Effect of weed competition on growth, nutrient uptake and yield of wheat as affected by irrigation and fertilizers

Journal of Agricultural Science, Cambridge (1999), 133, 45 51. 1999 Cambridge University Press Printed in the United Kingdom 45 Effect of weed competition on growth, nutrient uptake and yield of wheat as affected by irrigation and fertilizers T. K. DAS* AND N. T. YADURAJU Division of Agronomy, Indian Agricultural Research Institute, New Delhi-110 012, India (Revised MS received 8 March 1999) SUMMARY The composite effects of two irrigation frequencies (one irrigation at crown root initiation stage and five irrigations at five critical physiological stages of wheat), eight nutrient treatments consisting of N, P and K either applied alone or in combinations at the recommended doses (N:P O :K Oat 120:60:40 kg ha) on population and dry weight of weeds and on the growth, nutrient uptake and yield of wheat were investigated. Observations on the components of the weed population and their biomass made at 60 DAS did not reveal any significant difference between the high and low frequency irrigation. Among the nutrient treatments, the N-treated plots (N, NP, NK and NPK) had a higher population and biomass of grass weeds, whereas sole P and K application or their combination produced the greater growth of broad-leaved weeds. However, the overall weed competition was significantly higher in the P- and K-treated plots than in the N-treated plots. The NP, NPK, NK and N treatments produced significantly higher values for dry weight, crop growth rate, leaf area, number of tillers, nutrient uptake, number of ear-bearing tillers, protein content and grain yield than the other treatments. Weeds in unweeded control plots did not significantly affect wheat growth (CGR, dry weight, tillers plant) and uptake of the nutrients except of the P at 60 DAS. However, the number of ear-bearing tillers, grains per ear and yield were significantly higher in the weed-free plots than in the unweeded control treatment. INTRODUCTION A sound knowledge of crop weed competition is a prerequisite for evolving a suitable weed control strategy. Competition between crop plants and weeds is influenced by numerous factors including their morphology and physiology. Crop husbandry practices such as choice of crops or crop cultivars, rowspacing, seed rate, intercropping, tillage, selective stimulation of crops by placement of fertilizers, irrigation schedules also influence the germination, growth and proliferation of weeds and thereby the extent of competition (Sandhu et al. 1981). The ultimate effect of weed competition is to reduce the growth and yield of the crop, but determining the way in which yield reduction occurs is important in understanding the complex phenomenon of crop weed competition. Williams (1976) reported that while sole application of either P or K stimulated legume growth at the expense of grasses, nitrogen stimulated * To whom all correspondence should be addressed. Email: das bic-iari.ren.nic.in the growth of grasses. Ammonium sulphate acidified the soil and discouraged legumes. Several workers (Thurston 1959; Thrasher et al. 1963; Carlson & Hill 1985; Yaduraju & Ahuja 1992) in India and other countries have reported differential use of nitrogen by wheat and weeds. Many workers believe that nitrogen should be a decisive factor in the management of weeds. The role of nutrients other than nitrogen is, however, less well-understood. Some (Sexsmith & Russell 1963; Siddiqi et al. 1985; Konesky et al. 1989) have demonstrated the differences in competition for potassium and phosphorus between crops (e.g. wheat, barley) and weeds. However, detailed studies with regard to the competition of weeds, particularly grass weeds in wheat under Indian conditions, are lacking. Another important component for crop weed competition is water. and water have a synergistic interactive effect on the productivity of a crop (Bhardwaj & Wright 1968). The greater productivity of dwarf wheat in India is due to its positive response to both fertilization and irrigation (Singh & Kolar 1992). A comprehensive study encompassing all three major nutrients, water and weeds on the

46 T. K. DAS AND N. T. YADURAJU growth, nutrient uptake and yield of wheat was, therefore, undertaken. MATERIALS AND METHODS An experiment was conducted during the winter seasons (Nov April) of 1991 92 and 1992 93 at the farm of the Division of Agronomy, Indian Agricultural Research Institute, New Delhi, to study the weed interference, as affected by nutrients and water, on wheat. The soil was sandy loam, medium in fertility (1165 kg total N, 19 kg available P and 218 5 kg available K per ha) with ph 8 3. The treatments consisted of a combination of two frequencies of irrigation (five irrigations at the critical stages of crown root initiation (CRI), tillering, jointing, flowering and milk ripe of wheat and the single irrigation at the crown root initiation, a sensitive stage according to Bhardwaj & Wright 1968), and eight nutrient treatments (none (control), N, P, K, NP, NK, PK and NPK applied at their recommended doses) in main plots and an unweeded control (UWC) and weed-free treatment (WFT) in sub-plots were assigned in a splitplot design with three replications. The gross and net plot sizes were 4 0 1 6 m and 3 0 1 1 m, respectively. A pre-sowing irrigation was given to the entire field before sowing to facilitate the uniform establishment of the crop. As per recommendation, irrigation of about 6 7 cm depth (384 448 litres per gross plot) at each critical stage irrespective of the year of experimentation was uniformly applied in all the treatments except the single irrigation treatment where irrigation was withheld after CRI stage. Recommended doses at 120 kg N ha, 60 kg P O ha and 40 kg K O ha were applied either separately or in combination depending on the treatment, by broadcasting before sowing the wheat. The entire amount of phosphorus and potassium was applied basally, whereas 50% of the nitrogen was applied as a basal-dressing and the rest was top-dressed at the time of the first irrigation at the CRI stage of wheat. Nitrogen, phosphorus and potassium were applied in the form of urea, single superphosphate and muriate of potash, respectively. Weed-free plots were weeded manually as and when necessary. The crop (cv. HD 2329) was sown in the second fortnight of November in both years with a seed rate of 100 kg ha and a row spacing of 22 5 cm. The observations on weeds were made at 60 and 90 days after sowing (DAS) and at harvest by throwing a quadrat of 50 50 cm from where counting of the component weeds was made and the weeds collected for estimating their dry matter production. The observations on wheat were made at 60 and 90 DAS and at harvest by pulling out wheat plants from one row of 1 m length. The leaves were separated and their area was measured using a L1-3100 Area Meter, before drying them in an oven at 70 C for 48 h for dry matter estimation. Crop growth rate was calculated according to Radford (1967). Tiller number per plant was recorded from 10 randomly chosen plants. The plant samples were analysed for N, P and K using standard procedures (Jackson 1973). For test weight, 1000 grains were counted and weighed. The data for each year were analysed separately, but showed no variation in the overall significance non-significance of the treatment effect over the years. They were, therefore, pooled, underwent statistical analysis again and are presented here. Data on weed population and weed dry weight varied widely and hence the data were subjected to square-root ( X 0 5) transformation before analysis of variance. The data were analysed by the Basic statistical package and the significance of treatments (at P 0 05) was tested by variance ratio as described by Cochran & Cox (1957). RESULTS Weed flora and their growth The major weed species found were Avena ludoviciana Dur., Phalaris minor Retz., Melilotus indica L., Chenopodium album L., Fumaria parviflora L. and Cyperus rotundus L. Avena ludoviciana among the grass weeds and Melilotus indica among the broadleaved weeds were the most dominant. At 60 DAS, the population and dry weight of grass, broad-leaved and composite (total) weeds (Table 1) did not differ significantly between the irrigation treatments, but differed significantly between the nutrient treatments. Grass weed population (Table 1) in the NPK treatment was similar to that in the N, NP, NK and control treatments but significantly greater than in the PK, P and K treatments which had a significantly greater population of broad-leaved weeds than all the former treatments except the control. However, the composite weed population was significantly greater in the PK, P and K treatments than in the treatments consisting of nitrogen (except the control). The dry weight of grass weeds in control, N, NPK, NP and NK treatments was similar and significantly higher than in the rest of the treatments (Table 1), whereas the broad-leaved weeds accumulated a significantly higher biomass in the P, PK, K and control treatments than in the N-treated plots. However, the weeds composite biomass was also higher in the P- and K- treated plots and in the control treatment than in the treatments where N was applied. Wheat growth and nutrient uptake Although identical growth of wheat in terms of crop growth rate (CGR), dry weight, leaf area and tillers plant (Table 2) and nutrient (N, P and K) uptake (Table 3) was observed in both irrigation treatments up to 60 DAS, there was significant

Effect of irrigation, fertilizers and weeds on wheat 47 Table 1. Population (number per m ) and dry matter weight (g m ) of grass, broad-leaved and total weeds in wheat at 60 DAS (mean of two years) Population Dry matter weight Treatments Grass Broad-leaved Total Grass Broad-leaved Total Five 5 1 12 6 13 7 3 1 3 4 4 2 One 5 0 12 3 13 5 3 2 3 6 4 9 S.E. (D.F. 30) 0 25 0 34 0 31 0 14 0 10 0 12 None (Control) 4 8 12 1 13 1 3 8 6 5 7 2 Nitrogen (N) 5 3 9 5 11 9 4 3 3 1 4 9 Phosphorus (P) 4 5 15 2 15 8 2 3 6 7 6 9 Potassium (K) 4 4 13 9 14 9 2 5 6 5 6 8 NP 5 3 10 8 12 2 4 0 3 2 4 3 NK 5 6 11 0 12 5 4 4 3 4 4 6 PK 4 7 15 0 15 8 2 8 6 6 7 1 NPK 5 9 9 4 12 0 4 5 3 2 4 8 S.E. (D.F. 30) 0 37 0 69 0 63 0 27 0 21 0 26 All the data presented above are transformed mean values. Their original values for each category of weeds such as grass, broad-leaved and total weeds observed over the replications in the field underwent transformation separately through square-root method ( X 0 5) before analysis of variance. Table 2. Crop growth rate (CGR) (g m day), dry weight (g m ), leaf area (dm m ) and tiller number per plant of wheat (mean of two years) CGR* Dry weight Leaf area Tillers plant Treatments 60 DAS 90 DAS 60 DAS 90 DAS 60 DAS 60 DAS Five 1 95 2 46 118 9 191 9 134 5 2 9 One 1 94 2 14 118 9 180 9 120 6 2 9 S.E. (D.F. 30) 0 02 0 08 1 81 2 98 6 55 0 08 None (Control) 1 44 2 13 87 7 152 1 65 2 2 6 Nitrogen (N) 2 13 2 73 129 7 212 3 156 8 3 4 Phosphorus (P) 1 86 2 05 113 3 175 2 100 5 2 4 Potassium (K) 1 73 1 87 110 2 157 8 76 1 2 3 NP 2 24 2 53 135 0 209 7 183 1 3 5 NK 2 16 2 40 132 0 205 0 168 1 3 2 PK 1 79 2 06 109 2 171 8 73 9 2 5 NPK 2 21 2 62 133 8 211 2 196 6 3 5 S.E. (D.F. 30) 0 05 0 17 3 61 5 96 12 87 0 16 Weed control Unweeded control 1 95 2 09 118 0 181 6 121 0 2 9 Weed-free treat. 1 95 2 51 120 0 192 2 132 3 2 9 S.E. (D.F. 32) 0 02 0 08 1 41 2 33 2 94 0 07 * CGR for 0 60 DAS period; CGR for 60 90 DAS period. variation in dry weight, CGR and uptake of nutrients later between the irrigation treatments, the high frequency irrigation being superior to the low frequency one. Wheat plants registered significantly higher biomass, CGR, leaf area, tiller number and greater uptake of all the above nutrients (except for the uptake of P at 60 DAS) in the NP, NPK, NK and N treatments than in the other nutrient treatments. Besides lowering the leaf area of wheat at 60 DAS, weeds significantly reduced the wheat s dry weight and CGR at 90 DAS (Table 2) and uptake of N, P and K at harvest (Table 3).

48 T. K. DAS AND N. T. YADURAJU Table 3. Uptake of N, P and K (kg ha) by wheat at 60 DAS and at harvest (mean of two years) 60 DAS Harvest Treatments N P K N P K Five 21 3 4 9 31 8 49 6 55 5 77 6 One 22 2 5 0 30 5 41 0 41 0 62 5 S.E. (D.F. 30) 0 39 0 13 0 53 1 18 1 19 1 63 None (Control) 14 1 3 9 21 5 32 2 33 1 44 0 Nitrogen (N) 25 8 5 0 34 8 59 7 62 5 88 8 Phosphorus (P) 18 7 5 0 28 1 32 3 39 3 51 3 Potassium (K) 17 5 4 4 27 9 28 3 34 9 50 7 NP 29 8 6 2 37 3 62 2 58 3 100 6 NK 25 3 5 1 35 3 59 3 60 5 89 6 PK 17 9 4 5 25 9 29 5 35 3 42 5 NPK 26 1 5 5 38 0 58 7 62 3 93 0 S.E. (D.F. 30) 0 78 0 25 1 07 2 35 2 40 3 26 Weed control Unweeded control 21 2 4 8 30 5 43 4 46 0 66 6 Weed-free treat. 22 0 5 1 31 7 47 2 50 6 73 6 S.E. (D.F. 32) 0 37 0 09 0 53 0 84 0 71 1 06 Table 4. Number of ear-bearing tillers (EBT) per metre row, length of ear (cm), grains per ear, test weight (g), protein (%) and harvest index (HI) of wheat (mean of two years) Treatments EBT per metre row Ear length (cm) Grain per ear Test weight (g) Protein (%) HI Five 63 5 8 5 34 2 45 2 8 0 0 41 One 55 4 8 1 31 8 36 0 9 6 0 38 S.E. (D.F. 30) 1 00 0 08 0 36 0 45 0 06 0 007 None (Control) 50 2 7 6 32 7 40 8 7 1 0 43 Nitrogen (N) 71 0 8 8 32 8 41 4 9 8 0 37 Phosphorus (P) 45 7 7 8 33 0 39 2 8 4 0 40 Potassium (K) 46 1 7 5 32 9 42 8 6 9 0 43 NP 73 9 9 2 33 3 38 5 10 6 0 38 NK 70 5 9 1 33 8 39 2 10 6 0 36 PK 44 2 7 7 32 7 43 6 7 4 0 43 NPK 73 6 8 9 33 0 39 1 10 1 0 36 S.E. (D.F. 30) 2 00 0 17 0 73 0 91 0 13 0 014 Weed control Unweeded control 58 2 8 3 32 3 40 5 8 9 0 39 Weed-free treat. 60 6 8 3 33 8 40 8 8 8 0 40 S.E. (D.F. 32) 0 59 0 06 0 36 0 39 0 07 0 006 Yield attributes, protein content, harvest index and grain yield The high frequency irrigation treatment resulted in significantly higher values for ear-bearing tillers, ear length, grains per ear, test weight and harvest index (Table 4) and grain yield (Table 5) than the low frequency one. The protein content in wheat grain was, however, significantly higher in the low frequency irrigation treatment. Yield attributes such as the number of ear-bearing tillers, ear length and protein content and grain yield were significantly higher in the

Effect of irrigation, fertilizers and weeds on wheat 49 Table 5. Interaction effect of irrigation and nutrients on grain yield (t ha) of wheat (mean of two years) Five irrigations One irrigation UWC WFT Mean UWC WFT Mean Mean None (Control) 2 18 2 38 2 28 1 83 2 00 1 91 2 10 Nitrogen (N) 3 69 4 19 3 94 2 31 2 67 2 49 3 21 Phosphorus (P) 2 14 2 10 2 12 1 38 2 09 1 73 1 93 Potassium (K) 2 07 2 21 2 14 1 65 1 91 1 78 1 96 NP 3 77 4 08 3 92 2 63 1 97 2 30 3 11 NK 3 32 4 02 3 67 2 22 2 19 2 21 2 94 PK 2 08 2 33 2 20 1 62 1 76 1 69 1 95 NPK 3 75 3 73 3 74 2 08 2 32 2 20 2 97 Mean 2 87 3 13 3 00 1 96 2 12 2 04 S.E. (D.F. 30) 0 067 S.E. (D.F. 30) 0 135 Weed control S.E. (D.F. 32) 0 041 nutrients S.E. (D.F. 30) 0 191 UWC, unweeded control; WFT, weed-free treatment. N, NP, NK and NPK treatments than in the rest of the treatments. The number of grains per ear was, however, not affected by the nutrients. The control, PK and K treatments recorded significantly higher harvest index than in the other treatments except the P and NP treatments. Weeds significantly reduced the number of ear-bearing tillers and grains per ear (Table 4) and consequently the grain yield of wheat (Table 5). The interaction between irrigation and nutrients, however, affected all the nutrient treatments to produce significantly higher yield of wheat under frequent irrigations as compared to under limited irrigation. DISCUSSION Effect of irrigation Apart from the two common irrigations one presowing and another at crown root initiation (CRI) stage (20 25 DAS), a well-distributed rainfall of 30 mm (Table 6) was received each year between sowing and 60 DAS. This obviously resulted in identical growth (population, dry weight, CGR, leaf area, tillers plant, nutrient uptake) of both weeds and crop recorded at 60 DAS under both irrigation Table 6. Rainfall received (mm) during crop growing period in both years Growth period 1991 92 1992 93 0 30 DAS 10 4 18 6 30 60 DAS 21 8 10 4 60 90 DAS 21 2 1 0 90 DAS harvest 19 2 treatments. However, both because of lack of rainfall later and subsequent irrigation, the high frequency irrigation proved superior in terms of growth, uptake of nutrients, yield attributes, grain yield and harvest index of wheat than the low frequency one. However, the protein content (%) in the wheat grains was significantly higher where irrigation occurred once than where it occurred frequently. As the grain yield was lower in the single irrigation plots, the N per cent in the wheat grains was appreciably higher (inverseyield nitrogen relationship, Wilcox 1937) and the higher the N per cent, the higher was the protein content (per cent). Effect of nutrients Wild oats (Avena ludoviciana) had a similar growth pattern (tillering, dry matter production, height) to that of wheat. However, wild oats have been reported to be more responsive to applied N than to P and K (Thurston 1959; Sexsmith & Russell 1963). This could be the reason for its strong competition with wheat in the N-treated plots. Whereas, in the control treatment, the poor growth of wheat crop may have offered weak competition to grass weeds, particularly wild oats, resulting in higher dry matter accumulation by grass weeds. Greater growth of broad-leaved weeds in PK, P, K and control treatments was mainly due to Melilotus indica which competed well with the wheat which showed less tillering, less dry matter weight, and reduced height in these nutrient treatments. Moreover, the vigour of Melilotus may be because it is a legume and thus exhibits the response to P and K commonly found for members of this group (Williams 1976). Singh et al. (1992) also reported the predominance of M. indica in soils having a medium phosphorus content. Their number

50 T. K. DAS AND N. T. YADURAJU and dry matter accumulation were, however, less in N-treated plots (N, NP, NK and NPK treatments) due to smothering by vigorously growing wheat plants in these treatments. However, the overall weed competition in terms of population and biomass of composite weeds was significantly higher in the PK, P, K and control treatments than in the N, NP, NK and NPK treatments due to broad-leaved weeds which outnumbered and outweighed the grass weeds in the respective plots treatments. The growth (dry weight, CGR, leaf area and tiller number), nutrient (N, P and K) uptake, yield attributes (ear-bearing tiller and ear length) and grain yield of wheat were consequently higher in the N-treated plots than in the P- and K-treated plots. The effect of nitrogen alone is reflected here. These N-treatments, however, could not significantly alter the number of grains per ear. The difference in test weight among the treatments was significant but erratic. It was, therefore, the number of ear-bearing tillers which contributed most to the yield in the N-treated plots. Effect of weeds Weeds in the unweeded control plots, excepting the leaf area and uptake of P, could not significantly inhibit the wheat plant s CGR, dry weight, number of tillers and uptake of N and K at 60 DAS. However, later they reduced significantly the wheat s growth (CGR, dry weight), nutrient uptake, number of earbearing tillers, grains per ear and grain yield than in the weed-free treatment. The competition between weeds and wheat for resources particularly for nutrients and water might not have been acute in the early stage (up to 60 DAS). But, when the plants grew older, the demand for resources also increased. The greater negative effect of weeds on crops is, therefore, more perceptible at 90 DAS and later than at 60 DAS. It may, therefore, be concluded that the N-treatments (N, NP, NK and NPK), although encountering greater competition from grass weeds, had significantly lower total composite (grass broad-leaved) weed growth than the P, K and PK treatments mainly because the broad-leaved weeds in the latter treatments outnumbered and outweighed the grass weeds in the former treatments. This resulted in significantly higher growth, nutrient uptake, yield attributes and yield of wheat in the treatments involving N than in the P and K treatments applied alone or in combination. Among the nutrients (N, P and K) in the N, NP, NK and NPK treatments, the effect of N only was reflected. The lack of response to P and K applied with N could be due to medium availability of P and K (19 kg P and 218 5 kg K per ha) in the soil. 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