maximum potential productivity – its apparent limitations

7/29/2019 Maximum Potential Productivity – its apparent limitations

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Plant and environmental

factors, yield, plant

distribution, strategies for

maximizing solar energy

utilization

Dr G.L.Sharma



Crop productivity or yield is a function of

environmental, plant, management, and social-

economical factors and their interaction.

Mathematically, crop yield can be expressed by

the following equation:

Y = f (E, P, M, S)

Where Y=yield, E=environment, P=plant,

M=management, and S=social-economical.

Figure 1 shows factors affecting crop Yield.



Fig.1 Factors affecting crop yield



Technological factors

In the past decade yields of important field

crops have been improved through the use of

improved cultivars, fertilizers, irrigation,

fungicides, insecticides, and herbicides and

improved cultural practices. All these can be

classified as technological factors.



1. ENVIRONMENTAL FACTORS

1.1 Climatic

1.1.2 Temperature

1.1.2. Moisture Supply

1.1.3. Solar Radiation

From an agricultural point of view, there are twomain types of climates: tropical and temperate. It

is generally assumed that temperate climatemeans cold weather and tropical climate, hot weather.



1.1.2 Temperature

Soil and air temperatures are important and

often critical environmental factors for plant

growth and productivity.

The optimum temperature for maximum

production of root material for several species

ranges from 20 to 30°C.



Fig. 2 Relationship between

temperature and photosynthesis in

C3 and C4 plants.



Crop yield can be reduced at both very low and very

high levels of moisture. Excess moisture reduces soil

aeration and thus the supply of O2 available to roots. With poor aeration, activities of beneficial micro-

organisms and water and nutrient uptake by plants are

seriously inhibited. There may be exceptions with

aquatic plants such as flooded rice. Severe drought can

cause stomata in the leaf to close, reducing

photosynthesis. Moisture stress causes reductions in

both cell division and cell elongation and, hence, ingrowth.



The supply of water (W), as expressed by the

hydrological budget, is equal to precipitation (P) plus

irrigation (I) and the change in storage (S), less runoff (R) and Drainage (D):

W = P + I + S -R - D

Plants vary widely in efficiency of water use. The ratioof dry matter production to the amount of water

transpired by a crop is known as water use efficiency.

Generally, C4 plants are about twice as efficient as C3

plants in utilizing water.



Solar radiation affects photosynthesis and consequently crop productivity.

At the upper boundary of the atmosphere, and at theearth’s mean distance from the sun, the total irradiance

is 1360 J rn-2 s-1, which includes ultraviolet and infrared wavelengths. Approximately 900 J m-2 s-1 reaches plants,

depending on latitude, time of day, elevation, and otherfactors. About half of the radiation is in the infraredregion of the light spectrum, roughly 5% is in theultraviolet, and the rest, approximately 400 J m-2 s-1 is at

wavelengths between 400 and 700 nm, which arecapable of causing photosynthesis. This is calledphotosynthetically active radiation.



Appreciable variation in maximum photosynthetic rateoccurs between varieties and even between individualgenotypes and is often associated with differences in

the leaf mesophyll structure or in the activity of thecarboxylating enzymes. In the subtropical plant speciessuch as corn and sugarcane, photosynthetic ratescontinue to increase in response to light intensities up

to more than 60,000 lux, with maximum values of over70 mg CO2 dm-2 h-1, equivalent to conversion rates of 5to 6% of these high light intensities. For most tropicalgrasses, the production of 1 gram of dry matter

corresponds to the fixation of about 4130 to 5020 calof chemically bound energy, and for most temperategrasses it corresponds to 4250 cal.



1.2. Soil

1.2. 1. Physical Properties

1.2.1.1 Texture

1.2.1.2 Structure 1. 2. 1.3 Consistency

1. 2. 1.4 Pore Space and Density

1.2.1.5 Tilth



1.2.1.6 Strategies To Improve Soil Physical Properties

1.2.1.6a. Maintenance of Organic Matter

1. 2.1.6b Conservation Tillage

1. 2.1.6c Organic Farming



1.2.2 Chemical Properties

Soil Chemical properties such as nutrient

deficiencies and toxicities, cation exchange

capacity, oxidation-reduction, and salinity are the

important properties determining growth andproduction of crops. These soil properties can

be modified through management practices for

higher crop production.



1.2.3 Biotic

Biotic factors which affect crop production are related to soilmicroorganisms such as bacteria, actinomycetes, fungi, and

nematodes. From the point of view of their relationships with

plants, microorganisms can be classified into three groups: (1)

saprophytes , usually opportunists, but benefactors in somesituations (2) parasitic symbionts or pathogens , potentially harmful

to the plant; and (3) mutualistic symbionts , usually called symbionts

1. 2. 3. 1. Symbiotic Nitrogen Fixation

1. 2.3.2. Mycorrhizae

2 PLANT



2. PLANT

2.1. Genetic Variability2.2. C3 and C4 Plants

2.3. Photosynthetic Efficiency

2.4. Plant Architecture

2.5. Harvest index

2.6. Plant Density



3. SOCIAL-ECONOMICAL

3.1. Marketing

3.2. Price

3.3. Extension Service

3.4. Availability of Credit

maximum potential productivity – its apparent limitations

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