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There are some weeds which prefer to in crop field and some of them have a distinct association with some crops.

Crop: Plants grown in association, sown (or planted) and also harvested by human being, are collectively known as crop.
Crop plants have some economic values and there is an interaction or competition among the plants.

Comparison of different cropping systems with reference to land use and yield advantages is possible through various efficiency indices. The various cropping and farming systems practiced in an area have to be properly evaluated to decide their suitability and relative advantages. The comparisons can be made with reference to many factors viz., yield, monetary, water use efficiency, nutrient use efficiency, total dry matter production, intensity of land use etc., The cropping as well as farming systems research are being perused at national level with major focus for identification of location specific efficient systems since 1990. However, on perusal of research publications we find that the data of cropping systems are interpreted in different ways with major focus only on production and net return on hectare basis. In fact, these two aspects are not the indicator of the efficiency of a particular system. Many advances have been made in recent years to identify the efficient system for a particular location. Some of the methodologies, which are of concern to crop scientists in general and agronomists in particular, are highlighted here for ready reference to the researchers, agronomists and crop planners. Different indicators of system efficiency are as follows (Gangwar et al., 2003).

What is Crop?
Crop refers to plants sown and harvested by man for economic purposes. 
Cropping Seasons: There are three main seasons and two sub seasons.
1. Rainy or Kharif Season – Main characteristics of the Kharif season are 
    ·    It starts from June and spreads to September.
    ·    There is high temperature and high humidity.
    ·    More than 2/3^rd of annual rainfall is received in a year.
    ·    In the beginning, days are longer than nights while days and nights are equal when season ends. 
    ·    Important crops grown are maize, rice, sorghum, Moong, Urd, groundnut, cowpea, soybean etc. 

1.1. Cropping pattern

Yearly sequence and spatial arrangement of crops or crops and fallow on a given area.

1.2. Cropping seasons in India

1.2.1. Kharif season: Southwest monsoon

Crops - Rice, cotton, jute, jowar (sorghum), bajra (pearl millet) and redgram (Pigeon pea).

Terms associated with cropping and farming systems are:

1. Cropping system: is an important component of a farming system. It represents cropping pattern used on a farm and their interaction with farm resources, other farm enterprises and available technology which determine their makeup.
2. Cropping pattern: means the proportion of area under various crops at a point of time in a unit area. It indicates the yearly sequence and spatial arrangement of crops and fallow in an area.
3. Cropping scheme is a plan according to which crops are grown on individual plot of a farm during a given period of time with the object of obtaining maximum return from each crop without impairing soil fertility. Thus a cropping scheme is related to the most profitable use of resources, land, labour, capital, and management.
4. Multiple cropping: Growing two or more crops on the same piece of land in one calendar year is known as multiple cropping. It is intensification of cropping in space and time dimensions. It includes intercropping, mixed cropping and sequence cropping.
5. Quadruple cropping: Growing of four crops in a year in sequence.
6. Competition effect: Competition of intercropped spp. For light, nutrients, water, carbon dioxide, and other growth factors.
7. Complementary effect: Effect of one component on another which enhances growth and productivity.

In agriculture, the ideal management practices were developed for individual crops through regular research and feedback received from the farmers. However, farmers are growing various crops in different seasons based on their adaptability to a particular season.

System is a set of principles or procedures according to which management is done; it is an organized scheme or method. A system is a group of interrelated or interacting elements (crops or livestock) that act according to a set of rules to form a unified whole.

5.1 Introduction

Rainfed agriculture accounts for about 60-95% of farmed land in major areas of the world covering Saharan Africa, Latin America, North Africa and East Asia and South Asia. Agriculture in about 60 percent of 142 m ha of net cultivated area in India is rainfed without access to any source of irrigation. Rainfed agriculture is mostly practiced in arid, semi-arid and sub-humid regions where the rainfall is low in quantity, erratic in distribution and is also characterized by high inter-year variability. Together with poor and degraded soils, this limits the length of growing season as well as the choice of crops that can be grown sustainably. Coarse cereals, pulses, oilseeds and cotton dominate the cropping pattern in the regions where rainfed agriculture is concentrated. More importantly, these rainfed regions provide a livelihood to a majority of the rural poor, and as a result they are often described as concentrations of mass poverty and hotspots for civic strife. The productivity of crops grown in rainfed areas is considerably lower than its potential and much lower than that of irrigated crops. Enhancing the productivity of rainfed crops is therefore important from the viewpoints of growth, equity and sustainability.

Cropping systems are designed to mimic nature and bring diversity into our farming system. The cropping system should provide enough food for the family, fodder for cattle and generate sufficient cash income for domestic and cultivation expenses.

The objective of any cropping system is efficient utilization of all resources viz., land, water and solar radiation, maintaining stability in production and obtaining higher net returns. The efficiency is measured by the quantity of produce obtained per unit resource used in a given time. The objective of traditional agriculture was to increase the production by two means:

a) By increasing area under cultivation.

b) By increasing the productivity per unit area of the crop.

The types of crops and the practices used to grow them and the sequence in which they are grown altogether refers to cropping system. It comprises of all components required for the crop production and their relationships with the environment. Traditionally the cropping systems aim at maximizing the per unit area productivity, which can be done by growing improved high yielding varieties, by adequate and scientific crop management practices and by increasing cropping intensities with the help of different cropping patterns.

In today’s world cropping system should produce more, at the same time the practices should be ecologically and environmentally sustainable. There should be efficient utilization of land and water. It should be designed to conserve soil, soil moisture and improve soil resilience.

A cropping system refers to the type and sequence of crops grown and practices used for growing them. It is based on the available technologies of crop production. Cropping systems have been traditionally structured to maximize crop yields. Now, there is a strong need to design cropping systems, which take into consideration the emerging social, economic and ecological or environmental concerns for each ecosystem. The goal of a cropping system must be to conserve natural resources i.e. soil, water and sustain crop production. Conserving soil and water and maintaining longterm soil productivity depend largely on the management of cropping systems, which influence the magnitude of soil erosion and soil organic matter dynamics. Crop diversification is an important option in sustainable agricultural systems. Management of cropping systems implies management of tillage, crop residue, nutrients, pests, and practices for soil conservation. Difference between dry land and rainfed farming is as follows.

Growing more than one crop in sequence or simultaneously as a mixed crop is an ancient practice. In Indian Vedas, there is a mention about double cropping. In early periods, the objective to adopt sequential cropping practices was to reduce the risk of total crop failure due to uncertain monsoon and to have a variety of produce to meet food requirement of farmer’s family, fodder to animals and to meet his cash requirements. Other benefits of yield increase was due to complementary effects of the component crops in improving the soil fertility, spreading the labour requirement throughout over a period of time and to reduce damage caused by weeds, pests and diseases were only incidental.

Multiple cropping in simple terms refers to the practices that increase production in a unit area of land through two or more growing crops simultaneously. The importance of intensive cropping in sustainable agriculture has been well understood by the agricultural scientists of late and there has been surge of interest in the research community to explore these complex systems in detail and to see what can be learnt from the farmers in our quest to make cropping system more sustainable progress made in the past through intensive research carried by the various agricultural universities, ICAR, research institutes/ coordinated research projects and international research institutes such as IRRI, ICRISAT, IITA and CIMMYT, it has shown that and more efficient utilization of the natural resources is possible by suitably modifying the present cropping systems in the various regions of the world.

The present cropping intensity in India is 136 per cent. There is a great prospect for increasing the cropping intensity both in irrigated and rainfed areas. In many irrigated areas, cropping intensity can be increased to 200-300 per cent. There is good scope to increase cropping intensity to 180-200 per cent with proper policies and technology options in rainfed conditions also.

A system is a set of components that are interrelated and interact among themselves. A system may be natural, social or artificial. Natural systems consist
of all the materials both physical and biological and are independent of human beings. Our role in relation to natural systems is to try to understand these
systems and make use of them as per our needs. 

15.1 INTRODUCTION

Cropping system is defined as a cropping pattern followed on a farm and its interaction with farm resources, other farm enterprises and production technology. In other words, cropping system refers to a combination of crops in time and space. When annual crops are considered, a cropping system usually means the combination of crops within a given year (Willey et al., 1989). This cropping system might provide insurance against crop failure by reducing disease (Fininsa and Yuen, 2002) and insect incidence (Gahukar, 1989) or against unstable market prices by planting two or more crops under intercropping and thus, reducing the risk of unexpected changeable prices. Intercropping in scientific way should be viewed from a theme of competition to one of collaboration with mutually beneficial relation with proper planning to get more return from limited natural resources. Legumes have been the common intercrops in any intercropping system owing to their short duration, N-fixing ability etc. Even though non-leguminous vegetables require longer duration than legumes and are non-N-fixers, they can also be suitable as intercrops because of their high profitability and higher yields.

In general crop is an organism grown or harvested for obtaining yield. Agronomically crop is a plants cultivated for economic purpose.

Classification of Crops

Classification is done to generalize similar crop plants as a class for attaining better understanding of them. Field crops are classified in the following ways.

1. According to range of cultivation
2. According to the place of origin
3. Botanical classification
4. Commercial classification
5. Economic / Agricultural / Agrarian classification
6. Seasonal classification
7. Classification based on ontogeny

The occurrence of periods of water deficit for crop production, referred to as climatic drought, is commonly observed and leads to low water availability for crops. Besides climatic drought, crop water stress may also result from low levels of plant available water in the soil profile due either to the existence of physical barriers to water infiltration (e.g., surface sealing) or to soil chemical or physical limitations to plant root growth and root water uptake. Drought resulting from such factors will be referred to as edaphic drought since it is caused by soil specific conditions rather than by limited rainwater supply, and can occur even under conditions of sufficient and well-distributed rainfall. Finally, even where water is very scarce, particularly in the driest areas, a surprisingly small proportion of the available water is actually transpired by the crop. Non-productive losses include surface runoff, deep drainage, evaporation from the soil surface and deep cracks, and transpiration by weeds. Dry land farming is a system of crop cultivation depending on rainfall as the only source of moisture and the technologies refers to the cropping pattern/ rotation and agronomic practices adjusted and adopted in accordance with the moisture regime. The crops selected should have short duration, deep root system, erect leaves, moderate tillering and photosynthetically efficient.

Rainfed farming has a distinct place in the Indian agriculture, occupying 67 % of cultivated area contributing 44 % of food grains to our national food basket, supporting 40% of human and 65% of livestock population. The system is characterized by resource poor farmers, poor infrastructure and low investment in technology inputs. Even when full irrigation potential of the country is realized, 50% of the net sown area is continued to be rainfed. The important problems encountered in rainfed areas are unfavorable weather, limited choice of crops and varieties, low cropping intensity and unstable productivity. The research work done by the net work of AICRPDA (All India Co-ordinate Research Project for Dryland areas) centres and SAUs (State Agricultutal Universities) indicated that the production in rainfed environment could be enhanced by 200 % compared to the productivity of farmers’ field by adopting improved cropping systems and agro techniques.