How do biotic and abiotic factors affect crop production? 

Biotic factors such as pests, insects and diseases reduce the crop production. These adverse effect on the plants and thus decrease the production. A pest causes damage to our crops by feeding. Weeds also reduce crop productivity by competing with the main crop for nutrients and light.
Similarly, abiotic factors such as temperature, wind, rain, drought, salinity etc. affect the net crop production. For example droughts and floods have a great impact on crops sometimes, destroying the entire crop. Salinity can lead to the death of crops if they are not resistant to it. 

Macro-nutrients are those nutrients which are required in large quantities for growth and development of plants. They are so called as they are required in large quantities. There are six macro-nutrients that are required by plants are nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur.

(i)  Cereals - provide us with carbohydrates. They fulfill our energy requirements. Wheat, rice, maize are cereals.
(ii) Pulses -  provide proteins, Gram, pea and lentil are pulses.
(iii) Fruits and vegetables provide vitamins and minerals. They also provide small amount of  proteins, carbohydrates, and fats are also present in them.

Plants get nutrients from air, water, and soil. Soil is the major source of nutrients. Thirteen of these nutrients are available from soil. Plants absorb nutrients along with the water from the soil. The remaining three nutrients (carbon, oxygen, and hydrogen) are obtained from air and water.

The desirable agronomic characteristics for crop improvements are:
(i) Tallness and profuse branching for the fodder crop.
(ii) Dwarfness in cereals, so that the crops consume less nutrients.