Good Soil Care Practice in the Tropics: Toward a New Challenge
Abstract
The Japan International Research Center for Agricultural Sciences (JIRCAS), in collaboration with various partner institutions, has conducted some long-term field experiments on soil fertility management and disease control in Vietnam and Indonesia. The studies observed that by using locally available resources like rice straw manure, chemical fertilizer use could be significantly reduced with little yield reduction and that by introducing various crops and fallow, some disease occurrence could be reduced, resulting in more stable yield rotation practice in vegetable production. This paper discusses the importance of studying the interactions among crop, pest and soil for more sustainable and safer crop production in the tropics.
Key words: JIRCAS, soil management, Vietnam, Indonesia
Introduction
Recently, in Southeast Asia, with the slump of prices of rice and other cereals resulting from the weakening of demand and supply, the diversification of agriculture (e.g., shift to horticultural and other high value crops) in search of alternative income sources has become an important issue.
At the same time, the development of the rural economy and the drain of agricultural population as well as the rapid dissemination of high-yielding crop varieties have accelerated the tendency toward high-chemical input agriculture initiated by the Green Revolution. It has been pointed out that such tendency has resulted in crop yield stagnation and environmental degradation, growing concerns for food safety and the implementation of good agricultural practices (GAPs).
Therefore, it seems that there is more interest in establishing new soil management guidelines that can respond to these socioeconomic changes. JIRCAS has carried out relatively long-term soil management experiments in Vietnam (lowland), Indonesia (highland) and so on. These experiments have taught us some possibilities to establish such guidelines.
Rice Straw Compost Application Trials in Mekong Delta, Vietnam
Continuous rice straw compost application trials have been conducted at Cuu Long Delta Rice Research Institute (CLRRI) (Cantho, Vietnam) (Man et al.) since the wet season of 2000. Rice (IR64, 100-day growth period) have been cultivated twice a year, and seven compost and chemical fertilizer treatments (Table 1) were applied in a randomized block design with three replications (30 m2 for each plot):
Rice straw compost and phosphorus fertilizer were plowed in surface soil (0_5 cm deep) for land preparation. Pre-germinated seeds were broadcast at 200 kg ha-1. Moisture content and Total C, N, P and K concentrations of the rice straw compost applied into the field are shown in Table 2.
Nitrogen fertilizer was equally split-applied at 10, 20 and 30 days after sowing (DAS), and potassium fertilizer was also equally split-applied at 10 and 30 DAS. Recommended rates were 100 N, 40 P2O5 and 30 K2O kg ha-1 for dry season. Total C, N and P concentrations in the surface soil were 35.1 g C kg-1, 3.3 g N kg-1 and 240 mg P kg-1 in air-dried soil sampled after the first harvest, respectively.
SPAD (chlorophyll) meter was used to measure the nutrient situation of rice plants and it was observed that both in wet season (Table 3) and in dry season (Table 4), the more chemical fertilizer was applied, the higher the SPAD values. It was reported that an optimum SPAD value for directly seeded rice plants ranged from 32 to 36 in dry season and 29 to 32 in wet season (Huan et al. 1998, 2000). It appeared that rice plants in RSM treatments plus less chemical fertilizer would maintain the optimum range of nutrient concentration both in wet and dry seasons.
Soil microbial population in the wet season tended to be higher than that in the dry season (Table 5 and Table 6), and the population in the RSM treatment was always higher. Similar tendency was found in soil electron transport system (ETS) activities and soil protein content (Data are not shown).
There was also no significant difference in average rice yield between T3, T4, T5, T6 and T7 both in the wet season and the dry season (Table 7 and Table 8) except for that in the dry season of 2003, when rice plants suffered from blast disease (Table 9), and yields were lower as compared with those in the other years.
Our results indicated that chemical fertilizer could be reduced by 40_60% from the present recommended application rate and replaced with RSM without decreasing rice yield in the Mekong Delta region and that we could even expect higher yield when blast disease outbreak would occur.
Crop Rotation Trials to Prevent Cabbage Clubroot Disease in the West Java Highlands, Indonesia
Crop rotation trials have been conducted in order to prevent cabbage clubroot disease at the Indonesian Vegetable Research Institute (Lembang, Bundung, Indonesia) since 2000 (Yamada et al.). Various vegetable crops have been grown three times a year, and each cropping season has one month of preparation for nursery and three months for growth. Cabbage (Green Coronet), carrot (Local Cisarua) and potato (Granola) are widely cultivated in the West Java Highlands and these were chosen as major crops in our rotation sequence.
Each major crop was grown both as a constituent of a rotation and as continuous cropping. Four series of rotation patterns were tested: a) cabbage-carrot-potato (R) or cabbage-potato-carrot (R2) series in a year; b) a fallow in dry season with two major crops (RF); c) corn (local var.) with R or R2 (RC, RC2); and d) R or R2 with leaf onion (local var.) and tomato (Arthaloka) as companion crops (RM). Each plot (10.8 m2) had two replicates, and plant spacing was 60 cm row, 35 cm hill distance for cabbage, 5 lines, in 120 cm rows for carrot, 60 cm row, 30 cm hill distance for potato, and 60 cm row, 35 cm hill distance for corn, onion and tomato.
Lime was broadcast at a rate of 100 g m-2. Manure was applied at a rate of 1 kg plant-1 in wet condition for cabbage and potato, and moist manure was applied at a rate of 1 kg plant-1 for cabbage and potato. Then, chemical fertilizer was applied at the following rates: 11.3-9.6-12.0 (N-P2O5-K2O, g m-2) for cabbage; 4.5-19.2-9.0 for carrot; and 10-10-10 for potato and corn. The fertilizer was applied on planting holes for cabbage and potato and to the whole area of seeding bed for carrot.
Conventional pesticides and fungicides were applied about once a week. Weeds were removed with a hoe. Some plant parts such as outer leaves and stems with unusually thick roots in cabbage, auxiliary stems in corn and excess leaves in carrot were also removed and moved out from the field. Aerial parts of potato plants were left in the field and decayed till harvest time.
Until 2002, six series of rotation had been examined. In the fourth season, cabbage yields in the rotation treatment ranged from 7.02 to 7.39 kg m-2 and were higher than those in the continuous cropping treatment (C: 2.57 kg m-2). In the seventh season, cabbage yield in the rotation treatment ranged from 5.30 to 7.35 kg m-2 and were higher than those in C (4.50 kg m-2). However, such difference tends to decrease at the later seasons (Fig. 1).
Cabbage of the C plots was attacked by clubroot, as indicated by wilting symptom from the early stage of growth. Fig. 2 shows the root damage score by clubroot at harvest time. Although half of the rotation treatment plots (R and R2) were also affected by clubroot in the fourth and seventh season, the high yields were still maintained. It was also suggested that both carrot and potato decreased the clubroot damage similarly and that it would be more important to lie land fallow for a host.
Kiriyama and Otomo (2003) reported that yield loss of cabbage was not considered severe until clubroot disease index reached 30%. It was also reported that trap crops such as resistant kale and turnip would also reduce the disease (Yamagishi et al. 1986). However, for longer periods, it is recommended that the fallow practice will be more useful to avoid accumulation of clubroot disease pathogen in soil.
Conclusions and New Challenges
Our soil management experiments led to the following tentative conclusions:
- 1. Chemical fertilizer can be reduced significantly without yield reduction with locally available resources like rice straw manure. It can be also expected that such alternative practice can reduce some disease occurrence and result in less pesticide application and more stable yield.
- 2. Rotation practice, by introducing various crops and fallow, in vegetable production can reduce some disease occurrence and result in more stable yield and income generation.
Our conclusions were based on long-term treatments in Vietnam (9 seasons) and Indonesia (13 seasons). We also observed more stable yields in more than 20 year-long organic matter treatment as compared with chemical fertilizer-oriented treatment for corn-mungbean cropping system in Thailand. Unfortunately, our data collected from these experiments are typical agronomic data such as yield, disease occurrence and soil chemical composition. We feel that more attention should be paid on the interaction among crop, chemical nutrients, organic matter and soil microorganisms in tropical conditions.
Our experiments have paid little attention to reducing pesticide use. It has been said that the climate condition in the Southeast Asian region is favorable to weeds, insects, fungi and bacteria and that using pesticide is inevitable to produce high-quality products. It becomes apparent that some cultural practices can reduce pest occurrence considerably in this region, and it is necessary to study the interactions among the various cultural practices and pest occurrence in the region.
For 2006, we have a plan to initiate a regional research network on soil care practice and other cultivation practices in order to reduce chemical input and attain sustainable production in Thailand, Vietnam and Indonesia. The research will focus on the effects of long-term application of organic matter and biofertilizer in combination with some cultivation practices on crop productivity nutrient balance and microbial and physical properties in soil.
We would like to challenge this initiative in order to provide a better scientific basis to improve the present GAPs in the region and step up efforts to a next generation of GAPs.
References
- Huan T.T.N., Khuong T.Q., Kon T. and Tan P.S. 1998. Nitrogen management in rice using chlorophyll meter. OMON RICE, 6: 53_58.
- Huan T.T.N., Tan P.S. and H. Hiraoka 2000. Optimum fertilizer nitrogen rate for high yielding rice based on growth diagnosis in wet seeded culture of rice. In: Proceedings of the 2000 Annual Workshop of JIRCAS Mekong Delta Project; 14_17 November 2000. pp. 60_67.
- Kiriyama N. and R. Otomo. 2003. Relationship between damage degree of clubroot disease and cabbage yield. Res. Prompt rep. (Tohoku agric., 2002). pp. 263_264 (In Japanese).
- Man L.H., Khang V.T. and T. Watanabe. 2003. Improvement of soil fertility by rice straw manure. In: Proceedings of the Final Workshop of the JIRCAS Mekong Delta Project. pp. 362_372.
- Yamagishi H. et al. 1986. Effects of resistant plants as a catch crop on the reduction of resting spores of clubroot Plasmodiophora-brassicae in soil. Journal of the Japanese Society for Horticultural Science, 54(4): 460_466.
- Yamada M., A.A. Asandhi , E. Purwati and M. Dianawati. 2005. Control of cabbage clubroot disease by employing one-year crop rotation with three vegetable combination in the West Java Highlands of Indonesia. JIRCAS Working Report, 43: 175_184.
Index of Images
Figure 1 Effect of Crop Rotation on Cabbage Yield.
Figure 2 Effect of Crop Rotation on Cabbage Root Damage.
Table 1 Compost and Chemical Fertilizer Treatment
Table 2 Moisture and C, N, P, K Concentration of RSM
Table 3 Effect of RSM and Chemical Fertilizer on Spad Value at 50 Das in Wet Season
Table 4 Effect of RSM and Chemical Fertilizer on Spad Value at 50 Das in DRY Season
Table 5 Effect of RSM and Chemical Fertilizer on Microbial Population of Soil in Log10 of C.F.U/G DRY Soil (Wet Season)
Table 6 Effect of RSM and Chemical Fertilizer on Microbial Population of Soil in Log10 of C.F.U/G. DRY Soil (DRY Season)
Table 7 Effect of RSM and Chemical Fertilizer on Rice Yield in Wet Season
Table 8 Effect of RSM and Chemical Fertilizer on Rice Yield in DRY Season
Table 9 Blast Disease in DRY Season 2003 and Grain Discoloration in DRY Season 2005
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