Rice
Rice is the most important cereal and in many countries an important staple food for the rural population and their food security. It is grown mainly by smallholders on farms of less than one hectare. The largest rice producers are China, India, Indonesia, and Bangladesh with their huge populations. In proportion to production, trade is smaller, with countries such as India, Vietnam, and Thailand being the largest exporters.
Efficient production of the world's most important staple crop requires good nutrient management
Nitrogen is the most yield limiting nutrient for rice production, especially under flooded conditions. This is the reason, why a large number of growers, particularly smallholders, mainly focus on the application of this nutrient, neglecting the other nutrients, P and especially K, Mg and S. As for other crops, the latter three nutrients play important roles in biomass production, improvement of yields, nitrogen use efficiency, and quality.
- Potassium is required for photosynthesis, starch, and protein production, as well as nitrogen use efficiency, reducing losses to the environment.
- Magnesium is needed for CO2-fixation, sugar translocation, and starch accumulation in grains and roots.
- Sulfur is required for protein formation and nitrogen use efficiency.
- Applying adequate K, Mg and S is therefore a prerequisite for improved yields and utilization of nitrogen.
Rice - The most important food
For more than the half of the world’s population, rice is the most important food. About 90% of the world rice supply is produced in Asian countries. The production systems differ widely in cropping intensity and yield. Ranging from single-crop, rainfed lowland and upland rice with small yields (1-3t/ha) to triple-crop, irrigated systems with annual yields of up to 15–18t/ha.
Optimum nutrient management is vital for making full use of the genetic yield potential at a particular site thereby helping to satisfy the food demands of a growing population in relation to the decreasing availability of water and land.
The most important nutrients for rice
Sole application of nitrogen, as the main driver of biomass production in cereals, has been a long tradition which, however, in the long run led to a depletion of soil nutrients, e.g. P, K, and Mg. The consequence of this practice is that yields decline use efficiency of applied nitrogen decreases, leading to an increase in pollution caused by unused nitrogen. The focus here is therefore on the other nutrients, important to reverse these trends for an optimum rice production.
Potassium – For healthy plants and higher yields
Rice yields are dependent on the number of spikelets per panicle, the proportion of filled grains, and thousand grain weight. These yield parameters are influenced by the management systems used. A well balanced fertilization program is of central importance. The use of potassium within the fertilization program is essential due to the important functions of potassium in plant physiology:
- Potassium is required for a variety of functions in plant metabolism, such as enzyme activation, osmotic turgor regulation, and transport of assimilates.
- Adequate potassium supply is necessary to improve the integrity of cell membranes and cell walls.
- Potassium contributes to greater canopy photosynthesis and plant growth by increasing leaf area and chlorophyll content.
- Potassium positively affects the health of plants by increasing their tolerance to adverse climatic conditions, storage, pests and diseases.
| Plant part | Typical observed range * | Observed average ** | ||
|---|---|---|---|---|
|
uptake (kg kt-1 grain-yield-1)
|
||||
| Grain + straw | 14 - 20 | 17.0 | ||
| Grain | 2 - 3 | 2.5 | ||
| Straw | 12 - 17 | 14.5 | ||
| K content (%) | ||||
| Grain | 0,22 - 0,31 | 0,27 | ||
| Straw | 1,17 - 1,68 | 1,39 | ||
| Unfilled spikelets | 0,61 - 1,20 | 1,07 | ||
* 23 - 75 % interquartile range of farmers fields and field experiments
in Asia (n = 1300)
** Median of farmers fields and field experiments in Asia (n = 1300)
Throughout the growing season it is important to keep the leaf K concentration at certain levels. If the leaf K concentration drops below the critical level the yield potential cannot be fully achieved due to K deficiency.
| Growth state | Plant part | Optimum (%) | Critical deficiency level (%) | |||
|---|---|---|---|---|---|---|
| Tillering to panicle inition |
Y leaf
|
|
1,8 - 2,6
|
|
< 1,5
|
|
| Flowering |
Flag leaf
|
|
1,4 - 2,0
|
|
<1,2
|
|
| Maturity |
Straw
|
|
1,5 - 2,0
|
|
<1,2
|
Magnesium – providing for yield and quality
Although rice has the lowest magnesium requirements among cereal crops, magnesium fertilization to rice crops is becoming standard practice especially on high yielding cropping systems because of magnesium depletion in many soils. Magnesium plays essential roles by forming yield and quality:
- Magnesium is the central atom of the chlorophyll molecule.
- Magnesium is involved in CO2 assimilation and protein synthesis and has an important impact on the nutritional value on rice.
- Magnesium activates many enzymes.
- An adequate magnesium supply leads to a higher proportion of milled rice.
| Treatment |
Milled rice
(%) |
Crude protein
(% of dry matter) |
Starch
(% of dry matter) |
|---|---|---|---|
| Control |
73,3
|
10,7
|
80,6
|
| With Mg |
76,4
|
12,8
|
85,3
|
Mg deficiency can be caused through low availability of soil Mg or a decrease in Mg uptake due to a sub-optimum ratio between exchangeable Ca : Mg. The optimum Ca : Mg ratio in rice shoots between tillering and panicle initiation is 1-1.5 : 1. In order to prevent magnesium deficiency, the leaf Mg con-centration should be kept within the required range. The Mg soil concentration should be > 3 cmolc Mg.
| Growth stage |
Plant part
|
Optimum
(%) |
Critical deficiency level
(%) |
|---|---|---|---|
| Tillering to panicle initation |
Y leaf
|
0,15 - 0,30
|
< 0,12
|
| Flowering |
Flag leaf
|
0,15 - 0,30
|
< 0,13
|
| Maturity |
Straw
|
0,20 - 0,30
|
< 0,10
|
Sulfur, boron, and manganese – improving quality and nutritional value of rice
Sulfur
- The leaf S concentration should not drop below 0.10% before flowering.
- Sulfur is a constituent of essential amino acids (cysteine and methionine), which are important for the human diet.
- Sulfur improves the nutritional value of rice.
- Sulfur is involved in chlorophyll production and hence needed for protein synthesis, plant function, and structure.
- Sulfur increases the efficiency of nitrogen use and has positive effects on yield formation.
Boron
- Boron improves the stability of rice plants because of its important role for cell wall synthesis as well as for carbohydrate metabolism.
- Boron activates the sucrose production and speeds up the transportation from the leaf to grains.
Manganese
- Manganese is required for a range of tasks within the plants, e.g. for the formation and stability of chloroplasts, protein synthesis, O2 evolution in photosynthesis, and enzyme activation.
- Through the formation of side-roots, manganese improves the efficiency of nutrient use by rice plants.
Fertilizer recommendations
Fertilizer is applied to maintain the fertility of the soil so that its natural yield potential can be protected over the long term. This requires the maintenance of an optimal nutrient content in the soil. Nutrients removed with the harvest have to be replaced through an adequate application of fertilizer. Together with the replacement of removed nutrients adjustments have to be added for site specific losses (e.g. leaching or erosion).
The total removal of a plant results from the nutrient uptake of the main crop (e.g. grain, tubers or beets) and the uptake of harvest residues (e.g. straw, leaves). If the harvest residues remain on the field, only the removed nutrients by the main crops have to be replaced.
Recommendation for soil fertilization
Depending on the target yield and the existing K supply from the soil, between 100 and 180 kg/ha of MOP (Muriate of Potash) is recommended to satisfy the crops potassium requirements. Ensuring adequate magnesium is available, 80-100 kg/ha ESTA Kieserit is recommended to help produce better quality grains especially where yields are more than 6 t/ha.
Product recommendation
Recommendation for foliar fertilization
In order to fully exploit yield potential of high yielding varieties grown in continuous cropping systems, it is also recommended to supply the two micronutrients boron and manganese. This can be done effectively in the form of 2-3 foliar applications with a 4-5% solution of epsoMICROTOP (4-5 kg/100 l water).
