Effect of Variety, Sowing Date and Photo-Degradable Plastic Cover on the Yield and Quality of Maize Silage

METHODOLOGY

In 2000, a fully-randomised trial including three sowing dates (April 10, May 9 and May 24) and three establishment systems (complete cover, punch plastic and uncovered) was sown on a medium-loam site at Knockbeg using the variety Hudson. For weed control, atrazine at 3.5 l/ha was incorporated before each sowing. On July 4, crop progress was assessed by measuring plant height and by weighing ten plants per treatment. Up to October 30, treatments were harvested when they were deemed to have reached maturity, i.e. when the whole-plant DM content reached 30%. At that date all remaining treatments were harvested.

A separate variety trial was sown on the same site in which two early (Hudson and Optimus), two medium (LG21.85 and Avenue) and two late (Benicia and Mecemis) varieties were sown using three establishment systems (CC, PP and uncovered) in a split-plot design. The crop was sown on May 5 and harvested on October 26.

RESULTS

In the time-of-sowing trial, the harvest dates were spread over the period September 18 to October 23 (Table 1). The level of maturity (DM content) attained is presented in Table 2. The data from the measurements of plant height and weight are presented in Table 3.

 

 Table 1: Harvest dates for the nine treatments, 3 sowing dates x 3 sowing systems

Establishment system	Uncovered	PP	CC
Sowing date	Harvest date
April 10	October 3	September 18	September 18
	October 18	October 3	October 3
May 24	October 23	October 23	October 23

 

 Table 2: DM content at harvest of each treatment (3 sowing dates x 3 sowing systems)

Establishment system	Uncovered	PP	CC
Sowing date	Dry matter content at harvest (%)
April 10	35.6	32.6	33.3
May 9	32.4	33.7	34.8
May 24	25.7	35.0	34.6

 

Table 3: Plant weight and height on July 4 for each treatment

Date	April 10	May 9	May 24

Sowing system	Weight (g DM)	Height (cm)	Weight (g DM)	Height (cm)	Weight (g DM)	Height (cm)
Uncovered	47.3	402.2	15.0	263.0	5.4	187.0
PP	239.2	1112.8	88.9	557.0	37.3	358.3
CC	204.7	1077.0	83.2	578.4	32.8	328.5
s.e.	+31.02	+28.01	+5.66	+6.14	+2.23	+1.84

Plant weight and height were significantly reduced by late sowing (Table 3). Within each sowing date both plastic systems significantly increased growth. The difference between the two plastic systems was not significant at that stage, although the growth rate under the CC system was noticeably higher for the first four to five weeks’ growth. By harvest time there was little difference in mature crop height of any of the nine treatments.

The yield data at maturity are presented in Table 4. For uncovered maize, the delay in sowing produced a significant loss in total dry matter yield, which fell from 15.7 t/ha DM for the April 10 sowing to 10.7 t/ha DM for the late May sowing. In contrast, the two plastic systems showed no reduction in yield with later sowing. For both systems the highest yield of approximately 20 t/ha DM was achieved at the second sowing (May 9). The differences in dry matter yield between the two plastic systems were small but significant in favour of the PP system. This advantage increased as the sowing date was delayed. All the yields above were achieved at approximately the same DM content (Table 2) but at different dates (Table 1). The average increase in DM yield due to plastic varied from less than 1.0 t/ha DM for the April 10 sowing under complete cover to nearly 10 t/ha DM for the late-sown (May 24) crop under the punch plastic.

 

 Table 4: Total dry matter yield of the maize cv. Hudson sown on three dates using three production systems

Treatment	Uncovered	PP	CC
Sowing date	Total DM yield (t/ha)
April 10	15.7	18.4	16.3
May 9	13.8	21.4	19.8
May 24	10.7	20.4	17.5
s.e.	+1.30	+0.98	+1.10

Grain yield was substantially increased by both plastic treatments in the second and third sowings (Fig. 1). The differences in grain yield between the two plastic systems were not significant at any of the three sowing dates.

• Fig. 1: Effect of sowing date and cover system on grain DM yields

Both sowing date and sowing system had significant effects on thousand-grain weight (TGW) (Table 5). Delayed sowing resulted in a large reduction in TGW in each of the sowing systems. Both plastic systems significantly increased TGW at each sowing date. Again there was no difference between the two plastic systems.

 

Table 5: Thousand-grain weight (TGW) for all treatments (3 sowing date x 3 establishment systems)

Sowing date	April 10	May 9	May 24
Establishment system	Thousand-grain weight (g)
Uncovered	230	162	131
Punch plastic	269	228	197
Complete cover	263	238	197
s.e.	+0.76	+0.84	+1.10

In the variety trial, the final harvest was taken on October 26. At that stage only two treatments, both late varieties in the uncovered treatment, had failed to reach the 30% DM stage of maturity.

The average increase in total dry matter yield in the covered treatments over the six varieties was 21.4% for the PP system and 16.1% for the CC system (Table 6). Grain yield was increased by 33.7% and 40.4%, respectively, for the two plastic systems. Over the six varieties evaluated, the PP system produced the highest total dry matter yield with a slightly lower grain content than the CC system.

Significant interactions between variety and establishment system were recorded. The two late varieties, Mecemis and Benicia showed the highest response to plastic under both systems, while LG21.85 and Avenue produced a below-average response under the CC system.

 

Table 6: Total dry matter yield of six maize varieties under three production systems

System		Uncovered		PP	CC
Variety	Maturity		DM yield (t/ha)
Hudson	Early		15.4	19.1	19.3
Optimus	Early		16.2	17.7	20.3
LG21.85	Medium		16.3	20.3	18.4
Avenue	Medium		16.0	19.7	17.1
Mecemis	Late		15.0	21.4	19.2
Benicia	Late		20.1	25.2	23.0
s.e.			+1.58	+1.67	+1.41

METHODOLOGY

In 2001, three varieties (Loft, Passat and Justina) were sown using the same three establishment systems (complete cover, punch plastic and uncovered). The randomised split-plot trial was sown on April 23. Atrazine (3.7 l/ha) was applied for weed control. Treatments were harvested when visually judged to be mature.

To measure the duration of plastic film cover needed to achieve maximum yield, a trial with the PP system using a French-manufactured photo-degradable product was planted on May 7 with ten treatments. All the plots were sown with a commercial machine in a fully randomised layout. The plastic film was then removed from one set of plots to create an uncovered or control treatment. Starting 30 days after sowing, the plastic was removed from a set of plots every seven days until Day 77 (eight treatments). For the final treatment the plastic was left in situ to degrade naturally.

RESULTS

In the variety/establishment system trial, harvest dates for the nine treatments varied from September 17 for Loft and Passat under CC to October 20 for uncovered Justina, the latest-maturing variety. The harvested crop DM percentages were within the range 29.3% to 33.6% across all treatments. The 2001 season was very favourable for maize production, with no frost and good growing conditions up to early November.

Overall, the advantage of using plastic was smaller in 2001 than in previous years (Table 7). A very good autumn meant that the conventional uncovered treatments attained a high yield and reached full maturity with a high grain content. The PP system increased total yield and grain yield by 2.28 t/ha and 1.89 t/ha, respectively. The CC system, in contrast, resulted in a crop yield loss of 1.39 t/ha and a marginal increase (0.16 t/ha) in grain yield.

 

Table 7: DM yields of three maize varieties grown under three cover systems

System	Uncovered	PP	CC	Uncovered	PP	CC
Variety	Total DM yield (t/ha)			Grain DM yield (t/ha)
Passat	15.55	17.88	13.76	7.11	8.88	6.98
Justina	17.70	19.63	17.61	7.35	8.87	7.37
Loft	14.38	16.97	12.17	5.53	7.90	6.12

There was a significant interaction between variety and covering system. Justina produced the highest yield of total DM and grain in all three systems. All three varieties showed a significant response to the PP system for both total and grain yields. However, both Passat and Loft showed a significant loss of crop DM yield under CC, while there was no significant change in the performance of Justina. The data suggest that variety interactions are likely where the CC system is used and that variety selection is critical if significant benefits are to be obtained with this system.

Both plastic cover systems significantly increased grain size (Table 8). The PP system produced the biggest grains in each of the three varieties. Overall, the PP system proved superior to the CC system in 2001, although the benefits in terms of yield and grain content (starch) were less than in previous years.

 

Table 8: Effect of three production systems on the 1000-grain weight (TGW) of three maize varieties

Variety	Passat	Justina	Loft
System	1000-grain wt. (g)
Uncovered	194	168	189
PP	231	208	233
CC	213	173	213
s.e.	+6.20	+5.08	+7.22

The plots were harvested on October 2, when all but the uncovered control had reached maturity, i.e. a whole-crop DM of approximately 30%. The uncovered plots were measured at 25.8% DM, while the plastic plots were up to 31.6%.

The maximum response, both in total crop DM yield and grain yield, was achieved at Day 63 from sowing. No significant response was recorded beyond this date (Fig. 2). No natural breakdown of the plastic film was recorded until August 9, 91 days after sowing. Other commercial plastic films on trial at the same site did not show any natural breakdown until early November.

• Fig. 2: Effect of duration of plastic cover on maize DM yield and grain yield

METHODOLOGY

In 2002, four maize varieties (Goldcob, Tassilo, Justina and Benicia) were sown in a fully-randomised split-plot trial with five replicates. Three sowing systems were used: conventional (no-plastic), complete cover (X-Tend) and an adaptation of the complete cover system in which the plastic film was removed 30 days after sowing, i.e. just before the young plants broke through the covering film. The objective of the study was to study:

• The response of different maize varieties to the plastic film cover
• The effect of removing the plastic cover just before the developing plants exhibit the stress symptoms associated with breaking through the plastic film

To look more closely at optimum harvest date, three of the varieties (Tassilo, Justina and Benicia) were sampled every ten days from September 10 to November 8. Two samples of six consecutive plants were cut by hand to ground level. Each sample was weighed and separated into stover (stem and leaf) and cob fractions. Dry matter content (DM%) was determined for each fraction.

RESULTS

The trial area was sown on April 24 in good soil conditions. Atrazine at 4.0 l/ha was sprayed and incorporated one week before sowing; this gave satisfactory season-long weed control despite the very late and poor growth of the crop. The plastic was removed immediately (no plastic) and 30 days later (P/30) to create the additional treatments.

The 2002 season was very difficult for maize. Low temperatures and high rainfall throughout April, May, June and much of July led to a significant delay in tasseling (Table 9).

 

Table 9: Tasseling date of four maize varieties grown under three covering systems

	Goldcob	Tassilo	Justina	Benicia
X-Tend	July 29	July 30	July 31	August 6
P/30*	July 30	August 1	August 2	August 12
Uncovered	August 15	August 20	August 19	August 29

All tasseling dates were delayed in 2002. Even under complete cover tasseling did not occur until the end of July, up to three weeks later than the previous three seasons. As expected, the use of plastic gave significantly earlier flowering with all four varieties, from 17 days for Goldcob to 23 days for Benicia. In the uncovered plots, the tasseling dates reflect the maturity class of the four varieties sown.

The difference between the two covered treatments was slight. Removing the plastic after thirty days had very little effect on tasseling date; flowering was delayed by one or two days for three varieties and by about six days for the late variety Benicia.

The first plants penetrated the plastic on May 25, one month after sowing (Fig. 3). For Goldcob, Justina and Benicia over 98% had come through by June 17. As in previous years, Justina was the most advanced. Tassilo had the lowest penetration rate and also the lowest final plant emergence at 89.3%. These differences were statistically significant.

• Fig. 3: Penetration rate of plants through the plastic cover for maize sown on 24 April 2002

The total crop dry matter yields for the four varieties and three sowing systems are presented in Fig 4. Two points are worth noting in these results.

(a) The response to cover was very large compared to earlier years. For the three varieties Tassilo, Justina, and Benicia the yields of total DM were between 5.1 and 5.7 t/ha over the uncovered yield. The average response over the last three seasons was 3.75 t/ha.

(b) The response from Goldcrop was less at 2.92 t/ha. This may be a once-off poor response or a reflection of a lower potential in this variety.

The increase in grain dry matter was even greater, a response of approximately 200% or 4.2 t/ha. The increase in grain yield accounted for over 87% of the overall increased output (Fig. 5).

• Fig. 4: The total dry matter yield of four maize varieties using three establishment systems
• P/30= Plastic removed at 30 days from sowing

• Fig. 5: Grain dry matter yields of four maize varieties grown using three sowing systems

The response of Goldcob to plastic cover was significantly less for both total DM yield and grain yield (Figs. 4,5). Goldcob did however produce the highest grain yield under the uncovered system. This suggests that Goldcob may have attained its yield potential without plastic in 2002, despite the very adverse growing conditions.

The plastic treatments had a very significant positive effect on the grain fill, again with little or no difference between the full plastic cover and early plastic removal (Fig. 6). For the uncovered plots the TGW figures follow exactly the maturity classification of the varieties. Benicia, the latest variety grown in Ireland showed a reduction of over 80% in TGW relative to that of the seed sown. With a TGW of only 50 g, the starch content of this grain would be very close to zero.

• Fig. 6: Thousand-grain weights (TGW) of four maize varieties grown under three sowing systems in 2002

For each of the characters measured (tasseling date, DM yield, grain yield and TGW), there was no significant difference between the complete cover and the P/30 (plastic removed 30 days after sowing) treatments. This is a surprising result given the adverse growing conditions in Spring 2002. The removal of the cover before the young plants suffered any adverse effects in breaking through the plastic appears to have compensated for the loss of any subsequent benefits from the cover.

The total dry matter yields at each of the seven harvest dates show that although the maximum yield was not reached until October 19, very little increase in yield after the end of September (Fig. 7). This applied both to the covered and uncovered crops.

• Fig. 7: Dry matter accumulation, mean of three maize varieties (Tassilo, Justina, Benicia) grown under complete cover plastic and uncovered

It is worth noting that for both establishment systems maximum dry matter yield and cob DM% were attained around Oct 19 (Fig 8). On that date the covered crops had a cob DM of 51% while the uncovered crops were much lower at 28.5%.

This supports the suggestion that crops should be harvested at a cob DM of approximately 50% for mature crops. Later harvesting can result in a loss of DM yield. Leaving less mature crops in the field after 15 to 20 October may not lead to any improvement in either dry matter content or yield, but may lead to harvesting in poor weather conditions.

• Fig. 8: Cob dry matter development; mean values for three maize varieties grown with and without plastic cover in 2002