(d) Validation of Soil Available Nutrient Tests The relevant studies in soil tests have determined the available nutrient extractants for certain types of soils. The soil effective nutrient test values ​​and the crops' nutrients extracted by the extractants have been determined. There is a good correlation between the absorption or relative absorption, or vice versa, when there is no good correlation between the two, this extractant cannot be applied to such soils. Since this is only a relevant study, it cannot be pointed out whether the level of available soil nutrient levels tested is sufficient or lacking for crops. The latter is to be completed by a validation study of the soil's effective nutrient tests.
The purpose of the inspection study is to divide the measured values ​​of soil available nutrients into "abundant", "middle" and "low" indicators based on the actual yield responses of the crops to the field. The necessity of this work is also related to the concept of relative relativity of soil nutrient content. For the same soil, when extracting with different extractants (assuming that these extractants are all applicable), the effective soil nutrient content extracted by them is likely to be different, and some extractants have higher test values. Some test values ​​are lower, and this difference certainly cannot reflect the level of effective soil nutrients in this soil, but can only be regarded as belonging to the same level of content without any difference. Similarly, if the effective nutrient test value of the same soil is used as a reference standard for different crops, the same nutrient content of the same test will be applied to a crop because of the physiological characteristics of the crop and their ability to absorb nutrients from the same soil is different. It may be enough, but it may not be enough for another crop. The above situation can be illustrated by the examples in Table 10-10.
Table 10-10 Soil Available Phosphorus Test and Abundance Level in Fluvo-aquic Soil in Beijing Suburbs
Soil sample number
Test value (P 2 O 5 mg/kg)
Abundance
Olsen method
Bray I method
wheat
tomato
1
2
3
4
5
55
33
25
15
5
97
48
46
30
12
Very high
high
in
low
Extremely low
in
in
low
Extremely low
―
For the effective phosphorus extraction of fluvo-aquic soils in Beijing suburbs, the Bray I method is not as good as the Olsen method. Here it is only used as an example. Since the available soil P extracted by the Bray I method is higher than the Olsen method, there is no reason to believe that the 97 mg/kg P 2 O 5 in the No. 1 soil sample is higher than 55 mg/kg P 2 O when comparing the two methods. 5, the difference between them is meaningless from the soil test. Similarly, the level of available phosphorus in soil No. 1 is already extremely high for wheat without the need for fertilization, but it is still a moderate level for tomato, and fertilization is still necessary. Therefore, the extraction test value of any soil available nutrient, if not graded through the calibration study, is not useful for guiding fertilization.
The so-called abundance of soil available nutrients refers to the extent to which the soil satisfies the nutrient requirements of a certain crop at a certain level of yield. Generally, the degree of soil nutrient availability is divided into three levels of “lowâ€, “medium†and “highâ€, or “very lowâ€, “lowâ€, “mediumâ€, “high†and “very highâ€. The basis for the division is the relative production of crops. When the relative crop yield is below 75%, the effective soil nutrient level in the soil is “lowâ€; when the relative crop yield is between 75% and 95%, the soil effective nutrient level is “middleâ€; the relative yield is greater than 95%. At this time, the effective soil nutrient level is a high grade. When divided by five grades, relative crop yield <55% is extremely low, between 55%-75% is low, between 75%-95% is medium, between 95%-100% is high,> 100% is Extremely high.
The relevant studies of soil nutrient content are generally conducted using potted plants, while the validation studies of soil effective nutrient tests must be conducted in the field. Select more than 20 test sites within the same soil type range, and the soil fertility between the test sites should be sufficiently different. The experiment was based on four treatments without nitrogen, phosphorus, potassium, and fertilizer (other nutrients should be kept at a sufficient level), with 3-4 repetitions. The ratio of crop yields in crops with a lack of nutrients to total crop yields is calculated as:
Relative yield = no nitrogen (or phosphorus-free, potassium-free) regional crop yield / total fertilizer crop yield × 100
Taking the relative yield as the vertical half standard, and the effective nutrient extraction test value as the horizontal curve, the mathematical model of the curve generally uses Y=a+blgX, which is in line with the principle of the Miez yield curve. Li Chengxu et al. (1985) conducted a validation study of soil available phosphorus (Soil Olsen method) tests in the salinized fluvo-aquic region of Heilonggang River Basin, Hebei Province. The crops were winter wheat. The calibration curve obtained is shown in Figure 10-7. The test curve can be used to classify the level of soil available phosphorus in the area as low, medium and high.
As the availability of nutrients in the soil is related to the nutrient requirements of the crops, the nutrient requirements of different crops are different. The classification of soil available nutrients should also be different. A set of grading indicators for soil available nutrients is only for a specified crop, and the indicators for other crops should be determined by separate experiments. In the calibration study, the tested crops are "targets," and the relevant crops in the relevant studies are "methods."
The use of the relative output of the ratio of nutrient-depleted treatment to total fertilizer treatment as the basis for valid grading of soil nutrients has the advantage that the design is simple and easy to obtain and the calibration results are easy to obtain; the disadvantage is that total fertilizer treatment is not necessarily due. The highest output. In view of this, Lv Dianqing (1987) proposed to replace the three-factor test with a multivariate fertilizer effect test with 3-5 fertilizers. Through the establishment of the fertilizer effect agenda, the nutrient treatment yield and the theoretical maximum yield can be calculated and calculated using these calculations. The relative grade of production and soil nutrient test values. According to this test data, the ideal maximum yield can be obtained, but care must be taken to select the amount of fertilizer used in the trial to prevent excessive extrapolation of the maximum yield value.
Another verification method is the threshold method. After the effective nutrient content method was selected, the dot distribution map between the relative crop yield and the test value was obtained through multi-point field experiments. A cross was drawn in the middle of the dot distribution map, and almost all the points were divided into the lower left and the upper right. In quadrants. At this point, the intersection of the vertical line and the abscissa is the critical value.
Figure 10-8 is an example of the determination of the critical value of response between soil available phosphorus and corn grain relative yield in upland soil of red soil.
According to Lu Yunxi et al. (1987), according to Fig. 10-8, the Bray 1 extraction method for extracting available P from soil is valid for corn in red soils with a critical value of 8 mg/kg (P). In soil tests, phosphate must be applied to soil below this value.
Yu Cunzu et al. (1984) conducted a validation study of the available manganese content in the loess area and wheat yield increase. The available Mn in the soil layer of the area is between 1.4-32 mg/kg (DTPA extraction), with an average of 7.6 mg/kg ± 0.5 mg/kg, based on Lindsay's proposed threshold of 1 mg/kg of soil available manganese, In the loess area, there is basically no shortage of manganese in the soil. However, in fact, manganese production in many areas in the area has a good effect of increasing production. It is reasonable for the calibration study to set the threshold value of soil available manganese to 7 mg/kg. For soils with a low fertility level of less than 2250 kg/ha, the soil may be set at 5 mg/kg. This also proves the necessity of conducting calibration studies in various regions based on local conditions such as soil, climate and crops.
According to the investigation and study on the content of trace elements in the soil of 7 provinces (autonomous regions) in the loess area, Yu Cunzu et al. (1984) proposed the grading indicators applicable to the content of several trace elements in the soil of the region as shown in Table 10-11. Among them, soil available zinc, manganese, copper, and iron were tested using DTPA extraction, flame atomic absorption spectrophotometry, soil water-soluble boron extracted with boiling water, curcumin colorimetric method, and soil available molybdenum extracted with oxalic acid-ammonium oxalate solution. Polarography.
Table 10-11 Grading Indicators of Soil Microelement Content in the Loess Region (mg/kg)
element
Very scarce
lack
insufficient
Proper amount
rich
Critical value
Zinc
manganese
copper
molybdenum
iron
boron
< 0.3
< 3
< 0.2
< 0.05
< 2.5
< 0.2
0.3-0.5
3-7
0.2-0.5
0.05-0.10
2.5
0.2-0.5
0.5-1.0
7-9
0.5-1.0
0.10-0.15
4.5
0.5
1-2
9-15
1-2
0.15-.20
4.5-10
1
> 2
> 1.5
> 2
> 0.2
> 10
> 1
0.5
7
0.5
0.1
4.5
0.5
A critical value study of trace elements in acidic soils in southern China demonstrated that when citrus was used as a test crop, the critical value of DTPA for zinc extraction was 0.46 mg/kg, copper was 0.2 mg/kg, and manganese was 1 mg/kg. Iron is 4.6 mg/kg (Panburg, 1987)â€
According to the results of the National Collaboration Study during the “6th Five-Year Plan†period, indicators of soil nutrient abundance in China's major farmland soils are listed in Table 10-12, Table 10-13, and Table 10-14.
Table 10-12 Nitrogen grading indicators for different soil types (nitrogen, mg/kg)
(Alkaline nitrogen solution was determined by 1.6-mol/l NaOH alkali solution diffusion method)
Soil type
low
(< 75%)
in
( 75%-95% )
high
(< 95%)
Prepare
Black soil
Meadow soil
Chao Soil (Beijing)
Salinized Chao Soil
Grey desert soil
Irrigation silt
Yellow soil
Purple soil
Brown earth
Cinnamon
Chao Soil (Shandong)
Red Earth (Guangxi)
Red soil paddy soil (Fujian)
Red soil paddy soil (Guangxi)
Purple Purple Paddy Soil (Shanghai)
Meadow paddy soil (Jilin)
Chengdu plain paddy soil
Hangjiahu Paddy Soil
Hunan medium-acid paddy soil
< 120
< 130
< 80
< 30
< 70
< 90
< 60
< 170
< 55
< 55
< 70
< 170
< 150
< 160
< 200
< 70
< 90
< 175
< 100
< 120
120-250
130-240
80-130
30-50
70-100
90-120
60-80
170-260
55-90
55-100
70-90
170-380
150-260
160-200
200-400
70-220
90-250
175-280
100-190
120-210
> 250
> 240
> 130
> 50
> 100
> 120
> 80
> 260
> 90
> 100
> 90
> 380
> 260
> 200
> 400
> 220
> 250
> 280
> 190
> 210
wheat
corn
wheat
wheat
wheat
wheat
wheat
wheat
wheat
wheat
corn
corn
Rice
Rice
wheat
Rice
Rice
Rice (flooding method)
Early rice
Late rice
Table 10-13 Classification index of soil available P in different soil types (P, mg/kg)
Soil type
low
(< 75%)
in
( 75%-95% )
high
(< 95%)
Prepare
Black soil
Meadow soil
Chao Soil (Beijing)
Salinized Chao Soil
Grey desert soil
Irrigation silt
Yellow soil
Purple soil
Brown earth
Cinnamon
Chao Soil (Shandong)
Red Earth (Zhejiang)
Red Earth (Guangxi)
Red soil paddy soil (Fujian)
Red soil paddy soil (Guangxi)
Purple Purple Paddy Soil (Shanghai)
Meadow paddy soil (Jilin)
Chengdu plain paddy soil
Hangjiahu Paddy Soil
Hunan medium-acid paddy soil
< 4
< 2
< 2
< 4
< 4
< 4
< 4
< 4
< 10
< 2
< 6
< 8
< 4
< 6
< 2
< 4
< 5.5
< 2
< 2
< 3
< 1
4-10
2-25
2-12
4-9
4-8
4-9
4-7
4-10
10-25
2-9
6-19
8-20
4-10
6-17
2-10
4-16
5. 5-17
2-8
2-11
3-10
1-14
> 10
> 25
> 12
> 9
> 8
> 9
> 7
> 10
> 25
> 9
> 19
> 20
> 10
> 17
> 10
> 16
> 17
> 8
> 11
> 10
> 14
wheat
corn
wheat
wheat
wheat
wheat
wheat
wheat
wheat
wheat
corn
Corn Bray-1
corn
Rice
Rice
wheat
Rice
Rice
Rice
Early rice
Late rice
Note: Soil available phosphorus is extracted with 0.5 mol/l NaHCO 3 (Olsen method)
Table 10-14 Classification index of soil available potassium in different soil types (K, mg/kg)
Soil type
low
(< 75%)
in
( 75%-95% )
high
(< 95% =
Prepare
Black soil
Meadow soil
Chao Soil (Beijing)
Brown earth
Cinnamon
Chao Soil (Shandong)
Yellow soil
Purple cinnamon soil
Red Earth (Zhejiang)
Red Earth (Guangxi)
Red soil paddy soil (Fujian)
Red soil paddy soil (Guangxi)
Soil Purple Purple Rice Soil (Shanghai)
Meadow paddy soil (Jilin)
Chengdu plain paddy soil
Hangjiahu Paddy Soil
Hunan medium-acid paddy soil
< 70
< 95
< 60
< 50
< 30
< 40
< 80
< 135
< 80
< 60
< 60
< 20
< 60
< 50
70-150
95-180
60-180
50-85
30-85
40-115
110
65
80-180
135-280
80-180
60-150
100
60-150
35
20-150
60-105
50-80
> 150
> 180
> 180
> 85
> 85
> 115
> 180
> 280
> 140
> 150
> 170
> 150
> 105
> 80
wheat
Corn wheat
wheat
wheat
wheat
corn
wheat
wheat
corn
corn
Rice
Rice
wheat
Rice
Rice
Rice
Early rice
Late rice
Note: Soil available potassium is extracted with 1 Mol neutral NH 4 OHC.
(5) Calculation of several parameters in field calibration test
Field validation tests of soil nutrient availability are not only used to classify the available nutrient test values, but may also be used to obtain a set of recommended fertilization parameters.
1. The experimental design is the simplest, and the more practical design is the NPK fertility determination test, which is to select the test sites (at least 20) with different soil fertility within the scope of the main farmland in the region. of:
Nitrogen, phosphorus and potassium three factors fertility determination test:
Treatment 1 blank area (without fertilization)
Treatment 2 Nitrogen-free area (without applying nitrogen fertilizer, other fertilizer application)
Treatment 3 Non-phosphorus area (without phosphorus, other fertilizers applied)
Treatment 4 Potassium-free zone (do not apply potassium, other fertilizers apply)
Treatment 5 Fertilizer Area (N, P and K Fertilizers Are Applied)
No organic fertilizer was applied in the test area to avoid interfering with the effects of chemical fertilizers. The amount of chemical fertilizers was used to strive for high yields in the whole fertilizer area. When there are enough test points, no repetition is required. Other requirements are the same as those for routine tests.
Before the harvest or the fertilization before taking the basic soil samples. The analysis of basic soil samples, in addition to routine items, should determine the soil available N, P and K contents of the selected soil.
At the end of the experiment, the plots were used to measure the yield in the plot, test and plant samples were taken and converted into hectares of output and hectares of biomass (in total). Analysis of plant samples in the whole fertilized area and blank area. Plants measured total nitrogen, phosphorus and potassium. Nitrogen-free plants measured total nitrogen. Plants without phosphorus measured total phosphorus. Potassium-free plants measured total nitrogen. The percent of nitrogen, phosphorus, and potassium determined by plant analysis × total hectares per hectare was the NPK uptake per hectare.
2. Demarcation of calibration classification In order to divide the effective soil nutrient content in the region into high, medium and low, the relative yield (%) is first calculated. The test values ​​of available nitrogen (or phosphorus, potassium) in the soil samples of the 20 test sites and the relative yields of nitrogen-free (or phosphorus, potassium) treatments were plotted on squared paper, and the ordinates were relative production (%). The coordinates are measured in soil (mg/kg). According to the distribution trend of scattered points on the graph, logarithmic or other curve agendas are used for fitting, and the values ​​calculated on the agenda are plotted on the graph. The experienced staff can also draw a curve directly on the map according to the trend of the curve. From the figure, the relative yields 100%, 95%, 75%, and 55% are parallel to the abscissa and the ruler line intersects the calibration curve, the intersection point is perpendicular to the abscissa, and the measured values ​​on the ruled line and the abscissa are measured. intersect. The relative nutrient content of soil with “<55% relative yield†is “very lowâ€, the same amount, relative output 55%-75% is “lowâ€, 75%-95% is “mediumâ€, 95%-100% is “ High, ">100% Relative yield is "very high", and their corresponding soil measurements are the soil's effective nutrient content. Table 10-15 shows the classification of soil fertility in the cabbage in the Beijing suburbs.
Table 10-15 Classification of Soil Available Nutrients in Beijing Jiaojiao (mg/kg)
Fertility level
Alkaline nitrogen (N)
Available Phosphorus (P 2 O 3 )
Potassium (K 2 O)
Extremely low
low
in
high
Very high
< 75
75-100
101-145
146-170
> 170
< 10
10-45
46-95
96-125
< 125
< 80
80-140
141-200
201-240
> 240
The effective phosphorus is Olsen method and the effective potassium is ammonium acetate method.
3, nutrient absorption of 100 kg crop yield
Nitrogen uptake by plants in the whole fertilizer area (kg/ha) = Plant nitrogen content in the all-fertilizer area (%) × Plant total dry weight in the whole fertilizer area (kg/ha)
Phosphorus uptake by plants in the whole fertilizer area (kg/ha) = Plant phosphorus content in the all-fertilizer area (%) × Plant total dry weight in the whole fertilizer area (kg/ha)
Potassium Uptake by Plants in Whole Fertilizer Area (kg/ha) = Plant Potassium Content in the Whole Fertilizer Zone (%) × Plant Total Dry Weight in Whole Fertilizer Zone (kg/mole)
Nitrogen uptake per kilogram of crop yield (kg) = Total N uptake by plants in the fertilizer area (kg/ha) 作物 Crop yield in the whole fertilizer area (kg/ha) × 100
Phosphorous uptake per kilogram of crop yield (kg) = Phosphorous uptake by plants in the whole fertilizer zone (kg/ha) 作物 Crop yield in the whole fertilizer area (kg/ha) × 100
Potassium uptake by one hundred kilograms of crops (kg) = Potassium uptake by plants in whole fertilizers (kg/ha) 作物 Crop yield in whole fertilizers (kg/ha) × 100
According to the different yields of crops in the whole fertilizer zone at the 20 test points, the NPK nutrient uptake of 100 kg of crops at different yield levels can be obtained. When crops form a certain yield, the amount of nutrients such as nitrogen, phosphorus, and potassium absorbed from the soil depends on the genetic characteristics of the crop and is affected by various environmental factors.
The research conducted by Liu Wei et al. (1985) in Jilin Province showed that within a certain range of varieties and cultivation conditions, the variation in nutrient absorption of a hundred kilograms of output was not significant and was close to a constant. The data they obtained on rice are listed in Table 10-16, Table 10-17, and Table 10-18. Table 10-16 100 kg of rice nutrient absorption capacity (kg)
nutrient
Changbai No. 6
Matsumae
Ji Xing 60
Asahi
Early Kam
Beijing cited 127
nitrogen
phosphorus
Potassium
1.8
1.0
2.3
1.7
0.9
2.0
1.7
0.9
2.3
1.8
1.1
2.6
1.8
1.1
2.3
1.8
1.0
2.2
Table 10-17 Yield of 100 kg of rice on different fertility soils (kg)
nutrient
low
in
high
nitrogen
phosphorus
Potassium
1.6
1.0
2.3
1.8
1.0
2.3
1.9
1.0
2.5
Table 10-18 100 kg of rice nutrient absorption in different years (kg)
nutrient
Beijing cited 217
Matsumae
1983
1984
1983
1984
nitrogen
phosphorus
1.96
1.00
2.00
0.94
1.89
0.94
1.69
0.86
However, strictly speaking, the nutrient absorption of a hundred kilograms of production is not a constant, and the nutrient uptake of one hundred kilograms of production is increased when the yield is increased. For example, the amount of nitrogen absorbed by a hundred kilograms of rice in Zhejiang Province is 6.6 kilograms when producing 4500 hectares of hail and 2.1 kilograms when more than 7500 kilograms are produced (Zhou Mingbiao, 1987).
Huang Deming et al. (1985) determined the N, P and K nutrient uptake of wheat in different yield levels in suburbs of Beijing. The group averages of the 86 wheat samples are shown in Table 10-19.
Yield level
nitrogen
phosphorus
Potassium
150-200
200-250
250-300
300-350
350-400
2.95
2.99
3.19
3.52
3.98
0.90
0.89
0.93
1.00
1.10
3.58
3.56
3.73
4.05
4.51
4. Soil nutrient supply
Soil nitrogen supply (kg/ha x 1/15) = soil available nitrogen test × 0.15 × soil available nitrogen use factor
Soil phosphorus supply (kg/ha × 1/15) = soil available phosphorus test × 0.15 × soil available phosphorus utilization factor
Soil potassium supply (kg/ha x 1/15) = soil available potassium test value × 0.15 × soil available potassium utilization factor
It has been difficult to measure the absolute amount of nutrients the soil can supply to a single crop in various soil testing methods to date, and the soil available nutrient test value is only a relative value indicating the soil fertility. The soil nutrient supply parameters used in the calculation of the required fertilizer amount cannot directly apply the soil nutrient test values, but must be verified through field experiments. The soil effective nutrient utilization coefficient can be obtained from the relationship with the crop yield and the uptake amount so as to make the soil available. The test value is quantitatively meaningful.
It must be pointed out that this utilization factor is also a variable, which changes with changes in the soil's available nutrient test values. When the effective soil nutrient test value is high, the utilization factor is small, and when the effective nutrient test value is low, the utilization factor is large, sometimes even exceeding 100%. The experiments conducted by Huang Deming et al. (1985) on the soil in Beijing indicate that there is a certain correlation between the effective soil nutrient utilization coefficient and the soil effective nutrient test value. Using this correlation can be used to calculate the available soil nutrient test values. coefficient. Figures 10-9, 10=10, 10, and 11 are the correlations between soil alkali-hydrolyzable nitrogen, available phosphorus, available potassium, and their respective soil measurements in Beijing and their functional agendas.
The coefficient of soil nutrient utilization varies greatly with the change of soil value. Taking alkali-hydrolysis of nitrogen as an example, when the test value of soil alkali-hydrolyzed nitrogen is increased from 40 mg/kg to 140 mg/kg, the utilization factor is reduced from 100% to 20%, not only in a large amplitude but also in a downward curve. Therefore, it is unreliable to use the average value of soil nutrient utilization factor. Of course, in areas where the soil fertility is relatively uniform and where the measured soil value does not change much, an average utilization factor is also acceptable.
In the calculation of effective soil nutrient supply and utilization factors in farmland soils, 0.15 conversion factor is often used. The unit of soil available nutrient test value is mg/kg, that is, there are several milligrams of nutrient per kilogram of soil, and soil nutrient supply should be measured in kilograms per hectare x 15 -1 , and x 0.15 should be used between the two. Conversion. ]
The area of ​​each 1/15 hectare is 666.7 square meters, and the sampling depth of soil is 20 centimeters. The volume of land per 666.7 square meters is:
666.7 × 0.2=133.34 square meters
The weight per unit volume of soil is called the bulk density and is expressed in g/cm3, which equals kilograms/m3. If the soil volume is 1.12 g/cm3, the weight of 0-20 cm soil layer per 666.7 m2 is calculated as:
133.34 meters 3 x 1.12 kilograms/meter 3 = 149340.8 kilograms
The effective soil nutrient test value is expressed in mg/kg, and when converted into kg/kg, it is kilograms 1/1000000 kg
The soil value measured at 1 mg/kg is converted into the nutrient content per 666.7 m2 of land: 1/1000000 × 149340.8 = 0.1493 ≈ 0.15
The conversion factor of 0.15 is a common number, and everyone is universal. In fact, it will vary according to the depth of the sampled soil and also according to the bulk density of the soil. If the sampling depth is changed to 15 cm, the coefficient will become 0.112. If the soil volume is 1.4 g/cm3, the soil bulk density is common in the North China Plain, and the conversion factor will become 0.187. With different conversion values, the calculated effective soil nutrient content will also change. For example, if the soil available phosphorus content is 10 mg/kg, the content per hectare is:
15 × 10 × 0.15=22.5 kg/ha
15 × 10 × 0.187 = 28.1 kg/ha
Table 10-20 Sample Depth, Soil Bulk Density, and Conversion Factor
Sampling depth
(cm)
Weight
.1
1.2
1.3
1.4
1.5
1.6
10
15
20
25
30
40
0.07
0.11
0.15
0.18
0.22
0.29
0.08
0.12
0.16
0.20
0.24
0.32
0.09
0.13
0.17
0.22
0.26
0.35
0.09
0.14
0.19
0.23
0.28
0.37
0.10
0.15
0.20
0.25
0.30
0.40
0.11
0.16
0.21
0.27
0.32
0.42
The difference between the two is up to 24.7%, so local governments should consider it when formulating formulas for specific applications. For ease of use, Table 10-20 lists the conversion factors for different sampling depths and different soil bulk densities.
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