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Essay on Crop Ecology
Essay Contents:
- Essay on Micro-Climate at Plant Level
- Essay on Micro-Climate at Soil Level
- Essay on the Harvest Index
- Essay on the Sink-Source Ratio
- Essay on Ideotypes (Model Plants)
- Essay on the Agro-Climatic Regional Planning
- Essay on the Agro-Climatic Zones
The term ‘Ecology’ is derived from ‘Oikos’ meaning home. Crop ecology means the relationship of a crop or crop communities with its surroundings say environment. A local climatic condition that differs from surrounding areas because of differences in relief, exposure or cover is called Microclimate. From the agricultural point of view the microclimate is studied at two levels i.e. at plant level or at soil level.
Essay # 1. Micro-Climate at Plant Level:
The ecoclimate of the plant i.e. the climate just above and beneath the plant’s canopy, is different from the climate of the surrounding environment. The microclimate at the plant level i.e. the ecoclimate varies with the type of plants, morphological features of plant i.e. height, condensed canopy, shape and size of leaf and stem and soil colour. Soil colour modifies the microclimate by affecting the sunlight, temperature, humidity, CO2:O2 level, air velocity and organisms.
The plants having large morphological features reduce the air movement and the penetration of sun rays to the ground surface. Even emerging seedling alters the climate near the soil surface by reducing air movement and by shading the ground. In the vegetation covered areas, the extreme variations in the temperatures of the soil surface are reduced and the eco- climate of the plant is more humid and cooler than the surroundings which favours the spread of insect pest and diseases.
The plant canopy changes the intensity and quality of light when the light rays pass through it. In the day time when sunrays directly fall on the leaves, the leaf temperature may be higher than the air temperature and at night may be lower than air temperature.
Essay # 2. Micro-Climate at Soil Level:
Soil colour is one of the factors which affect microclimate. Due to soil colour, part of incoming radiations are reflected. The percentage of the incoming radiations that is reflected, is called Albedo. Albedo varies according to soil type, plant cover, moisture content of soil, soil organic matters, etc.
Due to differences in albedo of the soil surfaces, different thermal regimes are set up even when incoming radiations are identical. For example, a mulch on the soil surface becomes very hot by absorbing most of the incoming radiations and keeps the soil cool during day time and vice – versa during night hours.
Wet soil absorbs more incoming radiations than dry soil. Most of the absorbed energy is used to evaporate the soil water due to which moist soil takes longer time to heat up or to cool down.
The heat gain or heat loss by the soil is five times quicker than by the water because the specific gravity of the soil is 0.2 and the sp.gr.of the water is 1.0.High soil temperature restricts the root growth. In the arid region warm (20°c-30°c) moist soil is the favourable medium for most of the cultivated crops.
Essay # 3. Harvest
Index:
The effectiveness of photosynthesis depends on:
(i) A large and efficient assimilating area.
(ii) An adequate supply of solar energy and CO2
(iii) Favourable environmental conditions.
The total product of photosynthesis throughout the lifetime of the crop growing in the given circumstances depends upon the following factors:
(a) The size of the assimilating area.
(b) The efficiency of assimilation and CO2 fixation.
(c) The period of efficient assimilation and CO2 fixation.
In the Agronomy, the efficient utilisation of assimilation and C02 fixation i.e. photosynthesis is expressed in terms of Harvest Index .H.I. is also called ‘Coefficient of Effectiveness.’
Grain yield can be calculated by the formula:
Y = a x b x c x d
Where,
y → grain yield per unit area.
a → no. of plants per unit area.
b → no. of fertile tillers per plant.
c → no. of grains per ear.
d → weight of the individual grain.
In wheat, barley and similar cereals, the photosynthetic activity of the ear, which is situated at the top of the stalk, makes a considerable contribution to grain formation. Practically all the dry matter of the grain is produced by the part of the shoot above the flag leaf node. Of this dry matter, the ear contribute about 50% in wheat and upto 70% in barley.
Essay # 4. Sink-Source
Ratio:
Source:
Such part of the plant where photosynthesis occurs; generally leaves are the source.
Sink:
Where photosynthates accumulate, is called sink. Generally grain is the sink but stem (e.g. potato), root (e.g. Sugarbeet) or leaf (e.g. Palak) may be the sink. For higher HI, development of sink is the most concerned.
But the development of sink depends on three factors:
(a) Good Source
(b) Partitioning of Photosynthates, and
(c) Translocation of Assimilates
In spite of good source if partitioning of photosynthates is not well developed, sink will be poorly formed and thus is the lower H.I.
Therefore for higher sink-source ratio, the followings are necessary:
(i) Source should be good.
(ii) Partitioning of source i.e. photosynthates should be well developed.
(iii) Translocation of photosynthates must be good.
(iv) And lastly photosynthates do accumulate as sink.
The formation of sink from source is a reversible process but source to sink is more pronounced.
With the appearance of inflorescence, competition for assimilates between the leaves and the inflorescence takes place. When the seed formation starts, most of the assimilates move to the grain. This internal competition is more severe as competition between plants increases i.e. plant population pressure, which is illustrated by the figure.
Essay # 5. Ideotypes (Model Plants):
The production of the every plant is affected by the plant’s type, climatic condition, soil type and management factors. According to Army and Greiver (1967), the production of the plant might be increased by changing plant’s type and increasing the period of grain- filling in a certain climatic condition where management and soil factors are not limiting.
There is a direct relationship between the plant’s type and the crop production because the orientation and number of leaves play the important role in the CO2 assimilation (Photosynthesis).
The concept of ldeotype was given by Donald in 1968. He illustrated that there should be minimum competition between the crops and the crop must be competent one to compete with weeds. The single plant would give the better result in a group when the crop has at least competition with the same type of the crop.
Ideotype is the model plant which may be defined as “a biological model which is expected to perform or behave in a predictable manner within a defined environment”. On the basis of environment Donald & Hamblin (1976) identified two forms of ideotypes i.e. isolation ideotypes and competition ideotypes. Competition ideotypes are suitable for mixed cultivation.
Ideotypes for Some Crops:
I. Wheat:
According to Donald (1968), the ideotype for wheat or the similar crop has following features:
(i) To avoid lodging, there should be short strong stem.
(ii) Few small erect leaves to allow the sunshine into its canopy.
(iii) A large erect ear.
(iv) The no. of fertile florets per unit area should be more so that HI is more.
(v) There should be awns to increase the photosynthetic area.
(vi) A single culm to avoid wasteful vegetative growth.
(vii)Resistant to insect pests & diseases.
(viii) There must be proper partitioning and translocation of assimilates.
II. Maize:
The plants have erect upper leaves and the lower leaves gradually become horizontal to allow the sunshine into its canopy and for proper movement of air into the field. The height of the plant is to be 1.5 metre in which 2-3 cobs may be produced on the nodes near the tassel.
III. Gram:
Pande and Suxena (1973) proposed the ideotypes for gram having following features:
(i) The vegetative growth must be stopped before the starting of reproductive stage.
(ii) The plant is to have erect branching. In the prevalent varieties of gram, the spreading and branching of its canopy is just like umbrella which interferes to penetrate the sunshine into its canopy causing humid conditions favourable for insect pests & diseases.
(iii) To harness the long photoperiod and favourable temperature at the time of flowering, there should be 2-3 longer pods in the leaf axis and 2-3 seeds in each pod.
IV. Arhar:
The growth of Arhar varieties in the beginning is too less i.e. in the first two months only one or two branches are come out. Therefore Arhar is unable to harness the solar energy properly in the first two months. The flower’s drop is also a major problem. The filling of pods according to Hydro-dynamic model sets up the competition between vegetative and reproductive phases.
Considering all the views Pande & Suxena suggested ideotypes having following features:
(i) The fast growth of plant’s canopy at least in the beginning.
(ii) The reproductive phase starts after the closure of vegetative growth.
(iii) Long floral axis having 2-3 flowers in each trifoliate axis.
(iv) Synchronised flowering i.e. all the flowers come out at the same time.
(v) Active root nodules for the long time.
(vi) Resistant to insect pests & diseases.
V. Rainfed Upland Rice:
(i) Short growth duration (85-100 days)
(ii) Effective deep root system.
(iii) Dwarf (less than 100cm) plant having erect leaves and thick stem.
(iv) Early strong fertile tillering.
(v) Synchronised flowering.
(vi) Good number of panicles at higher density about 400 panicles per square metre.
(vii) Highest number of grains per panicle.
(viii) Moderate seed dormancy.
(ix) Resistant to insect pests & diseases e.g. resistant to Helminthosporium sp.
An ideotype of rainfed wheat was conceived and proposed by Dr. Asana-
(i) Large no. of spikelets,
(ii) Large peduncle,
(iii) Strong and deep root system,
(iv) Flat leaves parallel to soil and
(v) A grain development period coinciding with mean max. temp., of 25°C.
Ideotypes for Dryland Farming:
(i) Short growth duration.
(ii) Effective root system.
(iii) Drought tolerance.
(iv) High yield potentiality with altered morphology viz.:
(a) Plant with few leaves just sufficient to maintain photosynthetic output and growth (to minimise the use of water).
(b) Leaves horizontally disposed for better light interception contrary to vertically disposed most effective under irrigated conditions.
Essay # 6. Agro-Climatic Regional Planning:
Agro – climatic Regional Planning in India was initiated in 1988 by the planning commission. It means under the seventh five year plan; Regional planning was come into force on the basis of agro- climatic factors for balanced regional growth .The agro-climatic factors are Rainfall, temperature, soil, topography , cropping and farming system and water resources.
Essay # 7. Agro-Climatic Zones:
Agro- climatic zone is a land unit is terms of major climates suitable for a certain range of crops and cultivars (FAO, 1983).
On the basis of criteria of homogeneity in agro- characteristics such as water surplus and water deficit, India was divided into 11 agro-climatic zones.
Later on, India was divided into 15 agro- climatic zones on the basis of water surplus, water deficit and cropping system.
An ecological region is an area of the earth’s surface characterised by distinct ecological responses to macro – climates expressed by soils, vegetation fauna and aquatic systems.
Agro- ecological region is the land unit cut out of agro climatic region when superimposed on land form and the kind of soils and soil conditions that act as modifiers to climate and length of growing period.
The classification is on the basis of:
(i) Growth period
(ii) Rainfall/potential evapotranspiration
(iii) Soil
(iv) Districts.
There are two components of ecological zones:
(i) Biotic factors viz. Fauna and Flora.
(ii) Abiotic factors viz. water, minerals, light etc.
At present India has been divided into 21 agro ecological zones.