*5.2.6 Grain harvest index (GHI)*

The grain harvest index (GHI) calculated for the different levels of N applied is shown in **Figure 5**. This is a measure of the ratio of economic yield (grain) to total yield (grain + straw). The higher the value, the better or higher the returns/gain from any fertilizer additions. GHI was significantly affected by N application for all the three varieties. The lowest GHI (0.27) was recorded for the control (no N applied), while the highest GHI (0.68) was recorded at 90 kg N ha<sup>−</sup><sup>1</sup> . Harvest index was in


**137**

**6. Conclusion**

of 2000 kg ha<sup>−</sup><sup>1</sup>

**6.1 Recommendations**

rate was observed to be 90 kg N ha<sup>−</sup><sup>1</sup>

in high rice grain yield of over 9000 kg ha<sup>−</sup><sup>1</sup>

yields, N application is best within 90–120 kg ha<sup>−</sup><sup>1</sup>

*Managing Soil Nitrogen under Rain-Fed Lowland Rice Production Systems in the Forest…*

**Growth parameter Grain yield** Plant height 0.7474\*\*\* Biomass 0.7533\*\*\* Tillers m<sup>−</sup><sup>2</sup> 0.5881\*\*\* Panicle weight 0.7567\*\*\* 1000 seed weight 0.5718\*\*\*

*DOI: http://dx.doi.org/10.5772/intechopen.89446*

*\*\*\*indicates significance at 1% probability level.*

*Correlation between grain yield and yield components.*

**Table 7.**

**Figure 5.**

the order 0 < 30 < 60 < 150 < 120 < 90 kg N ha<sup>−</sup><sup>1</sup>

*Effect of varying levels of nitrogen on grain harvest index (GHI).*

the three varieties and was significantly and positively correlated with grain yield. A similar observation was also reported by [23]. The above observations clearly show that higher doses of nitrogen for rice production in these lowlands do not only result in significant yield reductions but also lead to higher cost of production for the

Results show that fertilizer use significantly affects rice yield. However, higher rates of N tended to suppress grain yield but promote straw production. The optimum

depending on soil type, rainfall regime, and affordability of individual farmer. In the lowlands therefore appropriate crop, soil and water management practices can result

technologies can help to significantly improve yields over the current national mean

It is therefore recommended that, to sustain rice production and for increased

rainfall amounts, and soil types. The three tested rice varieties (Sikamo, Jasmine 85, Marshall) are all suitable for cultivation within the high rain forest and

country. The three rice varieties are highly productive under these nitrogen rates.

and contribute to enhancing food availability and security in the

mostly resource-poor farmers as cost of mineral fertilizer is high.

. GHI showed a similar trend for

, but this could be increased to 120 kg N ha<sup>−</sup><sup>1</sup>

. The introduction of such improved

based on location, specific

#### **Table 6.**

*Effect of different levels of nitrogen on 1000 grain weight (g) for the three varieties.*

*Managing Soil Nitrogen under Rain-Fed Lowland Rice Production Systems in the Forest… DOI: http://dx.doi.org/10.5772/intechopen.89446*


#### **Table 7.**

*Sustainable Crop Production*

(100 kg N ha<sup>−</sup><sup>1</sup>

at 120 kg N ha<sup>−</sup><sup>1</sup>

at 90 kg N ha<sup>−</sup><sup>1</sup>

with 60 kg N ha<sup>−</sup><sup>1</sup>

**Rate (kg ha<sup>−</sup><sup>1</sup>**

Sikamo at 90 kg N ha<sup>−</sup><sup>1</sup>

*5.2.6 Grain harvest index (GHI)*

90 kg N ha<sup>−</sup><sup>1</sup>

With results showing a linear trend and yield increase of 3 tons ha<sup>−</sup><sup>1</sup>

during year 1 and maximum yield (6.3 t ha<sup>−</sup><sup>1</sup>

increased dry matter and grain yield with maximum yield (6.4 t ha<sup>−</sup><sup>1</sup>

such as panicle length and panicle number per m<sup>2</sup>

weight between 30, 60, 120, and 150 kg N ha<sup>−</sup><sup>1</sup>

.

*5.2.5 Correlation between grain yield and yield components.*

in these components will affect grain yield, as was observed.

while the highest GHI (0.68) was recorded at 90 kg N ha<sup>−</sup><sup>1</sup>

**Nitrogen Rice variety**

fertilization with panicle number per m2

who recommended 90 kg N ha<sup>−</sup><sup>1</sup>

*5.2.4 Weight of 1000 grains*

establish optimum levels for the rain-fed lowlands of the northern Guinea savanna zone of Nigeria. In a similar study, [27] reported that N fertilization significantly

and 0.78) for 2 years. In this study, however, mean maximum yields were obtained

as the optimum rate.

The effect of varying levels of N on 1000 grains is presented in **Table 6**. Lowest 1000 grain weight recorded was 22.04 g, while the highest was 26.91 g, both under Jasmine 85. The application of N significantly affected the weight of 1000 grains over the control. However, there were no significant differences in 1000 grain

**Table 7** shows the relationships between grain yield and yield components. All the yield components strongly correlated with grain yield with plant height, biomass, and panicle weight giving the highest correlations. This signifies that changes

The grain harvest index (GHI) calculated for the different levels of N applied is shown in **Figure 5**. This is a measure of the ratio of economic yield (grain) to total yield (grain + straw). The higher the value, the better or higher the returns/gain from any fertilizer additions. GHI was significantly affected by N application for all the three varieties. The lowest GHI (0.27) was recorded for the control (no N applied),

 22.32 22.04 22.20 22.19 24.17 25.46 26.65 25.42 26.46 26.91 26.66 26.68 26.88 26.74 26.66 26.76 26.51 26.42 26.69 26.54 25.44 25.58 25.86 26.17

Mean 16.29 15.42 14.37 *LSD (0.05) Fertilizer = 1.35; LSD (0.05) Variety = 0.66; LSD (0.05) Fertilizer x Variety = 1.89.*

*Effect of different levels of nitrogen on 1000 grain weight (g) for the three varieties.*

**) Sikamo Jasmine 85 Marshall Mean**

) over the control, the authors recommended further studies to

in year 2. Ref. [27] further observed that other yield components

for all three varieties over the period confirming the findings of [9]

to produce the highest 1000 grain weight, followed closely by

) obtained

) obtained at

were significantly affected by N

application. Jasmine 85 interacted

. Harvest index was in

showing the highest correlation (r = 0.70

**136**

**Table 6.**

*Correlation between grain yield and yield components.*

**Figure 5.** *Effect of varying levels of nitrogen on grain harvest index (GHI).*

the order 0 < 30 < 60 < 150 < 120 < 90 kg N ha<sup>−</sup><sup>1</sup> . GHI showed a similar trend for the three varieties and was significantly and positively correlated with grain yield. A similar observation was also reported by [23]. The above observations clearly show that higher doses of nitrogen for rice production in these lowlands do not only result in significant yield reductions but also lead to higher cost of production for the mostly resource-poor farmers as cost of mineral fertilizer is high.

#### **6. Conclusion**

Results show that fertilizer use significantly affects rice yield. However, higher rates of N tended to suppress grain yield but promote straw production. The optimum rate was observed to be 90 kg N ha<sup>−</sup><sup>1</sup> , but this could be increased to 120 kg N ha<sup>−</sup><sup>1</sup> depending on soil type, rainfall regime, and affordability of individual farmer. In the lowlands therefore appropriate crop, soil and water management practices can result in high rice grain yield of over 9000 kg ha<sup>−</sup><sup>1</sup> . The introduction of such improved technologies can help to significantly improve yields over the current national mean of 2000 kg ha<sup>−</sup><sup>1</sup> and contribute to enhancing food availability and security in the country. The three rice varieties are highly productive under these nitrogen rates.

#### **6.1 Recommendations**

It is therefore recommended that, to sustain rice production and for increased yields, N application is best within 90–120 kg ha<sup>−</sup><sup>1</sup> based on location, specific rainfall amounts, and soil types. The three tested rice varieties (Sikamo, Jasmine 85, Marshall) are all suitable for cultivation within the high rain forest and

semi-deciduous rain forest agroecological zones of the country. Furthermore these rice varieties, in addition to other improved varieties like AGRA, Amankwatia, and CRI-Dartey, are suitable and recommended for lowlands in the other agroecological zones with similar biophysical and physicochemical characteristics. Land preparation methods and water management remain key and very critical factors, and the adoption of the "sawah" technology (bunding, puddling, and leveling) with easyto-adapt water control structures is most suitable for these areas.
