I. Topic

This lecture deals with crop characteristics and how these characteristics shape a cropping systems.

II. Learning Objectives

• Understand that only a few cultivated crops make up the most of food production.
• Learn the specific characteristics that crop plants are selected for.
• Relate these crop characteristics to cropping systems.
• Understand the effect of crops on succeeding crops.
• Learn the basic types of cropping systems.

Only a few hundred plant species have become cultivated crops.  Thirty-two contribute one million or more tons to world food supply, and wheat, rice, corn, and potatoes produce more tonnage than the total of the other 28 combined.

Crops are selected for high yield, desired quality, resistance to insects and disease and dependable economic returns.  Primary considerations on selection of crops for cropping systems are growing period, photoperiodism, and rooting type.  Another important consideration is the influence of a crop on succeeding crops.  These effects can be insect and disease buildup, nutrient depletion, moisture depletion, possible beneficial effects and alleochemics.

A cropping system can be a formal sequence of crops (rotation), a flexible arrangement of crops from year to year, or intensive successions of crops within single years or even within seasons.  Planning a cropping system involves an assessment of climate, soil, and water resources.

IV. Lecture

Introduction

1. Only a few hundred plant species have become important cultivated crops.

2. We now depend on relatively few.

3. 32 crops contribute 1 million or more tons to annual total world food.

4. Wheat, rice, corn, and potatoes contribute more tonnage than total of other 28 combined.

5. Large group of forage crops are important in farming systems and contribute food through indirect route of feed for animals.

6. Only 200 years ago, tomato was ornamental and considered poisonous.

7. Plant breeding and selection have modified growth and quality characteristics of crops and their adaptation.

8. Crops are selected for:

• High yielding capabilities
• Desired quality traits
• Resistance to insects and disease
• Dependable economic returns.

• Do not obtain high levels of productivity
• More concerned with subsistence than with producing for market

1. Primary goal in crop production system is to produce high yields of desired quality product at minimum costs (per unit).

2. In developed countries labor has become one of major costs.

3. High yields have become necessary to minimize the cost/unit of production.

• Crops are selected to make full use of yield-promoting inputs

5. In developed countries - yield of marketable crop (high harvest index) sought

6. Developing countries where livestock depend on straw or stover for feed, lower harvest index acceptable (often desired).

7. Growing period:

• Number of days required between date of plant emergence and maturity
• Potential yields of annual crops not necessarily related to length of growing period
• The effect of temperature on plant development expressed in heat units

• Length of day for initiation of certain stages of development.  E.g. flowering, tillering, or dormancy
• For many plants, length of night rather than daylight is critical
• Some plants are day neutral
• Breeding and selection programs have resulted in cultivars of many major crops that are largely day-neutral
• Sought because it adapts crop to a relatively large range of latitude
• Daylength 12 hours throughout year in tropical zone
• Only 12 hours at vernal/autumnal equinoxes in temperate zone
• When crop varieties are planted outside their zone of daylight adaptation, they are usually too early or too late in stages of development for best performance
• Growth habits are important
• Dwarf varieties - easier to harvest, can use machine, reduced lodging, earlier fruiting, higher harvest index
• Determinant vs. Indeterminate growth

• Two different types
• Fibrous - permeate soil intensively, hold particles together
• Tap root - tend to be deep rooted
• Major root volume in upper 30 cm of soil
• Root hairs major surface for water and nutrient adsorption
• Depth of rooting influenced by
• Soil moisture
• Compaction
• Texture
• Aeration
• Available nutrients

1. When same crop or different crops are grown in sequence on same area of land, situations may develop that benefit or harm succeeding crops.

• Buildup of harmful insects or disease organisms
• Nematodes in sugar beets - rotation of nematode-resistant crops, cereals, alfalfa, potatoes, corn best
• Best controlled by rotation with nonsusceptible crops

• 1l,000 kg/hectare corn crop removes 250 kg of N, 50 kg of P205 and 225 kg of K2O/hectare
• Match fertilizer program to each crop or sequence of crops.  E.g. wheat following well fertilized corn.

• Some plants use up so much soil moisture that provision must be made to replenish moisture for ensuing crops. E.g. sorghum with dense root system can extract moisture to low levels
• Moisture status of soil must be given before planting the succeeding crop

• Use of legumes in crop sequence and associated effect of N fixation, e.g. alfalfa can fix 200 kg of N/ha/year
• Annual legumes (soybeans) poor N fixers, only limited residue
• Green manure crops are questionable economically if harvested crop displaced e.g. - way to solve - Australian-clover alternate with wheat, N helps wheat, clover forage for livestock

• Chemicals released from plants that effect growth, health, etc. of other plants or microorganisms
• Released by root exudates, washed from leaves, produced from residues
• Oat release scopoletin - inhibit germination of oats, peas, and other plants
• Juglone from walnuts injure many plants

1. Crop production systems include both cropping systems and the associated crop production practices and technologies used to achieve the harvested yield of crops.

2. Can be formal sequences of crops - rotation.

3. Can be flexible arrangements of crops that change from year to year.

4. Intensive successions of crops within single years or even within seasons.

5. To consider in developing a cropping system:

• Cropping systems should be devised to provide growing crops with high photosynthetic capabilities for as great as portion of the year as practical
• A major goal should be to maximize annual crop production or net economic grains per unit of land area
• In order to promote sustained high yields and profit, cropping systems should:
• Maintain soil O. M. and tilth
• Reduce weeds, insects and disease
• Keep plant nutrients in balance
• Conserve water
• Minimize soil erosion
• Roots should form active and extensive network
• One crop may root deeper than another and be used to good advantage

1. Relative merits of two systems:

 Rotations

1. Deep rooted legumes may be grown periodically over all fields.

2. There is more continuous vegetative cover with less erosion and water loss.

3. Tilth of soil may be superior.

4. Crops vary in feeding range of roots and nutrient requirements: deep vs. Shallow, strong vs. weak feeder; nitrogen fixer vs. nonlegume.

5. Disease control is favored, changing crop residues fosters competition among soil organisms and may help reduce pathogens.

6. Weed and insect control favored.

7. Broader distribution of labor and diversification of income are affected.

 Continuous Cropping or Monoculture

1. Profits may be greater.

2. A soil may be especially adapted t one crop, e.g. corn.

3. The climate may favor one crop; corn instead of oats in corn belt.

4. Machinery and building costs are often lower.

5. The grower may prefer a single crop and become a specialist.  Few can become well enough informed to do an expert job of growing a large number of crops and also produce livestock.

6. Balanced crop rotations include a legume or sod crop to improve the N and O. M. and tilth of the soil, a cultivated crop to aid in weed control, and a close growing cereal crop.

 7. Crop sequence in rotation may be arranged in descending order or lime or fertilizer nutrient requirements to obtain maximum benefits from soil treatments.

Multiple Cropping

1. The production and harvesting of two or more crops from the same area of land in one year.

• Is most practical in warm temperate subtropical and tropical climatic zones (IV and V)

3. Soil preparation and planting of a second crop is hastened where appropriate technology is available.

• No-till or limited till procedures
• Herbicide treatment for weeds
• Disc used to cut up crop residue before planting

1. Is the interplanting of a second crop before the harvest of a maturing crop.

2. With development of high-yielding short-season varieties, there has been renewed interest in relay cropping.

3. Planting 1 to 3 weeks before harvest reduces the risk of failure in establishing a second crop.

4. Timing of the planting of the relay crop and of the harvest of the first crop is essential.

5. Examples of relay crops:

• Sorghum planted in early monsoon stages in semi-arid tropics and interplanted with pigeon peas
• Soybeans grown between young rubber trees

1. Involves two or more crops growing simultaneously in rows in a definite pattern.

2. In disaster (drought-insects) chances for success with mixed or intercrop systems may be increased.

3. Total yields can be increased by growing alternate or pairs of alternate rows of two different crops in place of solid plantings of either crop alone.

4. A fast-growing, early maturing crop may fit well with one that grows slowly.

Ratoon Cropping

1. Some crops have capacity to send up new shoots from the base after a crop is harvested:

• Sugar cane
• Some pearl millet
• Some sorghum
• Rice
• Cotton
• Pineapple

Shifting Cultivation Systems

1. Apply to ag systems that involve clearing forest or brush, burning the residues and then growing a crop for a few years, after which land allowed to revert back to natural vegetation.

2. Cropping 1-4 years, fallow period 4-20 years.

Planning Cropping Systems

1. Planning of cropping systems involves first an assessment of climate, soil and water resources.

• Temperature
• Length of growing season limits the potential for producing one or more crops
• A growing season of 180-200 days is commonly required to produce more than one major crop
• In areas with mild winters, a hardy legume or cereal grain crop can be grown during the winter and harvested in time to produce a second crop during the regular growing season
• Average daily temperature and range of temperature between night and day also limits suitability of specific crops
• Potatoes - mean temperature 21 degrees C
• Corn - mean temperature 22-26 degrees C
• Sorghum - stands temperatures to 30 degrees C
 
• Moisture
• Occurrence of drought is critical to crop growth
• Seedbed preparation, planting, and harvesting should take advantage of high probability of favorable moisture
• Crops vary in ability to withstand drought
• Rice/high rainfall - corn/less.  Rainfall - sorghum/arid zones - millet/displaces sorghum
• Reluctance to adopt the most suitable crop because of tradition and personal preferences
• Irrigation increases the available alternatives for crop selection and cropping patterns
 
• Soils
• Cropping systems planned to conform with special soil properties
• Sequences of crops can be arranged in order of increasing tolerance to acidity or aluminum
• Soils that hold good quantities of available water in the root zone help crops avoid or endure periods of drought
• A combination of crops grown in any one season should be selected to:
• Minimize peaks in labor requirements
• Minimize peak periods for use of power machinery
• Minimize demands for highly specialized or little used expensive equipment
• Provide a reliable source of income at a moderately uniform level
• Minimize buildup of insects or disease
• Protect soil against deterioration - erosion, water logging, salinity
• Where irrigation is practiced, peaks in water requirement should be minimized

The primary goal in crop production systems in developed countries is to produce high yields of desired quality product at minimum costs (per unit).  Labor has become ne of the major costs of food production.  High yields have become necessary to minimize the cost/unit of production.  In developed countries, yield of marketable crop (high harvest index) is sought.

 In developing countries, compromises in selection of crop types and of technologies are necessary.  In older security-oriented systems, crops are commonly grown in mixtures.  These crops do not obtain high levels of productivity.  Farmers are more concerned with subsistence  than with producing for the market.  In developing countries where livestock depend on straw or stover for feed, a lower harvest index is acceptable (often desired).

These differences in goals make for the wide diversity of cropping systems around the world.

VI. Self Assessment
 

• How many important cultivated crops are there?  Which four produce the most tonnage?  How does this compare to other important crops worldwide?

• What characteristics are crops selected for?  Describe how several of the characteristics influence cropping system development.

• Are the primary goals for crop production the same in developed and developing countries?  If not, how are they different?  Why?

• List several of the effects crops have on succeeding crops.  Explain the positive or negative effects of each.

• What is a cropping system?  What is the difference between a crop rotation and monoculture?  What are the advantages of each?

• List several types of cropping systems.  Give examples of crops in the system.  What are advantages/benefits of each one?