Residual Effects of 20 Annual Applications of Ammonium Sulphate and Triple Super phosphate for Corn on Properties and Productivity of Oxic Paleustults

A.  Suwanarit¹, I. Suwanchatri², J. Rungchuang³, V. Verasan¹, and S. Thongdaeng³

1.                          Department of Soil Science, Faculty of  Agriculture, Kasetsart University, Chatuchak, Bangkok 10900.

2.                          Central Laboratory, Faculty of Natural Resources, Prince of Songkla University, Hadyai, Songkla 90110, Thailand.

3.                          National Corn and Sorghum Research Center, Kasetsart University, Pakchong, Nakhon Ratchasima, Thailand.

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Residual effects of 20 successive annual applications of N and P fertilizers for corn production on properties and productivity of an Oxic Paleustults were examined by field experiment.  The experiment consisted of 4 rates of N and P fertilizers, i.e., 0-0, 60-60, 120-120, and 180-180 kg of N-P₂O₅/ha/year applied as ammonium sulphate and triple super phosphate.

PH of the surface soil and sub-soil decreased with increased rates of the fertilizers with more pronounced effects in the sub-soil.  EC of the surface soil was not affected by the fertilization while that of the sub-soil increased with increased rates of the fertilizers.  CEC of the surface soil was not affected by the fertilizers while that of the sub-soil decreased with increased rates of the fertilizers.  OM and total –N contents of the surface soil tended to increase with increased rates of the fertilizers while those of the sub-soil were not affected by the fertilization.  Available P of the surface soil was dramatically increased with increased rates of fertilizers while that of the sub-soil was less affected.  Exchangeable K, Ca, and Mg either tended to decrease or significantly decreased with increased rates of the fertilizers, with more pronounced effect in the sub-soil.  DTPA-extractable Fe of the surface soil increased with increased rates of the fertilizers while that of the sub-soil was not affected by the fertilization.  DTPA-extractable Mn, and Zn of the top-layer soil slightly increased with increased rates of the fertilizer whereas those of the middle-layer soil were similarly decreased by the three rates of fertilizers and those of the bottom-layer soil were not affected.  DTPA-extractable Cu of soil of the top and middle layers slightly increased with increased rates of fertilizers whereas that of the bottom-layer slightly decreased with increased rates of the fertilizers.  Bulk density of the surface soils showed slight trends to decrease with increased rates of the fertilizers while that of the sub-soil showed no effect of the fertilizers.  Aggregation of the soil decreased with increased rates of the fertilizers.  Hydraulic conductivity of the saturated soil was not affected by the fertilization.  The infection on corn roots of arbuscular mycorrhizal fungi (AMF) showed consistent trends to decrease with increased rates of the fertilizers whereas AMF spore intensity in the soil was not affected by low rates of the fertilizers but decreased with increased rates of the fertilizers at high rates of fertilizers.  Population of the free-living N₂-fixing bacteria in the soil showed consistent trends to increase with increased rates of the fertilizers.  Productivity of the soil increased with increased rates of the fertilizers.

 

 

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