eChapters

World population is expected to cross 8.5 billion by 2025 and it will be a gigantic task to produce enough to meet the future food demand by growing same set of crop varieties on anticipated reduced area. Most of the land that could be brought under cropping has been utilized with exception of some land in Sub-Saharan Africa and South America (Borlaug and Doswell, 1993). Therefore, it is warranted to produce more from less land, less water and less inputs which can be achieved by enhancing the efficiency of production system by devising more efficient crop management practices and developing input use efficient cultivars.

Low bioavailability of phosphorus (P) in soils is one of the major limiting factors influencing crop production throughout the world. Plants, however, are known to possess potential adaptive mechanisms at morphological, physiological, biochemical, and molecular levels to overcome P deficiency (Vance et al., 2003). Such adaptive mechanisms mainly include an increase in total root length and root hair growth (Bates and Lynch, 2000), enhanced organic acid (Singh and Pandey, 2003), acid phosphatase (Pandey, 2006) and ribonuclease (RNase) secretion into the rhizosphere (Hocking, 2001), increase in expression of proteins such as phosphatase, inorganic phosphate (Pi) transporter, RNase and phosphoenolpyruvate carboxylase (PEPcase) in plant tissues.

Nutrient use efficiency of crops is being improved through temporal and spatial management of the form and amount of nutrient inputs as being demonstrated by various agronomic practices. In addition, understanding of the genetic basis of nutrient efficiency would lead to the development of nutrient use efficient varieties thus reducing the application of nutrients. Earlier studies on genetics of nutrient use efficiency were limited as increasing productivity with heavy nutrient inputs was the main focus. But in the backdrop of environmental degradation due to the excessive nutrients and its impact in climate change, nutrient use efficiency in crops is need of the hour for sustainable and eco-friendly agriculture.

In plants, mineral uptake is the process in which minerals enter the cellular material, typically following the same pathway as water. The most normal entrance portal for mineral uptake is through plant roots. Some mineral ions diffuse in-between the cells. In contrast to water, some minerals are actively taken up by plant cells. Mineral nutrient concentration in roots may be 10,000 times more than in surrounding soil. During transport throughout a plant, minerals can exit xylem and enter cells that require them. Mineral ions cross plasma membranes by a chemiosmotic mechanism. Plants absorb minerals in ionic form: nitrate (NO₃^-), phosphate (HPO₄^-) and potassium ions (K+); all have difficulty crossing a charged plasma membrane. It has long been known plants expend energy to actively take up and concentrate mineral ions. Proton pump hydrolyzes ATP to transport H⁺ ions out of cell; this sets up an electrochemical gradient that causes positive ions to flow into cells. Negative ions are carried across the plasma membrane in conjunction with H⁺ ions as H⁺ ions diffuse down their concentration gradient.

Nutrient supply is one of the major inputs for agricultural crop production in a sustainable manner. The factor productivity of inputs especially the fertilizers in agriculture was found to be in a declining phase during the last four decades. This had a detrimental effect on annual compound growth rate of major crops as wells on soil quality. The current status of nutrient use efficiency in different cropping system is low in case of major macro nutrients likes Nitrogen (30-50%) and Phosphorus (15-20%). Because 50-70% of the nitrogen applied using conventional fertilizers, with particle size dimensions greater than 100 nm, is lost to the soil due to leaching, nutrient utilization efficiency (NUE) by plants is low. Attempts to increase the NUE in conventional fertilizer formulations have thus far resulted in little success. On the other hand, the emerging nano strategies indicate that, due to the high surface area to volume ratio, nano fertilizers are expected to be far more effective than even polymer-coated conventional slow-release fertilizers. In this context, nanotechnology offers an important role in improving the nutrient use efficiency of agricultural systems.

Through green revolution, we have developed high yielding varieties albeit with high nutrient requirements putting much more reliance on chemical fertilizers. The major challenge facing plant biology right now is to improve crop production and to feed an expanding world population. This is against a background of pressure on agricultural land use and climate change having negative impacts on growing conditions. The adverse effects of agriculture, and specifically fertilizer use, include damage to the environment, a large carbon footprint for the manufacture and use of agrochemicals, and the utilization of non-renewable resources. One solution is to increase the area of land for agriculture, as well as increasing production while maintaining the current rate of inputs; however, this is predicted to have substantial negative impacts on the environment (Tilman et al., 2002), is unsustainable in terms of phosphate use, and would have a huge economic footprint in terms of energy demands for nitrogenous fertilizer production. The challenge is to increase yield, decrease inputs, and improve resistance to abiotic and biotic stresses. Improving crop nutrient use efficiency ideally requires an understanding of the whole system, from the macro (agro-ecosystem) to the molecular level.

Nanotechnology is a field of study which deals with materials at nano-scale like nanometer which is one billionth of a meter (1 nm = 10-9 meter). At nano-scale, physics, chemistry and biology converge towards the same principles and tools. Nanotechnology is domain in science and technology, which is multidisciplinary in nature and any scientist, engineer, medical doctor can do research on nanotechnology. Presently, it is more of a science and less of a technology because of a lack of proper tools for studying the properties of nano-material. Nano-particles (NPs) are materials that are small enough to fall within the nanometric range, with at least one of their dimensions being less than a hundred nanometres. This reduction in size brings about significant changes in their physical properties with respect to those observed in bulk materials. The presence of naturally occurring NPs is implicated in interplanetary and interstellar space (Hochella Jr, 2002) as well as our earth in which life from the beginning has evolved in their presence (Becker and Reitmeijer, 2006). Currently it is observed that NPs can be synthesized from many biological organisms including plants.

Since the 1960s, the world population has doubled from three to seven billion, and this trend will persist in the coming decades. Because of this rapid expansion, a massive increase in crop production is required to meet the food and energy demands of future generations. Potassium is the third important plant nutrient after nitrogen and phosphorous. It is seventh most abundant element in the lithosphere. Being chemically active metal, it is never found in its pure elemental state in nature. Potassium (K) plays a particularly crucial role in a number of physiological processes vital to growth, yield, quality, and stress resistance of all crops. The K content of Indian soils varies from less than 0.5–3.0%. The average total potassium content of those soils is 1.52% (Mengel and Kirkby 1987).

The concept of sustainability in agricultural system

All forms of production systems exist today, from nomadic herding to continuous, intensive monocrop systems. Their distribution is determined by soil and climate conditions, and by social and economic factors. In very general terms, as one moves from drier to wetter areas, pastures and animals become less important, and trees more so. Population density is greatest where soils are most fertile, and management systems the most intense. Most production systems have evolved so that they are sustainable in terms of the environmental conditions prevailing at the time—including the level of demographic pressure.

Preamble

Crop nutrient management in the climate change scenario is carried out with the basic understanding of nutrient concentrations in soils, plants and their transformations but these strategies might not apply under changed climate conditions where there is an overall change in the environment. It is understood that nutrient acquisition by plants from the soil is closely associated with overall biomass and strongly influenced by root foraging area. It is speculated that change in soil factors due to climate change could restrict root growth and nutrient stress would also occur. Plant size may also change but nutrient concentration may not change; therefore, nutrient removal will scale with growth. The interaction of mineral behavior in the soil with global climate change variables is poorly understood.

Meeting food demand and escalating food prices are serious issues, as current food scenario indicate that crop demand will increase by 100 to 110% from 2005 to 2050 at global level (Tilman et al., 2011). Precision use of fertilizer is the crucial for achieving sufficient food production for growing population. It is costly input to produce and apply, both financially and environmentally. Fertilizer consumption measures the quantity of plant nutrients used per unit of arable land.

For efficient nutrient use, most important factors are the timely supply/recycling of adequate amount of nutrients to the production system and its retention and release by soil for timely and ready availability in the root zone for its mobility to the plant in the presence of optimum moisture content in the soil. For keeping the applied nutrients retained in the root zone one has to reduce the soil erosion and leaching losses through technologies available in hand which include direct measures of soil and water conservation and maintain the soil aggregation and porosity through suitable tillage and organic residue recycling. For movement of nutrients into plant system we need to ensure optimum soil moisture content through water management.

Phosphorus (P) is a critical nutrient in crop production, due to its low bioavailability in soils (Feng et al., 2004). Phosphorus is the vital component of DNA, RNA, ATP and photosynthetic system and catalyses a number of biochemical reactions from the beginning of seedling growth through to the formation of grain and maturity. Many factors influence soil P availability like type of parent material from which the soil is derived, degree of weathering and climatic conditions. In addition to this, erosion, crop removal and phosphorus fertilization and soil phosphorus levels also affect P availability in soil. Rock phosphate is the key raw material used for manufacturing phosphatic fertilizers on which the food production depend.

Introduction

Agricultural lands in India have mostly low native soil fertility. On these soils there must be a regular application of nutrient inputs through chemical fertilizers and/or organic manures for a successful and sustained crop production to replenish soil nutrient reserves depleted by crop removal and other losses. It is essential to recognize that even in agricultural production systems with relatively low productivity level, the quantity of nutrients available for recycling through plant and animal residues is not enough to compensate the amount being removed by crops. Under these circumstances mineral fertilizers play a key role in those areas having low fertile soils by increasing agricultural production to meet out growing food demand. Chemical fertilizers are the major contributors as source of plant nutrients to enhance crop production and also to maintain soil productivity.

To meet the food needs of the burgeoning population, India will need to produce 300 million tonnes of food grains by 2020. At present more than 75% of the total food grains produced in the country are of rice and wheat. Use of nitrogenous fertilizers has contributed much to the remarkable increase in production of rice and wheat in India that has occurred during the past three decades. During the last half-decade or so while fertilizer N consumption is touching new heights, the production of both rice and wheat is showing a trend of plateauing. In fact, fertilizer N efficiency of food grain production expressed as partial factor productivity of N (PFPN) has been decreasing exponentially since 1965. The PFPN is an aggregate efficiency index that includes contributions to crop yield derived from uptake of indigenous soil N. fertilizer N uptake efficiency, and the efficiency with which N acquired by the plant is converted to grain yield. A decrease in PFPN occurs as farmers move yields higher along a fixed N response function, unless other factors shift the response function up. In other words, an initial decline in PFPN is an expected consequence of the adoption of N fertilizers by farmers and not necessarily bad within a system’s context

Soil is a major source of nutrients needed by plants for growth. The three main nutrients are nitrogen (N), phosphorus (P) and potassium (K). Together they make up the trio known as NPK. Other important nutrients are calcium, magnesium and sulfur. Plants also need small quantities of iron, manganese, zinc, copper, nickel, chlorine, boron and molybdenum, known as trace elements because only traces are needed by the plant. The primary nutrients are nitrogen, phosphorus and potassium, because they are required in larger quantities than other nutrients. These three elements form the basis of the N-P-K label on commercial fertilizer bags. As a result, the management of these nutrients is very important. However, the primary nutrients are no more important than the other essential elements since all essential elements are required for plant growth. Remember that the ‘Law of the Minimum’ tells us that if deficient, any essential nutrient can become the controlling force in crop yield.

Plants require altogether 17 essential elements to nourish themselves and to complete their reproduction and life cycle. Among them nine elements are required in large amounts for their growth, the so called macro nutrients like C, H, O, N, P, K, Ca Mg and S.  The former three elements (C, H and O) are available to the plants through air and water over which we have relatively little control either in their application rates or uptake into plant system.

Biotechnological research started in early seventies with some impressive discoveries in the field of genetics, microbiology, biochemistry, biology and chemical bioengineering. The amalgamation of these sciences particularly integration of their basic principles and applied aspects gave rise to a new field, completely diverse and versatile in nature, what we call today ‘biotechnology’. Originating from research laboratories in universities, biotechnology rapidly captured the attention of industries as the number of its potential products increased. This newly developed frontier science later found broad application in medical science, pharmaceutical industry, agriculture, veterinary sciences and chemical industry for the welfare of mankind. Biotechnology by definition means ‘any technique that uses living organism or a part thereof to make or modify a product, to improve plant or animal or to develop microorganisms for specific purposes’.

Boost to crop production has been the ultimate goal of researchers involved in agriculture so as to feed the ever-increasing human and domestic herbivorous animal populations. Crop production is not only constrained by the limited inherent potential of available varieties currently in use, but is also largely affected by the limitations of soil nutrient availability and damages by diseases, insects and weeds. To counter later challenges, augmentation of soil nutrients through use of biofertilizers in integrated nutrient management programmes and restricting the use of chemical pesticide by integrating biopesticides in plant protection programmes has received much attention in recent years because of consumer’s preference for organic food.

In agricultural practices pesticide application is an inevitable factor for maintaining high crop productivity and is currently an integral part of modern farming. Pests (insects, microbes and weeds) cause approximately 20-30% loss in crop production so making pesticide use indispensable for crop protection.
 
Pesticide : A pesticide may be defined as ‘any agent or chemical or a mixture of chemicals/ substances intended to prevent, destroy, repel or irritate one or more pest populations causing economic loss in crop production’. Worldwide more than 450 active pesticide chemicals formulated into more than 10,000 commercial products are currently used by farmers. The most worrying aspect is that about two-third of the 800 chemicals tested so far have been found involved in causing or promoting tumor in rodents. Yet more than 50,000 synthetic chemicals/formulations remain untested so far.