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Details: Category: Pre-planting[150] | Published: 20 May 2013 | Hits: 998

Nutrient Management
The inherent soil nutrients are not adequate to supply the required plant nutrition throughout the growth and development phases. Available nutrients on a variety of soils ranging from red, grey, through to black cotton soils are varied. The soils are inherently low in mineral N fertility that could be restored through bush fallow system, but with continuous rice cultivation this is no longer possible. Continuous rice cultivation leads to low soil phosphates while potash status is generally adequate. This makes supplementary fertilizer inputs, especially phosphorous and nitrogen absolutely necessary.

Nitrogen
Nitrogen is an important component of rice production but is lost through:
•    Nitrification and Denitrification
•    Ammonia volatilization and Ammonization
•    Leaching
•    Ammonia fixation
•    Method and time of application

Black Cotton Soil
There are huge responses to nitrogen in the black cotton soils across the country. Nitrogen applied in two equal splits of 26 kg N ha-1 will attain some significant response. It is important to note that apart from inherent soil fertility, other factors which influence responses to nitrogen include moisture regime, bird damage, poor methods and time of application.

Red Loamy Clay
Coarse textured, naturally well drained soils require three split applications of N at planting, tillering and panicle initiation.

Due to the low recovery of N it is therefore important to increase nitrogen use efficiency. Calcium ammonium nitrate is the most common source of nitrogen and attains highest grain yield if applied in two equal splits at maximum tillering and panicle initiation stages under rainfed upland cropping system.

Note:
•    Excessive use of Nitrogen fertilizer increases susceptibility to blast and lodging
•    Apply nitrogen in split doses to minimize lodging and get maximum efficiency

Irrigated N Recommendation

Variety

Fertilizer type

Rate (kg N ha-1)

Grain Yield (t ha-1)

Basmati 217

ASN

SA

81

79

4

4.4

Basmati 370

ASN

SA

78

98

5

5.5

IR 2793-80-1

ASN

SA

98

101

5

6

BW 196

ASN

SA

98

104

6

7

Sindano

ASN

SA

81

79

4

4.2

Rainfed Upland N Recommendation

 Variety

Fertilizer type

Rate (kg N ha-1)

Grain Yield (t ha-1)

Dourado Precoce

CAN

52

3

NERICA 1

CAN

52

4.5

NERICA 4

CAN

52

5.5

NERICA 10

CAN

52

5

NERICA 11

CAN

52

5.8

Phosphorous

In Kenya, phosphorous deficiency is widespread in rice fields and is often associated with phosphorus fixation in soils with low pH such as Ferrosols and Inceptisols. There is positive response to low levels of phosphorous basally applied (13 kg P205 ha-1) gives significant response under rainfed upland ecologies.

Potassium
Potassium is adequately supplied in most Kenyan soils. Application of potash had no influence on grain yields in Wamumu, Hola and Mwea soils. However, there is need to confirm this now that potassium is mined not only through grains but also in straw.
Micronutrients

Zinc
Zinc is likely to be deficient in soils with high pH. Treatments with zinc oxide would increase grain yield.

Iron and manganese
Iron and manganese deficiency has not been a serious problem in most Kenyan soils. Rice requirements and accumulation of both elements is high under rainfed rice cultures. However, iron toxicity needs further investigation at some sites using NERICA 1.
Note: