National Institute for Soils and Fertilizers

Research
(this page is under preparation)

Use of quefts for calculation of
fertilization rates for rice

Dr. Tran thuc Son, National Institute for Soils and Fertilizers

       In Viet nam in the 1990s some agrochemists have calculated the fertilization rates for some crops following the method worked out by scientists in the Former Soviet Union. The scientific basis of this method was:
       1. Expected crop yield or crop yield increase.
       2. Amount of NPK to produce 1 ton of product.
       3. Capacity of nutrient supply of the soil
       4. Capacity of nutrient supply of FYM and crop residues.
       5. Fertilizer use coefficient of FYM and mineral fertilizers.
       However, these calculations have only been applied on experiment scale, but not on larger scale. Recently, some mathemathic models or microcomputer software have been used for that purpose, such as DSSAT (Decision Support System for Agrotechnology Transfer) or QUEFTS (Quantitative Evaluation of Fertility of Tropical Soil).
       During past years, in the framework of the NISF-IRRI Collaborative Project on "Reversing Trends of declining productivity in intensive irrigated rice system in the Red River Delta" , the system of QUEFTS has been used for calculation of recommended fertilization rates.
       The parameters needed for fertilization rate calculation are:

I. Nutrient supply capacity of the soil, through:

1. Soil analysis: C, N, P, K (g/kg); pH (H₂O) 1:1; CEC (Cmol kg^-1); K⁺ ,Na⁺, Ca⁺⁺, Mg⁺⁺; P-Olsen (Cmol kg^-1).
2. Experiment: Use the treatments of no fertilizer or Pk, NP, NK (use the nutrient uptake by crops from the experiment, kg ha ^-1 ).

II. Crops:

1. Amount of N, P, K to produce 1 ton of agricultural product (including the nutrient amount needed by by - products) (kg).
2. Physiological efficiency of N, P, K (number of kg paddy formed by 1 kg N, P, K taken up by the plants) (kg paddy/1 kg nutrient taken up).
3. Efficiency of mineral fertilizer use, %: Nutrient amount used by crop, total nutrient amount applied to the crop.
4. Yield potential, ton/ha.
5. Planned yield , ton/ha.

III. Organic fertilizer:

1. Nutrient content of organic fertilizer, % (N, P, K)
2. Nutrient use coefficient of organic fertilizer for the first rice crop (%)
3. Application rate of organic fertilizer (ton/ha).
The fertilization rate for rice used by a farming household in the Red River Delta is as follows:

Spring rice crop:

1. N supply capacity of soil = 54.6 kg N/ha
    P supply capacity of soil = 18.6 kg P/ha
    K supply capacity of soil = 82.5 kg K/ha
    Applied FYM amount = 9 tons/ha 2. Yield potential (Ymax) = 10 tons/ha
3. Planned yield = 8019 kg/ha (about 80% maximal yield )
4. Fertilizer amount needed to apply = 130 kg N, 10 kg P, 70 kg K/ha
5. Expected nutrient uptake = 157 kg N, 23 kg P, 125 kg K
6. Expected physiological efficiency = 63 kg paddy/1 kgN, 347 kg paddy/ 1 kg P, 64 kg paddy/1 kgK.

Summer rice crop:

1. N supply capacity of soil = 57.9 kg N/ha
    P supply capacity of soil = 20.2 kg P/ha
    K supply capacity of soil = 66.4 kg K/ha
    Applied FYM amount = 9 tons/ha
2. Yield potential (Ymax) = 7.5 tons/ha
3. Planned yield = 6623 kg/ha (about 88% maximal yield )
4. Fertilizer amount needed to apply = 80 kg N, 10 kg P, 70 kg K/ha
5. Expected nutrient uptake = 106 kg N, 24 kg P, 103 kg K
6. Expected physiological efficiency = 62 kg paddy/1 kgN, 277 kg paddy/1 kg P, 65 kg paddy/1 kgK.