eChapters

Introduction

Nitrogen constitutes 78% of the atmospheric gases and there is about 75,000 Mg N on each hectare of land. However, 99% of the atmospheric N is as N₂ and is inert and non-reactive, while the rest 1% or even less is the reactive-N. Reactive-N is linked with H, O and C and is responsible for the creation and sustenance of all life on the planet Earth. Nitrogen is the key nutrient that separates proteins from carbohydrates and fats, the three major macronutrients for humans. As a component of proteins, N is present in DNA and RNA, which carry the hereditary characters and then as the major constitute of the body muscles of humans (and animals). Plant growth and crop production are also very much dependent on the adequate availability of N in soil.

SOIL WATER

Soil water and oxygen share the pore space in soil and generally the oxygen content is determined by the water content, which is added by irrigation or rains and then keeps on changing due to evapotranspiration. Water is the vehicle by which most nutrients move from the soil to root surface. But for the lowland rice, nutrients are most available to plants at ?eld capacity moisture (about 0.3 atmosphere soil water tension) and the availability decreases as the moisture content decreases to wilting point (about 15 atmosphere tension). That is why rainwater or irrigation increases nutrient availability, while extremely dry condition decreases it. There is thus a signi?cant interaction between water and nutrient availability in soil (Singh et al., 2014). In a study in India (Singh et al., 1980) the yield of wheat was signi?cantly affected by irrigation water and nitrogen treatments; maximum yield was obtained with irrigation at 50% available soil water in 60 cm soil depth and 120 kg ha ^–1 nitrogen addition. A study on wheat at Delhi (Kumar et al., 2015) very well shows the effect of irrigation water on yield and uptake of nutrients (NPK) (Table 5.1).

German chemist Justus Freiherr von Liebig (1803–1873), Professor at the University of Geissen and the French chemist Jean-Baptiste Joseph Dieudonne’ Boussingault (1801–1887), Professor at the University of Lyon and later Chair, Conservatoires des Artes et Matier in Paris are to be credited for analyzing the plants and coming with the idea that plants absorbed nitrogen and other mineral nutrients from the soil for their growth. D.I. Arnon and P.R. Stout, Plant Physiologists and Plant nutritionists at the University of California, Berkeley, USA, grew plants by hydroponics using pure chemical compounds and established following 3 criteria for the essentiality of nutrients for plant growth

All life on planet Earth is carbon centered; hereditary characters are controlled by DNA and RNA, growth by proteins and activities by energy from carbohydrates and fats – all these are carbon compounds. Not only this, but the life also ends as carbon compounds CO₂ or CH₄, depending on aerobic or anaerobic decomposition. Incidentally soil fertility also depends very much on soil organic carbon (SOC). In ancient days, farmers used to apply manure to maintain soil fertility and even now, urea, the nitrogen fertilizer used in the largest amounts, is a carbon compound. All living forms on the Earth including all plant and animal species and their activities are a part of global carbon cycle. The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the earth.

INTRODUCTION

In biology, fertility is de?ned as capacity to produce off-springs; however, in Soil Science a ?ne difference is made between a fertile and a productive soil. Soil Productivity is the ability of a soil to produce a crop using the entire spectrum of its physical, chemical and biological attributes, while Soil Fertility refers to the capacity of a soil to supply all essential plant nutrients in the desired amounts. Thus, soil fertility management is basically the nutrient management. To put it in simple words, a productive soil is always fertile, while a fertile soil may not be productive for a variety of factors, such as lack of adequate moisture in drier regions or lack of adequate air due to water-logging for most upland crops. Of late, a term ‘ Soil Health’ has been introduced. Soil Health is an assemblage of chemical, physical and biological parameters that closely relate to native or acquired production capacity and sustenance of ecologically important regulatory role (Katyal et al., 2016). It is measured against prede?ned parameters of soil’s status of fertility, compact ability, erodibility and biology. This again tends to relate soil fertility to nutrient content, availability and management.

LAND VERSUS SOIL

Land is a part of Earth’s surface that is not covered by water. It is used for agriculture, building houses, of?ce buildings, schools, hospitals, roads, railroads and even water canals. Land is measured by area [length (l) × width (w)] and the units are square meters (m²), square centimeters (cm²) etc. On the other hand, soil is Earth’s crust, which could vary from a few centimeters to a few meters in thickness (depth), needs a measure of volume [length (l) × width (w) × depth (d)] and the units are cubic meters (m³), cubic centimeters (cm³) etc. Soil is thus a three-dimensional natural body on Earth’s surface that provides anchorage to growing plants/ trees and shelter to soil biota and is responsible for the storage of water and plant nutrients, which are essential for crop production. In addition, it helps in the biodegradation of soil pollutants and puri?cation of ground water, the major source of drinking water in the world. Soil feeds all living beings on Earth and its degradation is one of the reasons for inadequate human nutrition

Introduction

The resource conservation technologies (RCTs) is primarily focussed on resource savings through minimal tillage, ensuring soil nutrients and moisture conservation through crop residues and growth of cover crops, and adoption of spatial and temporal crop sequencing. These practices have long been practised by the farmers in the Indo Gangetic Plains (IGP) but it got eroded in recent times due to various geo-socio economic- political reasons. This region (10.5 million ha) comprises of Punjab, Haryana, Uttar Pradesh, Himachal Pradesh, Bihar and West Bengal and have major share in production of rice and wheat due to adoption of green revolution technologies followed by area expansion. It has been reported that rice-wheat system has strained the natural resources of this region (Swarup and Singh, 1989; Kumar and Yadav, 1993; Lal et al., 2004). In present scenario there is little scope to meet future target by earlier approaches like area expansion and intensive use of natural resources. Therefore, RCTs can be regarded as energy, water and labour efficient system to sustain soil health and production environment and produce more at less cost (Jat et al., 2012; Gathala et al., 2011b).

Major emphasis is given upon the RCTs components like zero/reduced tillage, direct seeded rice, crop residue management and crop diversification. However, other RCTs like site specific nutrient management, leaf colour chart, laser land leveller, nutrient use efficient genotypes, integrated crop and pest management provide options to the farmers as per their resource endowment.

Introduction

Persistent income from agriculture is most important for sustaining the farming sector. Conservation agriculture (CA) is a resource-saving agricultural production system that aims to achieve production intensification and high yields while enhancing the natural resource base through compliance with three interrelated principles, along with other good production practices of plant nutrition and pest management (Abrol and Sangar, 2006). Conservation agriculture is largely promoted as one of the few win–win technologies affordable to farmers, in the sense that potentially it improves farmers’ yields (in the long term) at the same time conserving the environment. CA is described by FAO (http://www.fao.org.ag/ca) as a concept for resource saving agricultural crop production which is based on enhancing the natural and biological processes above and below the ground. As per FAO definition CA is to a.) Achieve acceptable profits, b.) High and sustained production levels, and c.) Conserve the environment. It aims at reversing the process of degradation inherent to the conventional agricultural practices like intensive agriculture, burning/removal of crop residues. Shifting from tillage-based agriculture to no-tillage CA systems removes unsustainable elements in the current tillage based systems and replaces them with CA elements that make the production systems profitable and ecologically sustainable. Conservation agriculture offers an opportunity for arresting and reversing the downward spiral of resource degradation, decreasing cultivation costs and making agriculture more resource – use-efficient, competitive and sustainable.

Introduction

Precise and continuous measurement the greenhouse gases (GHGs) fluxes/ emissions in agricultural systems are required for accounting and budgeting of carbon. Further, the long-term measurements of GHGs fluxes are equally important as precise measurement. Therefore, high frequency and long-term measurement of GHGs across the cropping systems are essential for chalking out the GHGs emissions mitigation strategies. Various technologies with definite working principles are used for estimation of GHGs emissions in agriculture.

Greenhouse Gases Estimation Techniques

Two basic principles are followed to estimate greenhouse gases in agriculture. One is the collection of GHGs from the field and subsequent analysis of the concentration of gases through gas chromatography (GC). Another principle is based on sensors measurement with the help of infrared gas analyze (IRGA). The two techniques used for the measurement are (i) ‘closed chamber method’ (manual/automatic), and (ii) ‘sensor-based method’. Generally, the GHGs fluxes in agricultural crop field are estimated by ‘closed chamber method’ for methane (CH₄) and nitrous oxide (N₂O). And for carbon dioxide (CO₂) measurement either soil respiratory chamber or canopy chamber is used that measures CO₂ with the help of infrared gas analyzer (IRGA).

Introduction

Intensive soil tillage, burning of crop residues and over use of fertilizer and irrigation water under current agricultural practices has accelerated the pace of degradation in Indian agriculture. Intensive soil tillage increases soil erosion and nutrient runoff into nearby waterways. Crop residue burning resulting in loss of plant nutrients and release of greenhouse gases (GHGs) in the atmosphere. Imbalanced use of chemical fertilizer leads to soil compaction, slows down the fertilizer utilization rate and contaminates the local environment. Increasing demand of irrigation water causes water shortage and harms the environment in several ways including increased salinity, nutrient pollution, and the degradation of flood plains and wetlands. In the face of these management and environmental challenges, there is a need to formulate such agricultural practices which improve the productivity of natural resources as well as of external inputs and help to prevent soil degradation. Conservation agriculture (CA) practices such as reduced tillage, residue retention and proper crop rotations offer such solutions. CA also helps in making agricultural systems more resilient to climate change and safeguard ecosystem services.

Introduction

Conservation of biodiversity and mitigation of global warming are two major environmental challenges today. In the context of climate change and the global carbon cycle, the relationship between plant biodiversity and soil organic carbon (SOC) sequestration has become a subject of considerable scientific interest. The Earth’s terrestrial vegetation plays a pivotal role in the global carbon cycle. Not only are tremendous amounts of carbon stored in the terrestrial vegetation, but large amounts are also actively exchanged between vegetation and the atmosphere. Anthropogenic perturbations exacerbate the emission of CO₂ from soil caused by decomposition of soil organic matter (SOM) or soil respiration (Schlesinger, 2000). The emissions are accentuated by agricultural activities including tropical deforestation and biomass burning, plowing, drainage of wetlands and low-input farming or shifting cultivation. In addition to its impact on decomposition of SOM, macroclimate has a large impact on a fraction of the SOC pool which is active. Conversion of natural to agricultural ecosystems increases maximum soil temperature and decreases soil moisture storage in the root zone, especially in drained agricultural soils (Lal, 1996). Thus, land use history has a strong impact on the SOC pool (Pulleman et al., 2000). The dynamic relationship between plant biodiversity and SOC depicts that any land use practices that increase vegetative cover, or reduce its removal, could have an influence on the global carbon budget by increasing the terrestrial carbon sink.

Introduction

The inevitability of detrimental effects of climate change is looming large not only on the sustenance of agriculture, but also on the survival and progress of mankind. Estimates by the Organization for Economic Cooperation and Development (OECD) reveal that the atmospheric concentration of GHG would exceed 680 parts per million (ppm) CO₂-equivalents by 2050, which is about 50% higher than baseline year 2010 (OECD, 2012). Additionally, global temperature is predicted to increase by 2°C within this period, resulting in meansea level rise and erraticweather conditions. Consequently, the catastrophic effects on food consumption pattern by the end of 2050 will create malnutrition in at least 290 million people. Agricultural crops provide 63% of the human protein, and additionally supply almost 100% protein to the livestock, which are the second major sources of protein in human diet. Altogether, the detrimental effect of climate change on agriculture would make about 300 million additional people malnourished. Add to that a 2.7 billion increase in human population by 2050, coupled with shortage of water availability that would affect 3.9 billion people by 2050, and one can easily perceive the grim scenario for our kind in not so distant future.

Introduction

The basic needs of life are food, clothing and shelter. In the 21^st century a fourth need added to mankind is energy. According to the laws of physics, energy is defined as capacity to do work. Energy, economics and the environment are mutually dependent. Also, there is very close relationship between agriculture and energy. The level and pattern of energy use in agricultural production system depends on variety of agronomic and socio-economic factors. Energy use in agriculture encouraged maximization of yields from limited available arable land, minimization of labour intensive operations and improving standard of living. Efficient and effective energy use in agriculture is one of the conditions for sustainable agricultural production, since it provides financial savings.

Introduction

India agriculture is now at turning point as we have travelled a long way after the advent of green revolution. Over the past four to five decades our strategies, policies and actions were guided by goals of ‘self-sufficiency’ in foodgrains production via green revolution. Indian agriculture has been successful in achieving increased food grains production albeit at a low level of satisfaction. While the mission of increasing foodgrains production stands somehow achieved, these gains were accompanied by widespread problems of resource degradation and high factor productivity, which now pose a serious challenge to the continued ability to meet the demand of an increasing population and lifting our people above the poverty line (Tan et al., 2010). Indian agriculture has reached a point where it must seek new directions – those by way of strategies, policies and actions which must be adopted to move forward addressing sustainable intensifications. The past strategies to increase food grains production, however, have resulted in massive exploitation of natural resources, contributing to unsustainable growth; there is need to change this approach in the future. This will call for strategies, which are different than the ones we adopted in the ‘green revolution’ era. High levels of fertilizer use and decreasing resource use-efficiency are increasingly contributing to groundwater pollution and increased emissions of green-house gases (GHGs) (Gupta, 2004). High level uses of pesticides in many areas have become a major health hazard. Thus, with continuously deteriorating resources, widespread problem of soil and water contamination and eroding ecological foundation, sustainability of agriculture is becoming highly questionable (Conway and Barbier, 1990). There is need to seriously debate on the strategies required to ensure that agriculture continues to play a critical role in the overall development.

Introduction

Conservation tillage is a model of sustainable agriculture as it leads to profitable food production while protecting and even restoring natural resources. Conservation agriculture benefits farmers because it reduces production costs and increases yields, but it also has positive impacts on the whole society: enhancement of food security thanks to a better soil fertility, improvement of water quality, reduction of erosion and mitigation of climate change by increasing carbon sequestration. Conservation agriculture (CA) systems are also less sensitive to extreme climatic events and therefore contribute to the adaption of climate change and the resilience of agricultural systems. Hence, CA becomes a fundamental element of sustainable production intensification, combining high production with the provision of environmental security.

CA is based on healthy functioning of the whole agro-ecosystem with a maximum attention and focus on the soil. The soil is the entry point and it has to be considered not only as simple physical support to roots and plants, but as a living entity with its physical, chemical and biological characteristics. The focus of CA embraces not only the nutrient contents of the soil but also its biological and structural status, which are determinants of sustained productivity.

The paradigm of CA is that an undisturbed soil has the opportunity to develop and produce healthier plants. Soil life can develop in a stable habitat in quantity and quality better than on tilled soils, the structural integrity of soil is maintained, so continuous vertical macro-pores are not destroyed and remain as drainage channels for rainwater into the soils. Seeding under conditions of minimum soil disturbance is achieved by direct seeding through the mulch cover without tillage.

Introduction

The main aim of conservation agriculture is to sustain and improve the crop productivity and to provide protection against biotic and abiotic stress, while at the same time protecting and enhancing the biological activities of the soil. The essential principles of conservation agriculture are no-tillage (and direct seeding) or reduced tillage, the maintenance of a cover of live or dead vegetative mulch on the soil surface and the wise use of crop rotations. The crop sequences are planned in such a way that which will discourage the buildup of pests or diseases and will help to optimize plant nutrient use by synergy between different crops of the rotation. While deciding the crop rotation, the locally important crops should be considered and there should be deep rooted and shallow rooted crops in the sequence so that the utilization of soil nutrients is maximized. At least one leguminous crop should be there in the crop sequence. The use of plant residues influences the soil physical, chemical and biological properties by reducing surface temperature, rate of evaporation and maintaining water content, nutrient load and rate of organic matter decay. The soils under conservation agriculture are happened to be highly active and diverse biologically and can supply plant nutrients for a longer period of time because of their higher nutrient loading capacities.

Soil biodiversity comprises of all organisms whether single-cell organisms or multi-cell animals or plants that live in the soil. Soil microbial diversity includes “genetic diversity, that is the amount and distribution of genetic information within microbial species, diversity of bacterial and fungal species in microbial communities, and ecological diversity, that is variation in community structure, complexity of interactions, number of trophic levels and number of guilds (Nannipieri et al., 2003).

Introduction

There is a widespread degradation of natural resource, e.g., soil erosion, nutrient loss, water-logging, salinity, alkalinity, acidity, decline in soil organic carbon (SOC) content, ground water depletion and micronutrient depletion. The major causes are washing away of topsoil and organic matter due to water erosion, intensive deep tillage and inversion tillage, dismally low levels of fertilizer application, mining and other commercial activities, faulty agricultural practices, no or low use of organics, indiscriminate use of herbicides, pesticides, fungicides etc. Other cause is loss of organic matter with higher temperatures, which increase rate of microbial decomposition of organic matter due to adverse effect of climate change. Climate change due to global warming as a result of increased concentration of GHGs in the atmosphere is a well-established fact. Impacts of climate change are experienced throughout the world. Increases in global mean temperature, rise in sea-level, and occurrence of extreme events are the consequences of climate change. These changes may deplete the SOC pool and soil structural stability, increase soil’s susceptibility to water runoff and erosion, disrupt cycles of water, carbon, nitrogen, phosphorus, sulphur and other elements, and cause adverse impacts on biomass productivity, biodiversity and the environment. Climate change is likely to have a variety of impacts on soil quality. In order to restore soil quality, enhance productivity, it is of utmost importance to focus on conservation agriculture practices on long-term basis. Conservation Agriculture (CA) is gaining importance as an alternative to conventional agriculture.

Introduction

Increase in population in our country with decrease in cultivable land is putting the challenges to the scientists and policy planners for increased food supply. There is very little scope for horizontal increase in cultivable land. Hence, the way to meet the need for providing food to ever increasing population is to increase the production of food per unit area of cultivable land.

Farmers, generally apply fertilizer to soil on blanket recommendation. Sometimes, the addition of nutrients is inconsistent. Sometimes, the application of fertilizer is much higher than the recommended dose. Imbalanced application of fertilizer to soil results in low nutrient use efficiency and low crop yield. There is need of site specific nutrient management for increased crop yield and for achieving higher nutrient use efficiency. Proper care should be taken for selection of fertilizer, method of application of fertilizer, rate of fertilizer application and also time of nutrient supply to the soil. Excess application of fertilizer has an adverse effect on soil health.

Traditional tillage may affect physico-chemical as well as biological properties of soil. Change in tillage practice from conventional tillage to conservation agriculture method may have an impact on soil properties and nutrient dynamics. Conservation agriculture affects soil health, proper fertilizer application, both rate and time, along with efficient use of soil moisture improves nutrient use efficiency. For obtaining a good crop yield nutrient should be available for plants in adequate quantity and in right proportion. Nutrients removed by the crop should be replenished by application of inorganic fertilizers alongwith incorporation of organic manures. Soil test is an important tool for determining the quantity of nutrients available in the soil. Based on soil test values and nutrient requirement of the crop rate of fertilizer to be applied in the soil for the plant is determined. Ample quantity of farm yard manure is not available nowadays. Hence, other organic manure such as town waste, green manure etc should be used.

Introduction

The green revolution is exemplified by too much adoption of high soil disturbance, modern varieties, energy exhaustive technologies, high amount of capital investment and simplification of farming systems (Meeus, 1993), resulting in uniform and featureless landscapes (Nassauer and Westmacott, 1987) in the most intensively farmed arable areas. In post-green revolution epoch, we had experienced a period of remarkable escalation in food productivity, despite rising land values and increasing land scarcity. Farmers from both developing and developed countries get exposed to several production constraints for achieving a sustainable, cost-effective and assured return from their field. Depending upon the circumstances and the scale of farm activities, farmers face varying degrees of climate risk, biotic invasion, and economic uncertainty. Thus, from the context of economical ambiguities, volatile food prices, social pressure to buffer ups and downs of agricultural production and achieving food security for ever growing population and curtailing poverty, farmers must be equipped with novel cultural practices to achieve a sustainable and assured cost-effective grain production. Research experiments throughout the globe found that the principal indicators for unsustainability of agricultural systems are: (1) intensive tillage induced decrement of soil organic matter (OM), structural degradation of soil, accelerated water and wind erosion, reduced water infiltration rates, surface sealing and crusting, soil compaction, (2) insufficient return of organic materials into soil, and (3) monocropping.

Introduction

Since the dawn of the civilization when mankind started agriculture, soil erosion has been the single largest environmental problem and has remained so till date (Sullivan, 2004). This is so because removal of the topsoil by any means has, through research and historical evidence, been severally shown to have many deleterious effects on the productive capacity of the soil as well as on ecological wellbeing. Doran and Parkin (1994) captioned the impact of soil erosion in their popular maxim that “the thin layer of soil covering the earth’s surface represents the difference between survival and extinction for most terrestrial life”. Soil degradation implies decline in its capacity to provide ecosystem services (ESs) of interest to humans and useful to nature’s functions. Principal processes of soil degradation are erosion, salinization, nutrient and carbon (C) depletion, drought, decline in soil structure, and tilth. Examples of ESs provided by soil include ecological/supporting (biomass production, nutrient cycling), regulating (water purification and flow, C sequestration, temperature fluctuations), provisional (food, fiber, fuel, and forages), and cultural (aesthetical, spiritual, and cultural). Erosion-induced degradation diminishes soil’s capacity to provide ESs, and support ecosystem functions.

Although fertile top soils could be lost when scraped by heavy machineries (Ngwu et al., 2005), the key avenues of topsoil loss include water erosion and wind erosion. Sometimes erosion can be such gradual for so long a time as to elude detection in one’s lifetime, thus making its adverse effects hard to detect. Eswaran et al., (2001) propose an annual loss of 75 billion tons of soil on a global basis which costs the world about US $400 billion per year. A review of the global agronomic impact of soil erosion identifies two severity groups of continents and reveals that Africa belongs to the more vulnerable group (Biggelaar et al., 2004). Soil erosion by water seems to be the greatest factor limiting soil productivity and impeding agricultural enterprise in the entire humid tropical region. This is evident in many regions of Africa (Dregne, 1990), mainly in the humid and subhumid zones of Sub-Saharan Africa (SSA) where population pressure and deforestation exacerbate the situation and the rains come as torrential downpours, with the annual soil loss put at over 50 t ha⁻¹ (FAO, 1995).