Decomposition and nutrient release dynamics of leaf litter of
Agroforestry systems with scattered trees in croplands have traditionally played a pivotal role in sustaining rural livelihoods in semiarid zones of the world. In Mandya district of southern dry agroclimatic zone of Karnataka, trees of the genus
Mandya district, spanning an area of 4961 km3 in southern dry agroclimatic zone of Karnataka state in south India (location map in Figure
Location map of Mandya district in Karnataka state (black dot indicates the experimental site).
In the present investigation, only leaf litter was studied for decomposition as this component constituted around 60% of the total litterfall of
Five samples each were drawn at monthly intervals from surface and subsurface treatments for one year starting from April 2009 to March 2010. The residual substrate (litter/paper) mass from bags was washed, oven-dried at 70°C, and weighed after excluding fine roots and macroarthropods penetrating the mesh. The samples were then pooled substrate-wise, powdered, and analysed for N, P and K. Decomposition rates of the substrates were estimated from the first-order exponential equation
Half-life period (
The association of litter decomposition with litter quality, climatic conditions, and soil properties was examined in the present study.
Litter quality determines in part rates of decomposition and release of nutrients from organic residues [
Monthly rainfall data recorded from the rain gauge at Bharathi Nagara, located 1.5 km from the study site, was collected from the District Statistics Office, Mandya. Air temperature and humidity were measured
Soil temperature was measured
Data on residual litter mass in bags and their nutrient contents after one year for surface and subsurface methods of placement were statistically analysed using two-way ANOVA technique (substrate and method of placement as two factors) in SigmaStat 3.5 statistical software, and Fisher’s least square difference (LSD) values were computed. Pearson’s correlation coefficients of mean monthly weight loss of litter with weather parameters and soil properties in the experimental plot were worked out following Panse and Sukhatme [
Previous studies have shown that litter decay can follow an exponential pattern [
Weight loss of
Weight loss of
Decomposition was found to be faster in subsurface method of application, with only 22.5% of initial litter mass remaining after one year of incubation, while in surface treatment, 28.3% of mass was remaining. Decay constant of litter was slightly higher for subsurface mode of application (0.125) compared to surface mode (0.107), and half-life of litter ranged from 5.54 months in subsurface treatment to 6.48 months in surface treatment indicating a modestly faster decay in subsurface treatment. But this difference in decay rate between treatments did not appear significant in two-way ANOVA (
Two-way ANOVA results also revealed that between substrates, there is a significant variation in decomposition (
Decay constant of
Litter quality parameters of
Species/substrate | Location | Initial N (%) | Initial lignin (%) | Initial total phenol (%) | C/N ratio | Lignin/N ratio | Half life (in months) | Reference |
---|---|---|---|---|---|---|---|---|
|
Mandya | 1.11 | 30.50 | 6.76 | 23.89 | 27.60 | 5.54–6.47 | Primary data |
Filter paper | Mandya | 0.04 | 0.50 | 0.47 | 70.49 | 12.19 | 2.45–2.60 | Primary data |
|
Garhwal, India | 1.97 | 13.82 | 7.10 | 19.88 | 7.01 | 8.00 | [ |
|
Garhwal, India | 0.96 | 12.14 | 11.64 | 39.58 | 12.64 | 12.00 | [ |
|
Kerala, India | 1.10 | 28.90 | 2.20 |
|
26.20 | 4.60 | [ |
Kerala, India | 1.73 | 31.40 |
|
|
18.16 | 3.40 | [ | |
|
Kerala, India | 0.91 | 15.20 | 2.00 |
|
17.60 | 2.40 | [ |
Kerala, India | 2.15 | 17.90 |
|
|
8.33 | 3.10 | [ |
Differences in decomposition rates can probably be explained by variations in litter quality [
Comparison of litter quality of
Association between
Correlations of litter weight loss with climatic and soil parameters of study site.
Parameter | Mean monthly weight loss | Soil temperature | Soil moisture | Air temperature | Relative humidity | Rainfall | Soil pH |
---|---|---|---|---|---|---|---|
Mean monthly weight loss | 1 | −0.39 | 0.608* | −0.077 | −0.197 | 0.736** | −0.234 |
Soil temperature | 1 | −0.735** | 0.719** | −0.762** | −0.681* | −0.311 | |
Soil moisture | 1 | −0.234 | 0.416 | 0.703* | 0.268 | ||
Air temperature | 1 | −0.628* | −0.139 | −0.446 | |||
Relative humidity | 1 | 0.19 | 0.338 | ||||
Rainfall | 1 | −0.096 | |||||
Soil pH | 1 |
Analysis of elemental composition of decomposing litter revealed an initial rapid loss of N for the first six-seven months, followed by an increase in the concentration in subsequent months (Table
Concentrations of major nutrients in
Month after incubation | N (%) | P (%) | K (%) | |||
---|---|---|---|---|---|---|
Surface | Subsurface | Surface | Subsurface | Surface | Subsurface | |
0 (initial) | 1.105 | 0.0845 | 1.004 | |||
1 | 0.903 | 1.089 | 0.152 | 0.220 | 0.681 | 0.183 |
2 | 0.967 | 1.050 | 0.129 | 0.096 | 0.994 | 0.080 |
3 | 0.940 | 1.050 | 0.291 | 0.230 | 0.357 | 0.191 |
4 | 0.992 | 1.005 | 0.486 | 0.211 | 0.206 | 0.175 |
5 | 0.947 | 1.030 | 0.172 | 0.119 | 0.199 | 0.099 |
6 | 0.740 | 1.080 | 0.273 | 0.197 | 0.199 | 0.164 |
7 | 1.340 | 0.660 | 0.066 | 0.075 | 0.384 | 0.062 |
8 | 1.230 | 0.974 | 0.171 | 0.070 | 0.284 | 0.058 |
9 | 1.470 | 1.250 | 0.343 | 0.077 | 0.374 | 0.064 |
10 | 1.410 | 1.190 | 0.420 | 0.103 | 0.325 | 0.085 |
11 | 1.297 | 1.240 | 0.129 | 0.115 | 0.261 | 0.091 |
12 | 1.320 | 1.023 | 0.166 | 0.110 | 0.410 | 0.110 |
LSD (0.05) | T : NS | P : NS | T : 0.0774* | P : NS | T : 0.153** | P : NS |
T: treatment; P: period; NS: not significant. *Significant at
When the percentage of nutrients remaining after one year of decomposition was computed from residual nutrient concentrations and litter mass, it was found that proportion of residual nutrients was less in subsurface treatment compared to surface treatment, indicating comparatively faster nutrient release when the litter is incorporated to the soil. After one year of decomposition, 33.80% of initial N content was remaining in surface treatment, while in subsurface treatment only 20.83% was remaining. However, two-way ANOVA of nutrient release showed that there was no significant difference in release of N between surface and subsurface treatments (
The pattern of litter decomposition and nutrient release has important implications for exploiting
The authors wish to acknowledge the University Grants Commission, New Delhi, and Indian Council of Forestry Research and Education, Dehradun, for financial assistance and Director, Institute of Wood Science and Technology, Bangalore, for logistic support. Mr. K. M. Shivaswamy, Karadakere village, Mandya, is sincerely thanked for providing space in his farmland for litter decomposition experiment, and reviewers are thanked for critical suggestions.