E L S E V I E R Ecological Engineering 8 (1997) 233 239

ECOLOGICAL ENGINEERING

Short communication

Reduction of nitrogen losses through erosion by Leonotis nepetaefolia and Sida acuta in simulated

rain intensities

Raju Kumar "'*, R.S. Ambasht ", Ajit Srivastava ~, N.K. Srivastava ", A. Sinha b

" Ecology Research Laboratory, Centre o[' Advanced Stud)' in Botany, Banaras Hindu University, Varanasi- 221 005, India

b University Department g[' Botany Magadh University, Bodh Gaya, hzdia

Received 19 June 1996; received in revised form 5 February 1997: accepted 25 February 1997

Abstract

Leonotis nepetaefolia, a tall herb and Sida acuta a medium size herb were selected to experimentally test the efficacy of vegetal cover in conservation of soil, water and nitrogen under varying intensities of simulated rain. Young seedlings of the species collected from the banks of the Rihand River, about 150 km South of Varanasi, India, were transplanted on sloping experimental plots. Simulated rainfall of 20, 25, 31, 38, 46 and 55 mm h - ~ was applied for 50 rain on the two vegetated and one bare plot. Water and soil running down from each of the sloping plots were collected separately in respective cemented reservoirs. They were analysed for different forms of nitrogen. The conservation value (Cv) of soil, water and nitrogen were calculated using Ambasht's formula. Depending upon the nature of vegetation protecting the surface, soil loss through erosion increased two to three times on doubling the rain intensity. As the rain intensity was raised soil conservation value of Leonotis increased from 63 to 88% and of Sida from 27 to 57%. Leonotis with better ground cover reduced particulate nitrogen erosion more effectively. The major fraction

* Corresponding author. Present address: Usha Martin Industries Ltd. (Usha Alloys and Steels Division) Post Box No. 147, Jamshedpur 831 001, India.

0925-8574/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0925-8574(97)0001 I-6

234 R. Kunlar et al. Ec'oh~gical Engineerine 8 (1997) 233 239

of nitrogen (total-N, ammonia-N and nitrate-N) transport down the slope was in soluble form. © [997 Elsevier Science B.V.

Kzvwordx: Leonotis nepeta~[blia: Nitrogen; Sida acuta; Simulated rain intensities

1. Introduction

The ability of ground plant cover in retarding soil, water and nutrient erosion is quite different for different species. Riparian bank slopes are very fragile and delicately balanced. The destruction of vegetal cover on such slopes and in watersheds are common.

The role of some riparian herbs namely ([vnodon cktcO'h)n, Pllyhl nod(flora, Cyperus rotundus, Digitaria adscendens, ()'oton bonpkmdianum and Crota/aria medicaginea in soil and water conservation has been studied by (Ambasht et at., 1984). Rain characteristics such as rainfall volume and rain intensity are the most common and dominant factors affecting the rate of soil erosion (Meyer, 1979).

An experiment was carried in the Botanic Garden of Banaras Hindu University on plants grown on artificially prepared sloping plots under simulated rainfall conditions for testing the efficacy of the two herbaceous species in checking soil, water and nitrogen movement in varying rain intensities.

2. Methods

The two species Leonotis nepeta~Jblia and Sida acuta were transplanted on sloping experimental plots (30%) each measuring 4.7 m 2. A total of 18 experimental plots were prepared six for each of three types of ground cover, two vegetated and one bare. Any particular plot was subjected to only one rain intensity type all through the experiment. At the lower end of sloping plots cemented collection tanks were prepared to collect the water runoff and eroded soil. At the time of planting, density was kept uniform at 121 individuals m 2. The extent of vegetal cover protecting the surface soil differed depending upon the growth behaviour of the two species,

The Canopy cover was expressed as per cent of the ground cover. Standing crop biomass g m 2 was measured by harvest method (Odum, 1971). The litter mass from unit area was collected, ovendried, weighed and expressed as g m 2. Soil moisture in percent was calculated by weighing the soil sample before and after oven drying. Number of terminal rootlets was counted in 10 x 10 x 15 cm 3 soil core and expressed as number m 2. The plot soil was sandy loam (sand, 55%; silt, 26%: and clay 17%).

All six simulated rain intensity treatments, adjusted by the tap knob, of 20, 25, 31, 38, 46 and 55 mm h ~ were given separately on six different plots for each type

R. Kumar et al . / Ecological Engineering 8 (1997) 233 239 235

of ground cover on any given day. The experiment was repeated five times for each intensity type at 10 days interval during October November. The high simulated rain intensities were selected for the experiment to generate sufficient kinetic energy to cause adequate runoff as these are not uncommon in nature either (Lal, 1988). To evade the natural rain effect during the intervening period, experimental plots were covered with polyethylene sheets immediately before the start of each rain and were removed thereafter. The vegetated bare plots were showered for 50 min using a multipore nozzle with 2 mm perforation from 1 m above the Canopy height.

The average value of five replicates of the quantity of soil eroded and water runoff collected in the reservoir were recorded. For the estimation of particulate and soluble fraction of nitrogen, the runoff water and soil were separated using suitable filters. Total nitrogen, ammonia-N and nitrate-N content in water were analysed selecting appropriate methods given in Standard methods (APHA, 1985) and for soil by Jackson (1967). The conservation value of both the species under six different rain intensities was calculated using the formula, conservation value (Cv)%= 100(1- Sp/Sod) as given by Ambasht (1970), where Sp and S,, are the quantities of soil, water, total-N, nitrate-N and ammonia-N washed off under identical erosional stresses from vegetated and bare plots, respectively.

Multiple stepwise regression analysis was performed using a computer pro- gramme package to assess the influence of rain intensity, rainfall and time lag individually as well as cumulatively on the quantity of nitrogen transport and their conservation by the vegetation.

3. Results and discussion

In the Leonotis plot, the number of terminal rootlets was 4.67 x 105 m 2 canopy cover 98%, litter mass on surface soil 46 g m 2 standing crop biomass 196 g m 2 and the soil moisture level was 12%. The values for Sida stand were 1.90 x 105 m 2 number of terminal rootlets, 79°/,, canopy cover, 82 g m 2 of litter mass, 150 g m 2 biomass and 11% soil moisture content at the start of the experiment.

Water and soil loss from both the vegetated and bare plots increased (Fig. 1) gradually as the rain intensity was raised from 20 to 55 mm h ~. The volume of water runoff and quantity of soil loss was higher from poor ground cover (79%), lower biomass (150 g m 2) and lesser number of fine roots (1.90 x 105 m 2) of Sida than from the Leonotis plot where the volume for said parameter was relatively higher. Maximum loss of soil and water was from the bare plot. Water conservation value decreased from 47 to 21% in Leonotis and from 39 to 11% in Sida as the rain intensity was increased during six successive showers. Unlike water Cv, the soil Cv, increased with increase in rain intensity in both species. In Leonotis increase was from 27 to 54%. This is because the ratio of soil loss from vegetated to bare plot increased more and more with increase in rain intensity. Further, the relative rise in runoff energy is more in bare condition due to a higher runoff (Aldrich and Slaughter, 1983). This explains the remarkable rise in soil Cv of both Leonotis and Sida with the increase in rain intensity. Here, rain intensity was found

236 R. Kumar et al. , Ecological k,37gineering 8 (1997) 2 3 3 - 2 3 9

to play a greater role in soil conservation by the vegetation where it explained 98% of variation in Leonotis and 96% in Sida (P < 0.01).

Total nitrogen loss through soil and water also increased with the increase in rain intensity. Minimum nitrogen loss occurred in the Leonotis stand (0.09 to 2.9 kg ha '). This differential increase in nitrogen loss during different treatment was mainly due to different levels of protection given to surface soil by the ground cover of Leonotis, Sida and bare plots. Concentration of nitrogen in deposited soil (Table 1) from Leonotis, Si&~ and bare plots decreased with the increase in the rain intensity. This is mainly attributed to the greater dilution of nitrogen by the increase in rainfall volume during the subsequent showers. The overall nitrogen Cv of both Leonotis (29-53%) and Si&l (30-59%) increased as rain intensity was raised from 20 to 31 mm h ~ but as it was raised further, the conservation value began to decrease. This is due to the fact that increase in nitrogen runoff from vegetated and bare plots was not of the same order at all the treatment intensities. Further, the nitrogen movement down the slope was mainly in organic forms (83 88%). This is because up to 98% of nitrogen remains in organic form in the soil.

The total ammonia-N loss (water and soil taken together) was also lowest from Leonotis stand (55 118 g ha J) during different rainfall treatments. Minimum ammonia-N concentration (Table 1) of 0.40 -0.53 mg 1 ' was also observed for the Leonotis stand. This may be due to greater loss of the nutrients through nitrification under the moist condition (soil moisture 12%) of the stand. Further, ammonia-N conservation value for the soluble fraction decreased with the increase in rain intensity. This was mainly because the increase in loss fiom vegetated stand was at a higher rate than the corresponding increase from the bare plot. Therefore, its conservation value decreased. But the reverse trend was observed in particulate

0 ' " o L . n e D e t a c f o l i a e - - - - . - o S , a c u t a o , : - - - O B a r e

35 ~ 50

25 . ~_..-c~. 3O

5 r ~" t t ' I I

20 25 31 38 Z,6 55 20 25 31 38 Z, 6 55 RAIN I N T E N S I T Y (ran hr-1) RAIN I N T E N S I T Y (ram h r -1 )

W a t e r r u n o f f W a t e r c o n s e r v a t i o n v a l u e

Boo! j ? soo r --'11

j- -4

2 0 2 5 31 3 8 46 55 RAIN f N T E N S I T Y (ram hr -1)

Soi l e r o s i o n

~ z , O F i . _ ~ o ~ - - 20 ~ .... 9 ~ , ,

20 25 31 38 46 55 RAIN INTENSITY ( ram hr -1)

Soi l c o n s e r v a t i o n v a l u e

Fig. 1. Water runoff and soil erosion from vegetated and bare experimental plots and conservation value (%) of the two species in response to 50 rain showering at different rain intensities.

R. Kumar et al. / Ecological Engineering 8 (1997) 233 239 237

Table 1 Nutrient concentration in runoff water (mg I ~) and deposited sediments (/~g g ~) from Leonotis, Si&l and bare plots in response to 50 min simulated rainfall at six different rain intensities

Parameter Simulated rainfall intensily (mm h ~)

20 25 31 38 46 55

Leonoli5

Total-N Water SoiP

Ammonia- Water N

Soil Nitrate-N Water

Soil Sida

TotaI-N Water Soil"

Ammonia- Water N

Soil Nitrate-N Water

Soil Bare

Total-N Water Soft'

Ammonia- Water N

Soil Nitrate-N Water

Soil

5.00+__0.14 4.00_+0.14 3.90-+{).32 3.50+_0.3l 4.4-+0.18 6.00-+0,26 0.09 -+ 0.01 0.09 -+ 0.0t13 0.08 _+ 0.01 0.//7 _+ 0.02 0.06 +_ 0.03 0.05 + 0,02 0,53_+0.01 0.51_+0.01 0.42_+0.02 0.45_+0.02 /).42-+/).(tl 0.40_+0,01

9 ,10+0 .17 7.30,+0.06 9.10_+0.07 9.10-+0.40 10.10_+0.13 8.3(t-+(t,35 0.28 -+ 0.003 0.24 _+ 0.01 0.22 -+ 0.01 {).3{) +_ 0.03 0.30 -+ 0.01 0.23 _+ {I./11 7.10_+0.30 8.60_+0.07 6.90-+0.40 8.0(I-+0.03 10.00_0.11 16,(1{I-+{I.58

4.00-+0.17 5.00+_0.14 2.90_+0.20 2.80_+0.29 3.50_+0,11 4 .40+0 .18 0.03_+0.13 0.04_+0.001 0.03-+0.003 0.03-+0.003 0.23_+0.003 0.02_+0.002 0.63_+0.01 0.63_+0.02 0.69_+0.01 0.57-+0.02 0.54_+0.92 0.53_+0.01

8 .80+0 .20 7.00_+0.32 8.20_+0.35 7.20_+0.32 8.70_+0.32 5.20_+0.18 0.20-+0.003 0.15+_0.01 0.25-+0.01 0.33-+0.02 0.34_+0.01 0.31 _+0.01 7.50 +_ 0.43 7.80-+ 0.46 6.50-+ 0.26 7.2{)-+ 0.26 7.10_+ 0.26 11.00 + 0.61

3.50 _+ 0.20 4.70 _+ 0.14 5.20 __+ 0.20 3.70 -+ 0.18 4.00 -+ 0.30 4.40 -+ 0.21 0.06 + 0.01 0.058 -+ 0.0030.04 + 0.003 0.04 _+ 0.01 0.03 __+ 0.01 0.02 + 0.01 0.90_+0.03 0.83__+0.02 0.71 __+0.01 0.57_+0.01 0.60_+0.01 ( l .56+0.(d

6.90 __+ 0.26 6.00 __+ 0.30 8.00 __+ 0.03 6.7(I __+ 0.14 8.00 __+ 0.31 5.2(t __+ 0.1 I 0.28__+0.02 0.19_+0.01 0.20_+0.003 0.30+__0.20 0.40__+0.01 0.45 __+ 0.(~1 7.50_+0.55 11.70_+0.60 7.20_+0.40 6.80_+0.22 5.30_+0.23 5.30_+0,14

~' Values are presented as percentages.

fraction. This led to the idea that existing vegetation has greater control on ammonia-N movement through soil than through runoff water. This is also substantiated by the regression equation where time lag (Table 2) explained 97% variation in particulate ammonia-N conservation by Leonotis and 95% in case of Sida. The overall ammonia-N Cv, was found to decrease with the increase in rain intensity from both the species. Rain intensity played a greater role in explaining overall ammonia-N conservation. It explained 88% variability in case of Leonotis and 98% in Sida at P < 0.01 level.

Minimum total nitrate-N loss was again from Leonotis stand which increased from 24 to 75 g h a ~ with the increase in rain intensity while the maximum total nitrate-N loss was from the bare plot. Better ground cover reduced the impact of falling raindrops which in turn affected the magnitude and quality of water runoff (Klausner et al., 1974). The nitrate-N concentration (Table 1) in runoff material varied narrowly during different rainfall treatments. The overall nitrate-N Cv increased successively for both the Leonotis and Sida especially when rain intensity

238 R. Kumar el ul. Ecological Engineering 8 (1997) 233 239

Table 2 Stepwise multiple regression equation relating rain intensity (RI) and time lag (TL) with runoff variables in relation to selected riparian herbs

Parameters Equation R ~

Leonolis Soil conserwttion value

Particulate ammonia-N conservation value Overall ammonia-N conservation value Sida Soil conservation value Particulate ammonia-N conservation value Overall ammonia-N conservation value

48.6+0.70 RI 0.98 49.1 +2.9 RI 0.99 95.1)5 - 0.28 Ft, 0.97 77.7-1).57 RI (I.88

8.4+11.85 R[ I).96 7 4 . 9 - 0 . 4 TI, 1t.95 63.03 0.8 RI /).94

multiple correlation coeflicient are also given. R 2 wdues are significant at the P<0.01 level. The squared

was increased above 31 mm h i. There was a gradual increase in soluble nitrate-N Cv but for particulate fraction, the values decreased successively as the rain intensity was raised.

The mode of nitrogen transport down the slope was mainly in soluble form (52-80%). This may be attributed to high energy of falling raindrops that forcibly desorb the nutrient from the soil particles and cause its transport through water runoff. Maximum share of water in total-N movement was from the Leonotis stand (59 80%). In case of ammonia-N movement the share of water wtried fi'om 83 to 96% and in nitrate-N from 72 to 92% from the three plots during the six rainfall events. This was mainly on account of high solubility of two nutrients in water (Black, 1973). Burton et al. (1977) and Rimer et al. (1978) also reported f¥om their work that a large percent of non-point source nutrients reach water bodies in soluble form.

Acknowledgements

Thanks are due to M.O.E., CSIR and UGC, Government of India, New Delhi, for providing financial support to M/S RK, AKS, NKS and AS.

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