Introduction

The biggest challenge for India is its ever increasing population and to match it with food production.  The population of India reached the one billion mark on 11th May, 2000 and is projected to reach 1.15 billion around 2020 AD.  We will need around 240 million tons of food grains to feed this population.  The world scenario also reveals equally startling figures.  The world human population which was 1.5 billion at the beginning of this century, increased to 6 billion today and is expected to reach 8.3 billion by 2025 AD.  In India, the arable land is limited and we have exceeded the carrying capacity of the land.  Under these circumstances, there is a compelling need to increase agricultural productivity.  Apart from the increasing population, the nutrient requirements of the people are also on the rise.  It is estimated that in the next two generations, the world will consume twice as much food as has been consumed in the entire history of humankind.  This situation unquestionably calls for a prudent approach for sustainable agricultural development as no other option would provide the answer.

The challenges of the next century are to be tackled with in our limited resources.  Specially, expansion in agricultural production is to be achieved within the available land, water and energy resources. Therefore judicious use of resources, evolving technologies which are cost effective, resource saving are essential.  The tasks are to be achieved within the frame work of protection of environment and preservation of natural resource base.  This calls for a firm commitment to evolve new technologies for increasing the productivity and continuous use of available resources in the 21st century by all concerned with agricultural development.

According to statistics, during 1987-88, the average use of fertilizers to a hectare of land was reported to be 687 kg in Netherlands, 422 kg in South Korea, 237 kg in China but it was a meagre 70 kg in India.  Each crop has its own pattern of nutrient uptake.  Under rice-rice-rice cropping system, 363 kg of N, 82 of P2O5 and 400 kg of K2O are removed from a hectare of soil annually.  But farmers attach undue importance to nitrogen fertilizers than others.  The ratio of the utilization of N, P and K fertilizers decreased from 1.0: 4.0: 0.14 during 1991 to 1.0: 0.29: 0.12 during 1995-96.  Because of unbalanced fertilizer utilization pattern for the past 3 decades, the crop productivity decreased from 14 kg yield / kg applied fertilizers during 1970-71 to 9.30 kg during 1992-93.  Such a skewed utilization of fertilizers has led to loss in soil productivity.  Moreover, the least importance attached to potassium fertilization led to explosion of myriad’s of pest and disease problems and ultimate crop yield losses.  Besides N, P, K, crop also needs nutrients like Ca, S, Zn, Fe, Cu Mn, B and Mo.  In some cases elements like Si and Cl are also essential for imparting special characters like pest and disease resistance.  Though they are needed in micro level, their requirement is most essential for growth and full expression of their genetic potential.  Although resistance and tolerance of crop plants to pest and diseases are genetically controlled they are considerably influenced by nutrient.  Mineral fertilizers not only affect the growth and composition of plants but also have profound effects on microbial activity in the soil rhizosphere an plant resistance and tolerance to root and shoot pathogens and pests indirectly.  Usually a balanced nutrient supply that ensures optimum plant growth also considered optimum for plant resistance.  An inverse relationship exist between nutrient supply and plant growth on the one hand and the severity of bacterial infection on the other.  Therefore one can conclude that plants with an optimum nutrient status have the highest resistance to pest and disease and  susceptibility increases as nutritional status deviates from the optimum.

In recent times, the yield potential of crop varieties has already reached a plateau owing to several constraints.  The most important among them is the deficiency of mineral nutrients noticed through the length and breadth of the country; where intensive cultivation has been practiced.  The depletion of nutrients particularly micronutrients in the soil is increasing due to adoption of modern technologies in crop production such as raising high yielding crop varieties, multiple cropping, inter cropping etc.  where the demand for nutrients is very high and varying.  The amount of nutrients depleted is not returned to the soil in the right proportion at right times leading to wide spread deficiency of nutrients especially micronutrients.

Micronutrients are required for normal growth, development and yield of crops.  Fore example, cotton needs Zn for the normal pollen production.  Boron application to groundnut reduced the occurrence of ill filled pods and enhance the yield. Whereas, Boron application to the coconut reduce the barren nut production.  Pulses need molybdenum for better nodulation.  Manganese application to gingelly increases its oil content an seed yield.  Copper deficiency in citrus causes die-back disease.  Besides the application of needed dose of N,P and K fertilizers, Zn application increased the yields by over 300 kg/ha in rice, 800 kg/ha in maize, 500 kg/ha in soybean and 200 kg/ha in groundnut.  By testing the soils, the farmers can apply the needed micronutrients, or they can also grow tolerant crop in their field.  For example certain varieties of soybean can tolerate Zn deficiency, the varieties M-2 and Davis can tolerate molybdenum deficiency.  Such tolerant varieties are being developed in other crops as well and they will be available for cultivation in micronutrient deficient soils in course of time. 

Each nutrient is needed to a particular level for each crop.  If any deficiency or toxicity arises in soil, phonological symptoms will be exhibited by the crops accordingly.  For example, Fe deficiency will cause chlorosis of younger leaves.  Nitrogen, phosphorus and potassium deficiency symptoms will be first exhibited in the older leaves.  Therefore, a thorough knowledge on the nutrient deficiency symptoms with respect of agricultural and horticultural crop is very much essential to take appropriate measures to offset the yield loss.  Any attempt to indiscriminate application of nutrients especially micronutrients are likely to cause deficiency of other nutrients leading to crop loss.  For example, excess application of Zinc will result in decreased uptake of Copper and Manganese leading to deficiency of Copper and Manganese.  Sometimes under certain situation like strongly acidic soils, toxicities of certain micronutrients is likely to occur due to their excess availability.  Further, the toxicities created by imbalance of applied nutrients or improper dose / concentration of applied nutrients has been encountered occasionally.  Therefore, there is an absolute need for a thorough knowledge on the deficiency and the toxicity symptoms of each nutrient.  It is also necessary to have a complete understanding and through expertise in the subject so as to distinguish the deficiency and toxicity symptoms of various nutrient elements from one another.

Much interest to micronutrients in India was shown only after the discovery of field scale Zn deficiency of rice at Pantnagar in mid 1960’s.  Within a short period of time, micronutrients research in Indian agriculture became a major field of activity and the Indian Council of Agriculture Research (ICAR) initiated in 1969, the all India coordinated schemes for research on micronutrients in soils and plants.  Extensive work has been done under this scheme as well as independently by the Universities, Institutes, Agricultural departments and Industries.  Major areas of research were on delineation of deficient areas, identification of deficiencies, establishment of certain critical limits for soils and crops, amelioration measures and crop response to application of micronutrient fertilizers.  Simultaneously promotion and marketing of micronutrient fertilizers were primarily done by the industries and government agencies.  Tamil Nadu Agricultural University has done extensive research on the micronutrients for the past more than 25 years.  The work done so for has been brought out as a book entitled “25 years of micronutrient research in soils and crops of Tamil Nadu”.