Page 114 - Ilmu Tanah

The Chemistry and Fertility of Soils under Tropical Weeds 101

fixing bacteria like legumes may easily build significant amount of soil N. However,
soil treatment may reverse the pattern. Conventional tillage may in the long run
decrease the soil C and other elements. Disposing plant residues out of treatment
plots may also lower the soil content of these elements.

1.8
1.6
1.4
Relative Content 0.8
1.2
1

0.6
0.4
0.2
0
0 Years 1 - 5 Years 5 - 10 Years

Organic C Total N Avail. P

Fig. 6.5. The changes in soil C, total N, and available P in cassava plantation of Gunung
Batin, Central Lampung (At 0 years organic C = 43, N = 2.6, and
-1
avail. P =5.03 mg kg ).

Salam et al. (1999b) observe the change in soil C, total N, and available P under
cassava plantation cultivated for the periods of 0, 1-5, and 5-10 years in Gunung
Batin Central Lampung Indonesia (Fig. 6.5). Unlike the available P, the contents of
soil C and N significantly decreased with cassava plantation. Compared to the
contents in the adjacent bushes never planted with cassava, the contents on C and
N in soil that had been planted with cassava for 1-5 years were 47 and 39%,
respectively and much lower in soil had been planted with cassava for 5-10 years,
about 30 and 31%, respectively for C and N. The available P in 1-5 years land was
lower, but in 5-10 years land was higher, probably due to P fertilization at the time
of land clearing. The decrease in soil C and N is obviously due to intensively
Abdul Kadir Salam and Nanik Sriyani – 2019