EFFECT OF PROMETRYN/BENZOIC ACID COMBINATION ON WEEDS, SEED YIELD AND YIELD COMPONENTS IN LENTIL (LENS CULINARIS L.)

Faida A. Sharara, T.A. El-Shahawy, Kowthar G. El-Rokiek
Department of Botany, National Research Centre, Dokki, Cairo, Egypt

ABSTRACT

The study aimed at investigating the combined application of prometryn (herbicide) plus benzoic acid at different concentrations for controlling weeds and on seed yield in lentil (Lens culinaris L. cv. Giza 370). The experiment was carried out in the new reclaimed land of Egypt (Experimental Station of NRC, El-Nobaria District, El Behera Governorate) during two successive seasons (2007/08 and 2008/09). The application of prometryn at 600 g a.i.·ha^-1 in tank mixture with benzoic acid at the concentration of 720 g·ha^-1 resulted in as effective-weed control and yield as applying the herbicide alone at the recommended dose (1200 g a.i.·ha^-1), without apparent toxicity on lentil plants. Using the herbicide at 900 g a.i.·ha^-1 in combination with benzoic acid at either concentrations (240, 480 and 720 g) was also good, however it was toxic to lentil especially at the higher concentration of benzoic acid. None of the herbicide treatments resulted in yields higher than the hand-weeded treatment performed twice. The primary benefit from the application of benzoic acid in this study was to reduce the herbicidal doses and then environmental pollution.

Key words: benzoic acid, combined effect, lentil, natural products, prometryn herbicide, weed control.

INTRODUCTION

Lentil (Lens culinaris L.) is one of the most important legume crops all-over the world. The nutrient value of lentil is very high. The seeds are composed of 60% of carbohydrates, 26% of protein, 7.5% of iron, 2% of sugars and 0.87 of thiamine (vitamin B1), which make it very essential in human and animal feeding where the stubble is also very rich in many valuable components.

The crop has a very special value in the developing countries, in particular in Egypt, where it is considered one of the main dishes for the many of the people there, especially the poorest of them. Despite its great value for the Egyptian people, the country is suffering a lot from some kind of a big shortage in lentil productivity because of the limited sown area. The yield per unit area in Egypt is one of the greatest values all-over the world approaching 2.03 tonnes per hectare in comparison with less than 0.8 tonnes for the global mean. According to the latest FAO statistics [12], 612 hectares were used for lentil production in Egypt, and 1214 tonnes is the total yield obtained in (2008), which is absolutely not enough to cover all the domestic demands of the country. The difference between the local production and the actual needing is covered by imports. India, Canada, and Turkey are the main market in this regard [16]. Traditionally, lentil is grown in winter in Upper Egypt in particular in Asuot and Kena Governorates. Today, there has been a grown concern to sow the crop in the new reclaimed areas in Egypt, e.g. in El-Behera and Kafr El-Shaik Governorates.

The efforts made on enhancing the yield and its components in lentil in Egypt are enormous. This includes expanding the sown area, importing and breeding new varieties coupled with improving the local ones. Controlling pest strategies (especially for weeds) were also included. Lentils, generally, are very poor weed competitors (especially as seedlings) for many weeds infesting fields due to low growth of plants which do not form dense canopy until flowering. The seed yield losses of up to 60% can occur if weeds are not controlled and could amount to 100% under heavy weed infestation [14]. Therefore, weed control is crucial for good agricultural production in lentils and for the health status of the subsequent cereal crop. For the best production results, weeds should be treated earlier (e.g. from the first week of emergence) to avoid losses could be more than 5% [11]. The critical period for weed control in lentil depends on the environmental conditions [17].

The results from cultural weed control methods (e.g. mechanical methods, hand hoeing/weeding, sowing time, seed intensity etc.) are variable. The level of weed control achieved is primarily dependent on environmental conditions. Some control could be achieved by one or two pre-emergent harrowing or hand-weeding operations following seeding [14,18]. This will improve the kill of winter annuals and firm and smooth the seedbed, however it requires great precaution not to damage the crop. Because of the slender early stem growth, the plants are easily damaged at this time. Increasing the seeding rate for up to 66 kg·ha^-1 may be more useful for controlling weeds in lentil than any other strategy reported in this regard [2]. The post-plant tillage including harrowing, rotary hoeing or hand weeding/hoeing is also effective, but can't be used independent of any of the other herbicide treatment recorded in this regard [3]. The success in such cases depend on the state and the type of weeds infesting lentil plants [8,18].

Due to short stature, relatively poor tolerance to herbicides, and limited herbicide registrations, chemical control for lentil weeds is facing some shortage. Herbicides for the control of certain broadleaf weeds and many of gasses either are not available or provide less than acceptable control. Metribuzin, linuron, prometryn, pronamide, sethoxydim, fluazifop-butyl, triflurin, imazethapyr and pendimethalin are all successfully used in controlling weeds in lentil [8,21,22]. Even though, some showed good activity some others negatively affected lentil growth such as metribuzin, pendimethalin and bentazon herbicides [13]. Mohamed et al. [17] presented a good formula for controlling weeds and increasing yield in lentil based on using imazethapyr (0.05 kg a.i.·ha^-1), terbutryn (1.0 kg a.i.·ha^-1) or prometryn (1.0 kg a.i.·ha^-1), in combination with pendimethalin at 1.2 kg a.i.·ha^-1. Oxyfluorfen (0.24 kg a.i.·ha^-1) with terbutryn (1.0 kg a.i.·ha^-1) or prometryn (1.0 kg a.i.·ha^-1) were also suggested by the authors.

Bearing that all in mind, the aim of the present work has been to investigate the ability of using benzoic acid in combination with prometryn herbicide for controlling weeds and increasing yield in lentil. Reducing herbicidal doses of the herbicide and then agricultural cost and, above all, environmental pollution were also considered in the study.

MATERIAL AND METHODS

A field experiment was conducted during two successive seasons (2007/08) and (2008/09) to study the potential effect of using prometryn [gesagard, 500 FW N,N-bis (1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine]/benzoic acid combination in controlling weeds and increasing yield in lentil. The experiment was carried out at the Experiment Station of the National Research Centre, Al-Emam Maliek Village, Al-Noubaria District, El-Behera Governorate. The soil texture was sandy soil (91.2% sand, 5.6% clay and 3.2% silt) with the chemical properties being as follows: pH 7.3, Ec 0.3%, CaCl₃ 1.3%, O.M. 0.3%, N 8.1 ppm, P 3.2 ppm and K (exchangeable) 20 ppm [4]. Lentil seeds (Lens culinaris L. cv. Giza 370) were purchased from the Ministry of Agriculture, Egypt. The land was prepared as usual, including ploughing, flatting and leveling into 20 cm width rows. Chemical fertilizers were added according to the applicable recommendations. The seeds were sown at rates of 108 kg·ha^-1 by drilling into the rows. The sowing date was the 1^st week of November each season. The prometryn herbicide was applied as pre-emergence either alone at 1200 g a.i.·ha^-1 (the recommended rate) or in combination with benzoic acid (240, 480, 720 g·ha^-1) at 300, 600 and 900 g a.i.·ha^-1. Two hand-weeding (4 & 6 weeks after sowing) treatment was also applied. Untreated plot (weedy check) was used as a control. The formulated concentrations were sprayed by knapsack sprayer using 480 litres of water·ha^-1. Three replications were used for each treatment in a completely randomized block design. The weather was, to some extent, constant along the two seasons (temperature: 14-17°C at night, 21-24°C at day, relative humidity: 48–55%, rainfall was very rare in the area).

Data recorded

Weed sampling
Weed samples were taken after 60 days from sowing by hand pulling of the whole growing weeds in one square meter of each plot. The fresh and dry weights (g) were estimated for each kind of weeds including broad- and narrow-leaved weed species. Annual weeds were found to dominate the area there.

Crop sampling
A vegetative sample was taken at the same time of weed sampling to determine also the fresh and dry weights (g·plant^-1), plant height (cm) as well as the number of branches per plant.

At harvest time
Two central rows from each plot were harvested and subsamples of ten plants were taken randomly to estimate the following characteristics: plant height (cm), seed yield (g·plant^-1), weight of 100 seeds (g) and straw yield (g·plant^-1 & t·ha^-1). All lentil plants were harvested from each plot to determine the total seed yield (t·ha^-1), biological yield (t·ha^-1) and harvest index (%).

Chemical composition of lentil seeds
Total nitrogen and carbohydrates (%) were determined following the methods by A.O.A.C. [1]. Nitrogen values were multiplied by the factor 6.25 to calculate total crude protein.

Statistical analysis

All data were statistically analyzed following the methods of Snedecor and Cochran [20]. ANOVA table was calculated and LSD test at 5% probability was used to compare the means.

RESULTS

Applying prometryn either alone at the recommended dose or in combination with benzoic acid at different concentrations significantly reduced the growth of the whole growing weeds (Table 1). This included different broad- (Brassica nigra L., Melilotus indica L., Amaranthus cruentus L., Chenopodium ambrosioides L., Chenopodium murale and Sisymbrium irio L.) and narrow- (Iragrastis cilianensis L., Phalaris minor Retz. and Poa annua L.) leaved species. Overall, the activity increased as benzoic acid increased and the best results obtained were for the concentrations of 600 and 900 g a.i.·ha^-1 of the herbicide, each in combination with benzoic acid at 720 g h·a^-1. Broad-leaved weeds were more sensitive than the grassy types to the treatments including hand-weeding performed twice. The hand-weeding treatment performed twice was comparatively the most effective over all in this regard.

The different treatments, on the other hand, showed great activity in increasing mass vegetative growth of lentil (fresh and dry weights) as well as plant height and the number of branches per plant in a similar trend of the results obtained on weed growth (Table 2). Prometryn at 600 g a.i.·ha^-1 plus benzoic acid at 720 g·ha^-1 was the most effective in this regard and was comparable to applying prometryn alone at the recommended dose (e.g. 1200 g a.i.·ha^-1). Even though it was very effective against weeds, prometryn at 900 g a.i.·ha^-1 plus benzoic acid at 720 g·ha^-1 ranked second as some toxicity appeared on lentil plants.

At harvest stage, all parameters increased in response of the treatments (Tables 3, 4). That includes plant height, weight of 100 seeds, seed yield per plant, yield per hectare, harvest index and straw yield per hectare. We can see prometryn (600 g a.i.·ha^-1) plus benzoic acid (720 g·ha^-1) again in parallel with hand-weeding treatment performed twice as the best over all.

In parallel with studying the effect on controlling weeds and increasing growth and yield in lentil, the chemical composition in yielded seeds of lentil was also investigated. The data showed good activity of treatments in increasing protein and carbohydrates contents in seeds. The best results were obtained for the prometryn plus benzoic acid at the concentrations of 600 and 720 g a.i.·ha^-1, respectively (Table 3). Hand-weeding twice was also in parallel with the most effective treatments.

DISCUSSION

Lentil ranks high among consumer preferences and very low in terms of the area and production in Egypt. Weed is a major constraint for lentil production as well as herbicides which can trigger great damage to the environment and public health. The experiment was designed with a preliminary objective to investigate the potential effect of using benzoic acid in combination with prometryn herbicide for increasing the herbicidal efficiency for controlling weeds and increasing yield in lentil. The experiment was carried out in the new reclaimed land of Egypt e.g., El-Nobaria District as it is considered the future of agriculture in Egypt and the best way for the treatment of the present dilemma of the big arable land shortage in Egypt.

Recently there has been an increasing concern in using natural products from plants and microbes for controlling weeds. The results obtained were very promising in this regard [5,7]. Benzoic acid is one of the oldest compounds amongst many compounds were isolated [15]. The halogenated benzoic acid derivatives such as dicamba, chloramben and picloram are widely used as herbicides [6]. A new trend of using natural products is restricted in using them as elicitors for currently available herbicides [9,10].

The present results demonstrate a good activity of benzoic acid in increasing the herbicidal efficiency of prometryn for controlling weeds and increasing the yield in lentil. It was also clear from the study that the concentration of 900 g a.i.·ha^-1 of prometryn plus benzoic acid at 720 g·ha^-1 was the most effective over all in controlling weeds, however the toxicity obtained on lentil was discouraging. That makes it (as a treatment) less promising than any others in the study, especially the concentration 600 and 720 g a.i.·ha^-1 of the herbicide and benzoic acid, respectively where no toxicity appeared at all. The inclusion of benzoic acid with prometryn at this (latter) concentration was also as effective weed-control and yield as applying the herbicide alone at the recommended dose (e.g. 1200 g a.i.·ha^-1) and also hand-weeding performed twice. Little data is available on using natural products as elicitors for the herbicides. However, Sharara and El Karmany [19] found good impact of using benzoic acid in combination with bentazon or fluazifop-P-butyle in increasing activity for controlling weeds and improving yield and its components in faba bean.

Eventually, the inclusion of benzoic acid with prometryn herbicide was very effective in controlling weeds and increasing yield in lentil, which is also promising in terms of e.g. reducing environmental pollution and agricultural cost.

CONCLUSIONS

1. Applying prometryn herbicide at the dose of 600 g of a.i.·ha^-1 in combination with 720 g·ha^-1 of benzoic acid was the most effective in controlling all weeds in lentil.

2. This treatment did not show toxicity to lentil plants and resulted in a greater plant productivity. The quality of lentil seeds was also increased in terms of carbohydrates and protein contents.

3. The treatments with high concentrations of prometryn (e.g. 900 g a.i.·ha^-1) were effective in weed control, but their toxicity against plants of lentil, especially at the concentration of 720 g·ha^-1 of benzoic acid, was discouraging.

4. Hand weeding was as effective in weed-control and increasing of yield as applying the most effective chemicals. However, it can't be used in a large scale in the farms because of the big shortage in labour not only in Egypt, but also all over the world.

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Accepted for print: 30.12.2010

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