Relationships between soil, fallow period, weeds and rice yield in slash-and-burn systems of Laos

Abstract

Decline in soil fertility accelerated by shorter fallow periods was expected to be a major constraint in slash-andburn rice production systems in northern Laos. In this paper we describe relationships between fallow period, soil fertility parameters, weeds and rice yield. Soil infertility is not perceived a major yield constraint by the farmers. Of the various soil parameters observed only soil organic matter showed consistent association with rice yield (r =0.42, p<0.01). Fallow period and rice yield showed no association and the relationship between fallow and organic matter was very weak (r=-0.16, p<0.01). Rice yield was negatively related to densities of Ageratum conyzoides and Lygodium flexuosum. Soil loss during the cropping period ranged from 300-29.300 kg ha -l . For the same period organic matter, total N, available P and available K content in the top 0-3 cm decreased by 11,12,17, and 17%, respectively, and loss of total N for the soil depth of 0-25 cm was estimated at 400 kg ha-I. Soil physical properties, moisture stress and available N are the most likely detriments to rice yields. Further attempts to relate soil properties to rice yield should include repeated measurements during the cropping season and observations on soil physical properties.

Environmental Consequences of the Demise in Swidden Cultivation in Southeast Asia: Carbon Storage and Soil Quality

“…Several studies have demonstrated that land use intensity is not independent of inherent soil quality as farmers adapt land use according to soil quality indicators and use shorter fallow periods on the more fertile land (Aumtong et al 2009;Roder et al 1995). The number of prior cultivation cycles is therefore also likely to be higher on the more fertile land so if the land use history of a given plot is not properly addressed, the effects of fallow length will be even more confounded.…”

“…In a study from Sarawak, the length of the fallow was linked to post burn levels of plant available N as well as to the yield of upland rice, but no signs of long term degradation of the soil resource and no relation between fallow length and SOC were found (Bruun et al 2006). Finally, a study from Laos found weak correlations between fallow length and contents of SOC and between yield levels and contents of SOC (Roder et al 1995).…”

Determining Greenhouse Gas Emissions and Removals Associated with Land-Use and Land-Cover Change

“…Many studies have found that land-use is often infl uenced by land features. For example, farmers may choose to cultivate areas with fertile, carbon-rich soils (e.g., Aumtong et al 2009 ;Ellis and Ramankutty 2008 ;Jiao et al 2010 ) or reduce fallow periods when the soil fertility is high (Roder et al 1995 ) and leave forests intact only in areas with poor soils. This preferential selection can make it diffi cult to determine that land-use is in fact causing a change in soil carbon stocks, and not the other way around (soil carbon stocks infl uencing land-use).…”

Evaluation of agricultural ecosystem services in fallowing land based on farmers’ participation and model simulation

“…For example, yield diminishes when soil fertility is degraded after farmers decide to abandon land. A 0 represents the reduced harvest area from " A t because of h Á a, where a denotes the percentage of farmers abandoning land and h is a parameter denoting a decrease in soil fertility as a result of abandonment (Roder 1994;Jordan 1985;Sanchez and Logan 1992;Warner 1991). From an ecological viewpoint, h Á a is the main factor that causes productivity declines and lessened soil fertility.…”