**3.2 Soil analysis**

Soil sample was air dried at room temperature. Dried sample was then ground and passed through a 2 mm sieve. Soil pH was measured in a soil/water ratio of 1:2.5 [17]. Total carbon was measured by the method of [18] and total nitrogen by the micro Kjeldahl method [17]. Available P was measured by the method of [19]. Exchangeable cations (Ca, Mg, K, Na) were extracted using a 1.0 M ammonium acetate solution and determined by atomic absorption spectrometry [20]. Exchangeable acidity was determined by titration and eCEC calculated as sum of exchangeable cations and acidity.

#### **3.3 Growth characteristics**

Number of tillers was counted after maximum tiller formation stage and mean number of tillers determined, while plant height was measured at harvest.

#### **3.4 Yield characteristics**

At maturity, an area of 1m2 excluding border rows was measured out in each subplot and harvested. Grain and stover yield were measured and yield per hectare estimated. Panicles were also collected from non-border rows and mean individual weight per panicle determined. The weight of 1000 grains was measured using an electronic balance. Grain harvest index (HI) was calculated as ratio of grain yield to total yield (grain + stover).

#### **3.5 Statistical analysis**

The statistical software STATISTIX 8 was used to analyze the data, and LSD (0.05) was used as the mean separator.

## **4. Characteristics of growing environment**

The agroecological zones have a bimodal rainfall pattern (**Figure 2**) and therefore have two main cropping seasons (major and minor). The major season has its peak rainfall in June to July, while that of the minor is in September to October. The two agroecological zones have a comparative advantage over other agroecological zones due to their good rainfall and higher water availability throughout a greater part of the growing season. The physicochemical properties of the soils of these zones are shown in **Table 2**. The soils are typically low in inherent fertility and poor in plant nutrients particularly total nitrogen (N) and available phosphorus (P). Soil texture ranges from pure sandy soils through loam to clay soils. Under such low levels of fertility, improved/efficient nutrient management is critical if higher rice yields are to be obtained and when increased and sustained total productivity are to be achieved.

**131**

m2

**Table 2.**

**Figure 2.**

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

*Rainfall amounts and distribution in the three main agroecological zones of Ghana.*

**Parameter Units High rain forest Semi-deciduous rain forest Savannah** pH (water) — 5.7 5.7 4.6 Total carbon g kg<sup>−</sup><sup>1</sup> 10.3 12 6.1 Total nitrogen g kg<sup>−</sup><sup>1</sup> 0.90 1.10 0.65 Av. phosphorus mg kg<sup>−</sup><sup>1</sup> 1.4 4.9 1.5 Ex. potassium cmol (+) kg<sup>−</sup><sup>1</sup> 0.22 0.42 0.22 Ex. calcium cmol (+) kg<sup>−</sup><sup>1</sup> 2.25 7.50 2.10 Ex. magnesium cmol (+) kg<sup>−</sup><sup>1</sup> 1.12 4.10 1.00 Ex. sodium cmol (+) kg<sup>−</sup><sup>1</sup> 0.26 0.32 0.12 Ex. acidity cmol (+) kg<sup>−</sup><sup>1</sup> 0.65 0.31 1.00 Effective CEC cmol (+) kg<sup>−</sup><sup>1</sup> 4.49 12.65 4.44 Clay g kg<sup>−</sup><sup>1</sup> 110 127 66 Silt g kg<sup>−</sup><sup>1</sup> 240 620 607 Sand g kg<sup>−</sup><sup>1</sup> 650 300 327

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

**5. Responses to nitrogen fertilizer application**

*Mean physicochemical properties of soils of the main agroecological zones.*

The number of effective tillers produced is a good indicator as it is a major determinant of yield. Tiller number increased with increasing N levels, but the increased was more pronounced from 0 kg N to 30 kg N than from 30 to 60, 60 to 90, 90

significantly increased by 53, 70, 72, 77, and 103% over the control for 30, 60,

in total dry matter production with increasing levels of N. These observations are

(**Table 3**). Generally, total number of tillers per

, respectively. There was also a corresponding increase

**5.1 Effect of nitrogen on growth parameters**

*5.1.1 Number of tillers m2*

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

90, 120, and 150 kgN ha<sup>−</sup><sup>1</sup>

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

**Figure 2.**

*Sustainable Crop Production*

tored until harvest.

exchangeable cations and acidity.

At maturity, an area of 1m2

(0.05) was used as the mean separator.

**4. Characteristics of growing environment**

**3.3 Growth characteristics**

**3.4 Yield characteristics**

total yield (grain + stover).

**3.5 Statistical analysis**

**3.2 Soil analysis**

P2O5 using triple superphosphate as phosphorus source, 60 kg K ha<sup>−</sup><sup>1</sup>

Muriate of Potash as potassium source, and 50% N using urea as nitrogen source was applied to each subplot immediately after transplanting as basal fertilizer. All fertilizer was uniformly broadcasted on the field manually. The remaining 50% N was applied as split, at 25 days after transplanting (maximum tiller formation) and 55 days after transplanting (at panicle initiation) using the same broadcast method. Weed control was manual, mainly by handpicking. Crop growth was then moni-

Soil sample was air dried at room temperature. Dried sample was then ground and passed through a 2 mm sieve. Soil pH was measured in a soil/water ratio of 1:2.5 [17]. Total carbon was measured by the method of [18] and total nitrogen by the micro Kjeldahl method [17]. Available P was measured by the method of [19]. Exchangeable cations (Ca, Mg, K, Na) were extracted using a 1.0 M ammonium acetate solution and determined by atomic absorption spectrometry [20]. Exchangeable acidity was determined by titration and eCEC calculated as sum of

Number of tillers was counted after maximum tiller formation stage and mean number of tillers determined, while plant height was measured at harvest.

subplot and harvested. Grain and stover yield were measured and yield per hectare estimated. Panicles were also collected from non-border rows and mean individual weight per panicle determined. The weight of 1000 grains was measured using an electronic balance. Grain harvest index (HI) was calculated as ratio of grain yield to

The statistical software STATISTIX 8 was used to analyze the data, and LSD

The agroecological zones have a bimodal rainfall pattern (**Figure 2**) and therefore have two main cropping seasons (major and minor). The major season has its peak rainfall in June to July, while that of the minor is in September to October. The two agroecological zones have a comparative advantage over other agroecological zones due to their good rainfall and higher water availability throughout a greater part of the growing season. The physicochemical properties of the soils of these zones are shown in **Table 2**. The soils are typically low in inherent fertility and poor in plant nutrients particularly total nitrogen (N) and available phosphorus (P). Soil texture ranges from pure sandy soils through loam to clay soils. Under such low levels of fertility, improved/efficient nutrient management is critical if higher rice yields are to be obtained and when increased and sustained total productivity are to be achieved.

excluding border rows was measured out in each

as K2O using

**130**

*Rainfall amounts and distribution in the three main agroecological zones of Ghana.*


**Table 2.**

*Mean physicochemical properties of soils of the main agroecological zones.*

#### **5. Responses to nitrogen fertilizer application**

#### **5.1 Effect of nitrogen on growth parameters**

## *5.1.1 Number of tillers m2*

The number of effective tillers produced is a good indicator as it is a major determinant of yield. Tiller number increased with increasing N levels, but the increased was more pronounced from 0 kg N to 30 kg N than from 30 to 60, 60 to 90, 90 to 120, and 120 to 150 kg N ha<sup>−</sup><sup>1</sup> (**Table 3**). Generally, total number of tillers per m2 significantly increased by 53, 70, 72, 77, and 103% over the control for 30, 60, 90, 120, and 150 kgN ha<sup>−</sup><sup>1</sup> , respectively. There was also a corresponding increase in total dry matter production with increasing levels of N. These observations are


**Table 3.**

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

similar to other findings. In 2006 [21], working on the effect of N and P fertilizers reported application of N up to 120 kg ha<sup>−</sup><sup>1</sup> increased the number of panicles per m2 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 m2 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 increasing levels of N. At higher levels of N (> 90 kg ha<sup>−</sup><sup>1</sup> ), more tillers tended to be 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.
