$13.$ Urea's high nitrogen content makes it a preferred fertilizer in modern agriculture, synthesized through a reaction between ammonia and carbon dioxide, forming urea and $\_\_\_\_,$ in a cycle known as the $\_\_\_\_$ cycle.

$-$ Options: water, urea, carbon, nitrogen, Krebs, Calvin

$14.$ Ammonium chloride is applied to agricultural fields not just as a nutrient source but also as a$($n$)\_\_\_\_$ agent, influencing soil and potentially affecting microbial $\_\_\_\_.$

$-$ Options: nematicidal, pH$,$ activity, fungicidal, texture, diversity

$15.$ Calcium ammonium nitrate's dual supply of $\_\_\_\_$ and nitrogen supports plant growth and soil health, reducing the risk of in plants and improving $\_\_\_\_$ uptake.

$16.$in super phosphate production, enhancing phosphorus $\_\_\_\_\_\_.$

$-$ Options: phosphoric, sulfuric, bioavailability, nitric, solubility, hydrochloric