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WHEAT

Winter Wheat Cultivar Performance as Affected by Production Systems in Croatia

Boris Varga, Zlatko Svenjak^* and Ana Pospisil

Dep. of Field Crops, Forage, and Grassl., Faculty of Agric. Univ. of Zagreb, Svetosimunska 25, 10000 Zagreb, Croatia

* Corresponding author (svecnjak{at}agr.hr)

Received for publication October 13, 2000.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The use of intensive production systems (IPS) may substantially increase winter wheat (Triticum aestivum L.) grain yields in Croatia because the national average yield of 4.14 t ha^-1 is low compared with the yield potential of currently grown cultivars. Field experiments were conducted during 1996 through 1998 to evaluate the agronomic responses of 15 modern cultivars grown at two seeding rates (440 and 770 seeds m^-2) in both an IPS and an extensive production system (EPS). The IPS consisted of plowing at 30 to 32 cm; fertilization at 194, 130, and 130 kg ha^-1 N, P, and K; and high input of crop protection chemicals. The EPS involved plowing at 20 to 22 cm; fertilization at 59, 104, and 104 kg ha^-1 N, P, and K; and less effective herbicide application. Grain yields significantly increased in the IPS and averaged 7840 kg ha^-1 compared with 5910 kg ha^-1 for the EPS. This difference was due to a 16.8 and 19.6% increase in spike number and kernel number per spike, respectively, while 1000-kernel weight for the IPS decreased by 6.0% compared with the EPS. Higher seeding rate maximized grain yields in both production systems except for one growing season in the IPS, primarily due to improved spike number. Cultivars responded similarly to seeding rates regardless of the production system. A significant interaction between cultivars and the two production systems was found because some cultivars were highly responsive to the IPS while others were not. Thus, cultivar selection is an important consideration for Croatian farmers when they decide to adopt the IPS.

Abbreviations: EPS, extensive production system • IPS, intensive production system

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
AVERAGE WINTER WHEAT GRAIN YIELD of 4.14 t ha^-1 for the last decade (1989–1998) in Croatia (Dravni zavod za statistiku, 1999) is low compared with yield levels in many western European countries and yield potential of currently grown cultivars. This is largely due to the low level of production inputs and lack of good management practices devoted to the crop.

Improved grain yield response due to intensive wheat management techniques has been found by many authors (Wiersma et al., 1986; Guy et al., 1995; Varga et al., 2000). However, Khan and Spilde (1992) reported that intensive cereal production, applied as a complete package under marginal production conditions in the northern USA environment, was not a viable option because of a lack of precipitation at critical growth stages of wheat. Moreover, response to intensive production inputs is known to be dependent on the environment, cultivar, or both (Beuerlein et al., 1989; Guy et al., 1989).

Dense seeding rates (650–750 seeds m^-2) are common in the winter wheat production systems of Croatia. Dense seeding rates reduce the risk of a thin stand at harvest caused by later-than-optimum planting date, winter freezing, and relatively poor tillering during winter and early spring growth. Roth et al. (1984) found that yield responses to changes in seeding rates were influenced by the environment while Frederick and Marshall (1985) reported that increasing seeding rates had little effect on yield for wheat planted at an optimum date. However, Pucari and Juki (1989) and Shah et al. (1994) achieved a grain yield increase at greater seeding rates for the late-planted wheat crop. Reducing seeding rates may result in more tillers and spikes per plant, more spikelets per spike, and more kernels per spikelet (Darwinkel, 1980) but, in many cases, reduced grain yield per hectare (Pucari and Juki, 1989).

Nitrogen application is an important input for winter wheat production. Increasing levels of N fertilizer usually improves grain yield (Bavec, 1999) though decreased grain yields from excessive N fertilization have also been reported due to lodging (Varga, 1980), increased water stress caused by excessive vegetative growth (Nielsen and Halvorson, 1991), and increased incidence of foliar diseases (Roth et al., 1984). Applying foliar fungicides to winter wheat may have a wide range of responses (Roth and Marshall, 1987) but, in most cases, has been shown to be beneficial, particularly when cultivars were susceptible to disease and yields were large (Guy et al., 1989; Kelley, 1993).

The objective of this study was to evaluate the agronomic responses of 15 modern Croatian winter wheat cultivars grown at two seeding rates and two production input levels, namely intensive (IPS) and extensive production systems (EPS).

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field experiments in a winter wheat–corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] crop rotation were conducted in northwestern Croatia at the Faculty of Agriculture Zagreb experimental field during the 1995–1996 (1996), 1996–1997 (1997), and 1997–1998 (1998) growing seasons on a silt loam soil (Typic Udifluvents). Fifteen currently grown winter wheat cultivars in Croatia were planted at low (440 seeds m^-2) and high (770 seeds m^-2) seeding rates in both IPS and EPS. Prior crops (corn and soybean) were also grown at these two production input levels. On adjacent plots, IPS and EPS were established. The experimental design for each production system consisted of five replications with two factors arranged in a randomized complete block in a strip-plot design. Cultivars were the horizontal factor, and seeding rates were the vertical factor.

A summary of production treatments is presented in Table 1. The IPS involved plowing at 30 to 32 cm; fertilization with 194 kg N ha^-1 (including three topdressing applications of 54, 27, and 27 kg N ha^-1 at Growth Stages 22, 24, and 31, respectively) (Zadoks et al., 1974), 130 kg P ha^-1, and 130 kg K ha^-1; and high input of crop protection chemicals. Herbicides amidosulfuron {N-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N-methylmethanesulfonamide} at 25 g a.i. ha^-1 and bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) at 225 g a.i. ha^-1 were applied at Growth Stage 24. Fungicide tebuconazol {-[2-(4-chlorophenyl)ethyl]--(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol} at 250 g a.i. ha^-1 and insecticide lambda cihalotrin {[1(S*),3(Z)]-cyano(3-phenoxyphenyl)methyl 3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate} at 5 g a.i. ha^-1 were tank-mixed and applied at Growth Stage 60 each year to control foliar diseases and cereal leaf beetle (Oulema melanopus L.) infestation.

In October of each year, 500 kg ha^-1 N–P–K fertilizer (8:26:26) combined with 100 kg ha^-1 of urea [(NH₂)₂CO] (46% N) in the IPS or 400 kg ha^-1 N–P–K fertilizer (8:26:26) in the EPS was broadcast before plowing. At seeding, plots consisted of 10 rows that were 11 cm apart and 7.0 m in length. Wheat was planted on 16 Oct. 1995, 28 Oct. 1996, and 20 Oct. 1997 within the optimum planting-date window for the region. Granular N [27% ammonium nitrate (NH₄NO₃)] was broadcast by hand in each topdressing application.

Spike density was determined from a central 0.55-m² plot area just before harvest. Thirty spikes were randomly hand-picked and threshed to determine grain production per spike and 1000-kernel weight. Average 1000-kernel weight was determined by counting and weighing two 100-kernel samples. Kernel number per spike was calculated from the spike number, grain production per spike, and 1000-kernel weight. Plots were combine-harvested, and total grain yields are expressed on a kilogram per hectare basis at a 130 g kg^-1 moisture basis. Test weight was determined from two grain samples taken at harvest from each plot using standard procedures.

Data were analyzed using mixed model procedures (SAS Inst., 1997). Combined analysis of variance across growing seasons was computed with growing seasons, production system, cultivar, and seeding rate considered fixed. Mean separation was calculated using the LSD values if the F-test was significant at P = 0.05.

	RESULTS AND DISCUSSION

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Grain Yield and Yield Components
Average grain yield across three growing seasons and all production treatments was 6870 kg ha^-1, which is 65.9% more than the national average. Despite the fact that pest severity was generally negligible during experimentation, the IPS treatment significantly increased grain yield by 32.7% and averaged 7840 kg ha^-1 compared with 5910 kg ha^-1 for the EPS (Table 2). However, spike number increased only by an average of 16.8% for the IPS compared with the EPS, demonstrating the importance of grain production per spike as a yield component. This improved grain production per spike was principally due to an increase in kernel number per spike, which averaged 29.3 for the IPS compared with 24.5 in the EPS treatment. Greater kernel number per spike resulting from more intensive N fertilization has been reported by many authors (Gotlin and Pucari, 1966; Varga, 1980; Bavec, 1999). In contrast, 1000-kernel weight decreased for the IPS by an average of 6.0% compared with the EPS.

Svenjak (1996)

A significant growing season x production system x seeding rate interaction existed for grain yield, spike number, and kernel number per spike (Table 3). Favorable weather conditions during winter and early spring in the growing season of 1998 resulted in a great number of spikes for the IPS treatment, even at the low seeding rate (Table 4). Consequently, grain yield did not significantly differ between seeding rates even though spike number was 18.0% greater at the high seeding rate. Moreover, the excessive rainfall during the late grain fill and preharvest period brought about more severe lodging at the high seeding rate compared with the low seeding rate (data not shown). This abundant precipitation also delayed harvest for more than 2 wk (Table 1). However, the decrease in 1000-kernel weight at the high seeding rate compared with the low seeding rate in the IPS was similar to previous growing seasons (Table 4), indicating that lodging occurred too late to have an important influence on this yield component.

A cultivar x production system interaction was found for grain yield and all yield components (Table 3), which indicated that cultivars responded differently under various production input levels, as also found by Guy et al. (1995). The average yield increase with the IPS compared with the EPS treatment for ‘Ana’ (a high-response cultivar) and ‘Marija’ (a low-response cultivar) was 2490 (44.7%) and 1480 kg ha^-1 (23.3%), respectively (Table 5). Ana required a very large spike number to achieve large grain yield in the IPS because it has relatively low 1000-kernel weight compared with other high-yielding cultivars. In the EPS treatment, spike number was primarily determined by seeding rate because of low N input (27 kg ha^-1) during tillering. Therefore, Ana had the greatest decrease in spike number (21.5%) and relatively low average grain yield in the EPS (5570 kg ha^-1) compared with the IPS (8060 kg ha^-1). Above-average grain yield response to the IPS treatment was also observed for cultivars Vitina (39.2%), Tina (37.7%), Kuna (37.1%), itarka (36.0%), and Magdalen (35.4%). Unlike Ana, these cultivars principally increased kernel number per spike, except Tina, which also improved spike number. Although Ana, Vitina, Kuna, itarka, and Magdalen did not differ in average grain yields in the EPS, Ana and Vitina had significantly greater yields than Kuna, itarka, and Magdalen in the IPS treatment. Cultivars Patria, Marija, Rina, Tina, and Sana had their greatest average grain yields in the EPS, but only Patria and Tina achieved similar performance in the IPS treatment. Although spike number has been reported by Simons and Hunt (1983) as the major component of grain yield in a wide range of winter wheat genotypes, the greatest yielding cultivar (Tina) in the IPS had a 20.2% lower spike number compared with ‘Srpanjka’ but achieved 8.2% greater grain yield. This difference was due to improved 1000-kernel weight (20.0%) and kernel number per spike (6.0%). Unlike Tina, a high-response cultivar, Patria, Marija, Rina, and Sana had relatively poor performance in the IPS compared with the EPS treatment. These poor yield responses in the IPS treatment can be attributed to the small increase in spike number for Patria, Sana, and Rina and kernel number per spike for Marija when averaged across growing seasons. Consequently, seven cultivars (Mladenka, Srpanjka, Davorka, Demetra, Vitina, itarka, and Ana), which had significantly lower average grain yield than Patria, Marija, Rina, and Sana in the EPS, achieved similar yield level in the IPS treatment.

Unexpectedly, all cultivars had a similar response for grain yield and all yield components at the two seeding rates in both production systems. The significant cultivar x seeding rate and production system x cultivar x seeding rate interactions existed only for 1000-kernel weight because some cultivars did not have reduced kernel weight at the high seeding rate, particularly in the IPS (data not shown). Although these results were somewhat surprising, the higher seeding rate also had no effect on kernel weight of two cultivars in research conducted by Shah et al. (1994). Moreover, the trend toward increased kernel weights with increased seeding rate was observed by Frederick and Marshall (1985), who speculated that it was due to the greater proportion of primary tillers per unit area.

Test Weight
Test weight is widely recognized as a wheat-grading factor because it may predict wheat grain flour (Ghaderi and Everson, 1971). Test weight increased in the IPS by an average of 5 kg m^-3 and ranged from 770 to 809 and 754 to 804 kg m^-3 across seeding rates for the IPS and EPS treatments, respectively (Table 4). Bruckner and Morey (1988) obtained similar results while Roth et al. (1984) and Nielsen and Halvorson (1991) reported a reduction in test weight with high-N treatments due to an increase in disease severity and water stress. However, test weight responses at both production input levels were highly affected by environmental conditions, as indicated by a significant growing season x production system interaction (Table 3). Unlike the results obtained in 1996 and 1998, test weight significantly decreased in the IPS compared with the EPS in the 1997 growing season when the greatest grain yield occurred for the IPS (Table 4). The lowest test weights across three growing seasons occurred in 1998 and averaged 770 and 755 kg m^-3 for the IPS and the EPS, respectively. Low test weights may occur as a result of various factors such as delayed harvest (Pool et al., 1958), disease severity (Roth et al., 1984), and lodging (Laude and Pauli, 1956; Weibel and Pendleton, 1964). Because lodging in this growing season occurred only in the IPS, low test-weight values were most probably due to delayed harvest. Interestingly, the greatest average test weight in each production system occurred in the growing season with the poorest grain yield level.

Averaged across growing seasons, test weight significantly increased at the high seeding rate in both production systems (Table 3). This response is consistent with those obtained by Roth et al. (1984) and Proti et al. (1988), who also found that test weight values were increased by greater seeding rates. The absence of a production system x seeding rate interaction indicated that average test-weight improvement with the higher seeding rate was similar in both production systems. However, growing season x production system x seeding rate interaction existed because average test weights failed to increase at the high seeding rate in the EPS and IPS treatments in 1996 and 1998, respectively (Table 4).

Cultivars differed significantly in test weights. Magdalen, one of the low-yielding cultivars, had average test-weight values that were significantly greater than all other cultivars (Table 5). A growing season x production system x cultivar interaction for test weight indicated that cultivar responses to various production input levels also differed with environmental conditions (Table 3). Only Sana succeeded to increase test weight values in the IPS treatment in three growing seasons (data not shown). However, cultivars showed a similar pattern of response for test weights at the high seeding rate in both production systems, regardless of the environmental conditions.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Croatian farmers should be aware of reduced productivity potential in the EPS because cultivars significantly increased grain yields in the IPS treatment by an average of 1930 kg ha^-1 (32.7%) due to an increase in spike number (16.8%) and kernel number per spike (19.6%). Increasing seeding rate appears to be a necessary practice to maximize grain yield in both production systems. Cultivars responded similarly to seeding rates in both production systems, regardless of the growing conditions. Although Tina and Patria demonstrated superior performance in both production systems across three growing seasons, our study indicated that among the tested cultivars, there may be different responses to the IPS treatment. Marija, Rina, and Sana had grain yields similar to those of Tina and Patria in the EPS but were significantly lower yielding than Tina in the IPS when averaged across growing seasons. In contrast, Ana and Vitina had poor performance in the EPS but had grain yields similar to the highest-yielding cultivars, except Tina, in the IPS treatment. Therefore, it seems obvious that cultivar selection is an important decision when changing from an EPS to an IPS for winter wheat.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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