Rice Straw Management
By A. Dobermann and T.H. Fairhurst
Straw is the only organic material 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.
Straw Removal
Removal of straw from the field is widespread in India, Bangladesh,
and Nepal, which explains the depletion of soil K and Si reserves at
many sites. Straw can be used as fuel for cooking, ruminant fodder,
and stable bedding or as a raw material in industrial processes (e.g.,
papermaking). In the process, some or all of the nutrients contained in
straw may be lost to the rice field, particularly where animal manure is
used in other parts of the farming system where the response to straw
application is greater than for rice
An assessment of farmer straw management practices is an important part of developing fertilizer recommendations. The major impact of straw removal is on the soil K balance. Complete straw removal over several cropping seasons without replenishing soil K with mineral fertilizer is likely to lead to increased incidence of K deficiency.
Dr. Dobermann is Associate Professor, University of Nebraska, Lincoln, and formerly Soil
Nutrient Specialist with IRRI; e-mail: adobermann2@unl.edu. Dr. Fairhurst is Director,
PPI/PPIC East and Southeast Asia Program, Singapore.
Burning
Burning causes almost complete N loss, P losses of about 25 percent, K losses of 20 percent, and S losses of 5 to 60 percent. The amount of nutrients lost depends on the method used to burn the straw. In areas where harvesting has been mechanized (e.g., Thailand, China, and northern India), all the straw remains in the field and is rapidly
burned in situ; therefore, losses of S, P, and K are small.
3.1.2. Soil Fertility
According to the Department of Agriculture, Government of Punjab, the soils of
Punjab typically contain low nitrogen content, low to medium phosphorus, and moderate
to high potassium. Besides, the organic carbon in the soil has decreased to very low, and
insufficient levels and organic manure and crop residue have not been properly applied.
Production of 7 t/ha rice and 4 t/ha wheat extract more than 300 kg of nitrogen, 30 kg
of phosphorus, and 300 kg of potassium from the soil per hectare. The burning of crop
residues contributes to the depletion of soil organic carbon, according to the Department
of Soil, Punjab Agricultural University. Moreover, CO2 and soil nitrogen balance changes
quickly, and nitrogen is converted into nitrate, leading to depletion of 0.824 million tons of
nitrogen-phosphorus-potassium (NPK) from the soil annually.
In addition, repeated burns can diminish by more than 50% the bacterial population.
Long-term burning also reduces the amount of 0–15 cm soil loss along with loss of total
nitrogen, biomass, and potentially mineralized nitrogen and organics. The burning of
agriculture residues raises the soil temperature and causes depletion of the microorganism
and flora population. The residue burning will increase the dirt temperatures to just about
35.8–42.2 ◦C at 10 mm depth [11], and semi-permanent effects will even reach up to 15 cm
of the highest soil. Furthermore, the frequent burning reduces the nitrogen and carbon
content in the soil and kills the microflora and fauna, which are useful to the soil, and
additionally removes a significant portion of organic matter. With crop residue burning, the
carbon-nitrogen equilibrium of the soil can be totally lost [5,24]. According to NPMCR [25],
open incineration of 1 tonne of stubble would result in the loss of all organic carbon, 5.5 kg of nitrogen (N), 2.3 kg of phosphorous (P), 25 kg of potassium (K) and 1.2 kg of sulphur (S) in the soil. If the crop residue is kept within the soil itself, it will enrich the soil with C, N, P and K additionally.
Mandal et al.’s study [26] revealed that the burning of rice and wheat residues contributes to a loss of about 80% of nitrogen, 25% of phosphorus, 21% of potassium and 4-60%
of soil sulphur, although it does destroy unwanted bugs and diseases borne by the soil.
Corp residue burning also contributes to a depletion in the crop essential nutrients.
Around 25% of nitrogen and phosphorus are kept in crop residues, making 50% of sulphur
and 75% of cereals potassium intake viable nutrient sources [13]. According to Singh
et al. [8], there was a loss of 2400 kg of carbon, 35 kg of nitrogen, 3.2 kg of phosphorus,
21 kg of potassium, and 2.7 kg of sulphur from burning of rice residues in 1 ha in Punjab
between 2001 and 2002. As presented in Table 3, burning of rice residue led to almost
complete loss of carbon and nitrogen, and about 20–60% loss of P, K and S.
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