Nutrient management for drought-prone rainfed lowlands:

The main reasons for drought stress of rice in rainfed systems are insufficient rains and/or uneven distribution of rains. Drought might occur at any time in the season but in some regions a drought happens most frequently at a certain growth stage (early season drought, mid season drought, late season drought). The drought risk of individual fields within a region is further affected by the toposequence and soil characteristics. Rice fields on upper terraces generally experience longer and more severe drought as compared with lower terraces. Rice on sandy soils suffers earlier from drought than rice on loamy, clayey soils because sandy soils can hold less plant available water.

 

Drought has 4 big effects on crop growth and rice yields:

 

  1. water shortage during the vegetative stage reduces the possible yields so yield targets and fertilizer rates should be lower in drought prone fields.

  2. water shortage around flowering causes spikelet sterility and may result in complete crop loss even if the rice plants recover after the drought.

  3. water shortage reduces the nutrient uptake of the plant; in the case of drought on poor soils, nutrients may be more limiting than water.

  4. water shortage affects rice more than weeds and makes weeding difficult; early drought may cause high crop loss because of high weed pressure only.

 

Plant under drought stress

 

General rules for fertilizer management in drought prone regions are as follows:

 

  • Especially on poor and sandy soils, organic fertilizers (crop residues, manure) are an efficient way to increase yield. If the farmer has a choice, organic fertilizers should be applied preferably on drought-prone coarse (=sandy) textured fields (usually upper fields) rather than on fine textured fields with less drought risk (usually lower fields).

 

  • If there is a high drought risk, use only little inorganic fertilizer.

 

  • Traditional varieties can give a similar yield response with inorganic fertilizers as improved varieties. However, this is only valid if lower rates of inorganic fertilizer are used for traditional varieties.  

 

  • N and P are the most limiting nutrients in most rainfed environments; K limitation is much less frequent. Rare nutrient deficiencies include S (sulfur), Mg (magnesium; on very acidic soils, in rainfed uplands), and Fe (iron, in rainfed uplands).

 

  • Frequently used upper inorganic nutrient rates in drought prone rainfed lowlands are 60 kg N, 39 kg P, and 18 kg K per hectare. On highly drought-prone fields (upper terraces, sandy soils) rates can be reduced to 20 kg N, 13 kg P, and 6 kg K per hectare; upper fertilizer rates for traditional varieties are about 40:26:12 kg NPK per hectare (all rates are given in N:P2O5:K2O). K application is rarely necessary when organic fertilizers like rice residues are applied regularly.

 

  • All of the P and K, and not more than 50% of the N should be applied in the first application. The first application can be made during final land preparation (basal) or broadcast (top dressed) within the first two weeks after transplanting. Basal applications are not recommended in regions where early season drought occurs frequently and/or on sandy fields with high percolation rates (high leaching losses). Inorganic fertilizer should only be applied when there is standing water in the field.

 

  • The N fertilizer can be applied in one split (for low rates), in two splits (for early duration varieties or traditional varieties) or three splits (medium and late varieties). Apply the 1st application within two weeks after transplanting and the 2nd split at panicle initiation. When using three splits, the 2nd and 3rd N applications should be applied at active tillering and panicle initiation. Applications can be made a week before or after these growth stages and should be made as soon as conditions are good for application. Do not apply N when (1) there is no standing water, (2) there is water on the leaves, (3) if a big rainstorm is expected, or (4) later than one week after panicle initiation.

 

Inorganic fertilizer should always be spread evenly and into standing water only.

Don't throw fertilizer on wet leaves and apply it after weeding.