The inorganic nitrogen fertilizer equivalency of hairy vetch (Vicia villosa Roth) as a winter green manure in Kanto and Tohoku district, Japan

ABSTRACT

It is well known that legume green manure (GM) supplies nitrogen (N) to succeeding crops. However, in Japan, there are few experimental field studies that have quantitatively evaluated the effect of GM on the N supply. To estimate the inorganic N fertilizer equivalency of GM for the succeeding corn crop, two field experiments were conducted in 2012 at Morioka, Tohoku district (cool climate region) and in 2014 at Nasushiobara, Kanto district (warm temperate region). Each experiment had a split-plot design with a factorial arrangement of two cropping systems, hairy vetch [HV; Vicia villosa Roth] GM and conventional cultivation, with four N fertilizer treatments (0, 75, 150, and 225 kg N ha⁻¹). In both sites, GM increased the N uptake and, as a result, the shoot yield of the succeeding forage (silage) corn. The apparent N recovery rates of HV shoot were 64% at Morioka and 24% at Nasushiobara. The inorganic N fertilizer equivalency rates of HV shoot were 82% at Morioka and 104% at Nasushiobara. In conclusion, by introducing HV as a GM, we can reduce the amount of inorganic N fertilizer applied to the succeeding corn crop with the same amount as at least 80% of N uptake in HV shoot.

KEY WORDS:

• Corn
• cropping system
• green manure
• hairy vetch
• inorganic nitrogen fertilizer equivalency

1. Introduction

Green manure (GM) is a crop that is cultivated during the fallow period before the main crop and is incorporated into the field (rather than harvested) just prior to sowing of the main crop. GM is advantageous because it supplies organic matter to the soil (Cherr, Scholberg, and McSorley 2006; MacRae and Mehuys 1985), prevents soil erosion (MacRae and Mehuys 1985), reduces nitrogen (N) leaching during the winter (Thorup-Kristensen, Magrid, and Jensen 2003), and decreases the population of parasitic nematodes (Chikaoka, Ohbayashi, and Suina 1982). In addition, legume GM supplies N to the succeeding crop by fixing atmospheric N (Cherr, Scholberg, and McSorley 2006; Fageria 2007) and thus increases the yield and N uptake of the succeeding crop (Seo et al. 2000; Sarrantonio and Scott 1988; Komatsuzaki 2002).

Hairy vetch [Vicia villosa Roth; (HV)] is widely used as a winter cover crop because of its high productivity and N fixation ability (Lu et al. 2000). In Japan, HV has recently gained attention as a winter GM because of its high tolerance to environmental stresses, particularly to cold and snow (Sato et al. 2007). In northern Japan, the introduction of HV as a winter GM has been reported to improve the physical condition of paddy field soil and the initial growth of the succeeding soybean (Glycine max (L.) Merr.) crop (Sato et al. 2007). HV GM supplies N to the succeeding corn (Zea mays L.) crop in eastern (Sharifi et al. 2011) and western Japan (Tarui et al. 2013), to the succeeding cabbage (Brassica oleracea L.) crop in northern Japan (Sato et al. 2019), and to the succeeding tomato (Solanum lycopersicum L.) crop in eastern Japan (Horimoto et al. 2002). However, most previous studies have qualitatively evaluated the effect of HV GM on the succeeding crops. There are few experimental field studies that have evaluated the inorganic N fertilizer equivalency of HV GM for the succeeding crop.

The present study aimed to estimate the extent to which the inorganic N fertilizer application rate for the main crop can be reduced by using HV as a GM while ensuring that the yield of silage corn is comparable to that from the conventional cultivation at two sites with different climatic conditions in Tohoku (cool climate region) and Kanto (warm temperate region) districts.

2. Materials and methods

2.1. Field sites

The experiments were conducted in 2012 at Morioka (Tohoku Agricultural Research Center [TARC], National Agriculture and Food Research Organization [NARO], Japan), and in 2014 at Nasushiobara (Nasu Research Station, Institute of Livestock and Grassland Science, NARO, Japan). Morioka (39°42′N, 141°09′E) is located in the Tohoku district of Japan, and its average temperature and average precipitation are 9.6°C and 1258.5 mm, respectively. Three soil samples (0–15 cm) were randomly obtained from the field in Autumn, 2011. The soil was classified as Pachic Melanudands, and its properties were described in Table 1. Nasushiobara (36°55′N, 139°55′E) is located in the north of the Kanto district of Japan, and its average temperature and average precipitation are 12.5°C and 1469.9 mm, respectively. Five soil samples (0–15 cm) were randomly obtained from the field in Autumn, 2013. The soil was classified as Entic Humudept, and its properties were described in Table 1.

Table 1. The chemical properties of soils in the experimental fields

	pH	Total C (g kg^−1)	Total N (g kg^−1)	NH4^+-N (mg kg^−1)	NO3 ^– -N (mg kg^−1)	CEC (cmol kg^−1)
Morioka	6.2	82.2	6.1	15.7	6.0	46.2
Nasushiobara	5.8	42.3	3.3	22.7	13.0	19.9

C: carbon, N: nitrogen

2.2. Experimental design

The experiments at both sites were split-plot arrangements in a completely randomized block design of three replications, with the two cropping systems as the whole plot factor and the four N fertilizer application treatments as split plot factor. The two cropping system treatments were (1) corn grown with HV GM and (2) corn grown without GM [conventional cultivation (CC)]. The four N fertilizer application treatments were at a rate of 0, 75, 150, and 225 kg ha⁻¹. The recommended N fertilizer application rate for silage corn in Japan is 200 kg ha⁻¹ (Kurashima 1983). Each experimental plot was 3 m × 4 m.

2.3. Crop management

In 2011 at Morioka, the field was planted with corn to establish uniform conditions throughout the field. In September 2011, the corn was harvested. On 5 October 2011 HV (V. villosa cv. Kantaro) was sown in the plots receiving GM treatment at a seed rate of 50 kg ha⁻¹ without fertilizer application. No crop was sown in the plots receiving CC treatment. On 22 May 2012 plots receiving both treatments were tilled without shredding hairy vetch. On 23 May 2012 N was applied as ammonium sulfate at rates of 0, 75, 150, or 225 kg ha⁻¹; phosphorus (P) as superphosphate at a rate of 131 kg ha⁻¹ [300 kg phosphorus pentoxide (P₂O₅) ha⁻¹] in all plots, and potassium (K) as potassium chloride at a rate of 249 kg ha⁻¹ [300 kg potassium oxide (K₂O) ha⁻¹] in all plots. The application rates of P and K were higher than the recommended fertilizer rates, 78.6 kg ha⁻¹ and 166 kg ha⁻¹, respectively (Kurashima 1983) for silage corn in Japan to mask the effect of GM on the P and K concentration of corn. All plots were then tilled, again. On 24 May 2012 corn (Z. mays L. cv. DKC34−20) with agrochemicals (thiuram and thiamethoxam) was sown to achieve a plant density of approximately 74,000 plants ha⁻¹ in 0.75 m rows and 0.18 m inter-hill distances. Herbicides (dimethenamid and linuron) were applied to all plots to suppress weed growth.

In 2013 at Nasushiobara, the field was also planted with corn to establish uniform conditions throughout the field. In September 2013, the corn was harvested. On 3 October 2013 HV (V. villosa cv. Kantaro) was sown in plots receiving GM treatment at a seed rate of 50 kg ha⁻¹ without fertilizer application. No crop was sown in the plots receiving CC treatment. On 7 May 2014 the same fertilizers were applied at the same rates as described for the Morioka trial. All plots were then tilled without shredding hairy vetch, and corn (Z. mays L. cv. 34B39) with agrochemicals (thiuram and thiamethoxam) was sown to achieve aplant density of approximately 74,000 plants ha⁻¹ in 0.75m rows and 0.18m inter-hill distances. Herbicides were applied as described for the Morioka trial.

Climate data (monthly average air temperature, precipitation, and sunshine hours) at Morioka were collected between October 2011 and September 2012 and at Nasushiobara between October 2013 and September 2014 from the meteorological observation systems in TARC, NARO and Nasu Research Station, Institute of Livestock and Grassland Science, NARO, respectively.

2.4. Plant analysis

On 21 May 2012 at Morioka and on 7 May 2014 at Nasushiobara, the HV shoots in a 0.5 m × 0.5 m sampling quadrat from each plot at Morioka and three points in GM treatment at Nasushiobara were harvested. For yield determination at harvest, corn shoots in 3 m² areas of each plot were harvested on 3 September 2012 at Morioka and on 25 August 2014 at Nasushiobara from the two central rows of each plot, while avoiding at least the plot edge by 0.5 m in each plot. Subsamples (1 kg) were collected for dry weight and N concentration analysis.

All shoot subsamples were oven-dried at 70°C for 48 h, weighed, and ground. The N concentration of the samples was determined using the dry combustion method (Committee of Soil Environment Analysis 1997). The N uptake in the shoots was determined by multiplying the N concentration and the shoot dry weight.

Apparent N recovery and inorganic N fertilizer equivalency rate of HV shoots were defined as follows, referring to Munoz et al. (2004).

apparent N recovery (%) = 

(N uptake of corn with N applied – N uptake of corn without N applied)/applied N × 100

inorganic N fertilizer equivalency rate of HV shoots (%) = apparent N recovery (GM treatment)/apparent N recovery (inorganic fertilizer treatment) × 100

2.5. Statistical analysis

Statistical analyses were performed using SAS Add-in for Microsoft Office (SAS Institute, Cary, NC, USA). Data were analyzed using a general linear model for the split-plot design. When the cropping systems × N fertilizer application treatments interaction was significant (P < 0.05), means were compared using Tukey method (Miwa 2015). Parametric correlation analysis was used to establish the association between the shoot yield of corn and both the N concentration and the N uptake in corn shoots with each plot as a replicate.

3. Results

3.1. Weather conditions

The weather conditions at Morioka and at Nasushiobara were showed in Figure 1. The growing degree-days (GDD) with a base temperature of 4°C during the HV-growing season (from sowing to incorporating) at Morioka and Nasushiobara were 671.4 and 839.4, respectively.

Figure 1. Monthly average air temperature, precipitation, and sunshine hours during the experimental period at Morioka in 2011 and 2012 (Tohoku agricultural research center, National Agriculture and Food Research Organization [NARO]) and at Nasushiobara in 2013 and 2014 (Nasu research station, Institute of Livestock and Grassland Science, NARO).

3.2. Shoot growth of hairy vetch and shoot yield of corn

The growth of HV shoots were showed in Table 2. Nuptake of HV shoots were 89kg ha⁻¹ at Morioka and 248kg ha⁻¹ at Nasushiobara, respectively. The growth and N uptake of HV shoots were higher at Nasushiobara than at Morioka.

Table 2. The dry weight, N concentration and N uptake of hairy vetch shoot

	Dry weight (kg ha^−1)	N concentration (%)	N uptake (kg ha^−1)
Morioka	2040	4.4	89
Nasushiobara	6772	3.7	248

N: nitrogen.

At Morioka, the shoot yield of corn increased with increasing the N fertilizer application rate up to 150 kg N ha⁻¹ in both the GM and CC cropping systems (Table 3). The shoot yield of corn was significantly higher under GM treatment than under CC (i.e., no GM) treatment at 0 and 75 kg N ha⁻¹. Conversely, there was no significant difference in the shoot yield of corn between the GM and CC treatments at 150 and 225 kg N ha⁻¹. The yields of corn under GM treatment at 75, 150, and 225 kg N ha⁻¹ were comparable to or higher than those under CC treatment at 225 kg N ha⁻¹, which is the N fertilizer rate at which the maximum shoot yield of corn was noted for the CC treatment. At Nasushiobara, the shoot yield of corn increased with increasing the N fertilizer application rate up to 150 kg N ha⁻¹ under CC treatment (Table 3). In contrast, the shoot yield of corn under GM treatment was similar, irrespective of the N fertilizer application rates. The shoot yields of corn were significantly higher under GM treatment than under CC treatment. The maximum yield of corn under CC treatment was 21.5 Mg ha⁻¹ at 150 kg N ha⁻¹, which was comparable to or lower than those in each of the GM treatments

Table 3. Shoot yield of corn

N rate (kg ha^−1)		Yield (Mg ha^−1)
		Morioka					Nasushiobara
Cropping system		CC		GM					CC			GM
	0	9.7(1.4)		14.7 (1.0)					18.9 (2.8)			23.1 (1.1)
	75	13.9 (1.0)		17.1 (0.8)					20.5 (1.8)			22.7 (0.2)
	150	16.6 (0.1)		17.9 (1.0)					21.5 (0.8)			23.5 (1.6)
	225	16.7 (0.7)		17.3 (0.9)					21.3 (1.8)			22.5 (2.0)
	†HSD (0.05)		2.4							-
	‡HSD (0.05)		1.6							-
ANOVA (P-value)
Cropping system		0.011						0.030
N rate		<0.001						0.189
Interaction		0.010						0.190

CC, conventional cultivation; GM, green manure; N, nitrogen. Data are represented as mean (standard error of mean). †HSD value for N rate effect within same cropping system. ‡HSD value for cropping system effect within same N rates level

The N concentration in corn shoots increased with increasing the N fertilizer application rate under both cropping systems (GM and CC) at both sites (Table 4). The N concentrations in corn shoots tended to be higher under GM treatment than under CC treatment at both sites.

Table 4. Nitrogen (N) concentrations of corn shoot at harvest

N rate (kg ha^−1)		N concentration (%)
		Morioka				Nasushiobara
Cropping system		CC		GM		CC		GM
	0	0.66 (0.04)		0.82 (0.02)		1.06 (0.06)		1.15 (0.04)
	75	0.83 (0.04)		1.16 (0.06)		1.06 (0.02)		1.14 (0.01)
	150	1.17 (0.05)		1.32 (0.08)		1.15 (0.02)		1.21 (0.03)
	225	1.40 (0.02)		1.47 (0.04)		1.17 (0.03)		1.22 (0.03)
ANOVA (P-value)
Cropping system		0.114				0.051
N rate		<0.001				0.009
Interaction		0.055				0.923

CC, conventional cultivation; GM, green manure. Data are represented as mean (standard error of mean)

At Morioka, the N uptake in the corn shoots increased with increasing the N fertilizer application rate in both cropping systems (Figure 2(a)). The N uptake in the corn shoot tended to be higher under GM treatment than under CC treatment. The increase of the N uptake in the corn shoots at 0 kg N ha⁻¹ by HV GM was 57 kg ha⁻¹. The apparent N recovery of HV shoots was calculated as 64% (= 57/89). There was a liner relationship between N application rate and N uptake of corn in CC cropping system (Figure 2(a)). The apparent N recovery of inorganic fertilizer was 78%. Therefore, the inorganic N fertilizer equivalency rate of HV shoots was calculated as 82% (= 0.64/0.78).At Nasushiobara, the N uptake in corn shoots increased with increasing the N fertilizer application rate in both cropping systems (Figure 2(b)). The N uptake in corn shoots was significantly higher under GM treatment than under CC treatment. N uptake in corn shoots under all GM treatments, irrespective of the fertilizer N application rates, was comparable to or higher than those under CC treatment at 225 kg N ha⁻¹, the latter being the N fertilizer rate at which maximum N uptake in corn shoots was recorded for CC treatments. The increase of the N uptake in the corn shoots at 0 kg N ha⁻¹ by HV GM was 59 kg ha⁻¹. The apparent N recovery of HV shoots was calculated as 24% (= 59/248). There was a liner relationship between N application rate and N uptake of corn in CC cropping system (Figure 2(b)). The apparent N recovery of inorganic fertilizer was 23%. Therefore, the inorganic N fertilizer equivalency rate of HV shoots was calculated as 104% (= 0.24/0.23).

Figure 2. Nitrogen (N) uptake in corn shoots grown in hairy vetch green manure and conventional cultivation at harvest (n = 3). Vertical bars represent the standard error of mean (SEM). ANOVA: Analysis of variance; CC: conventional cultivation; GM, green manure.

There were significant positive correlations between shoot N concentration and shoot yield at Morioka (r = 0.829; P < 0.001; n = 24) and at Nasushiobara (r = 0.726; P < 0.001; n = 24) (Figure 3)and between shoot N uptake and shoot yield at Morioka (r = 0.902; P < 0.001; n = 24) and Nasushiobara (r = 0.952; P < 0.001; n = 24) (Figure 4).

Figure 3. Relationship between nitrogen (N) concentration of corn shoot and shoot yield of corn at Morioka and Nasushiobara.

Figure 4. Relationship between nitrogen (N) uptake of corn shoot and shoot yield of corn at Morioka and Nasushiobara.

4. Discussion

Significant positive correlations were noted between the N concentration and yield (Figure 3) and between the N uptake and yield at both sites (Figure 4). Thus, a low N supply was a limiting factor for the shoot yield of silage corn in the present study. Introducing HV as a winter GM supplied N to the corn crop and, as a result, increased the shoot yield of corn (Table 3). This finding is supported by the trend of a higher shoot N concentration (Table 4) and N uptake in corn shoots (Figure 2 (a),(b)) under GM treatment than those under CC treatment at the same N fertilizer application rate.

There was a marked difference in the N uptake by HV shoots between Morioka and Nasushiobara (Table 2). Teasdale et al. (2004) reported that the growth of HV depended on temperature and there was a positive correlation between GDD with a base temperature of 4°C and HV biomass. In this study, the GDD during the HV-growing season was higher at Nasushiobara than at Morioka. We believe that this is the reason for the more vigorous growth and N uptake of HV shoot at Nasushiobara.

The inorganic N fertilizer equivalency rates of HV shoots were 82% at Morioka and 104% at Nasushiobara. These results showed that the inorganic N fertilizer equivalency rate of HV shoot is at least 80%. Thus, by introducing HV as a GM, we can reduce the amount of inorganic N fertilizer applied to the succeeding corn crop with the same amount as 80% of N uptake in HV shoot.

The apparent N recoveries of HV shoots at Nasushiobara (24%) was much lower than that at Morioka (64%). The apparent N recovery of inorganic fertilizer decreases at higher N application (Fageria and Baligar 2005). Yagi et al. (2019) reported that the apparent N recovery of inorganic fertilizer was lower at higher soil fertility. In this study, the N uptake of HV shoots at Nasushiobara was much higher than that at Morioka. The yield of corn under CC treatment at 0 kg N ha⁻¹ (Table 3) and the inorganic N content in the soil (Table 1) were higher at Nasushiobara than those at Morioka, namely, the soil fertility at Nasushiobara was higher than at Morioka. This was consistent with the smaller increasement in the shoot yield of corn associated with increasing inorganic N fertilizer application at Nasushiobara. We believed that the higher N supply by HV shoots and soil fertility at Nasushiobara were the reasons for the lower apparent N recovery of HV shoots. In addition, the decomposition of GM might influence the apparent N recovery of HV shoots. The decomposition of GM is affected by many factors, including the characteristics of GM, amount of GM, temperature, soil moisture, and soil physical and chemical properties (Singh, Singh, and Khind 1992) and the mechanism of decomposition of GM is complex. The decomposition of GM generally increases with temperature (Singh, Singh, and Khind 1992). On the other hand, Sato et al. (2019) noted the possibility that the rapid decomposition of HV GM caused by the high temperature during the N requirement of cabbage being low decreased the apparent N recovery of HV GM. More research is necessary to make clear the reason in detail for the difference in the apparent N recovery of HV GM between both sites.

At both sites, the maximum shoot yield of corn tended to be higher under GM treatment than under CC treatment at the highest N fertilizer application, i.e., 225 kg N ha⁻¹. The N concentrations of corn shoots under CC treatment at 225 kg N ha⁻¹ were similar to those under GM treatment at 225 kg N ha⁻¹ (Table 4), and those values were within or higher than the range of N concentrations for the maximum attainable yield (1.16%–1.25%) (Stanford 1973). The N nutrition resulting from CC treatment at 225 kg N ha⁻¹ was not insufficient for corn growth. Thus, it is highly unlikely that improved N nutrition was the reason for the higher shoot yields under GM treatment than under CC treatment at 225 kg N ha⁻¹. Moreover, P and K were applied at rates higher than the recommended rates in Japan. On the other hand, Fageria (2007) indicated that GM has positive effects on the soil physical, chemical, and biological properties, not only nutrient supply, and, as a result, increases the yields of succeeding crops. Further studies are necessary to investigate other effects of HV GM on corn shoot growth, apart from the supplies of N, P, and K.

In conclusion, introducing HV as a winter GM could reduce the need for a inorganic N fertilizer for succeeding forage corn to attain a yield comparable to that from CC. In Japan, the Kanto district is considered as the northern limit of the double cropping of forage corn and winter forage crops (for example, rye or Italian ryegrass) (Morita 2011). In the Tohoku district, which is located in the north of Kanto district, the cropping system of forage corn is a monoculture, with the corn field lying fallow in winter. The results of the present study demonstrated that HV can be introduced in monoculture areas like the Tohoku district, without decreasing the annual forage production, while reducing inorganic N fertilizer usage as well as having other benefits, such as soil surface protection and increased organic matter content in the soil. This technique would be useful for low-input sustainable agriculture in the forage corn monoculture areas.

Acknowledgments

We thank Dr. Kanno and Dr. Sunaga for their helpful suggestions and cooperation. We also thank for Ms. Kawakami and Mr. Saito for their technical assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).