible. Balanced fertilization is known to improve fertilizer use efficiency and at the same time profitability for the farmer. Using ever higher rates of nitrogen (urea) alone with improved better varieties. The resulting higher yields also remove ever large amounts of soil nutrients if not replenished the fertilizer use efficiency declines further resulting in stagnating and even declining yields.



This leads to paradox situation, where statistics tell use that fertilizer use constantly increases but the expected crop production increases are not taking place. Apart from N, P and K, sulphur (S) and micro-nutrients such as zinc (Zn), iron (Fe), manganese (Mn) and boron (B) are also gaining importance in recent years. The secondary nutrient sulphur becoming deficient over wide areas especially since the intensive use of high analysis fertilizer urea instead of sulphate of ammonia and triple super-phosphate (TSP) or di-ammonium- phosphate (DAP) instead of single superphosphate. Major effect of these and several other factors is the gradual decline in crop yield and fertilizer use efficiency, particularly in rice wheat cropping system areas in Pakistan. Regular applications of organic manure not only supply all the various secondary and micro-nutrients through in small quantities, but also improve soil, physical and biological properties.

Furthermore, return to the farm is the best way to take care of the large amount of animal wastes produced in the dairy and poultry farms, instead of being dumped and degrading the environment. Organic fertilizer sources include farmyard manure, animal dung or droppings, green manure, crop residues industrial wastes and sewage sludge and left over sherry from bio-gas digesters. Pakistan has more than 75 sugar mills large quantities of by-products are produced such as pith, bagasse, and press mud which is piling up at factory sites and so far only few nearby farmers are collecting and using it for manuring their fields. Other industrial wastes such as raw dust is available only in limited quantities and so far is not collected for composting and recycling. Traditionally, our farmers have been concerned mainly with FYM and only in a minor way with separate compost preparation. Farmers with livestock, usually a pair of bullocks, oxen or water buffalo is tethered and fed by-cut and carry not grazing and by using a fodder assorted by products of annual crops after harvest/threshing. Stalks of maize, sorghum or millet, straw of wheat or rice and stover of groundnuts, chickpeas, and gram are common cattle feed. Crop residues are therefore, not readily available for direct composting but are recycled instead in the form of animal dung in FYM. Storage of FYM in rural households is in leaps 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 not wind or washing out of nutrients, with heavy rains.

Crop residues in the long run also increases the organic matter content in the soil. Mulching with fresh straw or leaves is another good agronomic practice for conserving moisture and for recycling of nutrients, if the partly decomposed mulching material will be ploughed in for the following crop. Besides organic matter there are many types of naturally occurring microbes in the rice rhizosphere that are capable of fixing atmospheric nitrogen. Estimates of the amount of biologically fixed N per crop or vary, about 30-40 kg L/ha N seem to be reasonable. This amount of N biologically fixed in paddy soils is about two to three times higher than the amount of N considered to be fixed on average in upland soils planted to non-leguminous crops.

Green manure crops such as Sesbania aculenta (Dhaincha) ploughed into the soil after 45-60 days as practices by some Pakistan farmers may contribute about 30-40 kg/ha nitrogen for the following crops. Leguminous green manure, when incorporated certainly add the nutrients present in their biomass including the bulk of nitrogen they have captured from the air, but other nutrient have been absorbed from the soil. Green manuring apart from making net nitrogen addition basically recycles other nutrients back to the soil. When legume plants die out the end of growing season or after the 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 residues, so there is a great danger of nitrate leaching especially under hot, humid and high rainfall climatic conditions. Biogas plants which are numerous in Pakistan and becoming more popular produce as an end product digested slurry which can be applied directly in cultivated fields.



Such a slurry contains about 1.5-2.0 per cent nitrogen, 1.0 per cent phosphorus and above 1 per cent potassium. It is also a valuable of micro-nutrients. Pakistan with its large number of sugarcane processing factories produces substantial quantities of organic material by-products such as bagasse, pith and press mud. As some of the bagasse and crop residues are used for cardboard production, most of it is burnt as fuel in the sugar industry. Only a portion is mixed with press mud containing the whole range of macro and micro-nutrients, though in small quantities, has accumulated near sugar factories in large heaps and is only used by some nearly farmers as an organic manure. The use of raw dust and coir-dust is also important for using as organic manure in agricultural fields.

Biofertilizers have an important role to play in improving the nutrient supplies and their crop-availability in rainfed crop production. Although Rhizobium is the most researched and well known among these, there are number of microbial inoculants with potential practical application of integrated plant nutrition management systems. Such inoculants may 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 or by rapid decomposition of organic residues. Among nitrogen fixing bacteria such as Rhizobium (symbiotic), Azotobacter and Azospirillum (non-symbiotic), the most widely used inoculant in Rhizobium. Symbiotic N2 fixation by Rhizobium with legume crops contributes substantially to total BNF.

The most important biofertilizers for wetland rice are the water fern Azolla and Blue Green Algae (BGA). Both can grow alongside paddy and additionally, Azolla can also be used for green manuring and it can contribute 20-60 kg/ha N if growth conditions are optimal. Phosphorus is a key element and its deficiency results in poor growth and reduced N fixation. Azolla is considered to be an efficient scavenger for potassium and may serve as a K-source for rice in K-deficient soils. Azolla biofertilizer technology is labour intensive and apart from labour, irrigation water and phosphate fertilizer, pest control measures are necessary inputs. Nitrogen fixed by Azolla or BGA becomes available to the rice crop only after their decomposition. A number of micro-organisms known to have the ability to solubilize and transform inorganic P from normally insoluble source through excretion of various organic acids have been isolated.

The integrated nutrient supply and management through judicious use of organic, mineral and microbial fertilizers will lead to sustainable high yield crop production. The combined use of organic manures and biofertilizers help maintain soil productivity and soil productivity and soil health even under intensive cropping systems. The organic manure application helps to recycle the nutrients and to correct deficiencies, particularly those of micro-nutrients. The farmers need to be educated to practically realize the nutrient potential of organic manure/residues, composts and biofertilizers. The major extension effort has to be towards teaching the farmers efficient use of locally available organic manures and biofertilizers most suitable to the needs of the area and of the cropping systems.