Page 56 - Ilmu Tanah

The Chemistry and Fertility of Soils under Tropical Weeds 43

particular strips may solve this problem so that plant maintenance and harvesting
are not inhibited.

Table 3.1. The decrease in soil erosion rate in coffee plantation of
West Lampung by weed coverage.

Erosion Rate
-1
Soil Concervation Method kg ha
-1
6 months %
Control 25.270 100
(Local Farmers)
Paspalum conjugatum 29 0.11
Natural Weeds 124 0.49
Sriyani et al. (1999)

Even though not as significant as those fully covered, the use of various soil
covers in strips (one strip of soil cover every 3 strips of crops) lowered the soil
erosion in coffee plantation of West Lampung (Fig. 3.3). The erosion was reduced
by 70-80% in lands with strip of Arachis pintoi, Axonopus compressus, and
Cymbopogon citrates compared to those without strips of soil covers. Periodic
cutting of weeds on strips about 40 cm also decrease the soil erosion rates twice
better than those not cut (Fig. 3.3). This phenomena indicate that, if properly
managed, weeds can be used to conserve the agricultural land particularly to
depress the soil erosion.
Other than the use to conserve soils, particularly in decreasing the soil erosion
rates, weeds are also empoyed to increase the soil fertility. Setaria plicata,
Paspalum conjugatum, Crotalaria lappacea, Asystasia gangetica, and Widelia
montana show high potences to increase the soil organic C, soil CEC, and soil pH
(Sembodo et al., 2012). Salam et al. (1997a) also reports that alang-alang
(Imperata cylindrica) neutralized the pH of the root zone of soil poluted with Pb
and decreased the solubilities of Fe, Cu, and Pb. Alang-alang was also reported to
increase the activities of acid and alkaline phosphatases that are important in
accelerating the decomposition of organic P compounds producing inorganc P
easily absorbed by plant roots (Salam et al., 1997a).

Abdul Kadir Salam and Nanik Sriyani – 2019