Crop Nutrients: Agricultural Science Lesson Note

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Lesson Note

Subject: Agricultural Science
Topic: Crop Nutrients
Lesson Objectives: At the end of the lesson, learners should be able to:

Give the meaning of crop nutrients,
Identify destroyers of crop nutrients,
State ways of conserving crop nutrients.

Lesson Discussions

CROP NUTRIENTS
Nutrients in crops are whatever that serve as nourishment which could be obtained from crops. The nutrients are carbohydrates, proteins, fats and oils, vitamins, minerals and water. Varied nutrients are found in different crops. The tuber crops and cereals are very rich in carbohydrates and pulses have high content of proteins. Fats and oils are mostly found in oil palm, coconut palm, melon, groundnut and Shea butter. Fruits and vegetable crops are significantly endowed with vitamins and minerals.

DESTROYERS OF CROP NUTRIENTS
i. Time: Losses of nutrients in fruits and vegetables progress with time. As soon as fruits and vegetables are harvested, their nutrients begin to dwindle. Even unprocessed fruits and vegetables are capable of losing nutrients.

ii. Heat: Cooked fruits and vegetables show losses of ascorbic acid and other vitamins and this progresses with the length of time that they are kept.

iii. Enzyme Activity: Fruits and vegetables contain enzymes and these enzymes oxidize the leaves when they are crushed or mashed or when they wilt. Presence of alkaline or traces of copper can also oxidize fruits and vegetables even in the absence of enzymes.

iv. Invading Micro-organisms: Fungi and some bacteria which are saprophytes in nature infestation most fruits and vegetables and consequently lead to microbial spoilage.

v. Direct Contact with water: This must be avoided as some minerals are water soluble and can be leached out in cooking or soaking.

CONSERVATION OF NUTRIENTS IN HANDLING AND STORAGE OF FARM PRODUCE

The following factors favour conservation of nutrients especially in fruits and vegetables vegetables, namely;

i. Rapid harvesting: Delayed harvesting leads to ripening. This reduces the percentage of ascorbic acid (vitamin C) and carotene (pro-vitamin A) of which fruits and vegetables are the principal dietary sources.

ii. Cooling: Cooling or freezing reduces biochemical breakdown in fruits and vegetables that had been harvested.

iii. Avoidance of soaking in water: Moist conditions trigger off breakdown of fruits and vegetables either by fermentation or by conditioning the fruit/vegetable environment for microbial breakdown.

iv. Rapid cooking: Fruits and vegetables should be rapidly cooked. Cooking of fruits and vegetables involves reducing.

the amount of water used
the length of cooking period
the amount of surface area exposed.

v. Gentle Handling: Fruits and vegetables should be gently handled to avoid physical injuries and destruction of the produce.
vi. Controlled temperature and humidity: Fruits and vegetables that had been harvested must have their immediate temperature and humidity controlled until the food is marketed and served. High temperature and humidity, initiate early breakdown of harvested fruits and vegetables.

vii. Transporting/Marketing: Fruits and vegetables should be promptly transported to the market. Their transportation and marketing can never be delayed or else their nutritive values will be lost.

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