Abstract:
Copper and Zinc are essential micronutrients but at high levels could negatively affect plant growth. Long-term and
residual effects of cattle manure application were studied on forage yield and Cu and Zn concentrations under rain-fed and irrigation. Experiment started in 1973 and continued till 2009. Cattle manure was applied at 0 ,3 0 ,6 0 and 90
Mg h a 1 under rain-fed and 0, 6 0 ,1 2 0 and 180 Mg ha'1 under irrigation. One set of plots were subjected to continuous
application of manure for 36 years (1973 - 2009), second set of plots were subjected to continuous applications for 30
years (1973-2002) followed by no application and third set of plots were under cultivation only for 14 years
(1 9 7 3 -1 9 8 6 ) followed by no application. Continuous manure application increased the Cu (5 to 49 mg kg'1) and Zn (14
to 118 mg kg1) in forage. Copper and Zn contents were affected by the rate of manure application in some of the years
where highest manure rate giving highest Cu and Zn in forage. Manure effect on yield was significant (P<0.05) for
some of the years where lowest yields were recorded by the continuous highest manure application rate. Number of
years of continuous manure application (14, 30 or 36 years) was significant for forage Cu and Zn contents where
shortest length (14 years) recording significantly lower contents than 30 or 36 years. Long-term manure application
suggests possible nutrient imbalances though the forage Zn and Cu contents did not reach to toxic levels in this study.
