Q (16): Assertion : Diseases in plants are caused by pathogens such as bacteria, fungi and viruses.                                                                           

Reason : The pathogens can be present in and transmitted through the soil, water and air.

Q (17): Assertion : Removal of weeds from cultivated fields during the early stages of crop growth is essential for a good harvest.                   

Reason : Weeds take up nutrients and reduce the growth of the crop.

  Q (18): Assertion : Field crops are infested by a large number of weeds, insect pests and diseases.                                                                                      Reason : If weeds and pests are not controlled at the appropriate time then they can damage the crops so much that most of the crop is lost.

Q (19): Assertion : Mixed cropping is growing two or more crops simultaneously on the same piece of land, for example, wheat + gram.                                                                                                     Reason : Mixed cropping reduces risk and gives some insurance against failure of one of the crops.

  Q (20): Assertion : Dams are small storage reservoirs, which intercept and store the run-off of smaller catchment areas.

Reason : Fresh initiatives for increasing the water available for agriculture include rainwater harvesting and watershed management.

  Q (21): Assertion : Droughts occur because of scarcity or irregular distribution of rains.                                                                                              Reason : Drought poses a threat to rain-fed farming areas, where farmers do not use irrigation for crop production and depend only on rain.

Q (22): Assertion : Light soils have less water retention capacity.                          

Reason : In areas with light soils, crops get adversely affected by drought conditions.

Q (23): Assertion : Ensuring that the crops get water at the right stages during their growing season can increase the expected yields of any crop.              

Reason : Manure takes up nutrients and reduce the growth of the crop.

  Q (24): Assertion : Fertilizers supply nitrogen, phosphorus and potassium.                 

    Reason : Fertilizers are used to ensure good vegetative growth (leaves, branches and flowers), giving rise to healthy plants.

Q (25): Assertion : Deficiency of nutrients affects physiological processes in plants including reproduction, growth and susceptibility to diseases.                                                                                           Reason : To increase the yield, the soil can be enriched by supplying these nutrients in the form of manure and fertilizers.

Q (26): Assertion : Fertiliser is prepared by the decomposition of animal excreta and plant  waste.                                                                            

Reason : Manure helps in enriching soil with nutrients and organic matter and increasing soil fertility.

  Q (27): Assertion : The bulk of organic matter in manure helps in improving the soil structure. 

 Reason : This involves increasing the water holding capacity in sandy soils.

  Q (28): Assertion : There are sixteen nutrients which are essential for plants.                                                                                                Reason : Air supplies carbon and oxygen, hydrogen comes from water, and soil supplies the other thirteen nutrients to plants.

  Q (29): Assertion : Paddy, soyabean, pigeon pea, maize, cotton, green gram and black gram are kharif crops, whereas wheat, gram, peas, mustard, linseed are rabi crops.                                                                    

   Reason : In India there has been a four times increase in the production of food grains from 1952 to 2010 with only 25% increase in the cultivable land area.

Q (30): Assertion : Different crops require different  climatic conditions, temperature and photoperiods for their growth and completion of their life cycle.

Reason : Photoperiods are related to the duration of moonlight.