Explanation:

All statements are correct.

• Crop diversification is one option for obtaining more stable farm incomes while improving natural resource use and environmental sustainability.
• The new concept, known as legume intensification is a sustainable way of crop production intensification whereby farmers concentrate resources and expend energy on a smaller piece of land thereby reducing labor demand and resulting in higher productivity from lower investment.
• Tensiometers are used in irrigation scheduling to help farmers and other irrigation managers to determine when to water.
• Vertical farming is the practice of growing crops in vertically stacked layers. It often incorporates controlled-environment agriculture, which aims to optimize plant growth, and soilless farming techniques such as hydroponics, aquaponics, and aeroponics.

Hence option 4th is correct.