1. Introduction

Groundnut or peanut (Arachis hypogaea L.) is grown over 20 million hectares in the tropical and sub tropical part of about one hundred countries in the world. The total annual world production amounts to about 25 million tons of unshelled nuts, 70% of which is contributed by India, China and U.S.A. (Khidir, 1997; El Naim et al., 2010a). Groundnut is an excellent source of plant nutrients contains 45-50% oil, 27-33% protein as well as essential minerals and vitamins. They play an important role in the dietary requirements of resource poor women and children and haulms are used as livestock feed. Groundnut oil is composed of mixed glycerides and contains a high proportion of unsaturated fatty acids, in particular, oleic (50-65%) and linoleic (18-30%) (Young, 1996). Groundnuts are also important in the confectionary trade and the stable oil is preferred by the deep-frying industries, since it has a smoke point of 229.4°C compared to the 193.5°C of extra virgin olive oil. The oil is also used to make margarines and mayonnaise (Hui, 1996; Young, 1996). Sudan is one of the major groundnut producing countries.

The main problems limiting production of peanut are poor cultural practices (especially the practice of wide spacing) as well as inadequate weed management (EL Naim et al., 2010^a). If early weeding is done well, and crop spacing recommendations followed, then the weeds that come upLater are smothered with the vigorous growth of the crop. Once flowering and pegging begins it is advisable to weed by hand pulling rather than by using a hoe, as this is less likely to disturb any developing pods. Hand weeding (hoeing) is still by far the most widely practiced cultural weed control technique in field crop production throughout the tropics because of the prohibitive costs of herbicides and fear of toxic residue coupled with the lack of knowledge about their use. The objectives of this study were: to investigate the effect plant spacing and weeding on growth, yield and yield^’s components of groundnut grown under rain-fed in Sudan.

2. Materials and Methods

A field experiment was conducted in the North Kordofan, Elobied, Sudan, Latitude 13 ْ16´ N and longitude 30ْ 23´ E, for two successive seasons (2007 and 2008). The climate of the area is arid and semi arid zone. The soil is sandy with low fertility. Annual rainfall ranges between 350-500 mm. Average maximum daily temperatures was varied between 30 to 35ْ C, most of the year.

The experiment was laid at randomized complete block design (RCBD) with four replications. The plot size was 4 × 4 meters. The weeding treatments consisted of three levels: no weeding, weeding once (at two weeks after sowing) and weeding twice (at two and four weeks), designated as W₀, W₁ and W₂ respectively and four plant spacing of 10, 20, 30 and 40 cm were used, henceforth designated as S₁, S₂, S₃ and S₄ respectively.

Sowing dates were on first week of July. Seeds were sown on rows 60 cm apart, in hills. Four seeds were placed in each hill, which were then thinned to two plants per hill, two weeks later. Weeds counts made by placing the quadrate (0.5m x 0.5m) at random locations in plots repeated three times in order to obtain a reasonably good estimate of weeds.

A sample of four plants was taken at random from the inner rows of each experimental unit to measure the following attributes:

- Shoot length (cm): the height of the plant from ground level to the tip of the plant.

-.Number of nodes/plant: determined by counting the number of nodes of the main stem.

-Number of branches/plant.

- Leaf area index (L.A.I).

Leaf area index (L.A.I), a dimensionless quantity, is the leaf area (upper side only) per unit area of soil below. It is expressed as m² leaf area per m² ground area. Leaf area was determined using the leaf area Meter.

Leaf area index (L.A.I) was determined as follows.

- Days to 50% flowering: The number of days from sowing to the time when 50 Percent of the plants within the plot bear at least one flower each.

- Days to 50% maturity: Time to 95% physiological maturity was taken as the number of days from planting till 95% of the plants in the plot became yellow. Their leaves begin to shed and the pods had solid shell with wide veins before shoot dried.

-Number of pods per plant

-100- kernel weight.

-Final pod yield (t/ha) was determined as follows.

Data were analyzed statistically using analysis of variance according to Gomez and Gomez (1984) procedure for a randomized complete block design. The differences of means were identified by Duncan^’s Multiple Range Test (DMRT) at P ≥ 0.05.

3. Results

The majority of weeds in the experimental site were the broad leaves (dicotyledons), while grasses (monocotyledons) found in a lesser density (Table 1). The dominant weeds flora infesting groundnut during growing season were Cenchrus biflorus L, Zornia glochidiata L and Trienemara pentanture L. They had relative weeds density of 25%, 20% and 15% respectively.

Results of shoot length and number of nodes per plant are shown in Table 2. Weeding was significantly affected shoot length. Weeds decreased plant height in season (2007) by about 70% compared to weeding treatment. The highest shoot obtained at W₂ (weeding twice).

Weeds and weeding treatments had no significant effect on the number of nodes per plant. Plant spacing had no significant effect on plant height and number of nodes per plant. Results of number of branches and leaf area index are shown in Table 3. Weeding had significant effect on the number of branches per plant. Weeds decreased the number of branches per plant. The highest number of branches per plant was obtained at weeding twice (W₂)_. Weeding significantly affected the leaf area index. Weeding improved leaf area index. The closer spacing had higher leaf area index than the wider spacing. Plant spacing and weeding had no significant different in days to 50% flowering and 95% physiological maturity (Table 4).

Table 1. Weeds and Their Relative Density of non Weeded Groundnut Scientific name Classification local name Weeds density Cenchrous biflours. Monocot Alhuskaneet 25% Zornia glochidiata. Dicot Sheilini 20% Trienemra pentanture. Dicot Alraba 15% Sesamum alatum. Dicot Simsim Elgumal 6% Abutilon figarinum. Dicot Alniada 9.2% Allium spp. Bulb Bureaj 1.3% Echinocola colonum. Monocot Aldiffera 5% Rullia patula. Dicot Tagtaga 9% Corchorus olitorius. Dicot Almlukhia 3% Tribulus trerrestris. Dicot Aldraisa 0.3% Ipomea kordofana. Dicot Eltabar 3.2%

Table 2.. Effect of Plant Spacing and Weeds on Shoot Length and Number of Nodes per Plant of Groundnut Treatments 2007 2008 Shoot length (cm) No. of nodes per plant Shoot length (cm) No. of nodes per plant S1 20.0a 19.7 18.3 19.7 S2 21.8b 18.3 18.4 18.8 S3 16.6b 25.7 19.6 18.1 S4 20.1a 19.4 19.1 18.8 SE ± 2.0 5.8 0,9 1.2 W0 14.4c 18.3 18.7 18.3 W1 21.3b 58.0 18.9 19.0 W2 23.3a 71,0 20.3 19.4 SE ± 1.75 5.0 0.8 11.5 C.V% 30.9 34.3 30.9 50.1

Similar letters are not significantly different at the 0.05 level of probability according to Duncan Multiple Range Test

Table 4. Effect of Plant Spacing and Weeds on 50% Flowering and 95% Physiological Maturity of Groundnut Treatments 2007 2008 50% flowering 95% maturity 95% maturity 95% maturity S1 31.6 83.7 83.7 91.3 S2 31.3 83.9 83.9 91.3 S3 31.2 83.3 83.3 92.0 S4 31.4 84.3 84.3 92.0 SE ± 0.21 0.4 0.4 0.4 W0 31.4 83.8 83.8 91.5 W1 31.5 83.8 83.8 91.8 W2 31.3 83.8 83.8 92.0 SE ± 0.18 0.4 0.4 0.3 C.V% 2.07 1.5 1.5 1.2

Similar letters are not significantly different at the 0.05 level of probability according to Duncan Multiple Range Test

Results of number of pods and 100-kernel weight are shown in Table 5. Weeding had significant effect on the number of pods per plant in the first season. Weeds decreased the number of pods per plant. W₂ improved the number of pods per plant. Increased spacing increased number of pods per plant. Weeding significantly affected the 100- kernel weight. Increased weeding frequencies increased 100- kernel weight.

Table 5. Effect of Plant Spacing and Weeds on Number of Pods per plant and 100- Kernel Weight of Groundnut Treatments 2007 2008 Number of pods 100- kernel weight Number of pods 100- kernel weight S1 5.6 34.7 6.3 21.9 S2 8.6 36.6 8.0 18.9 S3 16.6 33.1 10.2 21.8 S4 18.7 36.5 12.1 20.4 SE ± 0.9 1.12 1.2 1.9 W0 11.0b 31.0b 7.8 20.9 W1 12.0ab 36.7a 8.4 21.7 W2 14.0a 37.9a 8.5 21.9 SE ± 0.8 1.1 1.0 1.7 C.V% 22.9 11.01 43.6 27.3

Similar letters are not significantly different at the 0.05 level of probability according to Duncan Multiple Range Test

Plant spacing had no significant effect on 100-kernel weight.

Results of pod yield are presented in Table 6. Weeding

treatments significantly affect the pod yield per plant.

Weeding twice increased pod yield per plant. Unweeded

Treatment had a poor yield. Weeding improved pod yield

(t/ha). W₂ had a highest pod yield compared to others.

Table 6.. Effect of Plant Spacing and Weeds on Seed Yield (g/plant) and Final Seed Yield (t/ha) of Groundnut Treatments 2007 2008 Pod yield (g/plant) Pod yield (t/ha) Pod yield (g/plant) Pod yield (t/ha) S1 40.4 1.3 20.2 0.5 S2 46.4 1.0 23.2 0.5 S3 41.1 0.6 29.1 0.4 S4 54.8 0.7 35.3 0.4 SE ± 4.1 0.1 4.2 0.1 W0 16.2 0.4 10.0 0.2 W1 53.9 1.0 31.0 0.5 W2 66.9 1.4 31.8 0.7 SE ± 3.9 0.1 3.6 0.1 C.V% 27.2 33.0 51.2 57.1

4. Discussion

Weeds have been defined as higher plants in the agro ecosystem, which are not sown, undesired, out of place or generally as plants which do more harm than good. They lead to direct yield losses of crop for water nutrients light, space and/or carbon dioxide. This degree of damage is mainly a function of their leaf area index, as compared with that of the crop (Ishag, 1971; Bedry, 2007; El Naim and Ahmed, 2010). This might explain the significant effect of weeds on most of the parameters measured in the present study.

Weeding twice had a highest plant height. Weeding facilitates plants to have more resources for growth, these results agreed with Joshi (2004), Mubarak (2004) and Bedry (2007); they found that, increasing weeding frequency increased plant height, due to efficient weed control.

Weeds decreased the number of branches per plant. The highest number of branches per plant was obtained at weeding twice. This result may be attributed to vigorous plant with less competition for light, nutrients, and free space in weed free environment. Yadava and kurnar (1981) and Weiss (1983) reported that weed control in peanut led to increased number of branches per plant compared to unweeded plants. Increased weeding frequencies increased leaf area index. This was due to better control of weeds. The reduced competition and increased availability of resources like nutrients, soil moisture and light paved way for higher leaf area per plant (leaf area index). These results are conformity with the findings of El Naim et al. (2010^a). Weeding increased number of pods per plant, 100 kernel weight, pods yield per plant and final pods yield (ton ha^-1). This is because hand-weeding resulted in a better performance of growth and yield components. Similar results observed by many workers; Ishag (1971), Mubarak (2004) Bedry ( 2007) and kumar (2009) in groundnuts crop. They observed that pod yield was greatly increased with weeding treatments, which encouraged early flowering, increased flowering, developed higher leaf area index, increased number of pods and branches per plant and finally maximized pod yield. Weeding twice resulted in increased 100-kernel weight. This may be due to better availability of nutrients and better translocation of photosynthates from source to sink and may be due higher accumulation of photosynthates in the seeds. Weeding twice had the highest harvest index. This may be due to better translocation of photosynthates from source to sink area and may be due to higher accumulation of photosynthates in the seeds (economical yield). The increased in number of pods per plant with increasing plant spacing observed in this investigation concurs with many researchers in different crops (El Naim et al, 2010^b and El Naim and Jabereldar, 2010). They reported that closer spacing reduced the number of pods per plant. These results may be attributed to the competition between plants and between the different parts of the individual plant under high planting population. Decreasing plant spacing decreased seed yield per plant during the two seasons. This was primarily because of a reduced number of pods per plant at closer spacing. Similarly, El Naim and Jabereldar (2010) found that seed yield per plant substantially decreased with decreased plant spacing. They attributed this reduction to inter plant competition for assimilates and low pod yield. In contrast, increasing plant spacing increased pod yield (t/ha). El Naim et al. (2010^c) reported supporting evidences.

The study revealed that the intra-row spacing of 10 cm and weeding twice should be preferred for groundnut production in North Kordofan of Sudan under rain-fed conditions.