Long-term Effects of Potassium Nutrition on Productivity and Sustainability of a Sorghum-Wheat Cropping System

Results

Treatment	Available K		K balance	K added in fertilizers	K removal by crops	Contribution of non-exchangeable K
	(kg K₂O/ha)
	1985-86 I	1997-98 II	III=I-II	IV	V	VI=V+III-IV
N₁₂₀P₆₀K₀	317	163	-154	0	1,375	1,221 !
N₁₂₀P₆₀K₆₀	336	227	-109	1,075	1,767	583
N₁₂₀P₆₀K₆₀+FYM	321	278	-43	1,459	2,056	554
N₁₂₀P₆₀K₁₂₀	318	342	+24	2,150	1,832	296
N₂₄₀P₁₂₀K₀	314	137	-187	0	1,570	1,384 !
N₂₄₀P₁₂₀K₁₂₀	300	252	-48	2,150	2,006	192

The non-exchangeable K contribution to the total K uptake by crops in plots without K application was more than 80%, accelerating the depletion of soil K with consequent crop responses to K application
K balance was negative in all treatments, except for the N₁₂₀P₆₀K₁₂₀ treatment
Increasing K application lessened the negative K balance, although it was not sufficient to replenish the K removals of crops
The positive K balance at the N₁₂₀P₆₀K₁₂₀ treatment explains the lower yield decline and the higher yields achieved after 12 years of continuous cropping
It is concluded that only balanced application of NPK can sustain productivity of both crops in the long term.

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