Detailed Description
According to the method, 35 test points in Zhanjiang area of main sugarcane area in Guangdong are selected, the yield of sugarcane and the phosphorus nutrient condition of soil under different phosphorus application treatments are investigated, the response relation of the yield of sugarcane, phosphorus absorption and phosphorus fertilizer utilization rate to available phosphorus and the phosphorus balance condition of soil are analyzed, the scientific management of the content level of available phosphorus in soil is explored, and a theoretical basis is provided for reducing application and improving efficiency of chemical fertilizers in sugarcane production.
1 materials and methods
1.1 test site
The research area is Yuexi sugarcane district, which comprises 35 different test points distributed in West county and cities such as Xunxu county, Renzhou county, Xunxu county and Huazhou county, wherein 16 Xunxu counties, 11 Renzhou cities, 6 Xunxu counties and 2 Huazhou cities are distributed in a specific way as shown in figure 1. The planting area of the sugarcane is about 15 ten thousand hectares. The soil type is red soil, and the change range of organic matters is 14.7-33.8 (the average value is 25.0g kg)-1) The pH variation range is 4.39-5.52 (mean value is 4.8, water-soil ratio is 5: 1).
1.2 design of the experiment
All test points included four different phosphorus treatments, P0: no phosphate fertilizer, P1: 120kg of P2O5/hm2(50% of local habitual fertilization), P2: 240kg of P2O5/hm2(local habitual fertilization) and P3: 360kg of P2O5/hm2(1.5 times of the local habitual fertilization). Each treatment was repeated 3 times, with a fully randomized block arrangement. The cell area is 66m2(10.0 m long x 6.6m wide), 2m wide isolation zones are arranged among the cells, and 1m wide protection rows are arranged around the cells. The nitrogen fertilizer and the potassium fertilizer are treated in the same amount, and the nitrogen fertilizer is treated in 345kg/hm2The dosage of N (urea) and potash fertilizer is 270kg/hm2K2O (potassium chloride). All-purposeAnd applying partial fertilizer as base fertilizer, wherein the variety of sugarcane is ROC22, the seeding amount is 3500 sections of double-bud seedlings, covering soil after seeding and applying the fertilizer, and performing whole-field coverage on a test field by adopting a weeding mulching film with the width of 1.5 m. Other field management is the same as general field production.
1.3 sample Collection and measurement
In the research, the planting time of the sugarcane is 2015 for 1 month, and the yield time of the sugarcane is 2016 for 3 months. Before testing, collecting soil samples of 0-20cm plough layer at each test point, sampling according to S shape with a soil drill, uniformly mixing multiple points to form a soil sample, air-drying indoors, grinding through a 2mm sieve, bottling and storing for later use, and using for measuring basic physical and chemical property indexes of soil. In the mature period of the sugarcane, plant samples are collected, 2 representative plants are taken from each cell, the roots of the representative plants are cut off and divided into two parts, namely stems and leaves (including leaves, leaf sheaths and the like), the two parts are all subjected to enzyme deactivation for 30min at 105 ℃, the parts are dried to constant weight at 70 ℃, and the biomass of the stems and leaves in the cells is weighed and estimated. All parts of the dried sample are crushed and sieved by a 0.5mm sieve, and the phosphorus content is respectively measured.
And (3) sample analysis: h for soil total phosphorus analysis2SO4-HClO4Digestion, molybdenum-antimony colorimetric resisting method; the soil quick-acting phosphorus content adopts 0.03M NH4F-0.025M HCl leaching, molybdenum antimony colorimetric-resisting method. Plant sample total phosphorus adopts H2SO4-H2O2Digestion, and vanadium-molybdenum-yellow colorimetric determination.
1.4 data statistics and analysis
The yield increase effect of the phosphate fertilizer is calculated as follows:
phosphate fertilizer yield increasing effect (PC,%) (yield of crops in phosphorus-affected area-yield of crops in non-affected area)/yield of crops in non-affected area × 100 (1)
The phosphorus absorption amount of crops is the total phosphorus absorption amount of overground parts and is divided into two parts, namely stems and leaves (including leaves, leaf sheaths and the like). The relevant calculation formula is as follows:
phosphorus uptake (kg/hm) of crops2) Yield of cane stalks (kg/hm)2) X the phosphorus content of the stem (%) + the yield of sugarcane leaves (kg/hm)2) X leaf phosphorus content (%); (2)
apparent phosphorus profit and loss (kg/hm)2) Total amount of phosphorus applied to soil (kg/hm)2) Crop (cane stalks + cane leaves)) Total amount of phosphorus absorbed (kg/hm)2); (3)
Phosphorus utilization (%) (total phosphorus uptake of crops in phosphorus-application area-total phosphorus uptake of crops in phosphorus-non-application area)/phosphorus-application amount × 100 (4)
The method adopts three models, namely a linear-linear model (LL), a linear-platform (LP), Mitscherlich (EXP) and the like, to simulate the relationship between the crop yield and the soil available phosphorus content, and further determine the agronomic threshold of the sugarcane. A double-line model (LL) is adopted to simulate the response relation of the quick-acting phosphorus and the total phosphorus.
To reduce differences between test points due to climatic factors and field management conditions, crop relative yield was used to calculate agronomic thresholds for the crops. The formula for the relative yields is as follows (Colwell, 1963):
YR=Yf÷Ym (5)
wherein: y isRRelative yield of crop, YfFor crop yield (kg hm) at different test points-2);YmMaximum crop yield (kg hm) for different test points-2)。
The calculation formula of the two-line model is as follows:
Y=a1+b1X if X<C (6)
Y=a2+b2X if X≥C (7)
wherein: y represents the relative yield (%) (or the available phosphorus content (mg kg) of the crop-1) A1 (or a2) is the intercept; b1 (or b2) is the slope, X is the content of the quick-acting phosphorus in the soil (mg kg)-1) (or total phosphorus content (g kg)-1) C is the turning point of the response relation of the two.
The calculation formula of the linear-platform model is as follows:
Y=a+bX if x<C (8)
Y=Yp if x≥C (9)
wherein: y represents the predicted relative yield (%); a is intercept; b is the slope, X is the soil Olsen P content (mg kg)-1) C is the soil Olsen P threshold (mg kg)-1) YP is the predicted relative platform yield (%).
The calculation formula of the Michelisia model is as follows
Y=A[1-e-bX] (10)
Wherein Y is the predicted relative yield (%), A is the maximum yield obtainable when X is not limiting, b is the response factor, and X is the content of available phosphorus in soil (mg P kg)-1). In the present invention, the critical value of the fast-acting phosphorus content is defined as the value when Y reaches 95% of a (Colomb et al, 2007).
All data were collated using Excel 2010; the dual-line, linear-platform, micheli models, etc. all run in SigmaPlot 12.5.
2 analysis of results
2.1 response of phosphate yield Effect to fast-acting phosphorus
Compared with the phosphate fertilizer without phosphorus treatment (P0), the phosphate fertilizer has the yield-increasing effect on sugarcane and the quick-acting phosphorus response relationship on soil under three different phosphorus-applying levels of P1, P2, P3 and the like as shown in figure 2. The percentage of increase of the phosphate fertilizer in different phosphorus application levels shows a decreasing trend along with the increase of the content of the available phosphorus, and the increase effects of P1, P2 and P3 respectively range from 43.9% to 2.3% (mean value of 17.6%), from 51.8% to 3.6% (mean value of 24.6%) and from 57.8% to 4.3% (mean value of 25.8%). Under the same soil quick-acting phosphorus level, the yield-increasing effect is improved along with the increase of phosphorus application amount, but the yield-increasing effect is different: when the available phosphorus content in soil is low (AP)<20mg kg-1) The yield increasing effect of different phosphorus application levels is greatly different, and P3 is higher than P1 by 16.2 percent on average; when the content of available phosphorus in soil is 20-100mg kg-1In time, the yield increasing effects of different phosphorus application levels are relatively small, and P3 is higher than P1 by 6.5% on average; when the content of available phosphorus in soil>100 mg kg-1When applied, the stimulation effect was essentially the same for the three phosphorus levels, with P3 being only 1.3% higher on average than P1. In general, when the content of available phosphorus in soil is low, the yield-increasing effect of phosphorus application is large, namely, the influence of phosphate fertilizer on the crop yield is large; when the content of the available phosphorus in the soil reaches a higher level, the yield increasing effect of phosphorus application is gradually reduced, and the influence of the phosphate fertilizer on the crop yield is smaller.
2.2 response of sugarcane relative yield to fast-acting phosphorus
Sugarcane yield pairs without phosphorus treatment (P0)The response relationship of the soil quick-acting phosphorus is shown in figure 3. In the linear model, a double-linear (LL) model and a linear-platform (LP) model divide the response relation of crop yield to the quick-acting phosphorus into two parts, and the turning point is the agronomic critical value of the quick-acting phosphorus in soil. In the mitchelische (EXP) model, the agronomic cutoff value is the rapid-acting phosphorus content corresponding to a maximum predicted relative yield of 95%. In the present invention, the response relationship between the relative yield of sugarcane and the available phosphorus at different test points can be well simulated by the above three models (fig. 3 and table 1): the coefficients of determination for the bilinear, linear-plateau and micheli models were 0.747, 0.659 and 0.678, respectively, all to a very significant level. Meanwhile, a double-line, linear-platform and Michelisia model is adopted, and the agronomic thresholds of the phosphorus of the sugarcane are different and are respectively 22.9mg kg, 49.9mg kg and 26.8mg kg-1The average of the three models was 33.2mg kg-1。
TABLE 1 Bistringy, Linear-plateau and Michelisia model calculated agronomic threshold for sugarcane phosphorus (mg kg)-1)
2.3 response of soil fast-acting phosphorus to Total phosphorus
The double-line model divides the response relation of the soil quick-acting phosphorus content to the total phosphorus into two stages, and the equation determination coefficient is 0.881, which reaches the extremely significant level. As can be seen from fig. 4, the response coefficients of the fast-acting phosphorus to the change of the total phosphorus content are obviously different before and after the turning point: before the turning point, the total phosphorus content is increased by 0.1g kg-1The content of available phosphorus is increased by 5.48mg kg-1(ii) a After the turning point, the total phosphorus content is increased by 0.1g kg-1The content of available phosphorus is increased by 25.4mg kg-1. The response coefficient after the turning point is about 4.6 times that before the turning point. In addition, the contents of total phosphorus and available phosphorus at the turning point in the present invention were 0.69g kg-1And 24.7mg kg-1. It can be seen that when the total phosphorus content of the soil exceeds 0.69g kg-1In the mean time, the content of available phosphorus rapidly increases with the increase of the total phosphorus content.
2.4 response of phosphate utilization to fast-acting phosphorus
The relationship between the season availability (PUE) of phosphate fertilizer and available phosphorus at each test point is shown in FIG. 5. Under the three phosphorus application levels, the change ranges of the PUE corresponding to different quick-acting phosphorus contents have certain fluctuation, and the change ranges of the PUE treated by the P1, the P2 and the P3 are 34.7-7.8% (mean value is 19.0%), 24.6-8.5% (mean value is 16.8%) and 22.6-9.9% (mean value is 25.8%) respectively. Overall, at the same level of available phosphorus, PUE gradually decreased with increasing phosphorus application. In addition, as the content of available phosphorus in soil increases, three PUEs with phosphorus application levels all show a downward trend. As can be seen by simulating the response relationship between the PUE and the quick-acting phosphorus by using a linear equation, the descending rates (namely the slopes of the linear equation) of the P1, P2 and P3 treatments are 0.10 percent, 0.06 percent and 0.05 percent in sequence when the content of the quick-acting phosphorus is increased by 1 unit.
2.5 soil phosphorus balance
Under the condition of not applying phosphorus (P0), all the soil phosphorus at the test points shows deficiency status, and the change range of the phosphorus deficiency status is-54.1-145.2 kg P2O5ha-1y-1. Three phosphorus treatments: the profit-loss change range of P1 for treating phosphorus of different test points is-39.0-35.9 kg P2O5ha-1y-1. Phosphorus in the P2 and P3 treatment at each test point showed surplus state, and the change ranges were 67.1-132.7 and 165.1-235.2 kg P2O5ha-1y-1(FIG. 6). It can be seen that the difference between the sufficient and deficient phosphorus contents at different test points and in different phosphorus application treatments is mainly caused by the large difference between the phosphorus application amount and the phosphorus carrying-away amount of crops. From the average of the phosphorus surplus and the phosphorus deficit of different test points under the same phosphorus application level, the higher the phosphorus application amount is, the larger the phosphorus surplus is, and the average phosphorus surplus of the P3 and P2 treated soil is positive, namely 201.7 and 99.3kg P respectively2O5ha-1 y-1(ii) a While the average surplus of phosphorus in the P1 and P0 treated soil is negative, and is respectively-2.6 kg and-100.3 kg of P2O5ha-1y-1. It can be seen that the soil phosphorus is greatly deficient when no phosphorus is applied (P0), and is accumulated when higher phosphorus is applied (P2 and P3)A large amount of phosphorus. In most test points, P1 treatment maintained the soil's dynamic balance of phosphorus nutrients.
3 discussion and conclusions
3.1 Rapid-acting agronomic threshold of phosphorus for sugarcane
In the invention, when the content of the available phosphorus in the soil is low, the application of the phosphate fertilizer has obvious yield-increasing effect on the sugarcane and increases along with the increase of the phosphorus application amount; when the content of the available phosphorus in the soil is continuously increased, the yield increasing effect of the phosphate fertilizer is gradually reduced; when the content of available phosphorus in soil exceeds 100mg kg-1When the three treatments with phosphorus (P1, P2 and P3) were applied, the yield of the sugarcane was substantially the same as that without phosphorus (P0), and the effect of yield increase was minimal (fig. 2). The method shows that when the soil has higher phosphorus nutrient and is no longer a crop growth limiting factor, the influence of the application of the exogenous phosphate fertilizer on the crop yield is small. Similarly, studies on canola have found that the yield increase of phosphate fertilizers is significantly greater in less fertile soils than in high fertile soils (Wu et al, 2004).
Under the P0 treatment, the yield of the sugarcane shows a trend of increasing rapidly and then slowly along with the increase of the content of the available phosphorus in the soil (figure 3). Three models, namely a double-straight line model, a linear-platform model and a Michelisia model, are adopted to fit the response relation of the sugarcane yield to the content of the quick-acting phosphorus in the soil under the treatment of P0. To reduce the error between different test points, relative yields were used for calculation, with the maximum yield being defined as 100% and the other yields as the ratio between absolute yield and maximum yield. Table 1 shows that all three models can be used for simulating the relation between the relative yield of sugarcane and the content of available phosphorus, and the bilinear model is optimal (R)2=0.747, P<0.01), followed by Michelisch model (R)2=0.678,P<0.01), and finally a linear-plateau model (R)2=0.659, P<0.01). In the linear model (including the double-linear and linear-plateau models), the turning point is defined as the agronomic threshold of the phosphorus, and the soil is artificially divided into two different types according to the response relation of the relative yield to the change of the quick-acting phosphorus content of the soil, which may not meet the actual situation, and the method is used for guiding the soil phosphorus management in agricultural production to have a large risk (Tang et al, 2009). And in the Michelisia model, phosphorus is calculatedIn agronomic thresholds, there is a certain deviation as the yield actually obtained is selected to be the maximum relative yield level (e.g. 80-100%) which requires a deliberate effort (Colomb et al, 2007; Poulton et al, 2013).
In order to obtain a reasonable fast-acting agronomic threshold for phosphorus in crops, several different models are usually used for calculation and comparison, and further determination is required in combination with the yield response of the crops. Tang et al (2009) corn agronomic thresholds obtained using different models for Chang Ping, Zheng Zhou and Yangling were 12.1-17.3 mg kg-1(average 15.3mg kg)-1) The agronomic threshold value of the wheat is 12.5-19.0 mg kg-1(average 16.3mg kg)-1). In the invention, the critical values of the available phosphorus obtained by the bicinear and micheli models are relatively close, and are respectively 22.9mg kg and 26.8mg kg-1And the linear-plateau threshold was 49.9mg kg-1Significantly higher than the first two. In view of the combination of yield response and decision coefficient of the model, the two-line model is selected to predict the result, namely the agronomic threshold value of the sugarcane is 22.9mg kg-1. The agronomic threshold for fast-acting phosphorous in sugarcane is higher than the agronomic threshold for corn and wheat, which may be related to the longer growth cycle and the greater nutrient demand of sugarcane. On the other hand, the soil in the sugarcane area is strong acid red soil (pH)<5.5), the fast-acting phosphorus assay selected was the Bray-I method, and the Olsen method used in the above study. It was found by the researchers that for the same soil species, the Bray-I method (0.03M NH)4F-0.025M HCl) is higher than that of the Olsen method (0.5M NaHCO)3pH 8.5) measurement (Song et al, 2012). Furthermore, the study of McCray et al (2012) in florida high organic matter soils demonstrated fast-acting phosphorous in sugarcane (Mehlich 3 process (0.2M CH)3COOH,0.25M NH4NO3,0.015M NH4F,0.013M HNO3And 0.001M EDTA)) an agronomic threshold of 30g Pm-3According to the higher organic matter, the volume weight of the soil is 1.2g cm-3Converted to 25mg of Pgk-1Closely similar to the results of the present invention. Bu and Magdoff (2003) concluded that both Bray 1 and Mehlich 3 are F-containing extractants,the main principle of extracting phosphorus from soil is the same, so that the two have good substitution.
3.2 turning point of soil phosphorus fertility
It is found in many soil types that the soil's available phosphorus content increases significantly with increasing total phosphorus content of the soil, but at different rates. For example, after the fertility rate turning point, the total phosphorus content increases by 0.1 kg per unit-1The increment of the quick-acting phosphorus content in the black soil and the purple soil is respectively 28.7 mg kg and 7.5mg kg-1(Bai et al, 2013). If the response curve relationship of the soil quick-acting phosphorus to the total phosphorus is kept unchanged for a long time, the response curves of the soil quick-acting phosphorus and the total phosphorus can be used for estimating the time for which the soil quick-acting phosphorus level can maintain the high yield and the duration of the crops under the condition of no P fertilizer input. According to the method, the response relation of quick-acting phosphorus in the red soil of the sugarcane region to the change of the total phosphorus content is fitted by using a double-straight-line model, the regression coefficients of two straight lines are respectively 54.8 and 254.0, and the difference of the response coefficients before and after the turning point is about 3.6 times, so that the phosphorus adsorption state of the red soil of the sugarcane region is obviously different under different total phosphorus levels, and the difference is probably related to the obvious change of the organic carbon (SOC) content and the pH value in the soil. Research has shown that: SOC can occupy adsorption sites on mineral surfaces to reduce P adsorption by soil, and SOC can form a complex with Fe and Al ions to increase phosphorus adsorption by soil (Daly et Al, 2010; Jalali and Jalali, 2016). Changes in soil pH can significantly affect the adsorption state and intensity of soil colloids to phosphorus (Abdala et al, 2012). In acid soils, phosphorus is likely to be adsorbed by soil clay minerals and hydrogen oxide by ligand exchange, making desorption difficult (Khare et al, 2007).
3.3 suitable range of available phosphorus in soil in sugarcane area and recommended dosage of phosphate fertilizer
At different phosphorus application levels, the utilization rate of the phosphate fertilizer shows a remarkable descending trend along with the increase of the content of the available phosphorus in the soil, and the descending rate (namely the coefficient of the equation) is reduced along with the increase of the application amount of the phosphate fertilizer (figure 5). Similar results have been found in maize and wheat (Li et al, 2002; Sun and Liu, 2014). At lower available phosphorus levels, the in-season availability of phosphate fertilizer was higher, but crop yield was significantly limited (FIG. 3 and5). Many studies suggest that when the soil available phosphorus content is near the agronomic threshold of phosphorus, the season availability of phosphate fertilizer is high, and the high and stable yield of crops can be guaranteed (Syers et al, 2008; Johnston et al, 2014). When the soil available phosphorus content is too high, crop yield is high, but the utilization rate of phosphate fertilizer in season is low, and a large amount of phosphorus is accumulated in the soil, and it can be seen that the available phosphorus content is not as high as possible (Simpson et al, 2015; Mardamotooo et al, 2013). When the total phosphorus content of soil exceeds the turning point of the fertility rate of phosphorus, the content of available phosphorus rapidly increases with the increase of total phosphorus, which causes a great reduction in the utilization rate of phosphate fertilizer, and the risk of environmental pollution caused by the entry of available phosphorus into water is high (Mcdowell et al, 2015). When the content of Olsen P exceeds 40mg kg-1Phosphorus leaching may occur in many soil types in china (Zhong et al, 2004). Horta and Torrent (2007) through a plurality of studies on acidic soil of the grapevine, the environmental critical value (runoff loss) of the soil phosphorus is recommended to be 50mg kg-1. Therefore, in order to ensure higher sugarcane yield, soil phosphorus fertility and phosphate fertilizer utilization rate, the suitable range of the quick-acting phosphorus content of the acid soil in the sugarcane region is 22.9-50mg kg-1。
In terms of profit and loss of the phosphorus in the soil, the phosphorus in the soil at different test points is in a loss state under the treatment of P0, which indicates that the phosphorus is not applied in the red soil in the sugarcane area, so that the phosphorus in the soil is consumed greatly and the phosphorus requirement of crops cannot be met. For the P2 and P3 treatments, the phosphorus in the soil at different test points is in a surplus state, namely the input amount of the phosphorus exceeds the amount of the phosphorus carried out by crops, and the soil is treated at P2 (the local conventional fertilizing amount is 240kg of P2O5Ha), a large amount of phosphorus is accumulated every year, and a large amount of phosphate fertilizer resources are wasted. In both cases, it is not advantageous to maintain reasonable levels of phosphorus in the soil. Under the treatment of P1, the phosphorus in different test points has different excess and average excess is close to 0, which indicates that the phosphorus input is basically the same as the phosphorus carried out by plants, and the soil phosphorus is in dynamic balance. For specific soil, when the content of available phosphorus is far lower than the agronomic threshold of phosphorus, the application amount of phosphate fertilizer is higher than the phosphorus carrying amount (Li et al, 2011), the invention can select the P2 dosage to make the content of available phosphorus graduallyIncreasing gradually until approaching an agronomic threshold; when the content of available phosphorus is close to or slightly higher than the agronomic threshold of the sugarcane phosphorus, the application amount of the phosphate fertilizer is slightly higher than or equal to the phosphorus carrying amount of crops (Wu et al, 2018), the invention can be used for preparing P1(120kg P)2O5Ha) as recommended fertilizing amount; the application of phosphate fertilizer can be temporarily stopped for a short time when the rapid-acting phosphorus content is much higher than the agronomic threshold for phosphorus (McCray et al, 2012). And simultaneously, measuring the content of the available phosphorus in the soil every 3-5 years to adjust the application amount of the phosphate fertilizer to meet the growth requirement of the sugarcane.
4 conclusion
The management of phosphorus nutrients in agriculture needs to consider the high yield of crops, the efficient utilization of phosphate fertilizers and the prevention of water pollution. First, the agronomic cut-off value of fast-acting phosphorus of the crop needs to be determined. The invention can be used for fitting the response relation (P) of relative yield of crops and quick-acting phosphorus by using three models of double straight lines, linear-platform and Michelisia<0.01), wherein the fitting effect of the double-line model is best, and the obtained quick-acting phosphorus agronomic threshold value is 22.9-49.9mg kg-1In the meantime. The yield increasing effect of the phosphate fertilizer shows that different phosphorus applying treatments have certain yield increasing effect, but the yield increasing effect is reduced along with the increase of the content of the quick-acting phosphorus in the soil. To synthesize the model effect and yield increase effect changes, we chose 22.9mg kg-1As the agronomic threshold of the available phosphorus of the sugarcane.
The over-high content of the available phosphorus in the soil can cause the reduction of the utilization rate of phosphate fertilizer, cause the waste of limited phosphate rock resources and possibly cause environmental problems of water eutrophication and the like. The proper range of the available phosphorus content of the soil in the sugarcane region is 22.9-50mg kg by analyzing the comprehensive yield reaction, the utilization rate of phosphate fertilizer, the soil fertility and the like-1. In addition, the soil phosphorus profit and loss analysis under different phosphorus applying treatments is combined with the condition that the content of the quick-acting phosphorus in the current sugarcane area is generally higher: for soil with rapid-acting phosphorus content close to the agronomic threshold of phosphorus, 120kg of P can be added2O5The recommended phosphorus application amount is/ha; for the soil with the quick-acting phosphorus content far higher than the agronomic threshold of the phosphorus, the application of the phosphate fertilizer can be stopped within 3 to 5 years.