Despite applying 10-15 metric tons of manure per hectare, SRI rice plants start to turn yellow 6 to 8 weeks after planting. Farmers believe this is due to a nitrogen deficiency, and treat the yellowing fields with urea (between 70 and 120 kg/ha) (see Fertilization Blog Entry).
Following the SRI guidelines (see Fertilization Blog Entry), we hoped to replace chemical fertilizers with application of organic manure. Field reality indicates that the applied organic manure does not supply nutrients needed at the time of tillering.
Reasons could be:
- Insufficient amount of organic manure.
- Manure quality and time of nutrient release not responding to plant needs.
- Due to soil depletion and the lack of previous organic matter applications to the soils, a one-time use of organic manure may not be enough to establish a balanced nutrient supply to the crops. A soil build up over several seasons may be necessary.
- Crop management practices are affecting nutrients availability to the plants.
One indication that the quantity of applied manure was insufficient can be seen in this photo of the SRI fields in Kessou Koreye. The dark green spots (see arrows) within the fields are places where the manure was piled before it was spread over the field (see picture in Fertilization Blog Entry). The number of tillers on the plants growing in these green spots is also much higher than in the rest of the field.
Mid August to early September, 2008
Yellowing of Fields
SRI Timbuktu Blog
Plants in SRI fields are turning yellow in Horogoungou. Unfortunately, proper soil analysis is not locally available. Soil analysis is expensive in Mali, and testing many or all the plots would require a substantial budget. Nevertheless, it is critical to understand soil processes, and applied research is needed to do that.
Application of urea brings a dramatic and rapid change to the plants, as seen in these fields in the village of Kessou Koreye: The field to the left received some urea while the field to the right remains unfertilized.
Not all fields react the same way, some turn yellow faster than others do. Crop management practices such as timely weeding had a visible impact on crop performance and plant colors, as further explained in the Impact of Weeding Blog Entry.
applied urea
no urea