Variations in Soil Physical Properties in a Cleared Forestland Continuously Cultivated for Seven Years in Eastern Nsukka, Nigeria.

摘要

In this study, soil physical properties were evaluated in the top 40 cm of cleared forestland that had been subjected to continuous cultivation for 7 years to ascertain selected crop or crop combinations that influenced the soil physical properties the most. There was no significant effect of crop treatment on particle-size distributions over 6 years of cultivation. In year 7, clay values were significantly (p = 0.05) greater in plots grown with solely cassava (SC) and solely maize (SM) than in the plots grown with solely pigeon pea (SP). The soil depth effects over the 7 years were significant on the clay content. The mean values of bulk density, pore-size distribution, and hydraulic conductivity obtained from each plot fluctuated over the years. The bulk density values in 1998 ranged from 1.29 to 1.43 g cm3, but from 1999 to 2004, the range was from 1.12 to 1.40 g cm3. Thus, bulk density generally decreased when compared with their respective values in 1998. The greatest decrease of 22% was in 2000. More than 70% of the macroporosity values were significantly less than their respective values in 1998. The greatest decease of 72% was obtained from SM plots in 2001. All the microporosity were significantly more than the 1998 values. All the increases were >100% of the original values. These increases were reflected in the variations of total and saturated hydraulic conductivity (Ks) values. However, in 2004, Ks values decreased in the plots grown to C + P, SP, and SM. Generally, the C + M + P mixture appeared to be the most consistent in improving micro- and total porosities and Ks among the crop treatments.