Review Article
Response of Weeds and Crops to Fertilization Alone or in Combination with Herbicides: A Review
Department of Phytotechny, Faculty of Agricultural Sciences, University of Lubumbashi, Lubumbashi, Democratic Republic of Congo
Weeds compete for nutrients, water, light and space with crops. Depending on the type of crops, these interactions generally result in the loss of yields in useful products namely; stems, leaves, tubers, roots and seeds1.
Therefore, the presence of weeds in a cultivated field would be overwhelmingly attributed to anthropogenic activities to replace them with crops. Reinfection of the modified habitat being widely promoted by the seed bank or other products propagating organs of the previous season2. Generally, the ability of crops to compete with weeds becomes more efficient when the mineral or organic elements of the substrate are easily assimilated by the crop and they are not limiting factors for the growth and yield3.
However, the types and quantities of amendments applied may influence either vegetative growth of the crop or weeds especially, both have the same nutrient requirements. For basic fertilizer (NPK), it was established in cultivated fields its spreading on the surface stimulates weed flora and unlike burial at a shallow depth4-7 such 5 cm.
Beyond the plant already established in the habitat, according to Bajwa et al.8 fertilization could influence the activation or inhibition of seed stock germination from previous years especially, when stimulus such as light, changes in temperature and rainfall are added9,10.
In developing countries, weed chemical control proves to be a quick option in terms of time savings to cover a large area, unlike manual weeding which consume about 50% of time spent on other operations of crop maintenance although, leading sometimes to good results for certain crops such as common bean especially, the frequency of interventions come before biological damage threshold of weeds to crops. Generally in this part of the continent, this practice is essentially family hence its inefficiency11-13.
With a view to provide better weed control to promote sustainable agriculture. This study has offered to make a digest of some studies on the evaluation of effects induced by fertilization alone or combined with chemical control of the flora of weeds and crops.
Fertilization effects on weeds and crops: The growth and development of plants are determined by their ability to remove nutrients available in the soil followed by their distribution to various organs14.
However, most weeds have high efficiency in nitrogen removement but, it depends on the types of species and environmental conditions such was the case of the strong competitiveness of wild oats (Avena fatua L.) in wheat culture15-17.
Physico-chemical properties of soil can not be ignored in explaining the effect of fertilizer on the seed bank because of sandy soil nitrogen fertilizer has greatly stimulated seed germination of wild oats (Avena fatua L.) unlike soil rich in organic matter when the same dose did not induce effects on the same seeds18.
According to Gallandt19 and Davis20, a soil has rich organic matter, there is a high diversity and abundance of microorganisms that destroy seed bank as a source of energy extracting the carbon or nitrogen to ensure their survival.
Moreover, Chee-Sanford et al.21 argued that the degree of microbial seed predation depends on several factors of colonization rates, mutual adaptation of each microbial population to environmental conditions and the physical nature of the seed coat etc.
Indeed, organic manure is more suitable in improving soil fertility compared to synthetic fertilizers. Moreover, growing period length of crops remains an important factor governing interactions with weeds which would justify splitting amendments in relation to different phenological phases of the crop. According to Alcoz et al.22 this practice allows the crop to ensure efficient use of nutrients while, further limiting losses of some elements such as nitrogen; denitrification, leaching in case of heavy rains and volatilization in presence of high temperatures.
In this perspective, the results of Paolini et al.23 showed strong competitiveness sunflower face Chenopodium album, Solanum nigrum and Xanthium strumanium after splitting nitrogen at 50% in pre-sowing growth and 50% in the production phase to control Sinapis arvensis. Supporting this idea, Soares et al.24 showed that in cassava culture NPK application or 70 kg N ha1, 17.5 kg P ha1 and 25 kg K ha1 at planting moment substantially reduces weed density unlike the formula (NK) or 60 kg ha1 N and 50 kg ha1 K applied 350 days after planting favored the massive invasion of culture by; Brachiaria plantaginea, Sida rhombifolia, Pavonia cancellata, Setaria parviflora and Cynodon dactylon following the inability of culture to produce enough leaves in the production phase. Moreover, the binding effect of water stress the cultivated plant to lose much of its leaves.
In cereal crops including rice straw and wheat, it was shown that the low dose of NPK (50%) stimulates Cyperus rotundus growth. Doubling the dose of NPK (100%) combined with 10 t ha1 of manure, high species richness and diversity were observed with the pre-dominance of hardwoods25. At this level, it should be emphasized that the farm manure enhances the action of mineral fertilizers but this is not evident if taking into account of manure nature26 cow manure-based fertilizer stimulates the dormancy of weed seeds which largely contributes to the rapid infestation of the field especially, when used alone. This emerges from a study by Gana27 in sugarcane culture where 10 t ha1 of cattle manure promoted the proliferation of weeds and the opposite trend was observed when combined with NPK (120 kg N ha1, 26 kg P ha1 and 37 kg K ha1).
The efficiency of farm manure on soil productivity, crop and weed control depends on the intrinsic and extrinsic factors. Therefore, Mahadi et al.28 demonstrated that the duration and conditions of farm manure conservation influence the content and availability of nutrients like N, P, K, Ca, Mg and C among them only organic carbon has seen its content will increase for two years of storage. Considering the origin of the organic matter, results obtained by Jiang et al.29 do not corroborate those of its predecessors because organic fertilizer made of pig excrement-based reduces significantly in the field the germination of seeds in the seed stock of six species, Eleocharis acicularis, Monochoriav aginalis, Polygonum lapathifolium, Ammannia baccifera, Cyperus difformis and Ammannia aarenaride. Huang et al.30 reported that 22.5 t ha1 of pig excrement combined with mineral fertilizers (NPK) substantially stimulate weed density in rice, unlike the N (90 kg ha1), P (20 kg ha1) and K (62 kg ha1) alone or in the form of NPK.
Some studies showed the impact of crop genotype on the uptake and the use of nutrients in order to understand the impact on weed flora. Results of the study conducted by Al-Tawaha et al.31 on 10 varieties of barley subject to mineral fertilization with 100 kg ha1 of diammonium phosphate (DAP) and 50 kg ha1 of area showed that high grain yield was observed on varieties with high ability nutrients uptake. The same observation was made by Azeez and Adetunji32 in maize crop where the best use of nitrogen has characterized genotypes with high uptake potential and 90 kg N ha1 applied in urea form helped to increase grain yield of the culture and its competitiveness against weeds. Observation backed by Aminpanah et al.33 who reported that the canola crop (Brassica napus L.) is less competitive in 0 kg N ha1, slightly competitive at 100 kg N ha1 and more competitive at 200 kg N ha1 against weeds. This ability is not observed in all genotypes whose yields are not similar. This opinion is complemented by Saberali et al.34 in common bean crop. Different nitrogen rates 0-200 kg N ha1 applied to semi-erected variety allowed to ensure a good control of Amaranthus retroflexus and get a high production, unlike the erected variety receiving from 0-140 kg N ha1. The competitiveness of Amaranthus retroflexus extends to many cultures, this opinion was supported by Blackshaw and Brandt35 who emphasized his high ability in the nitrogen uptake in wheat crop resulting in an important increase to its above ground biomass in proportion to each addition of nitrogen doses 60, 120 and 240 mg N g1. Such observation was made on Abutilon theophrasti in association with maize36.
In a comparative study of effects of composted organic amendments cassava peels, sawdust, corn stalks, leaves and dung hen with 900 and 400 kg ha1 NPK 15-15-15 on Tithonia diversifolia and Tridax procumbens led by Adesina et al.37 on tomato crop (Lycopersicon lycopersicum UC82B var). It was highlighted during two years of experience an increase in the density and biomass of weeds similar to unamended treatments because the mineral manure stimulate seed germination and regrowth, unlike organic amendments composted.
In maize crop, Khan et al.38 showed response of weeds to macronutrients N, P and K applied in simple or compound form. The high grain yield w as induced by the NP form. As for the degrees of densities of these species; Cyperus rotundus, Leptochloa sp., Echinochloa crus-galli, Sorghum halepense, Cynodon dactylon, Digitaria sanguinalis, Convovulvus arvensis, Amaranthus viridis and Digera muricata and Portulaca oleraceae, they are as following N>NPK NP>P>NK>K>PK. However, the study by Tang et al.39 showed that the formula of balanced fertilizer (NPK) has significantly reduced the density of four species of invasive weeds of wheat crop; Galium aparine L., Veronica persica Poir, Viciasativa L. and Geranium carolinianum L. compared to binary formulations NP, NK or PK which induced a high density of these species. Similar results were revealed by Iyagba et al.40 in okra crop (Abelmoschus esculentus L. var NHAe 47-4) in Nigeria only 200 kg ha1 of NPK were enough to increase the fruit yield and keep weeds at a low threshold of biological harmfulness.
Always on the same track on common bean crop nutrient appication in simple form or 50 kg ha1 P2O5 and 50 kg N ha1 (ammonium nitrate) and compound (NP, NK, PK and NPK) at sowing moment increased high density of Solanum nigrum, Bidens pilosa and Galisonga parviflora but the opposite trend was recorded in plots treated with 60 kg ha1 K2O41.
Unlike previous results, other studies have shown that a soil rich in phosphorus and nitrogen, only 10-20 kg P ha1 were enough to make the common bean very competitive with weeds42,43.
Effects of fertilization-herbicides on weeds and crops: The IPM is a technique including a combination of several methods of weed control for sustainable management and further reducing the amount of pesticides and fertilizers44,45. In this case, it is the direct control of weeds or spread their bodies by the herbicides applied either pre-emergent or post-emergent treatments that retard their growth and mineral or organic fertilizer whose main objective is to promote crop growth by making it more competitive.
Herbicide effects on flora and soil seed stock: Processing of pre-emergence or pre-sowing, once applied herbicides reach the ground, they are adsorbed to soil colloids and the passive phenomenon of water by soaking the seeds regulated by the nature of the seed coat, the herbicide will penetrate the seed germination physiology to disrupt or inhibit the recovery of stolons, rhizomes and tubers etc.46,47. While, in post-emergent treatment there is a residual action low or nil as their efficiency is important especially at the time of application. In general, herbicide does not master a single plant species but several at different levels depending on the sensitivity of active ingredient48.
Indeed, herbicides once mixed together with mineral or organic fertilizers may not induce the expected effects on both the culture of weeds, this depends on several factors including the physical and chemical properties of soils of active ingredients, application times and the nature of the fertilizer the type of weeds etc.
Furthermore, most herbicides containing radicals derived from urea have a double advantage whose action on the weeds and to some extent also on crops. One case is that raised by Soltani and Saeedipour49 revealed that graminaceous herbicide effect and the remarkable increase in grain yield of wheat crop after a combination with ammonical nitrogen on silty clay soil.
In maize production, grain yield increases after application of 3% urea as NPK (160-80-50) in combination with 1125 g a.i ha1 (Foramsulfuron isoxadifen-ethyl) post-emergence having allowed to reduce the density of three invasive species; Trianthema portulacastrum and Cyperus rotundus and Coronopus didymus50.
Although, concerning other barley crop, it was reported that there is a synergy created by foramsulfuron 0.06 kg a.i ha1 in the presence of nitrogen 50 kg ha1 to ensure good control of Convolvulus arvensis L., Amaranthus retroflexus L. and Physalis alkekengii L. because beyond 50 kg N ha1 there is increased density of these three species51.
The application in post-emergence Mustang 306SE herbicide (1 L ha1) on oat crop has substantially reduced the density of dicotyledonous, unlike the case where it is mixed either fertilizer foliar spray insol 3 alone or in combination with Folicare 18-18-1852. Futhermore, Mick et al.53 on bio fortified common bean crop (var prelon) argued that although, post-emergent glyphosate SL480 g a.i L1 was employed at pre-sowing on ferralsol at 1.5, 3 and 4.5 L ha1 and this with 200 kg ha1 of NPK 10-20-10, 17-17-17 and 14-18-18 not any glyphosate dose allowed to control weeds or increase crop grain yield except 200 kg ha1 of NPK 10-20-10. However, it was revealed the efficacy of certain post-emergence molecules applied at pre-sowing. For example, maize grain yield gain and better control of Echinocloa crus-galli, Sorghum halepense, Cynodon dactylon, Digera muricata and Portulaca oleracea, Convolvulus arvensis et Cyperus rotundus was induced by atrazine 1 kg a.i ha1 and 160 kg N ha1 compared to stomp 0.75 kg a.i ha1 subject to same conditions and 2.4 D-72 (ester) 0.80 a.i kg ha1 applied in post-emergence or 25 days after sowing54.
Ellis-Jones et al.13 also showed that atrazine does not lose its effectiveness on weeds when combined with other molecules as atrazine+metolachlor (2.6 kg a.i ha1) and atrazine+acetochlor+terbuthylazine (2.8 kg a.i ha1) that allowed increase significantly maize grain yield as when it combines the effects of 6 t ha1 of chicken manure buried in soil 14 days before sowing.
This view is consistent with that issued by Mick et al.55 in common bean culture that reveals compatibility during pre-sowing treatment of atrazine which 3 L ha1 associated with 3 L ha1 paraquat on ferralsol. In addition to corn, it was reported by Mick et al.56 in treatment post-emergence atrazine 3 L ha1 acetochlor associated with 3 L ha1 does not ensure good weed control and do not increases the crop seed yield.
How to understand herbicide-soil interactions on the fate of active ingredient? According to Mamy57, the decrease of the effectiveness of some herbicides once reached the ground would be governed by the type of soil that influences their adsorption to soil colloids. Moreover, Flogeac58 emphasizes the nature of the molecule in adsorption process. Thus, anionic herbicides such as triazines and carbamates have a low adsorption capacity to the soil colloids while, cationic herbicides such as paraquat, diquat and some organophosphates will be strongly retained. However, for certain herbicides combined with fertilization, their effectiveness is likely in the presence of low efficiency weeds in nutrient uptake, because Modhej and Kaihani59 revealed that the ineffectiveness of some herbicides due to increasing nitrogen rates (urea) 50, 100, 150 and 250 kg N ha1 that made weeds stronger by strengthening their defense systems.
The rotation of herbicide molecules and splitting of fertilizer were found as palliative practices among others concerning the ineffectiveness of certain active substances in the weed control because the study conducted by Sheibani and Ghadiri60 proved it after oilseed rape rotation (Brassica napus L.) wheat, it was reported that splitting nitrogen (urea) which 304 kg N ha1 at a rate of 152 kg N ha1 in sowing phase and 152 kg N ha1 in productive phase combined with post-emerging herbicides significantly reduced seed viability in stock from 0-30 cm deep including, Wheat 21 g a.i ha1 iodosulfuron-methyl-sodium plus mesosulfuron-methyl-sodium reduced seed around 53-73% and for Oilseed rape (Brassica napus L.) 108 a.i ha1 of haloxyfop (R) methylester have controlled the seed around 40-43%.
From the foregoing, The effects of mineral or organic fertilization would increase weed pressure either by strengthening the growth of seedlings present at the time of application or by the stimulating seed germination from seed stock of the past growing season. This can be seen most especially in marginal soils, case of tropical soils where one seeks to improve productivity by bringing amendments61. Furthermore, the chemical composition of organic and inorganic amendments proved to be a decisive factor on growth and development of plants62.
Therefore, nitrogen from its presence in the balanced form represented by the three major elements (NPK) or binary forms NP and NK, it should be noted that the form of nitrate (NO3), urea (CO (NH2)2) and ammonium (NH4). Nitrogen has proven to be one of macro nutrients which makes some weed species more competitive to affect the culture.
Physico-chemical properties of soils, application moments and compatibility of active ingredients are determining factors of fertilizer and herbicide efficiency. Sustainable management of weeds by fertilization alone or combined to herbicides remains an effective technical route especially, for organic or inorganic amendments taking into account the type, quantity, storage methods and application moments. This holds also true for herbicides except factors discussed above, their effectiveness depends on the physico-chemical properties of soils and the predisposition of several active ingredients to be able to combine and widen the spectrum of action that the active ingredients are characterized by different levels of weed control or spread their organs. But, some herbicides especially containing an urea radical further phytocide actions, they reinforce the action of nitrogen fertilizers and promote crop growth. For the IPM program (fertilizers and herbicides) more sustainable, it would be wise to involve other techniques such as crop rotation, sowing densities, sowing dates, crop association and eventually the choice of genotypes tolerating low soil fertility or high competitive capacity of weed in uptaking and using nutrients.
Beyond the plant already established in the habitat, according to fertilization could influence the activation or inhibition of seed stock germination from previous years especially stimulus such as light, changes in temperature and rainfall are added.
This study brings answers to following question:
• | Is fertilization an adapted weed management mode in Lubumbashi? |
• | Are herbicides application an effective method for weed management in Lubumbashi? |