Water Losses And Their Control In Rainfed Agriculture
A. Use of Mulching:-
1. Mulching like grass, weeds & crop residues applied to the crop@ 5t / ha, reduce the maximum temp, of soil at 10 cm depth by 1 to 70C during monsoon season (July to Sept) by 4 to 100 C during summer season (April to June).
2. Mulches improved soil environment by way of increased moisture availability, reduction in soil temp. To optimum levels & thus higher water use & water use efficiency.
B. Tillage: – Affect soil – water relationships, aeration status, thermal characteristics & the mechanical impedance to the root penetration. Soil acts as mulch & restricts the upward movement of water to the evaporating site by reducing diffusivity gradients.
C. Use of Antitranspirants: – Define as the materials which decrease water loss from the plant leave by reducing the size or number of stomatal opening decreasing thereby the rate of diffusion of water vapour.
Two imp. Points in use of Antitranspirants:-
1. The application or an antitranspirants should restrict the water loss from the leaf surface without reducing photosynthesis, as carbon dioxide diffuse through stomata & is necessary for photosynthesis.
2. Transpiration causes cooling of the leaf surface & the use of antitranspirants should not completely stop transpiration & thus raise the leaf temperature.
Antitranspirants effective in Two ways:-
1. Through films that coat the leaf surface.
2. Chemicals that close the stomata
Examples of antitranspirants:-
1) Phenyl mercuric acetate Inhabits stomatal
2) Alkanyl succinic acids opening
3) Waxy or plastic emulsions – Film forming antitranspirants
4) White wash or kaolinite – Acts directly on wet cell walls & lower leaf temperatures & reduces vapor pressure gradient.
Effect on Photosynthesis of Antitranspirants:-
Antitranspirant result in size & no. of stomata’s of the leaves, however, a supply of carbon – dioxide diffusion into the stomatal cavity is necessary for the occurrence of photosynthesis & it the reduction in opening results in restriction of actual photosynthesis & the yield reduction will be there.
Example of Anti -Tran spirants
Phenyl mercuric acetate (PMA )
DAMS, TIBA, MH& CMH
Alkenyl succinic adid, 2, 4 – dinitrohenol.
Desiccarts or defoliants
Crop – ripens such as
2, 4 – D
Ccc, carbanyl urea,
Na – chlorate