The correct option is C Plant ash
The residue obtained by burning the plant parts like bark, wood, sawdust, leaves, woody debris, pulp, husk, hulls, fronds etc., is known as plant ash.
If a dried leaf is taken in a crucible and heated to 600 oC, a grey coloured powder is left behind. It is referred to as plant ash. It can be used as compost and fertilizers as it is rich in potassium and calcium carbonate.
The amount of water a soil contains after plants are wilted beyond recovery is called the permanent wilting percentage.
The protein content of the plant is the total amount of protein which is available for the plant for its metabolism.
Dry weight is the solid nutrient present in the plant excluding water. It is obtained by slow heating of plant part at 600 oC overnight.
So, the correct answer is option C.