E L S E V I E R Bioresource Technology69 (1999) 181-183

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Short communication

Plant growth and nematode dynamics in response to soil amendments with neem products, urea and compost

M. Akhtar Department of Plant Protection, Aligarh 202 002, India

Received 15 January 1998; revised 28 July 1998; accepted 11 August 1998

Abstract

Two neem-based granular products, Achook and Suneem G (containing azadirachtin), urea and compost manure were incorporated in field soil at different doses. These treatments decreased the number of plant-parasitic nematodes with increasing doses of products. Combinations of both neem-products with urea were the most effective in suppressing plant-parasitic nematode populations. The neem products and product combinations with urea significantly decreased numbers of free-living nematodes compared with controls; however, populations increased in the compost-treated plots. The growth of pigeonpea (Cajanus cajan L.) was improved in all treatments; in part due to the control of plant-parasitic nematodes and in part due to manurial effects. Urea was phytotoxic at 330 kg N/ha when applied alone, however, it was not phytotoxic at this addition rate when given in combination with the neem-based products. © 1998 Elsevier Science Ltd. All rights reserved.

Keywords: Azadirachta indica; biological control; Cajanus cajan; Compost; Free-living nematodes; Plant-parasitic nematodes; Nematode control; Urea

1. Introduct ion

Neem (Azadirachta indica A. Juss.) products, including leaf, kernel and seed powders, seed extracts and oil have been reported to control several agricul- tural pests including plant-parasitic nematodes (Ivibi- jaro, 1983; Schmutterer, 1990; Akhtar and Alam, 1991; Akhtar and Mahmood, 1994). In the past few decades the efficacy of deoiled neem cake, neem oil and neem leaf as soil amendments has been studied with nematodes (Akhtar and Alam, 1993a,b; Akhtar and Mahmood, 1997). Because of concern about the conse- quence of the use of chemicals other means of control- ling pests and diseases are being sought. Reduction in population densities of plant-parasitic nematodes in response to application of organic amendments has been reported in many studies (Muller and Gooch, 1982). Practical use depends on a large and readily- available supply of these materials.

Free-living nematodes may accelerate the decom- position of soil organic matter (Abrams and Mitchell, 1980). Numbers of free-living, microbivorous nematodes increase rapidly in the soil following the addition of organic and inorganic fertilizers (Marshall, 1977), while there can be a corresponding decrease in

plant-parasitic nematodes (Mankau and Minteer, 1962; Heald and Burton, 1968; Tomerlin and Smart, 1969).

The present field study assessed the effects of different amounts of two neem-based products (Achook and Suneem G), urea and compost amend- ments on densities of plant-parasitic and free-living nematodes and growth of pigeonpea in field soil.

2. Methods

The experimental field was thoroughly ploughed to a depth of 10-15cm and divided into small plots measuring 2 × 3 m separated by 0.5-m wide alleys. The field soil was alluvial of pH 8.3, with 1.0% organic matter. The plots were treated separately with urea, or compost (cattle solid-manure and leaves) both at 110, 220, 330 kg N/ha; Achook (azadirachtin and nimocinol; Godrej Agrovet Ltd, India) and Suneem G (azadir- achtin; Sunida Exports, India) at 5, 10 and 15 kg/ha and 5 kg Achook+ 110 kg urea N/ha, 10 kg Achook+220kg urea N/ha or 15 kg Achook+330 kg urea N/ha. Untreated plots that did not receive soil amendments or fertilizers were also included. Compost

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182 M. Akhtar/Bioresource Technology 69 (1999) 181-183

materials were added to plot soil 4weeks before planting and other treatments were added when planting pigeonpea seeds (Cajanus cajan L.). The experimental design was a randomized complete block with five replications of each treatment including untreated plots. Cultivation, control of insects, foliar disease and weeds were done according to local use. The field was irrigated as required.

Soil samples for nematode assay were collected from each plot before sowing (May 1994) and one day after harvest (July 1994). A bulked soil sample of 30-40 cores was taken from the rhizosphere of each plot using a 2.5-cm diameter cylindrical corer. Cores were composited and a 100-g sub-sample was used for nematode extraction by Cobb's sieving and decanting followed by Baermann funnel extraction (Southey, 1986). Plant-parasitic and free-living nematodes were identified and preserved in a 5% formalin solution.

Sixty days after sowing, pigeonpea plants from the entire plots were harvested and dry weights of shoots and roots were recorded. Dry weights were determined after placing the plants in an oven for 12 h at 60°C. In each plot sample, nematodes were counted separately and identified as either free-living or plant-parasitic nematodes (Hoplolaimus indicus Sher, Helicotylenchus indicus Siddiqui, Rotylenchulus reniformis Linford & Oliveira, Tylenchus filiformis Bastian, and Meloidogyne incognita (Kofoid and White) Chitwood).

Data were subjected to analysis of variance (ANOVA) and Fisher's least significant difference (FLSD) was calculated for separation of means.

3. Results

3.1. Effect on plant growth

The growth of shoots in plants treated with Achook or Suneem G at the largest dose (15 kg/ha) was up to three times greater than that of untreated plants (Table 1). Addition of urea further increased plant growth in plots treated with Achook or Suneem G. Efficacy of the two neem-products was similar, and plant growth increased with increase in doses of these materials. Urea amendment was as effective as compost at single and double doses although urea was phytotoxic at 330 kg N/ha when added alone. However, urea was not phytotoxic at this addition rate in combination with the neem-based products. In the untreated plots, plant growth parameters were much reduced, presumably due to the increase in population of plant-parasitic nematodes.

3. 2. Effects on plant-parasitic nematodes

Populations of plant-parasitic nematodes differed greatly according to treatment, but increased in

Table 1 Effect of soil amendments on nematode population and growth of pigeonpea, Cajanus cajan after 60 days

Soil amendment Dose No. of nematodes per 100 g soil

Plant-parasitic

Dry weight per plant (g)b

Free-living Shoot Root Total

Initial population 2365 1695 Achook 110 kg N/ha 480 1130

220 kg N/ha 392 920 330 kg N/ha 300 810

Suneem G 110 kg N/ha 492 1021 220 kg N/ha 380 812 330 kg N/ha 295 772

Urea 110 kg N/ha 780 950 220 kg N/ha 580 1035 330 kg N/ha 402 1240

Achook + urea 5 kg + 110 kg N/ha 302 1014 10 kg + 220 kg N/ha 200 1245 15 kg +330 kg N/ha 105 1335

Suneem G+urea 5 kg+ 110 kg N/ha 315 1035 10 kg +220 kg N/ha 205 1430 15 kg + 330 kg N/ha 110 1512

Compost 110 kg N/ha 820 2372 220 kg N/ha 602 2840 330 kg N/ha 450 3130

Untreated (control) 8592 1760 LSD (P< 0.05) 46.1 37.1

15.8 12.3 28.1 17.3 12.5 29.8 19.1 13.1 32.2 15.7 12.2 27.9 17.4 12.5 29.9 19.2 13.0 32.2 14.3 11.3 25.6 15.4 11.9 27.3 a a a

16.7 13.0 29.7 18.1 13.4 31.5 19.5 14.1 33.6 16.4 13.0 29.4 17.8 13.2 31.0 18.9 13.9 32.8 13.8 12.0 25.8 15.1 12.5 27.6 16.2 12.8 29.0 6.0 4.3 10.3

2.63

Each value is the mean of five replicates. aplants died before the measurements were taken. bMean of plant weight from whole plot.

M. Akhtar/Bioresource Technology 69 (1999) 181-183 183

untreated plots because pigeonpea is a highly nematode-susceptible crop. The addition of Achook and Suneem G, compost and urea significantly reduced the total number of plant-parasitic nematodes (Table 1). The greatest reduction in plant-parasitic nematode populations was observed with Achook and Suneem G with urea amendments, followed by Achook and Suneem G alone, urea and compost. The reduc- tion in nematode numbers was observed with increasing doses of the treatments.

3.3. Effects on free-living nematodes

In unamended soil, the populations of free-living nematodes between the time of sowing and harvesting the crop were not significantly different. In all the treated plots, except those with compost manure, however, the population of free-living nematodes signi- ficantly decreased (P<0.05) especially with neem product treatments (Table 1). In the case of compost treatment, populations of free-living nematodes were significantly greater than in control plots. There were significant differences in numbers of free-living nematodes obtained at different doses of all treat- ments.

4. Discussion

All the doses of amendments significantly decreased the populations of plant-parasitic nematodes and increased the pigeonpea plant growth compared with untreated control plots. The results confirm earlier findings (Akhtar and Alam, 1993b) that applying an appropriate concentration of Nimin (a neem-based urea-coating material from Godrej Agrovet Ltd, India) with urea promoted crop yield as well as reduced the numbers of plant-parasitic nematodes. Nimin contains azadirachtin, a neem triterpene that acts by delaying the rapid transformation of ammonium nitrogen into nitrate nitrogen. This ensures slow and continuously available nitrogen during plant growth. In the present work, the largest dose of urea (330kgN/ha) was markedly phytotoxic, whereas at 110 or 220kgN/ha urea was effective in the suppression of nematode populations and enhanced plant growth performance. Urea plus neem products promoted even greater growth. Rodriguez-Kabana (1986) pointed out that nitrogen fertilizers that release ammonium N in the

soil are most effective in suppressing nematode popula- tions and they suggested that the rate required to obtain significant suppression of nematode populations is generally in excess of 150 kg N/ha.

Application of natural inhibitors, as here, provides an economical option for controlling plant-parasitic nematodes without disturbing agroecosystems. Further research on natural products is needed.

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