CORN SILAGE QUALITY RESPONSE TO CROP PLANTING DENSITY

CORN SILAGE QUALITY RESPONSE TO CROP PLANTING DENSITY Ali Baghdadi*1, Ridzwan A. Halim1, Majid Majidian 2 Department of Crop Science, Faculty of Agriculture, Universiti Putra Malaysia, 43400 Serdang, Malaysia 2 Department of Agronomy and Plant Breeding, University of Guilan, P. O. Box 41635-1314 Rasht, Iran. * Correspondence: Ali Baghdadi, Tel: +989111356118, Fax: +981334626071, E-mail: ali_baghdadi@yahoo.com 1 Abstract Corn silage serves as high-energy forage for livestock. This is most important for high-producing livestock and on farms experiencing problems with making or buying high quality forage. A field experiment was conducted in the spring and summer of 2010 at the Research Site of Guilan Province Agricultural and Natural Resources Research Center in Rasht, Iran to evaluate effect of different planting density of corn in terms of silage nutritive quality. The plant densities were 90,000, 110,000 and 130,000 plants/ha. Increasing plant density from 90,000 to 130,000 plants ha-1 resulted in decreasing nutritive quality of silage corn. The dry matter digestibility (DMD) and crude protein (CP) declined from the lowest to the highest plant density. Acid detergent fiber (ADF) increased from the lowest to the highest plant density. The reduction in nutritive quality may be attributed to the lower leaf to stem ratio at higher planting density. With the reduced grain yield, plant population above a critical density will have a negative effect on CP and quality of forage corn. Key words: crude protein, digestibility, nutritive value, plant density, forage. Introduction Forage from corn has high value for food, high yield capability, short-growth period, and is suitable as forage and feed for poultry and livestock and it is gaining an essential position in the cropping system (Saif et al., 2003). The low protein concentration in forage corn can be augmented simply by incorporating protein rich ingredients such as soybean or sunflower (Choukan, 1997). Successful corn production requires an understanding of various management practices related to the environmental conditions and agronomic practices. Planting with appropriate plant density according to the conditions of each region is one of the most important factor in corn for production (Norwood, 2001). Corn production practices have been intensively researched and constantly improved over the past years. Crop management practices and plant density have been one of the most important research priority areas in corn production (Sangoi et al., 2002). Curran and Posch (2000) reported that good forage crops must have high digestible energy, low fiber and the desired amount of dry matter at harvest for storage. Cox and Cherney (2001) indicated effect of plant density on production and quality of forage corn. They found that increased plant density had a negative effect on CP concentrations. Averaged across years, CP concentration averaged 3 g kg-1 less at 116,000 vs. 80,000 plants ha-1. On the contrary, Marsalis et al. (2009) demonstrated that none of the quality parameters of corn (e.g., CP, ADF) was affected by reducing the seeding rate from 74,200 to 55,600 plants ha-1. Plant population density main effects were significant for many of the quality traits. Concentrations of ADF increased linearly as the plant population density increased (Stanton et al., 2007). Basically, there was no advantage or disadvantage by increasing plant density with respect to feed value. Forage corn is an important source of high yielding and consistent feed and is the most important feed crop for animal husbandry in many areas of world. Therefore, it is important to understand how forage corn performance is influenced by agronomic practices, such as plant density. ˺ Materials and Methods Field experimental studies were conducted in the spring and summer of 2010 at the Research Site of Guilan Province Agricultural and Natural Resources Research Center in Rasht, Iran at latitude of 37°27'3.81"N and longitude of 49°37'31.34"E. The average annual temperature of the region is 15.9 oC. Annual average maximum temperature is 20.6 oC and average annual minimum is 11.3 oC. A composite soil sample was collected at random in the entire plot before the experiment to determine the physical and chemical characteristics. The soil type is Orthic Luvisols, gray brown podzolic soils. The three plant densities comprised of 90,000, 110,000 and 130,000 plants ha-1. Farming practices carried out in the experiment area were similar to those of the farmers in the region. One of the common corn varieties (KSC 500) was planted. The seed moisture and germination percentage were 15 and 95% respectively. The required levels of N, P and K to support the yield goals was 400 kg ha-1 of nitrogen (N), 50 kg ha-1 of phosphorus (P2O5) and 300 kg ha-1 of potassium (K2O) applied in the form of urea, triple super phosphate and potassium sulphate respectively. Phosphorus and potassium fertilizer and 1/3 of the total of N fertilizer were applied at the time of tillage. The rest of N fertilizer was applied at 8-leaf stage. Irrigation water was adequately applied using sprinkler. All agronomic practices except those studied were kept uniform for all treatments. The two centre rows of each plot were harvested when the kernel milk-line was between 50 and 75%. Five of plants were chopped and mixed mechanically, and a 500 g sub sample of each weighed fresh forage sample were dried for 7days in a 70 C forced-air oven to constant moisture to determine forage quality characteristics. Dried sub-samples were retained for forage quality assays. All dried samples were ground using a hammer mill to pass a 1-mm screen and analyzed for crude protein (CP), acid detergent fiber (ADF), dry matter digestibility (DMD). Near infrared reflectance spectroscopy (NIRS) technology using a global calibration equation was used to estimate nutritive quality of forage corn. The Least Significant Difference (LSD) was used to compare treatment means at the 0.01 and 0.05% probability levels Results and Discussions The regression of crude protein of forage corn on plant density showed that CP declined with increasing plant density (Figure 1). The response of CP to plant density was linear as y = 138.23 -13x (r2 =0.99, P<0.01) where y = crude protein and x is plant ha-1, and maximum crude protein (125 g kg-1) was attained at the lowest of plant density (90,000 plants ha-1) and minimum CP (99 g kg-1) was attained at higher plant density in this study. y = 138.23 - 13x r² = 0.99* * CP 140 120 100 80 60 40 20 0 ٩ ، ، ٣ ، Figure 1. Effect of plant density on forage corn crude protein (CP) concentration ** significant at P<0.01 ˻ The regression of acid detergent fiber of forage corn on plant density showed that ADF increased with increasing plant density (Figure 2). The ADF was 197.5, 183.2 and 156.9 g kg-1 for 130,000, 110,000 and 90,000 plants ha-1 respectively. The ADF showed a linear response to plant density as y = 138.1 + 20.3x (r2 = 0.98, P<0.01) where y = acid detergent fiber and x is plant ha-1. 250 y = 138.1 + 138.1 r² = 0.98* * ADF 200 150 100 50 0 ٩ ، ، ٣ ، Figure 2. Effect of plant density on forage corn acid detergent fiber (ADF) concentration ** significant at P<0.01 Results indicated that dry matter digestibility of forage corn reduced with increasing plant density. Lowest dry matter digestibility (655 g kg-1) resulted from the higher plant density of 130,000 plant ha-1 and the maximum DMD of 689.9 g kg-1 was obtained from the lowest plant density (90,000 plants ha-1). There was no significant effect of different planting densities on water soluble carbohydrates. The higher leaf to stem ratio of 0.46 was obtained in low plant density at 90,000 plants ha-1. Leaf to stem ratio decreased when plant density increased. The higher cob/whole plant ratio of 0.49 was obtained at a low plant density of 90,000 plant ha-1. The cob/whole plant ratio for different plant densities rang was 0.41, 0.46 and 0.49 for 130,000, 110,000 and 90,000 plants ha-1 respectively (Table 1). Table 1. Comparison of the means for nutritive quality of forage corn between different plant densities treatments Density D1 (17 cm) D2 (14cm) D3 (12 cm) LSD(0.05) DMD (g kg-1) 689.9a 668b 655b CP (g kg-1) 125a 112.7b 99c WSC (g kg-1) 310.5 314.3 318.6 ns ADF (g kg-1) 156.9c 183.2b 197.5a Leaf/Stem ratio 0.46 a 0.44 a 0.40 b Cob/whole plant ratio 0.49 a 0.46 a 0.41 b Means values followed by the same letter in the same column are not significantly different at P<0.05, based on least significant difference test LSD). D1, 90000 plants ha-1 D2, 110000 plants ha-1 D3, 130000 plants ha-1 ns, non significant Results showed that lower plant densities result in better quality silage. Corn seeds contain more protein, less cell wall carbohydrate and high digestibility (Coors et al., 1997). Reduced leaf-to-stem ratio is a major cause of the decline in forage quality with maturity. Leaves are higher in quality than stems, and the proportion of leaves in forage declines as the plant matures. At high plant density leaf to stem ratio and cob to whole plant ratio decreased. Also, reduced CP was probably due to decreases in leaf and increase stem and cell wall percentage. Snyman and Joubert (1996) and Hadjipanayiotou et al. (1996) reported similar results because leaves are considered the most important source of protein in vegetative organs. Cox et al. (1998) found that plant density of 116,000 plants ha-1 produced 3 g kg-1 CP less than 80,000 plants ha-1. Other researchers have also shown that ˼ CP concentration had a negative linear response to plant density (Widdicombe and Thelen, 2002; Wang et al., 2005). Forages with a greater amount of leaves are more likely to be of higher quality. Dry matter digestibility declined with increasing plant densities due to reduced leaf to stem ratio and increase in whole-plant fiber concentrations. ADF is a measure of the least digestible plant carbohydrate (cellulose and lignin). It is negatively correlated with digestibility and consequently is often used to estimate energy content of forages. As a plant matures it becomes more “stemmy” (i.e., the leaf/stem ratio reduces). Acid detergent fibre is important because it is negatively correlated with digestibility of forages (Ball et al., 2001). Increasing plant densities increased ADF; the highest value was recorded at 130,000 plants ha-1. Increasing plant densities decreased leaf to stem ratio and cob/whole plant ratio. Increasing ADF may be associated with the reduced leaf to stem ratio at high plant density. Corn stem has the highest lignin and lowest digestibility and crude protein. As the ADF increases, the forage becomes less digestible, primarily because the amount of indigestible lignin is increasing. With accumulation of lignin the digestibility of forage is greatly reduced (Feizi and Rezvani Moghaddam, 2011). Usually the amount of plant fiber increases with increase in plant density while digestibility decreases. The adverse effect of increased plant density on forage quality was similar to that reported by Widdicombe and Thelen, (2002), and Cusicanqui and Lauer (1999). Conclusion and Recommendations Forage quality decreased with increasing density this deficiency can be easily overcome with supplementation of livestock diets with other concentrate feeds. On the other hand, increasing plant density resulted in reduction of nutritive quality. If high nutritive value is a premium then the low plant density (90,000 plants ha-1) is recommended. References Ball, D., Collins, M., Lacefield, G. Martin, N., Mertens, D., Olson, K., 2001. Understanding Forage Quality. American Farm Bureau Federation Publication. 1-01. Choukan, R., (1997. Comparison of Corn Silage Hybrids Varieties for Yield and Yield Components. Seed and Plant. 12(2): 36-40. Coors, J., Albrecht, K., Bures, E., 1997. 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