Influence of Nitrogen Fertilizer on Ash, Organic Carbon, Phosphorus, Potassium, and Fiber of Forage Corn Intercropped by Three Cultivars of Berseem Clover as Cover Crops in Semi Arid Region of Iran

Supplementation of animal feeds with high quality needs new agriculture management, like intercropping system. In order to determine qualitative characteristics of forage corn intercropped by berseem clover cultivars in different levels of nitrogen fertilizer, an experiment was conducted in 2010 at Research Farm, Faculty of Agriculture, Islamic Azad University, Khorasgan Branch, Esfahan. A factorial layout within randomized complete block design with 3 replications was used. Cultivars were Karaj, Sacromont and Multicut, and nitrogen levels were included 0, 40 and 60 kg/ha. The nitrogen fertilizer was provided from urea source (46% pure N). Cultivar had significant effect on ash percentage, P, organic carbon of soil and soil nitrogen percentage. Nitrogen had significant influence on ash, K, organic carbon of soil, soil nitrogen percentage, light transmission, solar radiation absorption and extinction coefficient. Organic carbon of soil and soil nitrogen percentage just significantly influenced by cultivar and nitrogen interaction. In this experiment the highest ash percentage, organic carbon of plant, ENDF was obtained in forage corn intercropped by Multicut. The maximum organic carbon of soil and soil nitrogen percentage also related to forage corn and Multicut intercropping. The highest ash percentage, organic carbon, ENDF, organic carbon of soil, soil nitrogen percentage and solar radiation absorption was obtained in forage corn and Multicut intercropping.


Introduction
Plants growth may be limited either because of lack of sufficient light, water, and nutrients in the environment or because of competition for these resources from other plants (Friday & Fownes, 2000).Supplementation of animal feeds needs new agricultural management (Friday & Fownes, 2000).Two or more crops planted together were known as intercropping system in order to maximize beneficial interactions (Ghanbari et al., 2010).The increase in agricultural productivity during the 20 th century was obtained through the use of high levels of external inputs, and agricultural intensification produced environmental pollution by agrochemicals and excessive utilization of fertilizers (Unlu et al., 2010).Corn (Zea may L.) is one the most important cereal crop grown in Iran (Seyed Sharifi et al., 2009) and the world (Kamara et al., 2006;Bekavac et al., 2007;Doka & Pepo, 2009;Carpici et al., 2010).Maize is important crop in industrial and livestock production (Olaniyan & Lucas, 2004;Oktem, 2008;Kusaksiz, 2010).The yield of maize in Iran is very low as compared to other maize producing countries (Seyed Sharifi & Taghizadeh, 2009).Maize intercropped with a legume is the appropriate management to have surplus cash income (Shisanya, 2005).Forage maize has become a major constituent of ruminant rations in recent years (Javanmard et al., 2009).One of the most important effective factors is non application of optimal amounts of nitrogen fertilizer per hectare (Limon-Ortega, 2009;Seyed Sharifi & Taghizadeh, 2009;Cabrera-Bosquet et al., 2011).The rates of inputs especially nitrogen is important if the aim is to maximize, or make consistent, levels of nutrients in plants (Odunze et al., 2004;Russo, 2006).Basbag et al. (2009) reported that crude ash, ADF and NDF in alfalfa was 8.0-18.6%,16.8-33.3%and 63.0-75.8%,respectively.The amount of minerals in forages and their bioavailability need to be considered (Evitayani Warly et al., 2006).Warly et al. (2006) concluded that deficiency or imbalance of certain minerals of the forages is not suitable to feeding animals.Pieretii (2005) also demonstrated that nutritive value of forages is important for several reasons.Ash concentration of maize-cowpea was higher than that of sole maize, but sole cowpea had higher ash concentration compared to sole maize and intercrops (Dahmardeh et al., 2009).There were differences amongst various sole crops and intercropping mixtures in terms of organic matter (Yolcu et al., 2009).Intercropping is one sustainable idea that can greatly increase the use of solar radiation.The additional solar energy used by the intercrop canopy leads to improved crop production, and thus greater economic yield (Awal et al., 2006).The canopy , s extinction coefficient, the most critical element of Beer , s law, defined as the average projection of leaves onto a horizontal surface, is a function of the area and form of the leaf, the leaf inclination, the zenith angle of the sun, and the leaf , s azimuth (Awal et al., 2006).Organic carbon in arable in arable lands has a favorable effect on soil fertility, crop production, soil sustainability and soil biological productivity (Batjes, 1996;Marton, 2008).Lavado et al. (2001) illustrated that potassium and phosphorus content was varied between 11.2 to 11.0 g kg -1 and 1.2 to 1.6 g kg -1 , respectively.Fassio et al. (2009) concluded that the maximum and minimum ash percentage of grain corn was 1.3% and 3.8%, respectively.Kruse et al. (2008) reported that a maximum difference of 58.1 g NDF in silage maize.Different cultivars showed different reactions and responses to various agricultural managements (Soleymani et al., 2010).Pepo (2011) reported that the productivity of a specific field ecosystem is greatly influenced by the degree and length of the impact by the factors disturbing the equilibrium.There are no reported studies on Influence of nitrogen fertilizer on ash, organic matter, phosphorus, potassium, cellulose and fiber of forage corn intercropped by three cultivars of berseem clover.Therefore, the present study was aimed to evaluate those parameters in semi arid climatic condition of Iran.

Materials and Methods
The aim of this experiment was to determine ash, organic carbon, P, K, ENDF, organic carbon of soil, soil nitrogen percentage, light transmission, solar radiation absorption and extinction coefficient of forage corn intercropped by three berseem clover cultivars in different nitrogen levels in 2010.This research was done at Research Farm, Faculty of Agriculture, Islamic Azad University, Khorasgan Branch (Esfahan) (latitude 32 o 40' N, longitude 51 o 58' E, and 1570 m elevation).A factorial layout within randomized complete block design with 3 replications was used.Cultivars were Karaj, Sacromont and Multicut, and nitrogen levels were included 0, 40 and 60 kg/ha.The nitrogen fertilizer was provided from urea source (46% pure N).The soil preparation consisted of mouldboard ploughing followed by discing and smoothing with a land leveler.Ditches were prepared separately for each replication.Ditches were prepared separately for each replication.The distance between rows of forage corn was 100 cm and clover cultivars were planted on the basis of 20 kg seed per ha.Clover cultivars seed were planted at distance between forage corn rows.Plantation was done 15 June by skillful workers.The first irrigation was done after plantation, the second irrigation for better seedling establishment was done four years after first irrigation.Other irrigation interval was 8 years.Weeds were controlled by hand weeding.Clover cultivars were harvested at 15% of flowering stage.The second cut was used as green manure.Ash content determined by incinerating the samples in a muffle furnace at 550 o C for 4 h.Phosphorus estimated by colorimetric method (Badrzadeh et al., 2008).A flame photometer used for determination of K (Badrzadeh et al., 2008).Neutral detergent fiber evaluated by the method of Van Soest and Wine (1968) with enzyme addition.Soil organic carbon samples determined by the Tyurin method (Marton, 2008).For determining light transmission (T), solar radiation absorption (A) and extinction coefficient (K), equation number 1, 2 and 3 were used respectively.I and I0 mean the solar radiation under plant canopy and solar radiation absorption above of plant canopy.
Data were subjected to analysis of variance (ANOVA) using statistical analysis system, followed by Duncan , s multiple range test and differences were considered significant at P<0.05 by MSTAT-C software.

Results and Discussion
The effect of cultivar on ash percentage was significant, but organic matter was not influenced by cultivar significantly (Table 1).Among the three cultivars, intercropping of forage corn by Multicut performed better ash percentage, but there was no significant difference between Karaj and Sacromont.The maximum organic carbon was obtained in forage corn and Multicut intercropping, but there was no significant difference found between these three cultivars (Table 2).Fassio et al. (2009) noted that organic matter digestibility of corn varied between 77.6% and 92.1%.Phosphorus content was significantly influenced by cultivar, but K content and ENDF was not significantly influenced by cultivar treatments (Table 1).ADF and NDF have been regarded as good indicators of forage quality because of their negative relation to digestibility for livestock animals (Bao et al., 2007).Sacromont had obtained the highest P content.There was also significant difference in P content between cultivation of Karaj and Multicut.The differences in K content and ENDF between berseem clover cultivars were not significant (Table 2).The highest organic carbon of soil and soil nitrogen percentage was related to forage corn and Multicut intercropping.Forage crop production and quality is very important for successful animal production (Yolcu et al., 2009).Cultivar treatments did not influenced light transmission, solar radiation absorption and extinction coefficient to the level of significant (Table 1).The maximum light transmission and solar radiation absorption was related to intercropping of forage corn with Sacromont and Multicut, respectively.There was no significant difference in extinction coefficient between these three cultivars (Table 2).Ash percentage and K content was significantly influenced by nitrogen fertilizer (Table 1).Ash percentage in application of 60 kg N/ha was more than others.Application of 40 kg N/ha produced maximum K percentage (789.5ppm) (Table 2).Sing et al. ( 2009) indicated that the highest ash content in popcorn, white corn, sweet corn and dent corn was 2.7%, 1.2%, 1.8% and 1.2%, respectively.Nitrogen application had non significant effect on organic carbon, P content and ENDF, while cultivar had significant influence on organic carbon of soil (Table 1).Maximum and minimum organic carbon of soil were noted in application of 60 kg N/ha (1.26%) and control treatment (0 kg N/ha) (1.10%), respectively.Marton (2008) concluded that N fertilization resulted in a significant decline (16.6%) in SOC in comparison to the control plots in the 1 st 20-year interval, while in the 2 nd 20-year period a significant rise (up to 31.9%) was registered.ENDF was increased from application of 0 to 60 kg N/ha, but it was not significant (Table 2).Reduction in fiber content of forage cause significantly increase in digestibility of the forage (Javanmard et al., 2009).Soil nitrogen percentage and light transmission was significantly influenced by nitrogen (Table 1).The maximum soil nitrogen percentage and light transmission was obtained in application of 60 kg N/ha and 0 kg N/ha, respectively (Table 2).Among these three nitrogen fertilizer treatments, application of 0 and 40 kg N/ha produced the same soil nitrogen percentage (0.11%) (Table 2).Data showed that nitrogen has a significant effect on solar radiation absorption and extinction coefficient (Table 1).Soleymani et al. (2011) concluded that nitrogen had significant effect on solar radiation absorption, but light transmission was not significantly influenced by nitrogen fertilizer.Regarding nitrogen treatments, maximum solar radiation absorption was noted in application of 60 kg N/ha, but the difference between 40 and 60 kg N/ha was not significant.Extinction coefficient in no application of nitrogen fertilizer (0 kg N/ha) was more than other nitrogen treatments (Table 2).Wang et al. (2007) illustrated that significant differences content was found in barley cultivars, they also concluded that the plant quality was also sensitive to the growing conditions, especially nitrogen level.Soleymani et al. (2011) noted that phosphorus significantly influenced by cultivar and nitrogen, but the effect of cultivar and nitrogen on potassium content was not significant.In that experiment the maximum phosphorus and potassium content was found in application of 40 kg N/ha and 60 kg N/ha, respectively.Cultivar and nitrogen interaction had significant influence on organic carbon of soil and soil nitrogen percentage (Table 1).The maximum organic carbon of soil was obtained in forage corn and Multicut intercropping with application of 40 kg N/ha.Forage corn and Multicut interaction with application of 40 kg N/ha had obtained the highest soil nitrogen percentage (0.14%) (Table 2).Common letters within each column do not differ significantly.

Conclusions
Sustainability of the farming system can be improved by corn cropping with cover crops (Sainju et al., 2006).In this experiment the highest ash percentage, organic carbon of plant, ENDF was obtained in forage corn intercropped by Multicut.The maximum organic carbon of soil and soil nitrogen percentage also related to forage corn and Multicut intercropping.There was no difference between cultivars in solar radiation absorption, but forage corn and Multicut intercropping had obtained the highest one.The efficient use of solar radiation is one of the major criteria for obtaining a yield advantage through intercropping (Awal et al., 2006).Intercropping management and low input farming also can be applied to control soil erosion and reduce N leaching in the regions where cover crops can be grown and costs for energy requirement for N fertilization is a major concern.The response to N application depends upon the requirement of variety (Limon-Ortega et al., 2008).The highest ash percentage, organic carbon, ENDF, organic carbon of soil, soil nitrogen percentage and solar radiation absorption was obtained in forage corn and Multicut intercropping.Wang et al. (2007) illustrated that quality of the plant was dependent on growing conditions, especially N level in soil.A continuous measurement of the components of the radiation balance for different types of vegetation has become an almost standard procedure giving us information about the transformation of incoming solar radiation by vegetation (Svirezhev and Steinborn, 2001).Light transmission and extinction coefficient in no application of nitrogen fertilizer was higher than 40 and 60 kg N/ha.

Table 1 .
Analysis of variance for experimental characteristics