Abstract
To access the spatial differences in soil properties and crop yield at cascade level affected by either sediment induced or farmers’ fertility practice, field experiments were conducted in Cheing Khoi watershed area during spring and summer seasons with two different cascades. The cascades had fertilized and unfertilized parts and all the measurements were conducted at the top, middle and bottom field of each part. In both rice cascades, middle and bottom fields showed high silt and clay content while sand was the dominant type in the top field. Total nitrogen (TN) and carbon (TC) contents were significantly higher in lower lying fields than top field. Seasonal average surface water NH4 concentrations for top, middle and bottom fields were 2.7, 3.4 and 3.2 mg L-1 in spring and 2.8, 3.5 and 3.1 mg L-1 in summer, respectively. Differences were substantial in yield components parameters and grain yield depending on toposequence position. Grain yields in the middle fields of both rice cascades were higher than other field positions in both fertilized and unfertilized fields. The grain yields were significantly related with surface water NH4 concentration, TN content, sand and silt content of soil. The larger toposequential differences in crop yield require different field specific management practices for each position in order to improve rice production in this watershed area. Key words: Crop performance, double-cropping, paddy rice, spatial variability, toposequence.
Highlights
In Northern mountainous region of Vietnam, an important agro-ecosystem is a composite swidden agriculture which integrates annual food crops, such as maize, cassava and upland rice, and fallow in the uplands and permanent wet rice fields in valley bottoms of the catchment (Lam et al, 2005) to form a single household resource system (Rambo, 1998)
When comparing different toposequence positions, Total nitrogen (TN) content was significantly (p
There were no significant differences in TN and total carbon (TC) content of the soil taken before transplanting and after harvest
Summary
In Northern mountainous region of Vietnam, an important agro-ecosystem is a composite swidden agriculture which integrates annual food crops, such as maize, cassava and upland rice, and fallow in the uplands and permanent wet rice fields in valley bottoms of the catchment (Lam et al, 2005) to form a single household resource system (Rambo, 1998). Traditional agriculture methods involving fallows are more and more replaced by market oriented land use annual mono-cropping systems, that have a low soil cover during their establishment phase (e.g. maize), inducing severe erosion on steep slopes. Such land use alterations have dramatic environmental effects (Wezel et al, 2002) and high precipitation will lead to accelerate soil degradation due to erosion of the steep slopes used for agriculture. Upstream erosion will lead to sedimentation and siltation of downstream water bodies and paddy fields as well as nutrient transportation within sediments and irrigation water. Nutrients are removed and attached to eroded sediments, reallocated in the watershed
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