Abstract:
Soil nutrient dynamics are closely linked to soil moisture availability, particularly in dryland
ecosystems where water is a limiting factor influencing microbial and biochemical
processes. This study investigated how prolonged drought followed by rewetting affects soil
nutrient availability in the dry zone of Sri Lanka. Soil was collected (0-10 cm) from
Kalaththewa Grama Niladhari Division, Anuradhapura District. The soil is a reddish-brown
earth with a water holding capacity (WHC) of 0.36 g/g. A laboratory incubation experiment
subjected soils to three drought (~10% WHC) durations (2 weeks, 2 months, and 6 months),
followed by rewetting to 50%WHC. Soils were kept at drought (~10% WHC) by maintaining
them at a constant weight. The sampling was done at 2, 14, and 30 days after rewetting.
There were three (03) replicates for each treatment. Soil pH, electrical conductivity (EC),
available phosphorus (P), and organic matter (OM) were measured. Soil pH remained stable
without significant changes between the treatments, whereas EC, P, and OM showed
significant increases after rewetting, particularly following the 2-month drought period.
Results showed soil pH remained stable (pH ~7.0) with no significant change across
treatments. Electrical conductivity (EC) peaked at 0.19 dS/m two days after rewetting
following the 2-month drought, then declined. Available phosphorus (P) reached a maximum
of 55.5 mg/kg and organic matter (OM) peaked at 4.81% at 14 days after-rewetting in the 2-
month drought. The 6-month drought had lower P (28.3 mg/kg) and OM (3.2%) levels,
indicating reduced microbial activity and nutrient cycling. These findings highlight drought
duration’s critical role in soil nutrient dynamics. Rewetting dry soil activates dormant
microbes, enhancing short term nutrient release like phosphorus, which supports plant
growth and soil health. However, this sudden flush can lead to nutrient leaching, especially
after rain, reducing soil fertility. Nutrient flushes after moderate droughts can temporarily
enhance soil fertility, benefiting Sri Lanka’s rainfed agriculture. However, prolonged
drought diminishes microbial activity and nutrient availability, affecting long-term soil
health and crop yields. These results show the need for adaptive land management practices
to sustain the productivity of the soil under climate change.
