Improvement of Planosol Solum. Part 9: Fertilizer Distributor for Subsoil

J. agric. Engng Res. (1998) 71, 213—219 Article No. ag980308

Improvement of Planosol Solum. Part 9: Fertilizer Distributor for Subsoil F. Liu1; H. Jia1; C. Zhang1; H. Zhang1; K. Araya2; M. Kudoh2; H. Kawabe2 1

Hejiang Agricultural Research Institute, Jiamusi, Heilongjiang, People’s Republic of China; 2 Environmental Science Laboratory, Senshu University, Bibai, Hokkaido 079-01, Japan (Received 15 September 1997; accepted in revised form 10 March 1998)

Based on field cultivation tests by Zhao and soil investigations by Araya, a one-to-one mixing of the second (Aw) and third (B) horizons was conducted to improve the planosol solum in China, leaving the first (Ap) horizon undisturbed by a three-stage subsoil mixing plough. This paper deals with the development of a fertilizer distributor which applies chemical fertilizers into the subsoil, where the Aw and B horizons, which are lacking in phosphorous and calcium, are mixed. Additionally, based on root density distribution of plants, this paper deals with the development of a technique in which the fertilizer is placed more densely in the upper layer than in the lower layer within the 200—600 mm depth of subsoil. The results showed that when both granular and powder fertilizers were supplied at the rear of the first or second plough body, the fertilizers reached the bottom layer with soil mixing by the plough bodies, and the fertilizer distribution density was greatest in the lower layer of the subsoil. When the fertilizers were supplied at the side of the third plough body, an improved distribution was obtained. However, the fertilizer was not distributed over the entire operating width (300 mm), but was concentrated more around the side of the third plough body. As a result, when the fertilizer was supplied both at the rear of the third plough and the side of the third plough body, the distribution sought was obtained. Here, the distribution density of the fertilizer decreased linearly with the tilled soil depth in the subsoil. ( 1998 Silsoe Research Institute

1. Introduction Planosol solum, a low-yield soil, is widely distributed in the Sanjiang plain of Heilongjiang province, of the People’s Republic of China near the border with Russia. The first horizon (Ap) is a humic soil which is suitable for 0021-8634/98/110213#07 $30.00/0

Notation F

F , 2, F 1 3 F ,2, F 1i 3i M f b f 2f 1 9 h i i

0

m

grand total of granular fertilizer (number) or of powder fertilizer (percentage) measured total of granular fertilizer (number) or of powder fertilizer (percentage) in each layer idea total of granular fertilizer (number) or of powder fertilizer (percentage) in each layer fertilizer mixing rate operating width, mm granular fertilizer (number) or powder fertilizer (percentage) in each of nine grids operating depth, mm variance of the measured distribution of fertilizer variance corresponding to a uniform distribution of fertilizer soil expansion ratio (see Fig. 5)

plant growth and has a thickness of about 200 mm. The second horizon (Aw) is a lessivage soil which is dense and impermeable and has a thickness of about 200 mm. The third horizon (B), below about 400 mm depth, is diluvial heavy clay.1,2 With the impermeable Aw horizon, plants suffer both from drought and excess moisture. The soil hardness of the Aw horizon is more than 5)0 MPa (30° cone angle, 16 mm base diameter), and the roots of the plants cannot penetrate the Aw horizon, while soil microorganisms cannot live beneath it.1 In the field tests made by Zhao et al.3 and in the soil investigation of Araya,4 the improvement of planosol

213

( 1998 Silsoe Research Institute

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F . LIU E ¹ A ¸.

Table 1 Chemical properties of planosol solum Horizon Ap Aw B

Depth mm

Organic Matter mg/kg

Available P mg/kg

Available K mg/kg

Available N mg/kg

0—200 200—400 400—600

49)1 11)7 12)8

12)0 5)7 4)1

71)0 51)0 101)0

210)0 77)9 74)5

solum was achieved by mixing the Aw horizon, which is a lessivage soil, dense and impermeable, and the B horizon, which is diluvial heavy clay, in a one-to-one ratio below the surface, leaving the Ap horizon undisturbed. A special plough (a three-stage subsoil mixing plough), which mixes the Aw and B horizons, has been developed and is described in the Part 6 paper.5 Physical properties, such as the soil hardness of the subsoil where the Aw and B horizons are mixed, are improved by this plough and plant roots are able to penetrate into it. However, the chemical fertility of the subsoil, the Aw and B horizons, is still extremely poor 6 as shown in Table 1. In particular, the subsoil is lacking in phosphorous, calcium and organic matter compared with the Ap horizon. The density of plant roots is less7 at greater subsoil depths in general as shown in Fig. 1. Fertilizer such as phosphorous have to be added to the subsoil and should be distributed in accordance with the density of plant roots shown in Fig. 1. The reason for this is that the movement of nutrients dissolved in water is even over extremely small distances in soils, and especially, phosphorous is immobile in soils.7 Plants frequently show phosphorous deficiency symptoms at an early period in their life.7 The object of the work reported in this paper is to develop a fertilizer distributor which supplies chemical fertilizers to the subsoil at the same time as the Aw and B horizons are mixed by the three-stage subsoil mixing plough. Additionally, based on the root density of Fig. 1, this paper deals with the development of a technique by which the fertilizer is distributed more densely in the upper layer than in the lower layer within a 200—600 mm depth of subsoil.8

2. Experimental details The experiments were conducted in the planosol solum field at farm number 853 in the Hosei district in China. The three-stage subsoil mixing plough with a fertilizer distributor was mounted on a Russian wheeled tractor (TE150). A spinning disk fertilizer distributor, which was suitable for both granular and powder fertilizers,

Exchangeable Ca mg/100 g 264)0 128)0 196)0

pH 6)3 6)4 6)6

Fig. 1. Oat roots recovered from a slab of soil 10 cm thick7

was used. This was driven by a ground-driven wheel as shown in Fig. 2. The fertilizer from the distributor was supplied at the rear of each plough body through a plastic tube. The schematic drawing of the three-stage subsoil mixing plough in Fig. 2 is shown in Fig. 3 and the process of mixing the Aw and B horizons using the three-stage subsoil mixing plough is shown schematically in Fig. 4. Initially, the first mouldboard plough body (Fig. 3) tills the Ap horizon (0—200 mm) shown in (2) of Fig. 4. With the second plough body, the Aw horizon (200—400 mm) is then tilled and is transferred backwards and is put on the B horizon as shown in (3) of Fig. 4. The broken Aw horizon and B (400—600 mm) horizon are then tilled together by the third plough body and are raised on the

F ER TI L IZ ER DI S TR IB U TO R F O R S U BS OI L

mouldboard of the third plough body as shown in (4) of Fig. 4 and drop down from the end of the mouldboard, so that a random mixing is obtained as shown in (5). Subsequently, the first mouldboard plough body tills the next Ap horizon, inverting the Ap furrow slice thus covering the mixed soil in the preceding furrow so that (6) of Fig. 4 is obtained. The positions where fertilizers was supplied to the plough, are shown in Fig. 3. Position r was at the rear of the first body, s at the rear of the second plough body,

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t at the rear of the third plough body and u at the side of the third plough body. When the fertilizer is supplied at position r, it is mixed with the subsoil by the second and third plough bodies which cut and till the Aw and B horizons, respectively, as shown in Fig. 4. At positions s, it is mixed by only the third plough body. At position t, it is mixed when the Aw and B horizons drop down from the end of the third plough body. At position u, it can reach the deepest layer because the subsoil is cut and opened deeply by the third plough body. Granular and powder fertilizers were used for the experiments. The granular fertilizer was painted yellow so that the locations at which it was distributed could be readily identified from photographs. Slaked lime, a calcium fertilizer was used as a powder fertilizer.

3. Experimental design

Fig. 2. Three-stage subsoil mixing plough with a fertilizer distributor for subsoil

The extent of fertilizer mixing was determined from photographs of the soil sections after ploughing. In Fig. 5, the distinct horizons before ploughing were mixed and expanded after ploughing, and a new horizon was obtained. It is assumed that the original depth provides a datum and that the different horizons expand in proportion to distance from the datum. Figure 5b shows the soil section C@D@G@H@ after ploughing and the mixed Aw and B horizons which are divided into nine samples areas by means of grids. The number of granules or the

Fig. 3. Plough bodies and positions where fertilizer was supplied. Positions r was at the rear of the first plough body, r at the rear of the second plough body, t at the rear of the third plough body and u at the side of the third plough body

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sity should be in the ratio of 3: 2: 1 in the layers C@D@E@F@, E@F@I@J@ and I@J@G@H@, respectively, as shown in Fig. 5b. The total number of percentage in each layer within C@D@G@H@ is f #f #f "F (1) 1 2 3 1 f #f #f "F (2) 4 5 6 2 f #f #f "F (3) 7 8 9 3 where f , 2 , f is the number of granules or the percent1 9 age of powder fertilizer in each of the grids in Fig. 5b, and F , F and F are the total number of granules or the 1 2 3 percentage of powder fertilizer in each of the three layers. The grand total (F) is F #F #F "F (4) 1 2 3 amounting to 18 units in Fig. 5b. The ideal fertilizer distribution densities, F , F and 1i 2i F should be linear with depth within C@D@G@H@, so 3i F " 9 F"1 F (5) 1i 18 2 (6) F " 6 F"1 F 3 2i 18 (7) F " 3 F"1 F 6 3i 18 If the actual total number of granules or percentages of powder counted in each layer are, F , F and F , the 1 2 3 variances i from the ideal values of Eqns (5)—(7) are given by i2"(1 F!F )2 (8) 2 1 1 (9) i2"(1 F!F )2 2 2 3 i2"(1 F!F )2 (10) 6 3 3 The basic variances i where fertilizers are uniformly 0 distributed and, hence, F "F "F "1/3F, are 1 2 3 1 F 2 1 (11) i2 " F! F " 01 2 6 3

A A A

Fig. 4. Schematic diagram of mixing Aw and B horizons. Dimensions (mm) are for a full-scale furrow

percentage of powder fertilizer in each grid was counted on the photograph. The percentage of powder fertilizer in each grid was determined as the ratio of white soil area coloured by slaked lime and the whole area of a grid. It is assumed that the root density is linear with depth in Fig. 1 and hence, the ideal fertilizer distribution is that which has the greatest density in the upper layer (C@D@ E@F@) and least in the lower layer (C@D@ G@H@) with a linear variation in between depth. Hence, the distribution den-

B AB B B A B

1 1 2 i2 " F! F "0 02 3 3

(12)

1 1 2 F 2 i2 " F! F " ! 03 6 3 6

(13)

Here, the fertilizer mixing rate M is defined as f i2#i2#i2 18 3 "1! (i2#i2#i2) 2 1 M "1! 2 3 f i2 #i2 #i2 F2 1 03 02 01 (14)

A

B

where M "1 corresponds to the ideal distribution f where the distribution density is linear to the depth, M "0 corresponds to a uniform distribution, and if f

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217

Fig. 5. Definition of fertilizer mixing rate: (a) before ploughing; (b) after ploughing

M is negative, it corresponds to an unfavourable distrif bution such as reverse distribution where the fertilizer distribution density is greatest in the lower layer and least in the upper layer.

4. Results and discussion 4.1. Granular fertilizer Figure 6a shows the granular fertilizer distribution at the soil section after ploughing when the fertilizer was dispensed at position t in Fig. 3. Figure 7 shows the fertilizer mixing rate M [Eqn (14)] resulting from analyf sis of the photographs of Fig. 6 (mark m). When the materials were supplied at position t, a higher density of fertilizer was found in the upper layer and a lower density in the lower layer. However, the granular fertilizer was less well distributed than the powder and hardly reached the bottom layer, the density in the upper layer was extremely high as shown in Fig. 6a. Hence, M in Fig. 7 f was sometimes below 0)1. When fertilizer was supplied at position r or s, the granular fertilizer reached the bottom layer with soil mixing by the plough bodies and a reverse distribution to that desired was obtained. The distribution shown in Fig. 7 appear to be erratic ranging from positive to negative. The reason for this is that when fertilizer is

supplied at position r, the fertilizer is moved with soil twice by the second and third plough bodies. When using position s, the fertilizer is moved once by the third plough body. Thus, the fertilizer and soil move together and the fertilizer sometimes reaches the bottom layer of the Aw horizon because the soil drops randomly from the third plough body as shown in (4) and (5) of Fig. 4. When position u was used, a distribution nearer to that required was obtained. However, the granular fertilizer was not distributed over the entire operating width of 300 mm, but was concentrated around the side of the third plough body. When the fertilizer is supplied at position t or u, it is not affected by the movement of soil caused by the plough body but moves independently. When positions t and u were used at the same time, a distribution closer to that required was obtained. Figure 6b shows the result obtained when half of the granular fertilizer was supplied at position t and half at position u. The distribution density of granular fertilizer was linear to the soil depth, and M was 0)52—0)98 in f Fig. 7.

4.2. Powder fertilizer The slaked lime, as a powder fertilizer, was supplied at each position in Fig. 3. Figure 6c shows the powder fertilizer distribution when position s was used. Here,

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Fig. 6. Fertilizer distribution in subsoil: granular fertilizer dispensed (a) at t; (b) at t and u; powder fertilizer dispensed (c) at s; (d) at t and u

F ER TI L IZ ER DI S TR IB U TO R F O R S U BS OI L

Fig. 7. Fertilizer mixing rate as a function of supplied position m granular fertilizer; s powder fertilizer

there was a reverse distribution where the distribution density in the lower layer was higher than that in the upper layer. Figure 6d shows the result obtained when half of the powder fertilizer was supplied at position t and half at position u. Here, the desired distribution was obtained, similar to that for the granular fertilizer in Fig. 6b. The results of the analysis of these photographs are shown in Fig. 7 (mark s). The powder fertilizer gave nearly the same result as the granular fertilizer. Namely, when the powder fertilizer was dispensed at position r or s, the fertilizer sometimes reaches the bottom layer because of the random dropping of soil from the third plough body and an undesirable reverse distribution tended to take place. The mixing rate was sometimes negative. At position t, a distribution close to that required was obtained but the fertilizer barely reached the bottom layer, and the density in the upper layer was high. At position u, it barely entered into a narrow crack between the side of third plough body and the subsoil because the powder fertilizer could not roll down as did the granular fertilizer. Therefore, in Fig. 7, the mixing rate of the powder fertilizer was not as good as that of the granular fertilizer.

5. Conclusions

a high distribution density in the upper layer and low distribution density in the lower layer. However, the fertilizers barely reached the bottom layer, and the density in the upper layer was extremely high. The fertilizer mixing rate ranged between about zero and unity. 2. When the fertilizers were supplied at the rear of the first or second plough body, the fertilizers reached the bottom layer with soil mixing by the plough bodies and a reverse distribution to that required tended to take place. The corresponding fertilizer mixing rate was erratic, ranging from positive to negative values. 3. When the fertilizers were supplied at the side of the third plough body, something close to the required distribution was obtained. The values of the fertilizer mixing rate were in the range of zero to unity but the fertilizer was not well distributed over the entire operating width (300 mm), but was concentrated around the side of the third plough body. 4. When fertilizer was supplied at the rear of the third plough body and the side of the third plough body simultaneously, then the required distribution was obtained. The distribution density of the fertilizer was linear with soil depth, and the fertilizer mixing rate was in the range 0)5—1)0.

References 1

2

3

4

5

6

7

8

1. When both granular and powder fertilizers were supplied at the rear of the third plough body, a distribution close to that required was obtained, namely,

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