Soil C and N Pools in Chinese Fir and Evergreen Broadleaf Forests and their Changes with Slash Burning in Mid-Subtropical China

Soil organic carbon （C） and total nitrogen （N） pools of a Chinese fir （Cunninghamia lanceolata （Lamb.） Hook.） （CF） forest, and an evergreen broadleaf （EB） forest located in mid-subtropical, southeastern China, were compared before clearcutting, with the effect of slash burning on organic C and total N in the top 10 cm of soil before and after burning also being evaluated. Prior to clearcutting CF forest had significantly lower （P 〈0.05） organic C and total N in the soil （0-100 cm） compared to EB forest with approximately 60% of the C and N at the two forest sites stored at the 0 to 40 cm soil. In post-burn samples of the 0-10 cm depth at 5 days, 1 year, and 5 years for CF and EB forests, significantly lower levels （P 〈0.05） of organic C and total N than those in the pre-burn samples were observed. Compared to the pre-burn levels, at post-burn year 5, surface soil organic C storage was only 85% in CF forest and 72% in EB forest, while total N storage was 77% for CF forest and 73% for EB forest. Slash burning caused marked long-term changes in surface soil C and N in the two forest types.

Effects of Slash-and-Burn Practices on Soil Quality at Different Landscape Positions in the Raumoco Watershed, Municipality of Lautem, Timor-Leste

Slash-and-burn practices used by farmers in prior growing periods could affect soil quality, particularly topsoil properties. This study aimed to assess soil biophysical and chemical properties at different landscape levels within the watershed site. Soil samples were collected by a core method in the topsoil layer in slash-and-burn sites. Field analysis was on bulk density and porosity by the gravimetric method, while laboratory analysis was done on organic matter by the Loss on Ignitions Method and other macronutrients for crops (total nitrogen, phosphorus availability, and potassium availability) followed standard analytical methods. To see if there was a significant difference between sites, DMRT 5% was used. The results of the study showed slash-and-burn practice affects soil physical properties such that high bulk density in upstream, midstream, and downstream ranged from 1.55 g/cm3 to 1.71 g/cm3, 1.55 g/cm3 to 1.80 g/cm3, and 1.38 g/cm3 to 1.79 g/cm3 respectively. Poor porosity in upstream, midstream, and downstream ranged from 33.91% to 40.06%, 30.38% to 41.75%, and 30.91% to 46.65%, respectively. Organic matter content was low in the upstream, midstream, and downstream areas, ranging from 2.86% to 3.39%, 2.58% to 3.88%, and 2.91% to 3.88%, respectively. However, soil pH remains neutral, and nitrogen levels are low but near-optimal in the upstream and very low in the midstream and downstream. Phosphorus is extremely high upstream but very low in midstream and downstream. However, potassium remains at a low level close optimum level in the entire watershed.

Effect of Continuous Plantation of Chinese Fir on Soil Fertility

The changes in soil fertility under continuous plantation of Chinese fir were studied by comparing soilsamples from different forest stands: the first and second plantations of Chinese fir, evergreen broad-leavedforests, and clear-cut and burnt Chinese fir land located at Xihou Village, Nanping of Fujian Province. Thesoils were humic red soil originated from weathered coarse granite of the Presinian system. Soil PH, CEC,base saturation, exchangeable Ca￣(2+), exchangeable Mg￣(2+) and Al-P declined after continuous plantation ofChinese fir. The same trends were also found in the soils under broad-leaved stands and slash burnt lands.The explantation was that not merely the biological nature of the Chinese fir itself but the natural leachingof nutrients, soil erosion and nutrient losses due to clear cutting and slash burning of the preceding plantationcaused the soil deterioration. Only some of main soil nutrients decreased after continuons plantation ofChinese fir, depending on specific silvicultural system, which was different from the conclusions in some otherreports which showed that all main nutrients, such as OM, total N, available P and available K decreased.Some neccessary steps to make up for the lost base, to apply P fertilizer and to avoid buring on clear cutlands could be taken to preventsoil degradation and yield decline in the system of continuous plantation ofChinese fir.