Abstract
This study to examine soil fertility status was conducted on 10 citrus plantations in Hau Giang province within the Vietnamese Mekong Delta, Vietnam. Fruit trees are mostly grown on the raised beds to avoid annual flood with alluvial soil type. Soil sampling was done in the dry season of 2010 at two soil depths, for each raised bed. Development ages of raised beds were represented by two groups, young age group (≤ 30 years) and old age group (> 30 years). For chemical analysis, pH, organic matter, CEC, total nitrogen, NH4+, NO3– and exchangeable Ca, Mg and K were determined. The results showed that the pH (water) was strongly acid. The CEC was in average 19.2 cmol+.kg–1 in topsoil (0 - 20 cm depth) and 18.7 cmol+.kg–1 in subsoil (20 - 50 cm depth) for young age group. Similarly, the CEC was 16.7 cmol+.kg–1 in topsoil and 15.8 cmol+.kg–1 in subsoil for old age group. Organic matter on young age group (7.38 and 5.47% on average for topsoil and subsoil respectively) was significantly higher than that of old age group (5.20 and 3.81% on average for topsoil and subsoil respectively). Total nitrogen was not significantly different between the sites for the age groups of raised as well as the soil layers. Ammonium-N levels were excessive, and NO3--N levels were high. Potassium and Mg2+ were significantly different between age groups of raised beds and the same pattern between soil layers, while Ca2+ did not vary significantly. Potassium and Ca2+ levels were moderate, Mg2+ was high and P levels were very high. Soil fertility in the raised beds subjected to an adverse on plant growth and an imbalance in soil nutrients under low pH conditions. Loss of soil quality was exhibited in reduced organic matter with the aging of raised beds.
Highlights
There are seven major soil types in the Vietnamese Mekong Delta (MD); those are alluvial, acid sulphate, saline, saline acid sulphate, old alluvial, peat and mountainous [1,2].The MD is the main area of fruit production that covered approximately 285,300 ha by the year 2009 accounting for about 38% of the fruit tree area of Vietnam [3]
This study was conducted on 10 selected citrus plantations in Hau Giang province, Mekong Delta, Vietnam with different ages (Figure 1)
There were no significant differences between the two age groups of raised beds as well as between soil layers for the young age group, while the pH was significantly different between topsoil and subsoil for the old age group
Summary
There are seven major soil types in the Vietnamese Mekong Delta (MD); those are alluvial, acid sulphate, saline, saline acid sulphate, old alluvial, peat and mountainous [1,2].The MD is the main area of fruit production that covered approximately 285,300 ha by the year 2009 accounting for about 38% of the fruit tree area of Vietnam [3]. There are seven major soil types in the Vietnamese Mekong Delta (MD); those are alluvial, acid sulphate, saline, saline acid sulphate, old alluvial, peat and mountainous [1,2]. Most of the land used for fruit trees in the MD is lowland alluvial plain; raised beds are commonly constructed to avoid annual flooding. The ages of raised beds are widely different which lots of them have lasted more than 30 years old. Soil layers on the raised beds are commonly arranged in reverse or the same order as natural soil. Soil degradation is considered as a subsequent limitation on plant growth. Major reasons of soil degradation are compaction, loss of organic matter, salinization, nutrient depletion and pollution [4,5]. Degradation of top soils may be resilient, whereas degradation of sub soils is much more difficult to restore and the degradation may even be permanent [6]
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