Rice IPM: Module 2

Module 2. The First Rule of Rice IPM – Grow a Healthy Crop

Module Overview

Rule one is the foundation of all IPM programs and is particularly important for rice. So what is involved in observing this rule? Actually, it has very little to do with entomology or pathology but is based on practicing good crop management and following sound agronomic practices.

Growing a healthy crop is a season long process starting with land preparation and continuing through to harvest. Good crop management will result in the prevention of potential pest problems later on in the season. The most important management components include pre-planting land preparation, choosing suitable varieties, using clean disease free seed, seeding, controlling weeds and optimizing the nutritional and water status of the crop.

We will highlight each of these components in separate lessons in this module and supplement our discussion by directing you to visit selected Websites with relevant information. The Homepage of IRRI’s Knowledge Bank is – http://www.knowledgebank.irri.org.

Lesson 2.1: Land Preparation

The aim of land preparation is two-fold: To place the soil in the best physical condition for plant establishment and crop growth and to ensure that the soil surface is left level. Contrary to what you might think, good land preparation may or may not involve actual tillage of the soil. Many farmers are finding that, in certain conditions, it is preferable to plant their rice seed directly on untilled soil. This practice is known as zero or minimum tillage and has the potential to reduce costs, raise productivity and result in environmental benefits. A major drawback of this system is that it is much more difficult to control weeds that grow along with the seeded rice.

More commonly, land preparation does involve tilling the soil. Tillage is most often done to a depth that will make it easy for the plant to develop a root system which will physically support the plant and also allow the extraction of sufficient moisture and nutrients so yield potentials can be realized. This is also a key management practice to control weeds in the early stages of the crop.

A key consideration, whatever method of soil preparation is used, is that the resulting soil surface should be as level as possible. Level fields improve water use efficiency and help to control weeds.

There is a lot of information available on land preparation for rice and participants should spend some time looking at the sites listed below. The first ones are from IRRI’s TropRice decision support tool. Participants should access this site and browse the relevant sections under Land Preparation and Land Leveling.You may also use the shortcut links below to access these pages directly. Some additional sources of information are also listed and should be read.

IRRI’s TropRice:

Other sources:

Lesson 2.2: Rice Varieties

Farmers can generally choose from a range of rice varieties. Some of these are locally developed over many years and, through this process, are ideally suited to their environments and are quite tolerant of local pests and other stresses. Quite often these local varieties are of high quality and command a premium in the market place. Unfortunately, local varieties tend to be lower yielding than the high yielding varieties (HYVs) that have been developed by plant breeders working in national and international research programs.

A key characteristic of varieties in relation to IPM is something known as host plant resistance. This refers to the variety’s ability to resist or tolerate pest attacks without sacrificing yield or requiring any other interventions. If a plant has resistance to pests and diseases, the need for cultural, biological and chemical plant protection is reduced or even eliminated. Although scientists’ efforts to develop varieties with ever increasing yield potential often means that natural resistance is reduced, there are a number of HYVs with both high yield potential and resistance to pests. Many modern varieties have multiple resistance to a range of insects and diseases.

Resistant varieties are one important part of an integrated pest management program for rice for several seasons (Heong, 2001):

  • They do not increase farmers’ costs.
  • They limit damage at all levels of pest population throughout the season.
  • They require less pesticide than susceptible varieties do.
  • They can be integrated effectively with other control methods in a pest management program.

For additional information on rice varieties and host plant resistance we invite interested participants to browse the following sites:

Lesson 2.2.1: Genetically Engineered Rice

A lot of current breeding and research work to come up with better varieties is now focused on genetic engineering. This is a promising technology that has the potential to speed up the process and even provide types of resistance which could not be developed by a conventional breeding program. Most early engineering efforts have focused on implanting a gene from a different species which produces chemicals toxic to pest or disease pathogens. More recent work has involved the addition of genes that enhance the plant’s nutritional characteristics or give it resistance to abiotic stresses like drought or salinity.

While this approach to varietal development may offer some exciting potential benefits, particularly for IPM, it is not universally accepted as a good thing. In this course we do not take a position on the advisability of using genetically engineered plants as part of an IPM program but we would like participants to examine the currently available evidence and discuss this matter among themselves. Hopefully you will have selected this as one of the topics in the course discussion series.

For additional information on a few select rice biotech efforts, here are some sites to get you started. Looking forward to seeing your comments about these on the discussion board.

Lesson 2.3: Clean seed

It has consistently been proven that using good quality clean rice seed can result in yield increases in the order of 5-20%. This is really not so hard to understand. If seeds contain disease pathogens before they are planted, plants are unhealthy from the start. If weed seeds are planted along with the rice it increases the weed population and decreases yields because the weeds compete for resources. If seeds are selected from unhealthy or non-vigorous plants, the resulting crop will tend to also exhibit these properties. Fully mature, good quality and healthy seeds are more vigorous and have a much better capacity to overcome adverse conditions in early stage of plant growth. Seeds should have a germination rate of more than 80%.

Seed can contain a range of contaminants including disease pathogens, insects, soil and other plant matter. Seeds can be discolored, already germinated, broken, moldy or deformed. Any of these conditions can result in yield losses and contribute to pest problems.

Clean seeds are characterized by being (Mew, 1999):

  • Pure
  • Full and uniform in size
  • Free of weeds, insects, disease and other matter
  • Viable

Planting clean seed is a key practice in IPM and in observing the first rule of IPM. Some farmers have access to quality commercial certified or good seed and, if so, this is a good way to ensure that clean seeds are planted. For those farmers without access to commercial seed or who prefer to produce their own, procedures for cleaning seeds are relatively easy and often results in an equally good or even better product. Producing clean seed involves the following steps (Mew, 1999):

  1. Select a healthy part of the field for seed production
  2. Keep seed field weed free
  3. Rogue off-types during the growing season (pull and discard plants that are obviously different in terms of height, maturity, or flowering time)
  4. Rogue diseased plants (pull and discard unhealthy, non-vigorous plants or plants with discolored panicles)
  5. Winnow, clean or grade seed (to produce full, plump seed of uniform weight and size, to remove partially filled or empty grains and other light weight contaminants)
  6. Dry seed to a moisture content between12 and 14%.
  7. Store in a sealed clean container in a dry, cool clean area

In some areas it may be advisable to treat seeds to rid them of pests and diseases or to ensure that they have access to needed micronutrients. Treating with a fungicide is the most common. Growers should consult their local agricultural advisors or ask other farmers for their recommendations on this.

Here are a few links to sites with more information on clean seed, seed biodiversity and treating seed:

Lesson 2.4: Seeding (Crop Establishment)

Farmers have developed a range of seeding practices to suit their circumstances. Traditionally, crop establishment for wetland rice involves establishing a nursery or seedbed where plants are raised to a certain age (normally 25-30 days) before they are transplanted into the main production fields. Transplanting is usually done by hand and is quite labor intensive but various manufacturers have developed mechanical transplanters that claim to do a good job. Transplanting gives a uniform stand and is a very good way to help to control weeds.

More and more, however, farmers are switching to direct seeding, either dry direct seeding (on dry plowed land) or wet direct seeding (on flooded leveled fields). This switch has been driven by the decreasing availability of on farm labor and the associated increase in labor costs. Unfortunately, direct seeding results in other problems. Weeds are a much more serious problem in direct seeded rice. Direct seeding requires better land leveling and water management and planting depth is critical. Plant too deep and plants will not emerge or will be weak. Plant too shallow and seeds will be eaten by birds or rats and the mature plants will be more susceptible to lodging.

Whatever seeding method used, it is advisable to perform a final cleaning process on rice seed before sowing. This involves (Mew, 1999):

  • Soaking and rinsing seed in a container of water
  • Stirring for 3 minutes
  • Allowing light seed to float to surface
  • Removing and discarding floating seed
  • Draining the water and drying the remaining seeds (this is best done just prior to seeding to avoid needing to re-dry the grain)

IRRI’s TropRice contains detailed recommendation for crop establishment for different seeding methods. Participants should access this decision support tool and browse the relevant sections under Crop Establishment to learn more about the recommendations associated with their local predominant crop establish practices. You may also use the shortcut links below to access these pages directly.

Lesson 2.5: Water Management

Rice is typically produced on submerged soils. Soil submergence maintains soil organic matter and favors long-term sustainability of the nutrient-supplying capacity of soil. Water requirements for a successful rice crop varies with the method of land preparation, method of crop establishment and duration of the rice crop. It also varies with the soil, environmental conditions and the management of the subsequent rice crop. As rice is a semi aquatic plant, it does not need standing water to grow successfully. However, as water supply is usually uncertain and standing water is a very good way to reduce weed infestation, most farmers prefer to cultivate rice in continuously flooded fields. Standing water also helps to provide nitrogen from free living bacteria.

The response of the rice plant to water stress varies with its growth stage and other agronomic practices. Direct sown rice is less prone to drought than a transplanted crop. Highest water use is during the preparation of land, thus land preparation with minimum timing and maximum use of rain water at the correct time of the season is recommended.

Water is lost through evaporation (E) from free water surface, transpiration (T) from the crop, seepage and percolation down through the soil, bund leakages and runoff from the field. Many of these factors, particularly bund leakages and runoff from the field, can and should be managed to avoid water loss. Evapotranspiration is another source of water loss and is determined mainly by the vapor pressure deficit and the canopy size which is beyond the control of a farmer. Given these factors, the main determinants of water requirement (WR) are evapotranspiration, seepage and percolation (S & P) rates. These can be summarized as follows.

WR = E + T + (S + P)

Water loss through ET, S & P should be supplemented by either natural means such as rain, and seepage from adjoining plots or through irrigation. If an average of 5 mm of water is lost per day by ET, and about 3 – 6 mm/day by seepage and percolation from poorly drained and well drained soils respectively, a total of 8 to 11 mm of water is lost per day from a low land rice field. In this case, if irrigation water could be supplied to a depth of about 7.5 cm per issue, irrigation frequency could be maintained at 7 to 10 days intervals. When initial water height in the field is lower, more frequent irrigation is needed. To conserve water, many farmers choose to keep the crop without standing water for short periods between irrigations. However, if soil moisture level drops below field capacity for an extended period there is a possibility that the soil will form cracks. Soil cracking should be prevented to reduce percolation during subsequent irrigation.

For additional information on water management in rice we have listed several good sites. The first group is again from IRRI’s TropRice decision support tool. Students should access this tool and the information it contains and visit the items under Water Management or use the shortcuts below. Other sites are also listed.

Lesson 2.6: Nutrient Management

Nutrient management is critical to ensure a healthy crop and fully observe rule 1 – Grow a healthy crop. The key factor to remember when thinking about how to best manage the nutrition of a rice crop is that the crop must be provided with optimum levels of nutrients and these must be available to the crop at the time they are most required.

Rice cultivation removes a significant amount of needed nutrients as grain and often as straw removed from the field at harvest (see Table 1 below for some figures). If these nutrients are not replaced, subsequent crops will not be healthy.

Table 1. Nutrient removal by a rice crop


Content (%)

Removal (kg) – 5t/ha (grain) crop

Total removal































It is also important to consider balance as research has shown that the availability of various nutrients affects the others. For example, farmers tend to concentrate on nitrogen applications as this is the element most widely deficient and initial applications tend to produce large yield increases. However, this practice is a major cause of soil nutrient depletion in rice fields. De Datta (1985) showed that the application of 174 kg of N to a farmer’s field increased the rice yield by a factor of 2.9, but increased the removal of P, K and S by factors of 2.6, 3.7 and 4.6, respectively (Mutert, 1995). Table 2 below provides details.

Table 2. Nutrient removal with and without N application

amount of nutrients removed by crop harvest

Research has also shown that when nutrients are applied also has a big effect on yields. It is very important that nutrients are available when they are most needed. If applied at times when needs are not great, expensive nutrients may be wasted. If not available when needed, yield is lost.

Nutrient management is considered in detail in the IRRI Knowledge Bank at http://www.knowledgebank.irri.org/bmp/early-vegetative-phase/transplanted-rice/nutrient-management.html. There you will find detailed fertilizer recommendations for all major nutrients by season, cropping system, maturity class and variety.

Lesson 2.7: Importance of Organic Fertilizer

While many farmers try to provide needed nutrients through the application of only inorganic fertilizers, current research is increasingly showing the value of organic fertilizers – particularly bulk organic fertilizers like farm yard manure, compost or crop residues. Bulk organic fertilizers are known to have a strong positive effect on the chemical, microbiological and physical properties of soil. A key concept for IPM is that soils with high levels of organic matter have greatly improved microbial activity. This results in making soil nutrients more readily available to the plants and is also the foundation for a healthy agroecosystem. Soil organic matter is the starting point for energy cycles that ultimately support high populations of natural enemies. There is some recent evidence showing that rice fields with low levels of organic matter suffer from lower natural enemy populations and more frequent pest outbreaks (FAO, 2001).

While the importance of bulk organic fertilizer cannot be denied there are some associated factors to consider. Farmers tend to prefer inorganic fertilizers because of their convenience and their almost immediate effect on yield. The effect of organic fertilizer on crop yield is long term and requires the acquisition, transportation and application of tons of organic material. For example, it has been shown that changing the soil organic matter (SOM) of soil by one percent by weight will require approximately 20 tons of organic material (the recommended ideal SOM in soil is 5% by volume). A farmer’s socio-economic and cultural conditions will also have considerable influence on how much organic matter he or she can or will apply.

Using one source or another exclusively is not recommended. Much research has shown that neither inorganic fertilizers nor organic sources alone can result in soils with sustainable productivity under highly intensive cropping systems. This has led many experts to recommend the application of a combination of inorganic and organic fertilizers and this practice is widely recognized as a way of increasing farm yield, sustaining or improving productivity of the soil and ensuring a health crop. Inorganic fertilizers supply the basic chemical nutrients (N,P,K, etc.) and bulk organic fertilizers improve the soil, make nutrients more available to the crop and increase biological activity.

Again we would like you to visit some key informational sites and we have listed these below. The IRRI TropRice sites are found under Nutrient Management >> Organic and Inorganic Fertilizers or you may prefer to use the shortcuts below.

If you are still interested in learning more about nutrient management after going through the above sites here is some supplementary reading:

Lesson 2.8: Straw Management

Farmers manage straw in many ways – removal, burning, piled or spread on the soil surface, incorporated into the soil or used as mulch. Each of these practices has a very different effect on the soil’s nutrient balance and soil fertility and the most appropriate choice will depend on many factors.

However, given the previously discussed key role of organic matter in maintaining a healthy crop, the generally preferred way to manage straw is to get it back in the soil. Incorporated rice straw and stubble improve soil texture and tilth, improve drainage, and store nutrients in an available form for the next crop. Straw is a good source of organic material and is often the only one readily available in significant quantities to most rice farmers. About 40 percent of the nitrogen (N), 30 to 35 percent of the phosphorus (P), 80 to 85 percent of the potassium (K), and 40 to 50 percent of the sulfur (S) taken up by rice remains in vegetative plant parts at crop maturity (Dobermann & Fairhurst, 2002) and it is a shame to waste this.

Nutrient balance is also strongly affected by straw management. Straw contains more than 85 percent of the potassium (K) contained in the above-ground biomass. Thus, much greater amounts of K must be applied to maintain the soil supply where straw is removed from the field. Removal of N and P is mostly associated with grain harvest.

Refer to Table 1 to illustrate this concept.

Here are a few sites you should have a look at to improve your knowledge of straw management.