IPI International Potash Institute
IPI International Potash Institute

Table 6. Long-term effect of K fertilizer input in three different soil types.

                           
  Table 6. Long-term effect of K fertilizer input in three different soil types.  
  Location Period of experiment Soil type Soil K content Rotation Fertilizer rate K effect
(Comparison between NP and NPK treatment)
 
Total Readily available Slowly available N P2O5 K2O
    g kg-1 mg kg-1     kg ha-1    
  Changsha city, Hunan 1981-2007 Red paddy soil 14.1 62.3 173.9 Double
rice
Early rice 150 90 120 Effective immediately; the average annual yields of early rice and late rice increased by 15.2% and 17.2%, respectively, during each of the 27 years  
Late rice 180 90 120
  Fengqiu county Henan 1990-2009 Fluvoaquic soil 18.6 82.9 797.5 Wheat-
corn
Wheat 150 75 150 Effective after 12 years; the average annual yields of wheat and corn increased by 12% and 17%, respectively, from 2002 onwards  
Corn 150 60 150
  Yangling county Shanxi 1991-2010 Loess soil 21.6 200 1,500 Wheat-
corn
Wheat 165 57.6 68.5 No effect in 20 years  
Corn 187.5 24.6 77.8
  Source: Data from ISSAS field experiments and other sources.