Planting Structure Adjustment and Layout Optimization of Feed Grain and Food Grain in China Based on Productive Potentials

Abstract

Increasing feed grain supply, particularly domestic supply, is intended to guarantee feed grain security and, as a result, food security. Based on the Global Agro-Ecological Zones (GAEZ) model, the potential yield and actual yield of feed and food grain in China were estimated. According to the theory of factor endowment, the yield potential development coefficient and the yield efficiency advantage index were then constructed to determine whether the current spatial layout of feed grain is reasonable and how it could be adjusted. The results showed that: (1) There was an imbalance in feed crops production: yield loss in high-potential regions and excessive development in low-potential regions. The imbalances lead to a mismatch between feed production and resource endowment which causes productivity losses and ecological risks. (2) There was considerable potential for increasing the feed grain yield on the Northeast China Plain, the Loess Plateau and in the northern arid and semiarid region. The soybean yield can be increased by about 25%, and the maize yield can be increased by even more. (3) The feed grain should be planted in regions with sufficient potential yield but insufficient actual yield; 26.42% of China’s soybeans and 34.74% of its maize were planted in these regions. (4) Some 16.69% and 15.65% of wheat and rice planting areas could be adjusted to soybeans, respectively; 20.76% and 21.04% of wheat and rice planting areas could be adjusted to maize, respectively. Through agricultural technology research and development, infrastructure support, comprehensive planning design and policy design, the yield potentials of feed grain can be realized. This will redress the imbalance wherein a food grain surplus and a feed grain shortage coexist.

1. Introduction

With the upgrading of the food consumption structure of urban and rural residents [1,2], China’s consumption of meat, egg and milk products has increased [3,4]. This has driven dramatic growth in the demand for feed grain [5]. A guarantee of the secure supply of feed grain is the basis and condition for securing the supply of animal products such as meat, eggs and milk. However, China’s supply shortage of feed grain in recent years has been gradually intensifying, and the price increase of feed grain has fueled a significant increase in the production costs for animal products [6]. More importantly, the distortion of resource allocation caused by an unreasonable food–feed grain structure continues to intensify. Dependence on imports of important food and agricultural products other than food grain continues to increase [7]. Additionally, the external circulation risks have increased because of the complexity and increased instability of international relations and the foreign trade environment [8,9,10,11]. There is an urgent need to increase the domestic feed grain supply and decrease dependence on imports whilst maintaining supply chain security [12].

There are three traditional pathways by which the supply of feed grain can be increased. The first is to increase the amount of cultivated land for feed grain. However, there is currently a severe shortage of land reserves in China and very limited supply potential due to ecological problems [13]. The second pathway is via increasing the yield of feed grain. However, the productivity of high-quality cultivated land is practically saturated at present, and there is very little scope for grain yield growth of high-standard farmland [14]. Additionally, the degree of agricultural intensification of high-quality cultivated land is high. There are outstanding soil pollution problems caused by the large-scale application of fertilizers and pesticides [15], thus hindering further intensification. While there is some potential to increase the yield of mid- and low-productivity cultivated land, the difficulties associated with reconstruction and improvement are very high. Furthermore, the mid- and low-productivity cultivated land is mainly in regions with poor natural conditions, so it is considerably constrained by temperature and water resource conditions [16], high reconstruction costs and high ecological risks [17,18]. The third pathway is to increase the multiple-cropping level of feed crops [19]. The feed crop yield could be influenced by the migration of rural labor forces, low comprehensive agricultural benefits and the withdrawal of marginal lands from cultivation [20,21]. Therefore, it is extremely difficult to increase feed grain supply through traditional pathways and under the strong constraints of China’s per capita cultivated land shortage and the strict observation of the red line of farmland [22].

Accordingly, under the premise of no increases to cultivated land inputs and means of production, new ideas are required to increase the feed crops yield and achieve the productive potential of feed crops. Spatial layout optimization of feed and food grain based on resource endowment can increase the utilization efficiency of resources and the environment [23]. This can be approached in two ways. One is to optimize the spatial layout of feed crops, that is, adding investment in high-potential regions and withdrawing it from low-potential regions. The other is to adjust the planting structure of feed and food grain according to resource endowments, that is, withdrawing food grain from relatively productive feed crops regions [24]. The background of the second approach is that the upgrading of the food consumption structure has driven the continuous decline of the direct consumption demand for food grain and the dramatic growth in the demand for livestock products. However, the adjustment of the agricultural production structure lags the structural change of agricultural product consumption demand, resulting in a domestic food surplus and a feed grain shortage. To reduce costs, feed enterprises and breeding farmers use food grain such as wheat and rice to replace feed grain such as corn and soybeans, resulting in growth in the consumption of food grain used as feed grain. Compared with feed grain, the NEG (net energy for gain) or NEL (net energy for lactation) for the food grain used as feed grain has efficiency loss. For wheat, from 2015 to 2021, the proportion of feed consumption in the total consumption increased from 6.44% to 13.68%, and the per capita feed consumption increased from 10.84 kg to 63.71 kg. However, the NEG provided by silage corn is 4.0 times that of wheat used as feed grain. The metabolic energy provided by kernel corn is 1.53 times that of wheat [25]. Therefore, under the structural contradiction of excessive food grain and insufficient feed grain, moderately adjusting food crops to feed crops will ensure the “absolute safety of food grain”, better realize the “basic self-sufficiency of grains”, increase the domestic supply of feed grain and decrease the dependence on imports.

In the present study, the potential yield and actual yield of feed and food grain in China were estimated based on the Global Agro-Ecological Zones (GAEZ) model. The yield potential development coefficient was then constructed by calculating the ratio of potential yield and the actual yield; this was used to determine whether the current spatial layout of feed grain is reasonable and how it can be adjusted. The research conclusions provide a scientific reference for the formulation of policies about the production layout of feed grain and relevant production management towards the goal of achieving a high and stable yield of feed grain. This has important strategic significance to guarantee national supply security of food and feed grain.

2. Construction of Model and Indexes

2.1. GAEZ Model

The GAEZ model is a large-scale land productivity model that was jointly developed by the Food and Agriculture Organization of the United Nations (FAO) and the International Institute for Applied Systems [26]. The GAEZ model first evaluates the spatial pattern of the agro-climatic suitability of the specific crops according to the conditions of precipitation (precipitation, relative humidity, precipitation intensity, precipitation variability) and temperature (daily average temperature, daily maximum temperature, daily minimum temperature, accumulated temperature). Then, the potential yield is calculated using the stepwise restriction method under given agro-climatic suitability, soil and terrain conditions and applying specific management assumptions and agronomic input levels. The actual yield of specific crops is calculated using a “downscaling” method for attribution of aggregate national production statistics to individual spatial units (grid cells) by applying formal methods that account for land characteristics, assess possible production options and potentially use available evidence from observed or inferred geo-spatial information, e.g., remotely sensed land cover, soil, climate and vegetation distribution, population density, etc. Potential yield is the possible upper limit to produce specific crops, and the actual yield is the actual food productivity of cultivated land. The potential yield and the actual yield of specific crops can be obtained in the GAEZ v4 Data Portal (https://gaez.fao.org, accessed on 30 November 2021).

In this study, the potential yield and actual yield of feed grains (maize and soybeans) [27] and food grains (wheat and rice) in China were estimated using the GAEZ model. The data were divided into 9 km by 9 km grids, with units of kg·hm⁻². Regarding the current agricultural management level in China, the intermediate input/management level mode was set. Additionally, regional statistics based on provinces and agricultural zones were included. Thirty-one provinces (cities and districts) in the Chinese Mainland were selected. Agricultural zones included the Northeast China Plain (Heilongjiang, Jilin and Liaoning), the Huang–Huai–Hai Plain (Beijing, Tianjin, Hebei, Shandong and Henan), the Middle-Lower Yangtze Plain (Shanghai, Jiangsu, Anhui, Hubei, Hunan, Zhejiang and Jiangxi), southern China (Guangdong, Fujian and Hainan), the northern arid and semiarid region (Xinjiang, Inner Mongolia, Ningxia and Gansu), the Loess Plateau (Shanxi and Shaanxi), the Sichuan Basin and surrounding areas (Sichuan and Chongqing), the Yunnan–Guizhou Plateau (Yunnan, Guizhou and Guangxi) and the Qinghai–Tibet Plateau (Qinghai and Tibet) (Figure 1).

The Northeast China Plain is an important grain base and animal husbandry base in China because of its flat and open terrain, fertile soil and sufficient per capita cultivated land resources. The flat terrain, fertile soil and abundant water resources in the Huang–Huai–Hai Plain provide sufficient conditions for the development of agriculture. The Middle–Lower Yangtze Plain has a beneficial temperature and water resources. It is an important aquaculture and cash crop area in China. The non-agricultural economy in southern China is highly developed, and the level of economic development and farmers’ income are in the forefront. However, due to the scarcity of cultivated land resources and low agricultural land productivity, grain self-sufficiency is extremely low. Most of the northern arid and semiarid region is desert and Gobi. The region is one of the most sensitive regions to climate change due to its fragile ecological environment and low vegetation coverage. The average annual precipitation in this area is less than 300 mm, and the evaporation rate is high, so it easily suffers drought conditions. The unfavorable terrain and location conditions of the Loess Plateau restrict the development of non-agricultural industries, and the limited cultivated land resources restrict agricultural production. The landform of the Sichuan Basin and surrounding areas is complex and mainly mountainous. The rainfall is abundant. However, floods and geological disasters occur frequently. The development of animal husbandry has good regional advantages. However, limited by scarce cultivated land resources, agricultural development is relatively slow. The Yunnan–Guizhou Plateau is characterized by complex terrain, large undulation, numerous ethnic minorities and relatively backward economic development. However, its ecological service value is high. The Qinghai–Tibet Plateau is characterized by high altitude, cold weather, undulating terrain and a fragile ecological environment. Agricultural production is dominated by traditional plateau farming and animal husbandry, and the level of urbanization and agricultural modernization is low.

2.2. Yield Potential Development Coefficient

Due to factors such as insufficient inputs, excessive inputs and unreasonable planting structures, the actual yield of feed crops is usually different from the potential yield. A comparative analysis between the potential yield ($PY$) and actual yield ($AY$) of feed crops from cultivated land is conducive to judging the potential for increasing feed productivity or the degree of over-development of cultivated land. Hence, yield potential development coefficients of feed crops were established, expressed as the ratio of $AY$ to $PY$:

$$\mathrm{RAP}=\frac{AY}{PY}\times 100\%$$

(1)

where $\mathrm{RAP}$ is the yield potential development coefficient of feed crops, $AY$is the actual yield, and $PY$ is the potential yield. When $PY$ = 0 and $AY$ > 0, feed crops are produced in inappropriate planting areas. When $\mathrm{RAP}$ < 50%, the feed crop yield is far lower than the productive potential of the cultivated land. When $\mathrm{RAP}$ is 50–150%, the feed crop yield is close to the potential yield of the cultivated land. When $\mathrm{RAP}$ > 150%, feed crop planting is at risk of excessive use of the productive potential.

2.3. Yield Efficiency Advantage Index

For agricultural production, production factors such as labor or capital can be changed, but the factors such as precipitation, temperature, soil, and terrain that have a greater impact on agricultural production are fixed and cannot be altered. According to the theory of factor endowment, a region should produce agricultural products that have relatively high production efficiency in fixed factors and exit from agricultural products that have relatively low production efficiency in fixed factors [28]. The potential yield represents the maximum land productivity that a region can achieve by producing certain agricultural products. In this paper, the potential yield advantage index ($PYAI$) is constructed to reflect the relative advantage of potential land productivity for feed grain and food grain. Correspondingly, the actual yield represents the land productivity that a region has reached in producing a certain grain. The actual yield advantage index ($AYAI$) is constructed to reflect the relative advantage of actual land productivity for feed grain and food grain. Comparing the $PYAI$ and $AYAI$ can guide the adjustment of feed grain production so that the actual yield relative advantage is as close as possible to the potential yield advantage index. Based on the $PY$ and $AY$, the potential yield advantage index ($PYAI$) and actual yield advantage index ($PYAI$) were constructed, respectively.

$$AYA{I}_{bf}=\frac{A{Y}_{bf}/A{Y}_b}{A{Y}_f/AY}\times 100\%$$

(2)

$$PYA{I}_{bf}=\frac{P{Y}_{bf}/P{Y}_b}{P{Y}_f/PY}\times 100\%$$

(3)

where $AYA{I}_{bf}$ is the $AYAI$ of Crop f in Zone b, $A{Y}_{bf}$ is the $AY$ of Crop f in Zone b, $A{Y}_b$ is the average $AY$ of all crops in Zone b, $A{Y}_f$ is the average $AY$ of Crop f in China, $AY$ refers to the average $AY$ of national crops, $PYA{I}_{bf}$ is the $PYA{I}_{ }$of Crop f in Zone b, $P{Y}_{bf}$ is the $PY$ of Crop f in Zone b, $P{Y}_b$ is the average $PY$ of all crops in Zone b, $P{Y}_f$ is the average $PY$ of Crop f in China, and $PY$ is the average $PY$ of national crops. If $AYA{I}_{bf}$ < 1 and $PYA{I}_{bf }$ < 1, the production efficiency of Crop f in Zone b is below the national average level. If $AYA{I}_{bf}$ > 1 and $PYA{I}_{bf}$ > 1, the production efficiency of Crop f in Zone b is above the national average level. Higher values indicate superior production efficiency.

2.4. Yield Efficiency Advantage Type Zoning

Based on existing studies, the comparative advantage index method was used for zoning the production efficiency of feed crops in China. The AYAI and PYAI of different crops in grid units were used as the indexes, and the production efficiency of crops was divided into four types (

Table 1. Potential yield advantage and actual yield advantage of crop zoning.

Type	Name of Type	Judgment Indexes	Basic Characteristics
I	Excessive input advantage type	AYAI ≥ 1, PYAI ≥ 1	Region with ‘excellent’ potential and actual yield
II	Excessive input disadvantage type	AYAI ≥ 1, PYAI < 1	Region with actual yield higher than potential yield
III	Insufficient input advantage type	AYAI < 1, PYAI ≥ 1	Region with sufficient potential yield and insufficient actual yield
IVI	Insufficient input disadvantage type	AYAI < 1, PYAI < 1	Region with ‘weak’ potential and actual yields

). When the AYAI and PYAI of a crop were both ≥ 1, it was considered that planting this crop in the grid had both potential advantage and actual advantage; this was classified as the excessive input advantage type (Type I). When AYAI ≥ 1 and PYAI < 1 for a crop, the actual yield from planting this crop in the grid was higher than the potential yield; this was classified as the excessive input disadvantage type (Type II). When AYAI < 1 and PYAI ≥ 1 for a crop, there was sufficient potential yield but insufficient actual yield from this crop in the grid, which was classified as the insufficient input advantage type (Type III). When the AYAI and PYAI of a crop were both < 1, planting this crop in the grid had insufficient potential yield and actual yield, which was classified as the insufficient input disadvantage type (Type IV).

3. Results

3.1. Actual Yield and Yield Potential Development Coefficient Analysis of Feed Grain

3.1.1. Characteristics of RAP of Feed Crops in Provinces of the Chinese Mainland

Given current agricultural management and operation levels, crop variety selection, mechanisation and labour force inputs, the yield potential of feed crop in China has been explored well. The average PY, AY and RAP of soybeans were 1590.00 kg·hm⁻², 1650.00 kg·hm⁻² and 103.40%, respectively. The average PY, AY and RAP of maize was 4539.98 kg·hm⁻², 4220.03 kg·hm⁻² and 93.02%, respectively (

Table 2. The AY/PY and RAP structure of soybean and maize in China (kg·hm⁻², %).

Feed Crops	PY	AY	RAP	RAP Structure
				PY = 0	RAP	RAP	RAP	RAP
				AY > 0	(0, 50)	[50, 100)	[100, 150)	[150, ∞)
soybean	1590.00	1650.00	103.40	32.79	7.16	23.74	17.16	19.16
CV	0.35	0.14	0.30	−	−	−	−	−
maize	4539.98	4220.03	93.02	35.85	5.93	31.36	14.43	12.44
CV	0.30	0.21	0.26	−	−	−	−	−

Note: CV is the abbreviation of coefficient of variation.

). This implies that, given the current input and management levels, there is limited space to increase the yield of soybeans, and the maize yield can only be increased by 6.98% (100–93.02%) of the potential yield. The future improvement of yield of soybeans and maize will depend more on high input/management level mode, such as breed improvement [29], intelligent accurate control and protecting the fertility of cultivated land.

There was an imbalance in feed crop production: yield loss in high-potential regions and excessive development in low-potential regions. As shown in Table 2, although the coefficient of variation (CV) of PY for soybeans and maize in China was 0.35 and 0.30, respectively, the AY for soybeans and maize was more balanced, and the CV was only 0.14 and 0.21, respectively. The provinces were ranked in descending order according to their PY levels for soybeans and maize. The AY values and yield potential development coefficients of provinces were also determined. The results (Figure 2) showed that in high-potential regions the yield potential development coefficients of soybeans and maize was generally insufficient: the AY was often lower than the PY, and the RAP was generally less than 100%. The RAP of soybeans was 68.00–81.00% and that of maize was 57.58–100.80%. Liaoning Province had the highest PY of soybeans and maize (2660.25 and 6600 kg·hm⁻², respectively), with RAP of 80.94% and 81.30%, respectively. Shanxi and Ningxia were the two provinces with the lowest yield potential development coefficients for soybeans and maize, with RAP values of 68.06% and 57.58%, respectively. However, they ranked sixth of the 31 provinces for PY and were both in high-potential regions. In contrast, the yield potential development coefficients of soybeans and maize in low-potential regions were higher: the AY was usually higher than the PY, and the RAP was usually greater than 100%. The RAP of soybeans was 101.83–195.56% and that of maize was 95.11–169.87%. The PY of soybeans in Guangdong Province was the lowest, but the RAP was the highest, and the AY was almost twice the PY. The RAP of maize in Shanghai was the highest, while Shanghai ranked 27th in terms of the PY of maize (2960.03 kg·hm⁻²) and 9th in terms of the AY (5040 kg·hm⁻²).

The above imbalances lead to a mismatch between feed production and resource endowment which causes productivity losses and ecological risks. The phenomenon is attributed to the low benefits arising from grain planting, the decreased proportion of agricultural income in the total household income of peasants and the transition from livelihood agriculture to supplementary agriculture. High-potential regions had outstanding resource endowment advantages for feed crops planting, with relatively high yield and output values being achievable with relatively low production inputs. However, increasing inputs could incur the risk of reduced marginal yields. To maximise family income, peasant households are more willing to input more labour and production resources into non-agricultural employment—which has higher marginal income—and to maintain the highest marginal output of feed grain by decreasing the irrigation times and production inputs. In low-potential regions, the resource endowment constraints for feed crop planting were increased. However, the input and output prices of feed crop planting are decided by the market, without obvious differences for those in high-potential regions. Given the same inputs, the lower yield and output value of feed grain are insufficient to pay for the inputs. Against a background of increasingly strict management of farmland abandonment and highlighting agricultural guarantee functions, peasant households must explore feed grain potential production fully to achieve relatively high yields in low-potential regions.

3.1.2. Characteristics of RAP of Feed Crops in Different Agricultural Regions

To determine regional differences in the yield potential development coefficient of feed grain in China, AY and PY values of feed grain in different agricultural regions were compared. Agricultural regions were ranked in descending order of PY for soybeans and maize (

Table 3. The AY/PY and YPDC structure of soybeans and maize in China (kg·hm⁻², %).

Feed Crops	Agricultural Regions	PY	AY	RAY	RAY Structure
					RAY	RAY	RAY	RAY	PY = 0
					(0 50)	[50 100)	[100 150)	[150 ∞)	AY > 0
soybeans	the Northeast China Plain	2439.98	1850.03	75.82	4.81	63.18	4.56	3.77	23.68
	the Loess Plateau	2010.00	1490.03	74.13	2.02	27.92	27.95	20.84	21.27
	the northern arid and semiarid region	1850.03	1419.98	76.76	1.4	6.25	28.18	34.59	29.58
	the Huang–Huai–Hai Plain	1650.00	1839.98	111.52	5.02	3.41	20.43	47.52	23.62
	the Yunnan–Guizhou Plateau	1209.98	1470.00	121.49	29.14	23.31	5.38	4.27	37.89
	the Middle-Lower Yangtze Plain	1179.98	1779.98	150.85	4.7	36.91	9.98	1.53	46.87
	the Sichuan Basin and surrounding areas	1100.03	1550.03	140.91	0.89	9.89	27.43	29.78	32.02
	the Qinghai–Tibet Plateau	1040.03	1460.03	140.38	3.84	10.47	16.65	20.27	48.77
	southern China	830.03	1470.00	177.11	38.24	5.88	11.76	5.88	38.24
	China	1590.00	1650.00	103.77	7.16	23.74	17.16	19.16	32.79
maize	the Loess Plateau	6090.00	4350.00	71.42	1.59	43.15	6.29	0.92	48.05
	the Huang–Huai–Hai Plain	5760.00	5370.00	93.34	2.41	43.31	21.95	9.7	22.63
	the Northeast China Plain	5490.00	4590.00	83.59	2.59	62.29	5.43	3.98	25.71
	the northern arid and semiarid region	5220.00	3650.03	69.85	12.02	32.03	6.61	5.5	43.84
	the Middle-Lower Yangtze Plain	3770.03	4640.03	123.05	8.58	18.66	20.67	22.31	29.77
	the Sichuan Basin and surrounding areas	3459.98	4100.03	118.42	0.49	21.06	20	22.27	36.18
	the Qinghai–Tibet Plateau	3230.03	4179.98	129.35	19.85	0.59	0.3	0	79.26
	the Yunnan–Guizhou Plateau	3120.00	3350.03	107.47	2	14.71	18.84	14	50.45
	southern China	2540.03	3480.00	137.03	12.98	10.18	22.22	30.28	24.34
	China	4539.98	4220.03	93.02	5.93	31.36	14.43	12.44	35.85

). Notably, there was considerable potential for increasing the feed grain yield on the Northeast China Plain, the Loess Plateau and in the northern arid and semiarid region. These three regions ranked as the top three in China in terms of the PY for soybeans, at 2439.98, 2010.00 and 1850.03 kg·hm⁻², which was 849.98, 420.00 and 260.03 kg·hm⁻² higher than the national average production level, respectively. However, there was a gap between the AY and PY of soybeans in these three regions; the RAP of these three regions was about 75%, indicating that there was still the potential for an approximately 25% increase in soybean yield. Similar characteristics were observed for the PY and RAP of maize in these three agricultural regions. The RAP of maize in the northern arid and semiarid region was only 69.85%, and the maize yield could be increased by 1569.98 kg·hm⁻². The PY of maize in the Loess Plateau was 6090.00 kg·hm^–2, the AY was only 4350.00 kg·hm⁻² and the RAP was only 71.42%. Thus, the maize yield could potentially be increased by 1740.00 kg·hm⁻². Similarly, the Northeast China Plain has the potential for increasing the maize yield by 900 kg·hm⁻².

There are two reasons for the low yield potential development coefficient of feed grain in the Northeast China Plain, the Loess Plateau and the northern arid and semiarid region. First, feed grain was planted in inappropriate regions. In the Northeast China Plain, the Loess Plateau and the northern arid and semiarid region, 23.68%, 21.27% and 29.58% of soybeans were planted in inappropriate areas, as was 25.71%, 48.05% and 43.84% of maize, respectively. The resource mismatching of maize was more serious. Second, there were insufficient inputs in high-potential regions. The RAP was 63.18% for soybeans and 62.29% for maize on the Northeast China Plain, which was far higher than the national average level. The proportion of the Northeast China Plain with a RAP value greater than 100% was 8.33% (4.56% + 3.77%) for soybeans and 9.41% (5.43% + 3.98%) for maize, which was far lower than the national average level (Table 3).

3.2. Yield Efficiency Advantage Index and Planting Structural Layout Optimisation Schemes for Feed Grain

3.2.1. Spatial Pattern of Yield Efficiency Advantage Indexes of Feed Grain

The proportion of the grids for which the PYAI and AYAI values for soybeans and maize was ≥1 in the 31 provinces was calculated. The denominator of these proportions excluded grids with yield indexes of zero. A higher proportion indicated that the province had a stronger advantage in planting the crop. As shown in

Table 4. The proportion of the grids with the PYAI and AYAI values for soybeans and maize > 1 in provinces of China (%).

Provinces (Cities and Districts)	Soybeans		Provinces (Cities and Districts)	Maize
	PYAI	AYAI		PYAI	AYAI
Jilin	95.32	54.53	Jilin	87.67	57.59
Liaoning	89.02	71.86	Liaoning	86.39	71.95
Heilongjiang	85.43	44.05	Shaanxi	85.88	72.58
Inner Mongolia	84.59	72.63	Beijing	85.29	94.03
Yunnan	78.65	90.62	Hebei	80.58	48.65
Tibet	66.67	100	Inner Mongolia	78.51	79.75
Hainan	65.42	42.07	Shanxi	77.6	60.64
Shaanxi	55.32	72.23	Shandong	74.95	24.15
Shanxi	54.84	57.24	Heilongjiang	71.27	54.1
Ningxia	54.24	46.56	Henan	67.44	48.88
Xinjiang	53.43	16.73	Xinjiang	64.26	43.28
Sichuan	50.24	89	Ningxia	57.99	61.28
Guizhou	45.61	92.69	Guizhou	56.61	92.09
Chongqing	42.01	99.45	Sichuan	54.13	90.42
Gansu	41.34	49.76	Jiangxi	52.84	50.48
Hebei	33.15	42.83	Guangxi	51.17	64.46
Shandong	28.94	24.03	Chongqing	50	98.66
Hubei	28.08	91.8	Hunan	49.81	84.83
Fujian	25.77	39.13	Gansu	48.77	57.04
Beijing	22.06	92.45	Hubei	47.68	97.52
Hunan	17.54	83.67	Tianjin	39.88	42.86
Zhejiang	15.82	64.83	Fujian	37.59	35.51
Henan	11.66	47.17	Jiangsu	29.39	71.19
Guangxi	11.48	64.36	Zhejiang	28.52	84.19
Anhui	10.33	66.73	Anhui	28.09	93.73
Jiangxi	10.32	60.35	Guangdong	27.69	36.53
Guangdong	6.01	36.64	Yunnan	12.5	89.9
Qinghai	5.56	50	Shanghai	11.54	45
Jiangsu	4.49	21.12	Hainan	8.1	26.03
Tianjin	3.47	50	Qinghai	0.9	69.23
Shanghai	1.28	11.11	Tibet	0	96.61

, for soybeans, the potential yield advantage regions determined by natural resource endowment included three provinces in Northeast China, Inner Mongolia and other regions in northern China, while actual yield advantage regions included Sichuan, Chongqing, Hunan, Hubei, Yunnan, Guizhou and other regions in southern China. For maize, potential yield advantage regions included Jilin, Liaoning, Shaanxi, Inner Mongolia and the Shanxi–Chahar–Hebei regions, while actual advantage regions included the Yunnan–Guizhou Plateau, Hunan, Hubei, Sichuan, Chongqing, Anhui and Zhejiang provinces. The soybean and maize advantage regions in terms of PY and AY had large-scale spatial overlap, and there was competition between soybeans and maize for production space. Additionally, both soybeans and maize had imbalances of high PYAI values in northern China and high AYAI values in southern China.

3.2.2. Planting Layout Adjustment and Optimization Scheme of Feed Grain

The yield efficiency advantage type zones of soybeans and maize are shown in Figure 3. For soybeans, there were few grids of Type I, accounting for only 1.12% of all four types of grids, due to the imbalance between yield loss in high-potential regions and excessive development in low-potential regions. These grids were mainly distributed in the Northeast China Plain and the Loess Plateau. Type II—that is, excessive input disadvantage regions—and about 30.12% of soybean planting areas have higher AYAI than the PYAI. These were mainly distributed in the Yunnan–Guizhou Plateau, the northern arid and semiarid region, as well as the Middle-Lower Yangtze Plain. Type III grids—that is, the insufficient input advantage region—and about 26.42% of soybean planting areas have space to increase the yield. These were mainly distributed in the Northeast China Plain and the northern arid and semiarid region. Type IV was the insufficient input disadvantage region, accounting for 42.34%. The yield efficiency advantage type structure and spatial layout of maize were extremely like those of soybeans, which further proved that there was competition between soybeans and maize for production space. Notably, the Type III region has sufficient PY but insufficient AY and is the feasible region to increase feed grain supply based on inventory farmland in the future. Furthermore, 26.42% of soybeans and 34.74% of maize was produced in the Type III region on a large scale, thus providing considerable potential for yield growth.

3.2.3. Layout Adjustment and Optimization Schemes between Feed Grain and Food Grain

Optimising the planting structural layout of feed grain and food grain is conducive to releasing the yield potentials of feed grain. This study revealed competition for production space between soybeans and maize. Therefore, it is very difficult to achieve the productive potential of feed grain by adjusting the planting structural layouts of soybeans and maize; a more feasible approach is to optimise the planting structural layout of both feed grain (mainly soybeans and maize) and food grain (mainly wheat and rice) by planting feed grain on the cultivated land that originally produced food grain but was used as feed grain to optimise structures of feed and food grain. The overall goal is to decrease imports of feed grain. This study identified that if a region was both Type III of feed grain and Type IV of food grain, this region would have advantages for feed grain but no advantages for food grain. Furthermore, the actual yield efficiency advantage of feed grain in this region was still not pronounced, and there was still some space for improvement. Based on comprehensive consideration, this region would be a key region for transformation from food grain to feed grain. According to the statistics, 16.69% and 15.65% of wheat and rice planting areas could be adjusted to soybeans, respectively. For maize, 20.76% and 21.04% of wheat and rice planting areas could be adjusted to maize, respectively (

Table 5. The transfer matrix of different types between feed grain and food grain (%).

Crops		Wheat				Rice
		Type I	Type II	Type III	Type IVI	Type I	Type II	Type III	Type IVI
soybeans	type I	0.07	0.08	0.51	0.47	0.16	0.02	0.18	0.77
	type II	0.02	0.00	0.28	29.82	0.61	0.01	0.06	29.44
	type III	0.97	0.69	8.08	16.69	0.09	0.03	10.65	15.65
	type IV	1.56	1.92	19.46	19.39	0.32	0.03	22.24	19.74
maize	type I	0.80	0.60	0.48	0.46	0.01	0.00	0.57	1.76
	type II	0.69	0.66	0.25	33.70	0.03	0.00	0.57	34.69
	type III	0.48	0.36	13.14	20.76	0.38	0.07	13.25	21.04
	type IV	0.66	1.07	14.45	11.45	0.75	0.02	18.75	8.11

).

In terms of space, considering that a region may not only be suitable for the transformation from grain to soybeans, but also suitable for the transformation from grain to corn, a new judgment standard was added to avoid repeated calculations. Taking soybeans and wheat adjustment as examples, if a region was both Type III of soybeans and Type IV of wheat, and PYAI_soybean > PYAI_maize, it is better to adjust wheat to soybeans. Judgment criteria on whether adjustments from rice to soybeans, from wheat to maize or from rice to maize were better could be similarly inferred. The results (Figure 4) showed that grids appropriate for adjustment from wheat to soybeans were concentrated in northern Xinjiang, the Hexi Corridor, the Fen–Wei Plain, the Shanxi–Hebei–Inner Mongolia intersection area and the Jiaodong Peninsula. A few grids were appropriate for adjustment from rice to soybeans and were mainly concentrated in Yunnan and Fujian provinces. Grids appropriate for adjustment from wheat to maize were mainly concentrated in northern Xinjiang, the Huang–Huai–Hai Plain as well as the Middle-Lower Yangtze Plain. Grids appropriate for adjustment from rice to maize were concentrated in Fujian and southern Jiangxi, with scattered distributions in Guangdong and Guangxi provinces.

4. Discussion and Conclusions

4.1. Discussion

The spatial layout optimization scheme of feed grain and food grain based on re-source endowment can decrease dependence of feed grain on imports appropriately. With the upgrading of the food consumption structure, dramatic growth in the demand for feed grain has become a major factor that facilitates food consumption in China. In 2021, China imported 165 million tons of grain. Specifically, soybean imports reached 96.52 million tons, accounting for 58.50% of total imports. Corn imports reached 28.35 million tons, accounting for 17.18% of total imports. Soybean and corn imports account for about 75% of total imports. In the face of increasing feed grain demands and strengthening constraints of cultivated land resources, some studies [6,30,31] have considered that increasing domestic supply of feed grain is a way to decrease dependence on imports. However, with the increasing openness of agriculture to world trade, the international trade strategy of feed grain changes from a supply–demand gap to a difference-in-price gap [32]. The decisive role of difference-in-price between China and foreign countries in feed grain imports has been strengthened gradually. In fact, soybean and corn prices in China have broken the “ceiling” of the international price, and tariff and quota protections have been lost, which causes a sharp growth in imports. Driven by difference-in-price, breeding farmers or feed processing enterprises may also choose imports of feed grains even though domestic supply is increased. Increasing supply of feed grain but with high prices makes it difficult to change the high dependence on imports. However, the optimization scheme in this study can not only improve the distortion of the spatial layout of feed grain and resource endowments, explore potential yield and increase the production of feed grain fully, it can also increase resource utilization, decrease production cost and price of feed grains effectively, narrow differences in price between China and foreign countries, decrease imports and relieve the contradiction between the simultaneous growth of production and the import of feed grain effectively.

Different from the existing research on the distortion of grain production and farmland resources [23], this paper further proposed an optimization scheme and possible productivity improvement. However, it is worth noting that the optimization scheme is highly planned. Its effective implementation is faced with many practical challenges. First is the resistance brought by the inconsistent goals of the government and farmer households. The primary goal of policy regulations or plans of food safety issued by the government is often to realize “supply guarantee”, whereas the primary goal of farmer households is to realize “income guarantee”. The optimization scheme is mainly proposed according to actual yield and potential yield, and its goal is to maximize resource utilization and increase feed grain yield. This is consistent with the goal of “supply guarantee” emphasized by the government. However, the spatial layout of feed grain and planting structural adjustment from food grain to feed grain which are advocated in the proposed optimization scheme are hindered by the planting habit viscosity of farmer households. With the reduction of the portion of agricultural income to total income in farmer households, the motivation for farmer households to adjust the planting structure automatically according to resource endowment becomes increasingly insufficient. Additionally, adjusting planting structure implies the loss of old productive material and increased cost for new productive material. Above all, high yield attributed to the adjustment of planting structure does not mean high benefit. Increasing yield under the premise of slight changes in demand will cause prices to fall, thus influencing farmer willingness to adjust planting structure. The proposed optimization scheme cannot assure “income guarantee”. However, whether the goal of “income guarantee” can be realized determines whether the goal of “supply guarantee” can be realized. Only by realizing the goal of “ensuring income” can we stimulate the enthusiasm of farmers to plant feed crops and achieve the goal of “ensuring supply” by expanding feed grain area or increasing the yield of feed grain. Therefore, the proposed optimization scheme requires cooperation of other price support policies to assure simultaneous realization of “income guarantee” and “supply guarantee”.

Additionally, the proposed optimization scheme ignores the situation of multiple cropping. It is completely applicable to regions adopting the single-cropping system, especially in the agricultural areas such as the Northeast Plain, the Loess Plateau and the northern arid and semi-arid areas, which can achieve nearly one-third of the increase in feed grain production. However, winter wheat and early indica rice are often planted as supplementary crops in regions where implementing the multi-cropping system is not possible. Winter wheat is produced for its overwintering and early maturing characteristics that do not interfere with the next planting system. Under this circumstance, there is no way to adjust wheat into feed crops. To adjust food grain into feed grain in these regions, we must develop new feed grain varieties with short growth periods and early maturation periods through technologies such as biological breeding and replace the food-grain–feed-grain system with the feed-grain–food-grain system.

4.2. Conclusions

Increasing feed grain supply, particularly domestic supply, is intended to guarantee feed grain security and, as a result, food security. Given current inputs and management levels, there is limited space to increase the yield of soybeans, and the maize yield can only be increased by 6.98% of the potential yield. In the long-term, the future improvement of yield of soybeans and maize will depend more on high input/management level mode, such as breed improvement, intelligent accurate control and protection of the fertility of cultivated land. In the short-term, optimising spatial patterns of feed grain and food grain based on resource endowment and increasing resource potential development levels will be effective ways of increasing the feed grain yield; this is based on inventory farmlands against a background of strengthening farmland constraints and increasing demand for feed grain.

This study found that there is an imbalance in feed crop production: yield loss in high-potential regions and excessive development in low-potential regions. The above imbalances lead to a mismatch between feed production and resource endowment which cause productivity losses and ecological risks. According to the yield potential development coefficient analysis, there is considerable potential for increasing the feed grain yield on the Northeast China Plain, the Loess Plateau and in the northern arid and semiarid region. The soybean yield can be increased by about 25%, and the maize yield can be increased by even more. In addition, the results of AYAI and PYAI show that both soybeans and maize have imbalances of high PYAI values in northern China and high AYAI values in southern China. The feed grain should be planted in regions with sufficient potential yield but insufficient actual yield. Furthermore, 26.42% of China’s soybeans and 34.74% of its maize were planted in these regions, where there was also sufficient space to increase the yield of soybeans and maize.

Additionally, the soybean and maize advantage regions in terms of PY and AY had large-scale spatial overlap, and there was competition between soybeans and maize for production space. Therefore, it is very difficult to achieve the yield potential of feed grain by adjusting the planting structural layouts of soybeans and maize; a more feasible approach is to optimise the planting structural layout of both feed grain and food grain by planting feed grain on the cultivated land that originally produced food grain but was used as feed grain, thereby increasing resource allocation efficiency. According to the statistics in the present study, 16.69% and 15.65% of wheat and rice planting areas could be adjusted to soybeans, respectively; 20.76% and 21.04% of wheat and rice planting areas could be adjusted to maize, respectively. Regions where it is appropriate to adjust from wheat to soybeans were concentrated in northern Xinjiang, the Hexi Corridor, the Fen-Wei Plain, the Shanxi–Hebei–Inner Mongolia intersection area and the Jiaodong Peninsula. There were small areas where it is appropriate to adjust from rice to soybeans, which were mainly concentrated in Yunnan and Fujian provinces. Regions for which it is appropriate to adjust from wheat to maize were mainly concentrated in northern Xinjiang, the Huang–Huai–Hai Plain as well as the Middle-Lower Yangtze Plain. Regions for which it is appropriate to adjust from rice to maize were concentrated in Fujian and southern Jiangxi provinces.

Developing endowment advantages and resource potential through layout optimisation is an important basis for the industrial development of feed grain. In the long-term, the yield could be increased by depending more on high-level inputs and management modes, such as seed research and development, accurate intelligent agricultural development, soil improvement and restoration, etc. In the short-term, one issue that must be solved is the spatial mismatching of feed grain. In high-potential regions, it is suggested that infrastructure and supporting conditions be optimised and that production aids, such as irrigation, fertilisation and weed control, be further strengthened to encourage peasant households, especially part-time peasant households, to increase their input to feed grain production. In low-potential regions, it is recommended that the development and application of high-efficiency varieties and resource-saving agricultural technologies be accelerated and that ecological risks that could be caused by excessive development of feed grain be avoided as much as possible. Another short-term requirement is the structural adjustment from food grain to feed grain. Policy design must be based on an all-encompassing approach to food and prioritise food security, considering complementarity, substitutability and spatial competitiveness among crops. Furthermore, regions in which policies are to be implemented must fully consider the resource endowment advantages of crops. Through comprehensive planning design, the spatial layout of feed grain and food grain should be coordinated and agricultural policies formulated as decrees. This will redress the imbalance wherein food grain surplus and feed grain shortage coexist.