Introduction
In general in agro-ecosystems, soil receives considerable carbon inputs from a variety of sources including leaf fall, stubbles, roots and root exudates as well as through external sources including farm yard manure and compost. The semi-dry system of rice cultivation is mainly confined to tracts that depend on rains and have no supplementary irrigation facilities. In this semi-dry system part of the rice crop’s life cycle passes under aerobic conditions and part under anaerobic conditions. In the conventional rice cultivation practiced in irrigated areas, rice crops’ life cycle passes completely under anaerobic condition. The amount and quality of organic carbon are crucial factors influencing soil productivity. The endemic deficiency of organic matter in tropical sandy soils particularly those under the influence of arid and semi arid climates are a major factor contributing to their low productivity. To improve the soil organic carbon content, organic system of nutrient management is essential to meet the nutrient requirement of the crops as well as to improve the soil organic carbon status. Soil organic matter in soils with tropical upland conditions is more difficult than in soils used for lowland rice conditions.(Sahrawat,2005).Kaboneka et al (1997) found that wheat straw,corn stover or soybean stubble were mineralized during 30 days incubation. Mineralization of green manure is slow in semidry condition hence compost or animal manures can be used as an organic source for semidry rice. Experiments were conducted to explore the possibility of recycling a common weed in the study area, Ipomea cornea as an organic source for semi dry rice.
Materials and Methods
The study area, located in east coastal area of southern peninsular India at longitude (E) 78010’- 79027’ and latitude (N) 9005’- 9056’. The green leaves of Ipomea cornea harvested from wastelands near the experimental site were chopped and mixed with cattle / poultry manures and wetted with deionized water to bring the mix to 60 per cent moisture content. Under laboratory conditions, 5 kg of the green leaves of Ipomea cornea was composted with cattle manure and poultry manure @ 0.625, 1.25, 1.88 and 2.50 kg anaerobically for 30 days. The matured compost was obtained at the end of composting period (30 days). The nutrient contents of the organic materials composted are furnished in Table 1. The moisture content was maintained at 60 per cent. Since the composting was done under anaerobic condition, the mix was not turned. The ‘mix’ was subsequently maintained at this anaerobic condition. A total of nine treatments were replicated for five times. The CO2 –C evolution was measured at weekly intervals. (Bundy and Bremner, 1972). Separate containers were kept for each of the 5 sampling intervals so that once opened for CO2 –C measurement, the container could be discarded.
Field experiments were conducted in coastal sandy tracts with rice-rice cropping sequence under semi-dry condition. The experimental soil (Typic Tropaquept) was alkaline in soil reaction (soil: water ratio 1:2) (pH 8.7), low in
N (Subbiah and Asija, 1956) (90 kg ha-), P (Olsen et al., 1954) (4.2 kg ha-1) and high in available K (Stanford and English, 1949)(324 kg ha-1 ) .The initial soil organic carbon content was 1.2 g kg-1. The Ipomea cornea compost obtained from another batch of composting was applied basally (10 kg / plot) as per the treatment schedule. The experimental plot size was 5 x 4 m2. The design of the experiment was a randomized block design with three replicates. The oxidizable soil organic carbon content was measured (Walkely and Black, 1934) in various growth stages of rice, tillering, panicle initiation, flowering and harvest stages. At harvest stage, rice grain and straw yields and soil temperature were recorded.
Result and Discussion
CO2 -C evolution
Faster mineralization followed by a steady decline in the rate of mineralization with time. Initially, the mineralization was faster; with increase in the period of composting, there was a steady decline in the mineralization rate. The exponential nature of carbon mineralization from soil organic matter and added plant residues was previously reported by Vanlauwe et al., (1994). At all sampling intervals, the lowest amount of C was mineralized from poultry manure and the highest from cattle manure. The pattern of C mineralization from Ipomea cornea compost was similar to that of the control soil from fourth week after incubation onwards; indicating that most of the C added through compost had been mineralized within four weeks of incubation (Figure1). High rates of CO2-C evolution from the Ipomea cornea –cattle manure compost immediately after incubation was noticed. This could be due to the presence of easily decomposable organic compounds in the cattle manure as compared to less easily decomposable organic compounds in the poultry manure. Poultry manure contains large amounts of CaCO3, struvite and other basic compounds (Bril and Solomons, 1990). Low level of decomposition in Ipomea cornea-poultry manure compost could be attributed to high concentration of Ca and neutralization of organic acids and H+ by Ca and buffering reactions (Mahimairaja et al., 1995).
Field Experiment
Oxidizable soil organic carbon content
At all stages of crop growth, significant improvements in oxidizable soil organic carbon content were observed in the Ipomea cornea-poultry manure compost treatments as compared to in the control and Ipomea cornea-cattle manure compost treatments. Highest oxidizable soil organic carbon content (4.30 g C kg-1) was recorded for the Ipomea cornea-poultry manure (50% RD) compost treatment (Table 3). Many studies have revealed a direct linear relationship between soil organic carbon storage and gross annual C input to soil (Halvin et al., 1990; Paustian et al., (1992). With increase in the level of Poultry manure (50% RD) used in the compost, Oxidizable soil organic carbon content was increased.
Yield of rice
Application of Ipomea cornea-poultry manure compost (37.5%RD) recorded higher grain (3550 kg ha-1) and straw yields (4260 kg ha-1) which was on par with the application of Ipomea cornea-poultry manure compost (50% RD) (Table 4). This could be due to the higher amount of CaCO3 in the poultry manure. Calcium in poultry manure exchange with Na in the soil exchange complex, thereby reduce the ill effects of Na on soil and plant. The experimental site was alkaline in soil reaction. Despite a higher nutrient content in the poultry manure as compared to cattle manure the presence of CaCO3 in poultry manure could have favourable effect on the experimental soil. Low yield in Ipomea cornea-cattle manure compost applied plots could be due to the lesser amounts of nutrients added through cattle manure.
Soil Temperature
At harvest stage a negative linear correlation between soil temperature and soil organic matter status was observed (Figure 2). As soil organic matter status increased, decrease in soil temperature was noticed.
Conclusions
Ipomea cornea is one of the most rapidly spreading weeds in southern peninsular India. It is fast encroaching on cultivated lands, water reservoirs and waste lands. Significant amount of time, effort and money has been used for its eradication. Recycling of this weed Ipomea cornea could serve dual purpose of its eradication and serving as a better organic material. Ipomea cornea could be composted with animal manures and used as manure for semidry rice cultivation. Between cattle manure and poultry manure, Ipomea cornea composted with poultry manure recorded lower CO2 evolution,wider C:N ratio and higher rice yield and organic carbon status
REFERENCES
Bril and Solomons, 1990. Chemical composition of animal manure: A modeling approach. Neth.J. Agric. Sci, 38, 333-351.
Bundy, L.G., and Bremner, J.M. 1972. A simple titrimetric method for the determination of inorganic carbon in soils. Soil Sci. Soc. Am. Proc. 36, 273-275.
Havlin, J.L., Kissel, D.E., Maddux, L.d., Classen, M.M and Long, J.H. 1990. Crop Rotation and tillage effects on soil organic carbon and nitrogen .Soil Sci. Soc. Am. J, 54, 448-456.
Kaboneka,S.,Sabbe ,W.E.,and Mauromaustakos,A.1997.Carbon decomposition kinetics and N mineralization from corn,soyabean and wheat residues.Commun.Soil Sci.Plant Anal.28(15&16):1359-1373.
Mahimairaja, S., Bolan, N.S and Hedley. M.J. 1995.Dissolution of phosphate rock during the composting of poultry manure: An incubation experiment. Fert. Res, 40, 93-104.
Olsen, S.R., Cole, C.L., Watanabe, F.S., and Dean, D.A. 1954. Estimation of available phosphorus in soils by the extraction with sodium bicarbonate, U.S.D.A., Circ. 939.
Paustian, K., Parton , W. J. and Persson, J. 1992. Modeling soil organic matter in organic amended and N fertilized long term plots. Soil Sci. Soc. Am. J, 56, 476-478.
Stanford, S and English L. 1949. Use of flame photo meter in rapid soil test of K and Ca. Agron J., 41 : 446-447.
Subbiah, B.V. and Asija, G.L. 1956. A rapid procedure for the estimation of available N in soils. Curr. Sci., 25 : 259-260.
Vanlauwe, B., Dendooven, L. and Merckx, R.1994. Residue fractionation and Decomposition: the significance of the active fraction .Pl. Soil, 158, 263-274.
Walkley, A and C.A. Black. 1935. An examination of methods for determining organic carbon and N in soils. J. agric. Sci, 25, 598-609.
Table 1. Nutrient contents of manures (mg g-1 of dry matter) used in the
Study (Mean values)
Nutrients
Cattle manure
Poultry manure
Ipomea cornea
N
32.5
45.0
11.6
P
7.0
16.5
3.8
K
16.0
18.5
3.1
Ca
6.5
43.0
1.2
Mg
6.5
5.5
3.8
S
3.5
5.5
2.7
Organic carbon
112
238
601
Organic matter
193
410
1036
Table 2. Estimated quantity (kg ha-1) of nutrients added to the soil through the
manures evaluated in this study
Treatments
Amount of cattle/poultry manure added
(tha-1)
Nutrients added through manures (kg ha-1)
N
P
K
Cattle manure
12.5% of RD*
0.625
20.31
4.38
10.00
25.0 % of RD
1.250
40.63
8.75
20.00
37.5% of RD
1.875
60.94
13.13
30.00
50.0% of RD
2.500
81.25
17.50
40.00
Poultry manure
12.5% of RD*
0.625
28.13
10.31
11.56
25.0 % of RD
1.250
56.25
20.63
23.13
37.5% of RD
1.875
84.38
30.94
34.69
50.0% of RD
2.500
112.50
41.25
46.25
(*RD -Recommended dose-5t ha-1)
Table 3 . Oxidizable soil organic carbon in crop growing period (g kg-1 soil)
Treatments
Tillering
Panicle Initiation
Flowering
Harvest
Cattle manure
12.5% of RD
1.4
1.6
1.7
1.9
25.0 % of RD
1.7
2.0
2.2
2.5
37.5% of RD
1.9
2.3
2.6
3.0
50.0% of RD
2.3
2.5
2.8
3.1
Poultry manure
12.5% of RD
1.6
2.0
2.2
2.5
25.0 % of RD
2.1
2.3
2.6
3.2
37.5% of RD
2.5
2.7
2.9
3.4
50.0% of RD
2.8
3.3
3.6
4.3
Table 4 . Yield (Kg ha-1) as influenced by the incorporation of organics
Treatments
Grain
Straw
Cattle manure
12.5% of RD
2320
2784
25.0 % of RD
2574
3063
37.5% of RD
3265
3918
50.0% of RD
3097
3685
Poultry manure
12.5% of RD
2725
3270
25.0 % of RD
3287
3912
37.5% of RD
3550
4260
50.0% of RD
3425
4110
SEd
137
164
CD(P:0.05)
325
389
Table.5 Cumulative CO2-C mineralization (mg kg-1) in the compost
(i) Ipomea cornea – cattle manure compost
Treatments
Incubation intervals (weeks)
IC-CM
1
2
3
4
5
12.5% RD
300
650
810
790
720
25.0 % RD
345
687
835
797
754
37.5% RD
373
692
869
804
805
50.0% RD
410
724
925
910
831
SEd
3.86
5.09
2.69
2.39
1.61
CD(P=0.05)
9.45
12.47
6.58
5.85
3.94
Soil
1.0
1.2
1.9
1.6
1.5
(ii) Ipomea cornea – poultry manure compost
Treatments
Incubation intervals (weeks)
IC-PM
1
2
3
4
5
12.5% RD
200
390
454
442
420
25.0 % RD
227
415
475
457
443
37.5% RD
254
452
517
489
481
50.0% RD
273
469
534
510
528
SEd
0.95
0.93
0.81
1.99
3.45
CD(P=0.05)
2.33
2.28
1.99
4.88
8.45
Soil
1.00
1.20
1.90
1.60
1.50
R.K.Kaleeswari a and Richard Bell b
a Department of Soil Science and Agricultural Chemistry, TamilNadu Agricultural University, Coimbatore, TamilNadu, India
b Murdoch University,90 South Street,Murdoch.Perth,Western Australia 6150
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