*5.1.2 Plant height*

Plant height was significantly affected by N application (**Table 4**). Plant height was similar for 0 and 30 kg N ha<sup>−</sup><sup>1</sup> levels but significantly shorter than for 60, 90, 120, and 150 kg N ha<sup>−</sup><sup>1</sup> . The initial nutrient levels were probably good enough to produce plants of similar height to 30 kg N ha<sup>−</sup><sup>1</sup> . Nitrogen is a major contributor


**133**

**Table 5.**

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

plants were also observed when Marshall interacted with 60 kg N ha<sup>−</sup><sup>1</sup>

above. Generally when N was not applied, plants were significantly shorter.

The total biomass (straw + grain) increased with increasing levels of N

was similar to Jasmine 85 but significantly higher than Marshall. The effect of both

nificantly higher biomass than Sikamo or Jasmine 85 fertilized at 0 or 30 kg N ha<sup>−</sup><sup>1</sup>

Sikamo and Jasmine 85. Generally Sikamo and Jasmine 85 were taller than Marshall (**Table 3**), and higher N rates had more tillers than the control (**Table 4**). This

Reference [23] while looking at the effect of water management and N rates in a similar study reported that there were significant differences in straw and grain yield in other treatments compared with the control. According to the authors, yield and N use efficiency generally increased with increasing levels of N but declined at

**) Sikamo Jasmine 85 Marshall Mean**

*) for the three varieties.*

 10.27 9.60 9.90 9.92 14.30 14.47 13.00 13.92 16.73 16.70 13.17 15.53 16.57 15.97 15.47 16.00 20.20 18.03 16.67 18.30 19.67 17.77 18.00 18.50

Mean 16.29 15.42 14.37 *LSD (0.05) Fertilizer = 2.612; LSD (0.05) Variety = 1.148; LSD (0.05) Fertilizer × Variety = 3.475.*

N and variety interaction showed that Sikamo at 120 and 150 kg N ha<sup>−</sup><sup>1</sup>

largely explains the observed differences in biomass production.

**Nitrogen rate Rice variety**

*Effect of different levels of nitrogen on total biomass (t ha<sup>−</sup><sup>1</sup>*

to crop growth, size, and total dry matter production. The increase in height with increasing levels of N could not be explained better. While [23] in a similar study in Bida, Nigeria, observed that there were significant increases in plant height with increasing levels of N when compared with the Control, Metwally [24] also reported that plant height was significantly affected by nitrogen rate of 110 and 165 kg N ha<sup>−</sup><sup>1</sup> over the control. Ref. [24] further indicated that the interaction between mineral N rates and organic materials had a significant effect on plant height. [25], however, reported that there were no significant differences in N rates × variety interaction, while significant N effects were only found in plant height. In this study, comparing the three varieties, Sikamo and Jasmine 85 had similar plant heights which were significantly taller than Marshall. Two varieties (Sikamo and Jasmine 85) interacted

level and above to give significantly taller plants. Similar taller

at 0 kg N ha<sup>−</sup><sup>1</sup>

. Higher N rates of 120 and

produced lower total biomass than both

over the control for 30, 60, 90, 120, and

. At N rates of 30, 60, and 90 kg N ha<sup>−</sup>1, biomass

further significantly produced higher biomass yields. Total biomass

, respectively. Between varieties, total biomass production for Sikamo

level and

to a maximum

gave sig-

.

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

**5.2 Effect of nitrogen on yield parameters**

at 150kg N ha<sup>−</sup><sup>1</sup>

increased by 4.0, 5.4, 6.1, 8.4, and 8.6 t ha<sup>−</sup><sup>1</sup>

Marshall fertilized from 0 to 90 kg N ha<sup>−</sup><sup>1</sup>

(**Table 5**). Total biomass increased from 9.9 t ha<sup>−</sup><sup>1</sup>

yields were significantly higher than 0 kg N ha<sup>−</sup><sup>1</sup>

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

*5.2.1 Total biomass*

of 18.5 t ha<sup>−</sup><sup>1</sup>

150 kg N ha<sup>−</sup><sup>1</sup>

150 kg N ha<sup>−</sup><sup>1</sup>

**(kg ha<sup>−</sup><sup>1</sup>**

#### **Table 4.**

*Effect of the interaction of nitrogen levels and rice varieties on plant height (cm).*

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

to crop growth, size, and total dry matter production. The increase in height with increasing levels of N could not be explained better. While [23] in a similar study in Bida, Nigeria, observed that there were significant increases in plant height with increasing levels of N when compared with the Control, Metwally [24] also reported that plant height was significantly affected by nitrogen rate of 110 and 165 kg N ha<sup>−</sup><sup>1</sup> over the control. Ref. [24] further indicated that the interaction between mineral N rates and organic materials had a significant effect on plant height. [25], however, reported that there were no significant differences in N rates × variety interaction, while significant N effects were only found in plant height. In this study, comparing the three varieties, Sikamo and Jasmine 85 had similar plant heights which were significantly taller than Marshall. Two varieties (Sikamo and Jasmine 85) interacted with 60 kg N ha<sup>−</sup><sup>1</sup> level and above to give significantly taller plants. Similar taller plants were also observed when Marshall interacted with 60 kg N ha<sup>−</sup><sup>1</sup> level and above. Generally when N was not applied, plants were significantly shorter.

#### **5.2 Effect of nitrogen on yield parameters**

#### *5.2.1 Total biomass*

*Sustainable Crop Production*

**Nitrogen rate (kg ha<sup>−</sup><sup>1</sup>**

similar to other findings. In 2006 [21], working on the effect of N and P fertilizers

**) Rice variety**

Mean 350 353 354 *LSD (0.05) Fertilizer = 86; LSD (0.05) Variety = 36; LSD (0.05) Fertilizer × Variety = 112.*

*Effect of the interaction of nitrogen levels and rice varieties on the number of tillers m<sup>−</sup><sup>2</sup>*

 218 198 232 216 303 358 333 331 368 377 358 368 385 370 368 374 383 410 355 383 440 407 475 440

significantly apparently by increasing the number of productive tillers. However, the authors also reported that there was a reduction in the number of panicles per

unproductive resulting in lower paddy yield. There were also no significant differences in the number of effective tillers produced in the variety × N rate interaction in line with an observation earlier made by [22] who noted that interactions between N and variety were not significant for all measured traits for four lowland NERICA varieties in Nigeria and those of [23], who worked on the effect of minerals N and P on the yield and yield components of flooded lowland rice in Ethiopia.

 at the highest N application, attributing this observation to excessive vegetative growth of the rice crop. However, paddy yield did not show a similar trend with

Plant height was significantly affected by N application (**Table 4**). Plant height

**) Sikamo Jasmine 85 Marshall Mean**

 84 85 72 80 101 95 94 97 119 105 99 108 122 117 105 115 128 118 110 119 124 115 112 117

levels but significantly shorter than for 60, 90,

. Nitrogen is a major contributor

. The initial nutrient levels were probably good enough to

increased the number of panicles per m2

*.*

**Sikamo Jasmine 85 Marshall Mean**

), more tillers tended to be

reported application of N up to 120 kg ha<sup>−</sup><sup>1</sup>

increasing levels of N. At higher levels of N (> 90 kg ha<sup>−</sup><sup>1</sup>

**132**

**Table 4.**

m2

**Table 3.**

*5.1.2 Plant height*

**(kg ha<sup>−</sup><sup>1</sup>**

120, and 150 kg N ha<sup>−</sup><sup>1</sup>

was similar for 0 and 30 kg N ha<sup>−</sup><sup>1</sup>

produce plants of similar height to 30 kg N ha<sup>−</sup><sup>1</sup>

**Nitrogen rate Rice variety**

Mean 108 105 99 *LSD (0.05) Fertilizer = 14; LSD (0.05) Variety = 5; LSD (0.05) Fertilizer × Variety = 16.*

*Effect of the interaction of nitrogen levels and rice varieties on plant height (cm).*

The total biomass (straw + grain) increased with increasing levels of N (**Table 5**). Total biomass increased from 9.9 t ha<sup>−</sup><sup>1</sup> at 0 kg N ha<sup>−</sup><sup>1</sup> to a maximum of 18.5 t ha<sup>−</sup><sup>1</sup> at 150kg N ha<sup>−</sup><sup>1</sup> . At N rates of 30, 60, and 90 kg N ha<sup>−</sup>1, biomass yields were significantly higher than 0 kg N ha<sup>−</sup><sup>1</sup> . Higher N rates of 120 and 150 kg N ha<sup>−</sup><sup>1</sup> further significantly produced higher biomass yields. Total biomass increased by 4.0, 5.4, 6.1, 8.4, and 8.6 t ha<sup>−</sup><sup>1</sup> over the control for 30, 60, 90, 120, and 150 kg N ha<sup>−</sup><sup>1</sup> , respectively. Between varieties, total biomass production for Sikamo was similar to Jasmine 85 but significantly higher than Marshall. The effect of both N and variety interaction showed that Sikamo at 120 and 150 kg N ha<sup>−</sup><sup>1</sup> gave significantly higher biomass than Sikamo or Jasmine 85 fertilized at 0 or 30 kg N ha<sup>−</sup><sup>1</sup> . Marshall fertilized from 0 to 90 kg N ha<sup>−</sup><sup>1</sup> produced lower total biomass than both Sikamo and Jasmine 85. Generally Sikamo and Jasmine 85 were taller than Marshall (**Table 3**), and higher N rates had more tillers than the control (**Table 4**). This largely explains the observed differences in biomass production.

Reference [23] while looking at the effect of water management and N rates in a similar study reported that there were significant differences in straw and grain yield in other treatments compared with the control. According to the authors, yield and N use efficiency generally increased with increasing levels of N but declined at


**Table 5.** *Effect of different levels of nitrogen on total biomass (t ha<sup>−</sup><sup>1</sup> ) for the three varieties.*

80 kg N ha<sup>−</sup><sup>1</sup> . Ref. [24] while investigating the effect of mineral N fertilizer on rice reported that increasing N fertilizer levels resulted in a corresponding increase in straw yields, stating that the highest straw yields were obtained with the highest N rates of 165 and 110 kg N ha<sup>−</sup><sup>1</sup> . Ref. [24] attributed these observations mainly due to the fact that N fertilizer increased dry matter, leaf area index, and number of tillers. In this study, while total biomass increased with increasing levels of N up to 150 kg N ha<sup>−</sup><sup>1</sup> , grain yield declined after 90 kg N ha<sup>−</sup><sup>1</sup> . After 90 kg N ha<sup>−</sup><sup>1</sup> , further N addition seemed to contribute more to vegetative growth (greater straw production) at the expense of reproductive growth (grain production).

#### *5.2.2 Mean panicle weight*

The mean weight of individual panicles was determined for each level of N applied (**Figure 3**). Panicle weight was significantly affected by N application. Lowest individual panicle weights (< 3.0 g panicle<sup>−</sup><sup>1</sup> ) were obtained under the control where N was not applied. Individual panicle weight increased significantly (> 4.0 g panicle<sup>−</sup><sup>1</sup> ) with 30kgN ha<sup>−</sup><sup>1</sup> additions, rising to above 5.0 g per panicle<sup>−</sup><sup>1</sup> at 90 and 120 kg N ha<sup>−</sup><sup>1</sup> . Significantly lower panicle weights were recorded at 150 kg N ha<sup>−</sup><sup>1</sup> than 90 and 120 kg N ha<sup>−</sup><sup>1</sup> . These results are in conformity with other findings. Ref. [23] reported that plant height, grain yield, panicle weight, 1000 grain weight, and grain harvest index (GHI) were significantly influenced by N and genotype treatments. In the same vain, [24] also reported that mineral N and organic material application to rice significantly affected the number of grains per panicle. Treatments that received mineral N fertilizer in addition to organic materials had significantly higher panicle weights over those that did not, and it increased with increasing levels of fertilizer and organic materials. In this study, the significantly higher panicle weights of 90 and 120 kg N ha<sup>−</sup><sup>1</sup> significantly contributed to higher grain yields recorded for those treatments, particularly at 90 kg N ha<sup>−</sup><sup>1</sup> (**Figure 3**).

### *5.2.3 Grain yield*

Grain yield produced for the different levels of N applied is presented in **Figure 4**. Grain yield ranged from 1.7 t ha<sup>−</sup><sup>1</sup> (lowest) to 9.4 t ha<sup>−</sup><sup>1</sup> (highest) across N levels and varieties. Grain yield was significantly higher for Sikamo and Jasmine 85 fertilized at 90 kg N ha<sup>−</sup><sup>1</sup> than all the other N x variety interactions except Marshall × 90 kg N ha<sup>−</sup><sup>1</sup> and both Sikamo and Jasmine fertilized at 120 kg N ha<sup>−</sup><sup>1</sup> . Grain yield for all the varieties was almost similar at both 60 and 150 kg N ha<sup>−</sup><sup>1</sup> . Generally grain

**135**

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

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

yield increased with increasing levels of N from 1.7 t ha<sup>−</sup><sup>1</sup>

(90 kg N ha<sup>−</sup><sup>1</sup>

*Effect of varying levels of nitrogen on rice paddy yield.*

increased from 3240 to 3962 kg ha<sup>−</sup><sup>1</sup>

trol due to application of 30 and 60 kg of N ha<sup>−</sup><sup>1</sup>

trol (no N) to 60 kg N ha<sup>−</sup><sup>1</sup>

of 9.4 t ha<sup>−</sup><sup>1</sup>

**Figure 4.**

(0kgN ha<sup>−</sup><sup>1</sup>

with an increase in the levels of N from the con-

was 13.5% and 22.3%, respectively.

.

and decreased further with increase in applied N fertilizer.

) and thereafter declined, indicating that higher levels of N

suppressed yield. This is in accordance with the earlier findings of [25] who reported that excessive nitrogen application to rice in China caused environmental pollution, increased cost of farming, reduced grain yield, and contributed to global warming. Furthermore, [24] indicated that, filled grain percentage was affected by nitrogen fertilizer and organic materials, adding that plants that did not receive nitrogen produced the lowest number of filled grains while those that received 165 kg N ha<sup>−</sup><sup>1</sup> produced the highest filled grains, followed by those that received 110 kg N ha<sup>−</sup><sup>1</sup>

Ref. [21] working on the effect of N and P fertilizers on yield, and yield components of rice also reported that N had a marked effect on grain yield and that grain yield

Ref. [21] further reported that the magnitude of increase in grain yield over the con-

Grain yield was generally very high compared to the mean grain yield of 2.0 t ha<sup>−</sup><sup>1</sup> reported by the Ministry of Food and Agriculture, Ghana [15]. Such high levels of grain yield for the rain-fed lowlands could be attributed to the use of good varieties, fertilizer additions, and improved soil and water management under the "sawah" system (bunded and leveled fields). Ref. [8] reported that lowland rice significantly responded to N, P, and K additions in selected sites in southern Ghana. Ref. [26] also observed that while bunding significantly increased yield across sites in La Cote d'Ivoire by almost 40% and controlled weeds, mineral fertilizer N application significantly increased yield by 18% with N use efficiency being 12 kg compared to 4 kg of rice grain per kg of N applied in open field. Ref. [26] further indicated that across environments, about 60% of observed variability in rice grain yield was explained by water control and agronomic management (N application, weed control). With improved soil and water management under the "sawah" system, N use efficiency is increased, and higher grain yields are obtained when compared to open fields with poor soil management and no water control [4]. Under this study, N utilization was improved due to improved water management. Hence moderate levels of N recorded higher grain yields. Evaluating the response of four rain-fed NERICA varieties to N fertilization, [22] also reported that even though the interactions between N and variety were not significant for all measured traits, yield response to N was linear and

significantly increased with increasing levels of N up to 100 kg N ha<sup>−</sup><sup>1</sup>

) to a maximum

.

**Figure 3.** *Effect of varying levels of nitrogen on individual panicle weight (g) of rice.*

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

**Figure 4.** *Effect of varying levels of nitrogen on rice paddy yield.*

*Sustainable Crop Production*

rates of 165 and 110 kg N ha<sup>−</sup><sup>1</sup>

*5.2.2 Mean panicle weight*

(> 4.0 g panicle<sup>−</sup><sup>1</sup>

150 kg N ha<sup>−</sup><sup>1</sup>

*5.2.3 Grain yield*

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

90 kg N ha<sup>−</sup><sup>1</sup>

Grain yield ranged from 1.7 t ha<sup>−</sup><sup>1</sup>

at 90 and 120 kg N ha<sup>−</sup><sup>1</sup>

. Ref. [24] while investigating the effect of mineral N fertilizer on rice

. Ref. [24] attributed these observations mainly due

. After 90 kg N ha<sup>−</sup><sup>1</sup>

) were obtained under the

. These results are in conformity with other

significantly contributed to higher

(highest) across N levels

(**Figure 3**).

. Grain yield

. Generally grain

additions, rising to above 5.0 g per panicle<sup>−</sup><sup>1</sup>

. Significantly lower panicle weights were recorded at

, further

reported that increasing N fertilizer levels resulted in a corresponding increase in straw yields, stating that the highest straw yields were obtained with the highest N

to the fact that N fertilizer increased dry matter, leaf area index, and number of tillers. In this study, while total biomass increased with increasing levels of N up to

N addition seemed to contribute more to vegetative growth (greater straw produc-

The mean weight of individual panicles was determined for each level of N applied (**Figure 3**). Panicle weight was significantly affected by N application.

control where N was not applied. Individual panicle weight increased significantly

findings. Ref. [23] reported that plant height, grain yield, panicle weight, 1000 grain weight, and grain harvest index (GHI) were significantly influenced by N and genotype treatments. In the same vain, [24] also reported that mineral N and organic material application to rice significantly affected the number of grains per panicle. Treatments that received mineral N fertilizer in addition to organic materials had significantly higher panicle weights over those that did not, and it increased with increasing levels of fertilizer and organic materials. In this study, the significantly

Grain yield produced for the different levels of N applied is presented in **Figure 4**.

than all the other N x variety interactions except Marshall ×

(lowest) to 9.4 t ha<sup>−</sup><sup>1</sup>

and varieties. Grain yield was significantly higher for Sikamo and Jasmine 85 fertil-

and both Sikamo and Jasmine fertilized at 120 kg N ha<sup>−</sup><sup>1</sup>

grain yields recorded for those treatments, particularly at 90 kg N ha<sup>−</sup><sup>1</sup>

for all the varieties was almost similar at both 60 and 150 kg N ha<sup>−</sup><sup>1</sup>

*Effect of varying levels of nitrogen on individual panicle weight (g) of rice.*

, grain yield declined after 90 kg N ha<sup>−</sup><sup>1</sup>

tion) at the expense of reproductive growth (grain production).

Lowest individual panicle weights (< 3.0 g panicle<sup>−</sup><sup>1</sup>

) with 30kgN ha<sup>−</sup><sup>1</sup>

than 90 and 120 kg N ha<sup>−</sup><sup>1</sup>

higher panicle weights of 90 and 120 kg N ha<sup>−</sup><sup>1</sup>

80 kg N ha<sup>−</sup><sup>1</sup>

150 kg N ha<sup>−</sup><sup>1</sup>

**134**

**Figure 3.**

yield increased with increasing levels of N from 1.7 t ha<sup>−</sup><sup>1</sup> (0kgN ha<sup>−</sup><sup>1</sup> ) to a maximum of 9.4 t ha<sup>−</sup><sup>1</sup> (90 kg N ha<sup>−</sup><sup>1</sup> ) and thereafter declined, indicating that higher levels of N suppressed yield. This is in accordance with the earlier findings of [25] who reported that excessive nitrogen application to rice in China caused environmental pollution, increased cost of farming, reduced grain yield, and contributed to global warming. Furthermore, [24] indicated that, filled grain percentage was affected by nitrogen fertilizer and organic materials, adding that plants that did not receive nitrogen produced the lowest number of filled grains while those that received 165 kg N ha<sup>−</sup><sup>1</sup> produced the highest filled grains, followed by those that received 110 kg N ha<sup>−</sup><sup>1</sup> . Ref. [21] working on the effect of N and P fertilizers on yield, and yield components of rice also reported that N had a marked effect on grain yield and that grain yield increased from 3240 to 3962 kg ha<sup>−</sup><sup>1</sup> with an increase in the levels of N from the control (no N) to 60 kg N ha<sup>−</sup><sup>1</sup> and decreased further with increase in applied N fertilizer. Ref. [21] further reported that the magnitude of increase in grain yield over the control due to application of 30 and 60 kg of N ha<sup>−</sup><sup>1</sup> was 13.5% and 22.3%, respectively. Grain yield was generally very high compared to the mean grain yield of 2.0 t ha<sup>−</sup><sup>1</sup> reported by the Ministry of Food and Agriculture, Ghana [15]. Such high levels of grain yield for the rain-fed lowlands could be attributed to the use of good varieties, fertilizer additions, and improved soil and water management under the "sawah" system (bunded and leveled fields). Ref. [8] reported that lowland rice significantly responded to N, P, and K additions in selected sites in southern Ghana. Ref. [26] also observed that while bunding significantly increased yield across sites in La Cote d'Ivoire by almost 40% and controlled weeds, mineral fertilizer N application significantly increased yield by 18% with N use efficiency being 12 kg compared to 4 kg of rice grain per kg of N applied in open field. Ref. [26] further indicated that across environments, about 60% of observed variability in rice grain yield was explained by water control and agronomic management (N application, weed control). With improved soil and water management under the "sawah" system, N use efficiency is increased, and higher grain yields are obtained when compared to open fields with poor soil management and no water control [4]. Under this study, N utilization was improved due to improved water management. Hence moderate levels of N recorded higher grain yields. Evaluating the response of four rain-fed NERICA varieties to N fertilization, [22] also reported that even though the interactions between N and variety were not significant for all measured traits, yield response to N was linear and significantly increased with increasing levels of N up to 100 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> (100 kg N ha<sup>−</sup><sup>1</sup> ) over the control, the authors recommended further studies to 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 increased dry matter and grain yield with maximum yield (6.4 t ha<sup>−</sup><sup>1</sup> ) obtained at 120 kg N ha<sup>−</sup><sup>1</sup> during year 1 and maximum yield (6.3 t ha<sup>−</sup><sup>1</sup> ) obtained at 90 kg N ha<sup>−</sup><sup>1</sup> in year 2. Ref. [27] further observed that other yield components such as panicle length and panicle number per m<sup>2</sup> were significantly affected by N fertilization with panicle number per m2 showing the highest correlation (r = 0.70 and 0.78) for 2 years. In this study, however, mean maximum yields were obtained at 90 kg N ha<sup>−</sup><sup>1</sup> for all three varieties over the period confirming the findings of [9] who recommended 90 kg N ha<sup>−</sup><sup>1</sup> as the optimum rate.
