Agronomy Journal 92:283-288 (2000)
© 2000 American Society of Agronomy
SOIL MANAGEMENT
Row Spacing Effects at Different Levels of Nitrogen Availability in Maize
Pablo A. Barbieria,
Hernán R.Sainz Rozasa,
Fernando H. Andradea and
Hernán E. Echeverriaa
a Fac. de Ciencias Agrarias, Univ. Nac. de Mar del Plata (UNMP)–Est. Exp. Agropecuaria Balcarce, Inst. Nac. de Tecnología Agopecuaria (INTA), Unidad Integrada Balcarce, C.C. 276, (7620) Balcarce, Buenos Aires, Argentina
hecheverr{at}inta.gov.ar
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ABSTRACT
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No-tillage maize (Zea mays L.) grown without adequate N intercepts less than 95% of the incident radiation at flowering. Reducing the distance between rows could increase radiation interception and grain yield. A 2-yr experiment was conducted at INTA Research Station, Balcarce, Argentina (37°45' S; 58°18' W), to study the effect of row spacing and N availability on intercepted radiation, kernel number, and grain yield of no-till maize. Treatments consisted of a factorial combination of row width (0.35 and 0.70 m) and N (0 and 120 or 140 kg ha-1 each year) at a constant plant density. Low N decreased kernel number and grain yield. Narrow rows significantly increased kernel number per unit area and grain yield. Average increases in response to narrow rows were 14.5 and 20.5% for kernel number and grain yield, respectively. However, relative increases in response to narrow rows were greater at low N. A close association between kernel number and intercepted radiation during the bracketing–silking period was observed. With conventional row spacing, relative grain yield responses to narrower rows decreased as crop radiation intercepted at flowering increased. A decrease in row distance when N was limiting partially offset the negative effects of N deficiency on grain yield. Our results indicate that 27 to 46% increases in grain yield were obtained in response to narrow rows in N-deficient maize crops.
Abbreviations: IPAR, intercepted photosynthetically active radiation • IPARf, intercepted photosynthetically active radiation during the period from 15 d before to 15 d after silking • k, extinction coefficient • KN, kernel number • LAI, leaf area index • PAR, photosynthetically active radiation • Postf, 15 d after silking • Pref, 15 d before silking • RUE, radiation use efficiency
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INTRODUCTION
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KERNEL NUMBER (KN) is the main grain yield component in maize (Tollenaar, 1977; Hawkins and Cooper, 1981; Fischer and Palmer, 1984), and it is associated strongly with crop growth rate during the bracketing–silking period (Aluko and Fischer, 1987; Cirilo and Andrade, 1994; Uhart and Andrade, 1995a). Crop growth rate depends on the amount of radiation intercepted by the crop and on the efficiency of conversion of intercepted radiation into dry matter (Andrade et al., 1996).
Nitrogen stress decreases leaf area index (LAI), leaf area duration, and crop photosynthetic rate, and leads to lower radiation interception and lower radiation use efficiency (RUE) (Girardin et al., 1987; Muchow, 1988; Sinclair and Horie, 1989; Uhart and Andrade, 1995a). Thus, N stress during the bracketing–silking period decreases crop growth rate, and therefore kernel number and grain yield (Uhart and Andrade, 1995a).
Maize grown at a constant plant density intercepts a higher proportion of incident radiation in narrow rows (Aubertin and Peters, 1961; Bullock et al., 1988; Teasdale, 1995) because of an increase in LAI and in the efficiency of light interception per unit leaf area (Bullock et al., 1988; Westgate, 1998). However, grain yield increases in response to narrower rows under conventional tillage and adequate N were less than 10% (Hunter et al., 1970; Stivers et al., 1971; Bullock et al., 1988; Porter et al., 1997).
In Balcarce, no-tillage maize grown without adequate N intercepts less than 95% of incident radiation at flowering (Sainz Rozas, 1997). Decreasing the distance between rows could partially offset N stress effects and increase kernel number per square meter and grain yield. Because LAI and radiation interception respond to N supply (Novoa and Loomis, 1981; Lemcoff and Loomis, 1986; Muchow, 1988; Muchow and Davis, 1988; Uhart and Andrade, 1995a) the effect of narrower rows on grain yield and its components may be greater in low-N environments.
The objective of this study was to analyze the effect of row spacing and N availability on (i) intercepted radiation during a bracketing–silking period, (ii) kernel number, and (iii) yield of maize grown at fixed plant density in a no-till system.
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Materials and methods
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The experiment was conducted during the 1995–1996 and 1996–1997 growing seasons at INTA Research Station, Balcarce, Buenos Aires, Argentina (37°45' S, 58°18' W; elev. 130 m above sea level), on a soil complex of a fine, mixed, thermic Typic Argiudoll and a fine, illitic, thermic Petrocalcic Paleudoll (petrocalcic horizon below 0.7 m). This area is characterized by low average temperature during the growing season and a frost-free period of about 150 d. More details of climatic data were presented in Andrade (1995). The preceding crop was no-tillage-grown maize. Soil cover by maize residues ranged from 80 to 90%. The soil surface (0–20 cm) had an organic matter content of 58.4 g kg-1, a pH of 5.85, and 20.6 mg P kg-1 (Bray and Kurtz, 1945) in both years. Before fertilization, at the V6 stage (Ritchie and Hanway, 1982), soil mineral N content in the first 40 cm was 37 and 56 kg ha-1 in the 1995–1996 and 1996–1997 growing seasons, respectively. Plots were fertilized annually at planting with 20 kg P ha-1 and irrigated as needed. Weeds were controlled by preemergence applications of glyphosphate [N-(phosphonomethyl)glycine] as isopropylamine salt, at 2.24 kg a.i. ha-1; 2,4-D (2,4-dichlorophenoxyacetic acid) at 0.5 kg a.i. ha-1; atrazine (6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine) at 2.24 kg a.i. ha-1; and metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide) at 2.30 kg a.i. ha-1. Insects were controlled by application of deltamethrin {(S)-[cyano(3-phenoxyphenyl)methyl]cis-(4)-3-(2,2-dibro-moethenyl)-2,2-dimethylciclop ropanecarboxylate} at 5 g a.i. ha-1.
The experimental design was a split plot in randomized complete blocks with three replications, where the main plot was row width (0.70 and 0.35 m between rows) and the subplot was N rate (0 and 120 kg of N ha-1 in 1995–1996; 0 and 140 kg of N ha-1 in 1996–1997). Rows at 0.35 m were achieved by double planting and thinning to target plant densities after emergence. The experimental units were 14 m long and seven rows wide (two border rows on each side). Nitrogen fertilizer was applied broadcast at V6. The single-cross hybrid `Dekalb 636' was planted on 18 Oct. 1995 and the single-cross hybrid `Dekalb 639' was planted on 20 Oct. 1996. Dekalb 636 was not available in the market in the second growing season, so it was replaced by Dekalb 639, similar to the former hybrid in cycle length and other agronomic characteristics. Plant density at harvest was constant for all treatments (7.30 and 7.65 plants m-2 in the 1995–1996 and 1996–1997 growing seasons, respectively).
Global radiation was monitored with a pyranometer (SIAP bimetallic, Model PL1; La Plata, Argentina) and transformed to photosynthetically active radiation (PAR) by multiplying by 0.48. Percent PAR interception (IPAR) was calculated as [1 - (It/I0)] - 100, where It is the incident PAR at ground level and I0 is the incident PAR at the top of the canopy. The values of It and I0 were obtained with a radiometer (Model 188 B, Li-Cor, Lincoln, NE) connected to a line quantum sensor (Model 191 SB, Li-Cor). Determinations were taken at V6, 15 d before flowering, flowering, and 15 d after flowering following the technique described by Gallo and Daughtry (1986) for sensor placement. Five determinations per experimental unit were taken along three center rows at midday (1130–1300 h) on sunny days. Daily canopy IPAR between determinations was obtained by linear interpolation. Daily total incident PAR was multiplied by the corresponding daily fraction of PAR interception to obtain the accumulated PAR intercepted by the crop during the period from 15 d before to 15 d after silking (IPARf).
In 1996–1997 LAI was estimated at 15 d before and 15 d after flowering by measuring leaf area of five plants from the central rows of each experimental unit, using an AAC 400 area meter (Hayashi Denfoh, Japan). The extinction coefficient (k) was calculated as
. Nitrogen in these leaf samples was determined by Method A (without salicylic acid modification) reported by Nelson and Sommers (1973).
At physiological maturity, three 7.15-m-long interior rows were harvested and grain moisture was determined. Grain yield on a dry-weight basis and its components were determined. Average kernel weight was determined for each experimental unit by weighing two samples of 500 kernels each (dry-weight basis). The number of kernels per unit area was calculated from kernel weight and grain yield. Relative yield (as a fraction of maximum yield for each row spacing) was related to kernel N content as an indicator of N availability to the crop (Pierre et al., 1977). In both years, N content of kernels was determined following Method A (Nelson and Sommers, 1973).
Data were evaluated by analysis of variance procedures and by linear regression procedures using the routines included in SAS/STAT (SAS Inst., 1985).
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Results and discussion
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Water did not limit crop growth in any of the two growing seasons; rainfall and irrigation met the evapotranspiration demand (Table 1) . Moreover, mean air temperature and incident radiation were not different between years.
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Table 1 Monthly means of air mean temperature, incident photosynthetically active radiation, rainfall, and irrigation for the 1995–1996 and 1996–1997 growing seasons (Balcarce, Argentina)
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Figure 1
shows the relationship between relative yield and N content of kernels in response to N stress. The lowest kernel N contents were obtained with the treatments without N fertilization in the first growing season. This suggests that N availability to the crop was lower in 1995–1996 than in 1996–1997.
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Fig. 1 Relationship between kernel N content and relative yield for two row spacings (0.35 and 0.70 m) and two N levels (0 and 120 kg N ha-1 and 0 and 140 kg N ha-1, in 1995–1996 and 1996–1997 growing seasons, respectively)
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Interception of Photosynthetically Active Radiation
Narrower rows increased IPAR (Table 2
; Fig. 2)
. However, this effect was generally greater for the treatments without N application. This was reflected in a significant row spacing x N interaction in both years (Table 2). Percent PAR interception during the period bracketing flowering for maize grown without N fertilization and in 0.35-m rows was not significantly different from that of maize grown with N fertilization and in 0.70-m rows (Fig. 2). Narrower rows increased significantly the IPARf for both N rates in 1995–1996 and only for treatment without N in 1996–1997 (Table 3)
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Table 2 Analysis of variance for percent radiation interception at V6 stage, 15-d before flowering (Pref), flowering (Flow) and 15-d after flowering (Postf) of maize for two row spacings and two N levels in the 1995–1996 and 1996–1997 growing seasons (Balcarce, Argentina)
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Fig. 2 Percent photosynthetically active radiation interception (IPAR) by the crop during the 1995–1996 and 1996–1997 growing seasons. Arrows indicate development stages. Pref, 15 d before flowering; Flow, flowering; Posf, 15 d after flowering. Vertical bars indicate LSD (0.10) for comparing row spacing means at the same N level
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Table 3 Cumulative photosynthetically active radiation intercepted (IPARf) during a 4-wk maize bracketing–silking period for two row spacings and two N levels in the 1995–1996 and 1996–1997 growing seasons (Balcarce, Argentina)
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The literature also reported greater IPAR in response to narrower rows (Yao and Shaw, 1964; Scarsbrook and Doss, 1973; Bullock et al., 1988; Teasdale, 1995). In these studies, crops grown with conventional row spacing achieved less than 95% radiation interception at flowering. In contrast, Ottman and Welch (1989) and Westgate et al. (1997) found no effects of row spacing on IPAR at flowering. In these last cases, all row spacings had full or nearly full radiation interception at flowering. Our study and those reported in the literature demonstrate that the greater responses of IPAR at flowering to narrow rows were observed when vegetative growth was most limited (Fig. 2). The greater radiation interception observed with more equidistant plant spacing treatments indicates that a decrease in row width when N is limiting partially offsets negative effects of N deficiencies on radiation interception.
Leaf area index was not significantly increased by narrow rows at preflowering and postflowering stages. Therefore, the greater IPAR with narrower rows during the bracketing–silking period was due to an increase in light extinction coefficient (K), especially for the treatments without N fertilization (Table 4) . This indicates that narrower rows increased IPAR by a greater efficiency of light interception per unit leaf area. These results do not agree with those reported by Bullock et al. (1988), but agree with those reported by Westgate (1998) for maize grown without N stress in a conventional tillage system.
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Table 4 Light extinction coefficient (k) and leaf N per unit area leaf at 15 days before flowering (Pref) and at 15 days after flowering (Postf) in the 1996–1997 maize growing season (Balcarce, Argentina)
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Kernel Number and Grain Yield
Grain yields in 1995–1996 were greater than those in 1996–1997, especially in the treatments with N applications (Table 5)
. The differences in yields were unlikely related to climate differences (Table 1), but may have been caused by Maize Rough Dwarf virus diseases that infected less than 10% of the plants in 1996–1997. For the 1995–1996 growing season, grain yield of maize grown without added N and planted in 0.35-m rows was 47% greater than that of maize planted in 0.70-m rows. With N fertilization, yield response to narrow rows was only 10%. Kernel number was the only yield component measured affected by row spacing (Table 5). For the 1996–1997 growing season, yield increased by 27 and 13% in narrow rows without and with added N, respectively. Both kernel number and weight increased significantly in 1996–1997 in response to narrower rows (Table 5).
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Table 5 Yield and yield components of maize (140 g kg-1 moisture content) for two row spacings and two N levels in the 1995–1996 and 1996–1997 growing seasons (Balcarce, Argentina)
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Kernel number increased in response to decreasing row width and to N fertilization and was related to a greater IPARf. These treatments improved the physiological condition of the plants during the bracketing–silking period, which is the critical period for kernel set (Tollenaar, 1977; Aluko and Fischer, 1987). A positive and linear association (P < 0.01) between kernel number and IPARf was found (Fig. 3)
. The slope of the relationship was 17.5 kernels MJ-1 in 1995–1996 and 17.6 kernels MJ-1 in 1996–1997. The common relationship between KN and IPARf found for N and row spacing treatments suggests that other variables, such as RUE and dry matter partitioning to the ear at flowering, were less affected by N deficiencies than intercepted radiation. For the 1996–1997 growing season, N content per unit leaf area at pre- and postflowering (Table 4) was above the threshold value that affects RUE in maize (Sinclair and Horie, 1989). Uhart and Andrade (1995b) reported a similar relationship between kernel number and accumulated PAR during the bracketing–silking period under different levels of N availability. They found a slightly higher response of kernel number to IPARf for the same bracketing–silking period (22.6 kernel MJ-1), probably due to a greater effect of N stress on RUE in their experiment.
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Fig. 3 Relationship between cumulative photosynthetically active radiation during the bracketing–silking period (15 d before to 15 d after flowering; IPARf) and kernel number per square meter during the 1995–1996 and 1996–1997 growing seasons
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Row spacing x N interaction was not significant for grain yield (Table 5). However, the greatest relative responses of grain yield to narrow rows were obtained when IPAR was low for maize planted in conventional spaced rows. Figure 4
shows an inverse relationship between the yield response of narrow rows relative to conventional row spacing with IPAR of conventional-spaced rows at flowering. Data published in literature show the same trends (Fig. 4). Ottman and Welch (1989) and Westgate et al. (1997) did not find significant grain yield responses to narrow rows, probably because percent radiation interception at flowering was greater than 95% in all treatments. Other work, in which full ground cover was not achieved when maize was planted in conventional rows, however, showed greater grain yield responses to narrower rows (Scarsbrook and Doss, 1973).
In conclusion, relative grain yield responses to narrower rows decreased as crop radiation intercepted at flowering with conventional rows spacing increased. Decreasing the distance between rows when N was limiting partially offset the negative effects of N deficiencies on grain yield. Porter et al. (1997) suggested that plant distribution was a yield-limiting factor when other limiting factors, such as nutrient deficiencies, were eliminated. Our results, however, indicate that significant increases in grain yield (27–47%) can be obtained in response to narrow rows in maize crops subjected to N deficiencies during vegetative growth. With narrow rows, less N would be needed to achieve a target yield compared with conventional rows.SAS Institute 1985
Received for publication February 9, 1999.
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ABSTRACT
INTRODUCTION
