Nutrient and Water Management in Rice-Wheat Systems

- some current issues

Bijay Singh

Department of SoilsPunjab Agricultural University

Ludhiana 141 004 Punjab

MAJOR CONCERNS in RWS• Low fertilizer use efficiencies

• Depletion of soil nutrients reserves i.e. negative nutrient balances

• Emerging nutrient deficiencies/ toxicities in soils

• Loss of soil organic matter and yield sustainability

• Reduced nutrient recycling

• Inefficient water management in rice

• Achieving sustainable high yields of crops requires increased flows of N in the soil and large uptake by crop pants.

• Excessive application of N, or inefficient management means an economic loss to the farmer and can cause environmental problems

• Efficient management of fertilizer N implies that sustainable high yields are ensured and every effort is made to minimize losses of nitrogen to environment. There is no contradiction between these challenges.

Parameters of sustainable soil fertility management

• Indigenous supply of nutrients

• Yield attainable with optimal management

• Efficiency of nutrient input use

• Large field-to-field variability of soil N supply restricts efficient use of N fertilizer when broad-based blanket recommendations for fertilizer N are used

• N use efficiency can be improved by applying fertilizer N when it is needed most

• Innovative tools such as chlorophyll meter and leaf colour chart can help to find when plant needs N most

• Efficiency of applied N can be as high as 78% at time when it is needed most

Leaf color chartsLeaf color charts

Approaches to use of the LCC

• Real-time N management

• Fixed time – adjustable dose

Real-time N management

Basal – 14 DAT or 21 DAS

1) Apply N early

Plant N uptake

Days after transplanting (DAT) or sowing (DAS)

Monitor leaf color at 7-10 day intervals

2) Monitor leaf color

LCC reading below critical value

3) Apply N when LCC reading is below critical value

Plant N uptake

Days after transplanting (DAT) or sowing (DAS)

Critical stages for N application

Fixed time – adjustable dose N management

Monitor leaf color at critical stages

3) Adjust N dose up or down based on LCC reading

Basal – 14 DAT or 21 DAS

1) Apply early N

Tillering

Panicle initiation

Heading

2) Topdress N at predetermined critical times (growth stages)

RTOP 2004

Grain yields of rice and wheat (nine-year average) and total P input-output balance for different P management strategies

Grain yields of rice and wheat (ten-year average) and total K input-output balance for different K management strategies

K applied, kg K2O/ha

Grain yield, t/ha

K accumulation,

kg K/ha

Total K input-output balance, kg

K/haRice Wheat Rice Wheat Rice Wheat

0306090

0306090

5.505.625.765.74

4.785.045.165.05

143165173165

75919193

-115-102- 61- 3Average K input from irrigation water: 100 kg K/ha/year

Micronutrients

• Based on 90419 soil samples, extent of Zn deficiency is 55, 47 and 36 % in Trans-northern, central and eastern parts of IGP

• Reverse trend recorded for B (8, 37 and 68% respectively). Most wide spread in highly calcareous soils of Bihar

• Multimicronutrient deficiencies – Zn+Fe, Zn+Mn or Zn+Fe+Mn appearing in alluvial plain soils under RWS in Punjab, Zn+Fe+B or Zn+B in Bihar

Micronutrients• An application of 5 to 10 kg ZnSO4 ha-1

optimum to meet Zn needs

• Three foliar sprays of 1-2% FeSO4 at 10 d interval and/or reduced soil conditions induced by submergence and OM additions can control Fe deficiency

• Application of 4 (rather than 3) foliar sprays of 0.5% MnSO4 to wheat correct more effectively the Mn deficiency on highly Mn deficient soil (<2.5 mg kg-1 soil)

Micronutrients

• The optimum dose of B in calcareous and heavy textured soils ranged from 1.5 to 2 kg B/ha and in light textured soils it varied from 1 to 1.5 kg B/ha

• Borax is used for soil application and boric acid for foliar sprays (0.25% boric acid)

• In RWS, maximum response was recorded in treatment receiving 16 kg borax ha-1 in alternate crops.

In the coming decades, a major issue in designing sustainable agricultural

system will be the management of soil organic matter and rational use of

organic inputs such as animal manures, crop residues, green

manures, sewage sludge and food industry wastes

Use of FYM in the Indo-Gangetic plains – Diagnostic surveys

• Trans Gangetic plain and Upper Gangetic plain:

15-20 t FYM ha-1 once in 3-5 years

• Middle Gangetic plain

5-6 t FYM ha-1 once in 2-3 years

• Lower Gangetic plain

2-3 t FYM ha-1 once in 2-3 years

Fertilizer N equivalents

FYM in rice - 42 to 52% of the total N applied

Poultry manure for rice - 80 to 127%

Water Management in RWS

• Water shortage is a major constraint to sustaining and increasing the productivity of rice-wheat systems.

• Saving water can be elusive in that reducing seepage, percolation and runoff losses from fields does not necessarily save water if it can be recaptured at some other temporal or spatial scale, for example by groundwater pumping.

Water Management in RWS• For a farmer, “water saving” is likely to mean

using less irrigation water to grow a crop – ideally with the same or higher yield (or ultimately profit), leading to increased irrigation water productivity (g grain/kg irrigation water or Rs/kg irrigation water)

• Saving irrigation water per se has many benefits such as reducing costs to the farmer (e.g. pumping, water charges) but increasing both yield and total water productivity (g grain/kg water from rain + irrigation + soil water) are need of the time to meet the increasing demand for food, and to produce it from less water.

Water Management in RWS

• Many technologies appear to save substantial amounts of water through reducing irrigation water requirement, but whether these are true water savings is uncertain as components of the water balance have not been quantified.

• Such technologies include laser levelling, direct drilling, raised beds, non-ponded rice culture and irrigation scheduling.

Water Management in RWS

• Reducing non-beneficial evaporation losses is a true water saving.

• Optimal planting time of rice to avoid the period of highest evaporative demand and changing to non-ponded rice culture can save significant amounts of water.

• Moving away from puddled, ponded to more aerobic rice culture sometimes brings new production problems.

• Farmers faced with unreliable water supplies need to store water on their fields as insurance, and puddling assists retention of water during the rice crop.

Sowing/planting date

• In NW India the ET requirement of rice declines from around 800 to 550 mm as the date of transplanting is delayed from 1 May to June 30. Substantial irrigation water savings (25-30% or 720 mm) can be achieved by delaying transplanting from mid-May to mid-June

• Many farmers plant earlier than this (e.g. 57% in Punjab) because of external factors such as increased pest pressure on later planted crops and availability of labour and canal water or electricity for pumping

Sowing/planting date

• Direct seeding of rice could help overcome the problem of labour availability, but the optimum sowing date may need to be earlier than the optimum transplanting date which could increase the crop water use requirement

• It is not clear if changing to direct seeding will increase or reduce the water requirement for rice, and the impact may vary depending on sites and systems

Sowing/planting date

• While delaying transplanting in the NW IGP to the optimum time saves water, bringing forward transplanting in eastern India enables more productive use of rainfall.

• Here, irrigation water is scarce, and total system productivity increased by establishing rice with rainfall supplemented by irrigation from groundwater during the pre-monsoon period, and by raising bund height to 20 cm to capture rainfall (Gupta et al. 2002).

• This also benefits the subsequent wheat crop due to the opportunity for earlier planting.

Laser Land Leveling • Land leveling can reduce evaporation and

percolation losses from wheat by enabling faster irrigation times and by eliminating depressions. This also reduces waterlogging problems, especially on heavy textured soils.

• Laser leveling in Pakistan resulted in average wheat irrigation water savings of 25% in comparison with non-lasered fields while increasing yield by 20-35%

• Land leveling reduces the depth of water required to cover the highest parts of the field and for ponding for weed control in rice, and therefore percolation losses, more so on more permeable soils.

Continuous ponding in rice

• Many studies in India and China suggest that continuous ponding is not necessary to maintain rice yields at reasonable levels

• Results from NW India consistently show substantial irrigation water savings (24-40% or up to 650 mm) with no or small yield loss, and even a yield increase on a sodic soil, in changing from continuous submergence to irrigating 1 to 3 days after the floodwater has disappeared

• Irrigation water saving with reduced water depth is probably due to reduced percolation losses, and therefore may not be a real saving.

Raised beds• Potential benefits of beds for wheat production in

the IGP have been known for some time: typical irrigation savings range from 18% to 30-50%

• In Punjab, yields of wheat on beds and flats were similar on two loam soils, but lower on the beds on a sandy loam; it appeared to suffer from water deficit stress prior to the first irrigation, impairing tillering, and demonstrating the need for refinement of irrigation scheduling guidelines for bed layouts.

Raised beds• Farmer and researcher trials in the IGP suggest

irrigation water savings of 12 to 60% for direct seeded (DSRB) and transplanted (TRB) rice on beds, with similar or lower yields for TRB compared with puddled flooded transplanted rice (PTR), and usually slightly lower yields with DSRB

• Many studies in the NW IGP show little effect of rice on beds on water productivity (typically around 0.30-0.35 g/kg) as the decline in water input was accompanied by a similar decline in yield

• The causes of reduced rice yield include increased weeds and nematodes, sub-optimal sowing depth due to lack of precision, and micronutrient (iron, zinc) deficiencies.

Direct seeding of wheat• In direct drilled wheat, water savings of 20-

35% or 90-100 mm have been reported as compared with conventional tillage, with the largest savings in the first irrigations, and comparable or higher yields due to earlier sowing

• On heavier soils, direct drilling may even eliminate the need for a pre-sowing irrigation in the IGP

Best bets – water management in RWS• (1) Laser levelling, (2) shallow intermittent

irrigation for rice, (3) rice planting at the optimum time to reduce crop water use requirement, and (4) direct drilling of wheat

• The technologies to do this already exist, although it will take time for the adoption of laser levelling and direct drilling due to the need for additional machinery.

• However the necessary infrastructure to ensure the availability of water on demand to allow intermittent irrigation for rice is generally lacking in the IGP.

Thanks!