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Productivity and K-supplying power change by an eight-season potash application in different patterns on two paddy soils
Geoderma 115 (2003) 65 – 74 www.elsevier.com/locate/geoderma
Productivity and K-supplying power change by an eight-season potash application in different patterns on two paddy soils X.Q. Chen, J.M. Zhou *, H.Y. Wang Institute of Soil Science, Chinese Academy of Sciences, Beijing Street East, Nanjing 210008, PR China
Abstract An eight-season rice – wheat rotation field experiment was conducted on two paddy soils in Siyang County and Liyang City of Jiangsu Province, respectively, to study the influence of different potash application patterns on crop yields and K-supplying power of the soils. The potash application patterns were: 216 kg K2O ha 1 in the rice season and no K in the wheat season; 216 kg K2O ha 1 in the wheat season and no K in the rice season; and 108 kg K2O ha 1 in each season. The results show that potash application significantly increased the crop yield, and that the benefit from potash application followed the order: potash only applied in rice>splitting application in each season>potash applied only in wheat>CK. Soil tests indicated that the K-supplying power of the soils was in the reverse order after eight cropping-season harvests, suggesting that potash application priority be given to the rice season and that the application rate should be increased to get more benefit and to maintain soil K fertility. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Potash application patterns; K-supplying power; Paddy soil; Rice – wheat rotation
1. Introduction Many researchers have studied the effect of potash with different dressing methods on crop yield under rotation systems (Ma and Du, 1982; Bao and Xu, 1993; Suyamto, 1993; Janardan et al., 1994; Tao et al., 1994). In order to use potash most efficiently, some people compared the benefit from the intervallic application pattern (applying K only in one cropping season in a rotation system) with that from the successive application pattern * Corresponding author. Fax: +86-25-3353590. E-mail address: [email protected] (J.M. Zhou). 0016-7061/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0016-7061(03)00076-4
66
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
(applying K in each of the cropping seasons) (Long et al., 1992; Hu et al., 1993; Chen, 1997; Chen and Zhou, 1999). Hu et al. (1993) found that when K was applied only to wheat, more benefit could be gained. But results from Zhejiang Province indicated that the split application of K to each crop could benefit more than applying the total annual amount only in one cropping season (The Science and Technology Bureau of Ministry of Agriculture, 1991). Long et al. (1992) also demonstrated that the application pattern of K used in each season is more beneficial. In most of the above studies the total annual amount of potash was not the same under different K application patterns in the experiments. Although Chen and Zhou (1999) controlled the potash application rate and concluded that applying the total K in the rice season could be better than applying it in the wheat season or splitting it to each season, however, they only had the results for five seasons. In addition, none of the studies revealed the effect of K fertilization patterns on K-supplying power. The objective of this research was to compare the benefit and potash use efficiency of the different potash application patterns and to demonstrate the soil K-supplying power changes induced by these patterns through longer-term field experiments.
2. Materials and methods 2.1. Field experiment design A rice – wheat rotation, which is a main cultivation system in Jiangsu Province and some other provinces of China, was conducted on the paddy soils in Siyang County and Liyang City of Jiangsu Province, respectively. In the experiments, rice was planted in the first, third, fifth, and seventh season, and wheat was in the second, fourth, sixth, and eighth season. The field experiment in each place was designed with four treatments: (1) no K was applied (K0); (2) half of the total annual amount of K was equally applied to each crop (K1); (3) the total annual amount of K was applied only to rice but not to wheat (K2(rice)), and (4) only to wheat (K2(wheat)). Each treatment was replicated four times in a completely randomized block arrangement. Each plot has an area of 40 m2. The annual amount of potash was the same, 216 kg K2O ha 1, for all K treatments. The application amount and methods of other fertilizers were the same as farmers used (Chen and Zhou, 1999). 2.2. Potash use efficiency calculation The potash use efficiency of the first cropping year was calculated according to the following formula: K use efficiency ð%Þ ¼ ½ðT 1 þ T 2Þ ðC1 þ C2Þ=ðC1 þ C2Þ*100 Here, the ‘‘T’’ and ‘‘C’’, respectively, mean the K removed with the harvest of crops in K treatments (K1 or K2) and CK treatments (K0); and the ‘‘1’’ and ‘‘2’’ mean the first and
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
67
Table 1 Fertility conditions of the experimented soilsa Site
Liyang Siyang
pH
5.7 8.1
OM (%)
N
0.62 0.32
23.0 11.1
P
K
S
B
Ca
Mg
Cu
Fe
Mn
Zn
43.0 39.1
24.1 77.4
0.00 0.26
1623.2 1863.7
245.4 151.9
4.8 2.1
168.0 31.5
31.9 9.9
2.3 1.6
1
Ag ml
8.9 25.0
a
The critical values of N, P, K, S, Ca, Mg, Cu, Fe, Mn, Zn, and B in the systematic approach are 50, 12, 78.2, 12, 400.8, 121.5, 1, 10, 5, 2, and 0.2 Ag ml 1, respectively (Potash and Phosphate Institute of Canada (PPIC), 1992).
second cropping season, respectively. The K use efficiency of the first 2 years was calculated as follows: K use efficiency ð%Þ ¼½ðT 1 þ T 2 þ T 3 þ T 4Þ ðC1 þ C2 þ C3 þ C4Þ =ðC1 þ C2 þ C3 þ C4Þ*100 The ‘‘3’’ and ‘‘4’’ mean the third and fourth cropping seasons, respectively. The K use efficiency of the first 3 and 4 years is obtained in a similar manner. 2.3. Soil sampling and analysis Soils of 0– 15 cm depth were taken from the field before the trials were conducted and after each cropping season was completed. The soil samples were air-dried and gently ground to pass through a 2-mm sieve in preparation for laboratory analysis. The basic fertility properties of the soil samples were analyzed using the systematic approach (Potash and Phosphate Institute of Canada (PPIC), 1992) by the Sino –Canada Soil and Plant Test Laboratory in Beijing before the experiments (Table 1). Comparing with the critical values from Table 1, N and K were found to be deficient in both soils and B in the soil of Liyang and Zn in the soil of Siyang were rather deficient. 2.4. Soil K fertility analysis The exchangeable and nonexchangeable K of the samples were also determined with the conventional chemical analysis methods, i.e., exchangeable K was extracted with 1 M neutral NH4OAc for 30 min (Jones, 1973), and nonexchangeable K with 1 M boiling HNO3 for 10 min (Pratt, 1965). The potassium was measured using flame spectrophotometry.
3. Results and discussion 3.1. Effect of potash application patterns on crop yield The yields and yield increases of eight cropping seasons for different K treatments in the rice –wheat rotation experiments conducted on the soils in Siyang and Liyang were
68
Treatment First season
Second season
Third season
Fourth season
Fifth season
Sixth season
Seventh season
Eight season
Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) K0 K1 K2(wheat) K2(rice) a
8.00 8.70 8.00 8.97
ba a b a
– 8.8 – 12.2
7.42 8.01 8.29 7.85
c b a b
– 7.9 11.7 5.7
6.60 c – 7.46 ab 13.1 7.06 b 7.0 7.57 a 14.7
4.48 5.16 5.34 5.30
c b a a
15.26 19.39 18.47
7.46 9.06 8.92 9.08
b a a a
21.37 19.59 21.83
Column values followed by the same letter are not significantly different at the 0.05 probability level.
5.94 6.98 7.14 6.85
b a a a
17.49 20.17 15.44
8.33 9.52 8.90 10.1
d b c a
– 14.3 6.8 21.0
4.66 5.54 5.57 5.53
b a a a
– 19.0 19.7 18.8
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
Table 2 Yields and yield increases of eight cropping seasons in the rice – wheat rotation experiment conducted on Aquept in Siyang County
Treatment First season
Second season
Third season
Fourth season
Fifth season
Sixth season
Seventh season
Eight season
Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) K0 K1 K2(wheat) K2(rice) a
7.38 8.56 7.38 8.80
ba a b a
– 16.1 – 19.3
2.85 3.73 3.91 3.56
c – ab 30.7 a 37.2 b 24.7
4.73 6.75 6.65 6.81
b a a a
– 42.8 40.7 44.2
1.90 3.88 4.06 3.88
c b a b
104.48 113.74 104.14
4.43 6.58 6.59 6.67
b a a a
48.43 48.76 50.58
Column values followed by the same letter are not significantly different at the 0.05 probability level.
2.98 4.42 4.71 4.00
c a a b
48.16 58.08 34.18
7.81 9.49 8.55 9.90
d b c a
– 21.6 9.5 26.8
0.395 c – 2.04 a 415.8 2.11 a 434.9 1.36 b 245.3
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
Table 3 Yields and yield increases of eight cropping seasons in the rice – wheat rotation experiment conducted on Aqualf in Liyang City
69
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presented in Tables 2 and 3. The data show that the yields of treatment K2 in each current season, i.e., the yields of crops in the seasons with the total annual amount of potash were always the highest, although with increasing number of cropping seasons, yields for the three K application patterns were not significantly different. The yield increases of crops in the treatments K2(rice) of the four rice seasons or treatments K2(wheat) of wheat seasons were increasing with the increase of cropping years, except for those in the wheat seasons on Liyang soil. These results indicate that the benefit from potash application was inclined to getting larger. It may imply that the potassium fertility of soils with no potash applied was decreasing as cropping seasons increased. During the wheat seasons in Liyang, especially the fourth and sixth cropping seasons, serious drought in the early growing stage of wheat and too much rain and impeded drainage in the latter stage may have induced a great response of wheat yield to potash. The yield increases in all treatments on Liyang soil were always larger than those in corresponding treatments on Siyang soil which might indicate that the soil K-supplying power on Liyang soil was less than that on Siyang soil. Table 4 presents the K use efficiency of the first cropping year, the first 2 years, the first 3 years, and the first 4 years. The data show that the K use efficiency tended to become larger with the increase of the cropping year. Such results are consistent with those of yield increase. In Table 4, the highest use efficiency of potash is observed in K2(rice) treatment and the lowest in the K2(wheat) treatment on both soils. This indicates that applying the same amount of potash only in rice season may provide more benefit than splitting it in both rice and wheat season, and much more than applying it only to wheat. 3.2. Effect of potash application patterns on soil K fertility The variation of the contents of exchangeable and nonexchangeable K in the experiments after one to four cropping years are shown in Figs. 1– 4. Fig. 1 shows that on Siyang soil, the variation of exchangeable K for the same treatments is not very distinct with the increase of cropping year. Applying potash in the current cropping season could correspondingly increase the exchangeable K, however, there’s no significant difference found between the increases caused by the application of whole or half amount of K in the current season. But applying K only in the previous season, the exchangeable K is obviously less than that in the other two K treatments. On Table 4 The K use efficiency of different potash application patterns in the initial one, two, three, and four cropping years on Aquept and Aqualf Soil
Treatment
Aquept
K1 K2(wheat) K2(rice) K1 K2(wheat) K2(rice)
The first year
The initial 2 years
The initial 3 years
The initial 4 years
49.3 39.6 33.9 49.9 23.7 65.4
56.5 44.8 52.3 69.0 47.2 92.1
50.4 46.6 55.9 74.3 57.1 90.4
56.3 54.5 59.2 74.8 62.0 85.9
(%)
Aqualf
a b c b c a
a c b b c a
b c a b c a
b b a b c a
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
71
Fig. 1. Variation of exchangeable K of Aquept after one to four cropping years.
the Aqualf (Fig. 3), with an increase of cropping year, the exchangeable K in K1 and K2(rice) treatments visually decreases, while that in the K2(wheat) treatment varied little. The differences among the three K treatments were distinct. With no K applied, the exchangeable K is significantly decreased in both soils. Such results may imply that K application could increase K-supplying power compared with the K0 treatment, but the K application rate was not big enough to maintain the K fertility of the soils. Fig. 2 illustrates that with the increase of cropping year, the nonexchangeable K of Aquepts slowly declined. When the total annual potash was applied only in the rice season, the nonexchangeable K was always relatively lower. And the gap of nonexchangeable K between soils with or without K applied was widened, mainly caused by the relatively greater decrease of nonexchangeable K of soils in CK treatment. The nonexchangeable K values of soils in all treatments were lower than the original content of soil K indicating that some of the nonexchangeable K were released to maintain the exchangeable K during the growing seasons. The higher nonexchangeable K in the Siyang soil means a higher buffer capacity in K supply. For the Liyang soil, the nonexchangeable K of soils with K1 and K2(wheat) treatments was slightly higher than the original soil, while
Fig. 2. Variation of nonexchangeable K of Aquept after one to four cropping years.
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X.Q. Chen et al. / Geoderma 115 (2003) 65–74
Fig. 3. Variation of exchangeable K of Aqualf after one to four cropping years.
in K2(rice) treatment, the nonexchangeable K was always lower than that in the other two K treatments indicating that potash application patterns influenced the K-supplying power. The nonexchangeable K in K0 treatment was significantly lower than the original soil, demonstrating K exhaustion without K application in the rotation. Based on these results of exchangeable K, it appears that the K fertility level of the Liyang Aqualf is higher than that of the Siyang Aquepts. However, a more serious K deficiency and a higher crop response to potash indicate that the soil in Liyang has a lower K-supplying power. When the exchangeable K in soil is low enough, the nonexchangeable K may play the leading role in K supplying. On the Siyang soil, the growth of crops promoted the release of soil K mainly supplied by the part of nonexchangeable K. But on the Liyang soil, the content of nonexchangeable K was too low to supply sufficient K to meet the requirement of crops for normal growth and the K needed had to be supplied, in part, by exchangeable K of soils and the potash applied. In the K2(rice) treatment, both the exchangeable and nonexchangeable K were lower than those in the other two K treatments on Siyang and Liyang soils. This is mainly due to the higher K use efficiency of rice. In rice seasons, more potassium can be removed by the crop than by the harvest of the wheat seasons. Such results are not contrary to those of crop yields.
Fig. 4. Variation of nonexchangeable K of Aqualf after one to four cropping years.
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
73
4. Conclusions The results from the 4 years of field experiments conducted on soils at Siyang and Liyang show that different potash application patterns can greatly affect the growth of crops and the soil potassium fertility of the soils. The yield increase and potash use efficiency of crops under different K application patterns show that applying the same amount of potash only in rice season may be more beneficial than splitting it in the rice and wheat seasons, and much more than applying it only to wheat. On the soil of Siyang, with an increase of cropping seasons, the exchangeable K of soils with the same treatment varied little, but the nonexchangeable K was slowly declining. Among the K treatments, both the exchangeable K and nonexchangeable K were higher when applying K only in the wheat season and accordingly lower when K was applied only to rice due mainly to the higher potash use efficiency of rice. On soil at Liyang, the nonexchangeable K changed little with the same treatment along with the increase of cropping year, but the exchangeable K obviously decreased except for the exchangeable K when the total amount of K was applied only in the wheat season. Like on the soil at Siyang, the soil K was lower when the potash was used only on the rice, possibly indicating that the Ksupplying power of the soils at Siyang was larger than that at Liyang. When potash was used only in rice season, the K use efficiency was the highest, however, it also resulted in the lowest soil K fertility. This suggests that the limited K is better applied in the rice season and the K input still should be increased in order to help maintain the soil K fertility at the same time. In order to reduce crop yield risk, it is also recommended that more K should be provided to soils in Liyang.
Acknowledgements Potash and Phosphate Institute of Canada (PPIC) is greatly acknowledged for the fund support.
References Bao, S.D., Xu, G.H., 1993. A study of contemporary and residual effects of potassium applied to a wheat – rice rotation. J. Nanjing Agric. Univ. 16 (4), 43 – 48. Chen, F., 1997. The effect of long-term K application on the characteristics of fixation and release of soil K. PhD thesis, Huazhong Agricultural University, Wuhan, PR China. Chen, X.Q., Zhou, J.M., 1999. Effect of potash application patterns on crop yields under different cultivation systems. Pedosphere 9 (3), 219 – 226. Hu, S.N., He, C.F., Portch, S., 1993. Most efficient potassium use in a wheat – rice rotation in Sichuan Province, China. In: Barrow, N.J. (Ed.), Plant Nutrition from Genetic Engineering to Field Practice. Kluwer Academic Publishers, Sydney, 633 – 636. Janardan, S., Sharma, H.L., Singh, C.M., Singh, J., 1994. Direct, residual and cumulative effects of potassium fertilization in rice (Qryza sativa) – wheat (Triticum aestivum) cropping system. Indian J. Agron. 39 (3), 345 – 355. Jones, J.B., 1973. Soil testing in the United States. Commun. Soil Sci. Plant Anal. 4, 307. Long, C.F., Chen, F., Chen, X.C., Ning, C.H., Xu, Y.S., Cai, D.X., Luo, X.W., Yang, C.F., 1992. The
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studies on potash allocation under different crop systems. In: The Science and Technology Bureau of Ministry of Agriculture, Institute of Soil and Fertilizer, Chinese Academy of Agricultural Sciences, Potash and Phosphate Institute of Canada (Eds.), Studies on Soil Potassium and Potash. Chinese Agricultural Science and Technology Press, Beijing, pp. 65 – 69. Ma, M.T., Du, C.L., 1982. The role of potassium fertilizer in boosting rice yield in red earth areas of central China. J. Soil Sci. (1), 5 – 11. Potash and Phosphate Institute of Canada (PPIC) (Ed.), 1992. The Systematic Approach for Soil Fertility. Chinese Agricultural Science and Technology Press, Beijing, pp. 1 – 117. Pratt, P.F., 1965. Potassium. In: Black, C.A., et al. (Eds.), Methods of Soil Analysis, Part 2. Agronomy, vol. 9. American Society of Agronomy, Madison, pp. 1023 – 1031. Suyamto, S., 1993. Direct and residual effects of potassium fertilizer on rice – maize cropping rotation on Vertisols. Indones. J. Crop Sci. 8 (2), 29 – 38. Tao, Q.X., Liu, G.R., Li, Z.Z., Xu, Z.L., 1994. Study on the K fertilizer distribution for rape – rice – rice crop system in poor K paddy soil. Acta Agricultuae Jiangxi 6, 53 – 60 (Supplement). The Science and Technology Bureau of Ministry of Agriculture, 1991. Potassium in Agriculture in South China. Agriculture Press, Beijing, pp. 57 – 106.
Productivity and K-supplying power change by an eight-season potash application in different patterns on two paddy soils X.Q. Chen, J.M. Zhou *, H.Y. Wang Institute of Soil Science, Chinese Academy of Sciences, Beijing Street East, Nanjing 210008, PR China
Abstract An eight-season rice – wheat rotation field experiment was conducted on two paddy soils in Siyang County and Liyang City of Jiangsu Province, respectively, to study the influence of different potash application patterns on crop yields and K-supplying power of the soils. The potash application patterns were: 216 kg K2O ha 1 in the rice season and no K in the wheat season; 216 kg K2O ha 1 in the wheat season and no K in the rice season; and 108 kg K2O ha 1 in each season. The results show that potash application significantly increased the crop yield, and that the benefit from potash application followed the order: potash only applied in rice>splitting application in each season>potash applied only in wheat>CK. Soil tests indicated that the K-supplying power of the soils was in the reverse order after eight cropping-season harvests, suggesting that potash application priority be given to the rice season and that the application rate should be increased to get more benefit and to maintain soil K fertility. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Potash application patterns; K-supplying power; Paddy soil; Rice – wheat rotation
1. Introduction Many researchers have studied the effect of potash with different dressing methods on crop yield under rotation systems (Ma and Du, 1982; Bao and Xu, 1993; Suyamto, 1993; Janardan et al., 1994; Tao et al., 1994). In order to use potash most efficiently, some people compared the benefit from the intervallic application pattern (applying K only in one cropping season in a rotation system) with that from the successive application pattern * Corresponding author. Fax: +86-25-3353590. E-mail address: [email protected] (J.M. Zhou). 0016-7061/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0016-7061(03)00076-4
66
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
(applying K in each of the cropping seasons) (Long et al., 1992; Hu et al., 1993; Chen, 1997; Chen and Zhou, 1999). Hu et al. (1993) found that when K was applied only to wheat, more benefit could be gained. But results from Zhejiang Province indicated that the split application of K to each crop could benefit more than applying the total annual amount only in one cropping season (The Science and Technology Bureau of Ministry of Agriculture, 1991). Long et al. (1992) also demonstrated that the application pattern of K used in each season is more beneficial. In most of the above studies the total annual amount of potash was not the same under different K application patterns in the experiments. Although Chen and Zhou (1999) controlled the potash application rate and concluded that applying the total K in the rice season could be better than applying it in the wheat season or splitting it to each season, however, they only had the results for five seasons. In addition, none of the studies revealed the effect of K fertilization patterns on K-supplying power. The objective of this research was to compare the benefit and potash use efficiency of the different potash application patterns and to demonstrate the soil K-supplying power changes induced by these patterns through longer-term field experiments.
2. Materials and methods 2.1. Field experiment design A rice – wheat rotation, which is a main cultivation system in Jiangsu Province and some other provinces of China, was conducted on the paddy soils in Siyang County and Liyang City of Jiangsu Province, respectively. In the experiments, rice was planted in the first, third, fifth, and seventh season, and wheat was in the second, fourth, sixth, and eighth season. The field experiment in each place was designed with four treatments: (1) no K was applied (K0); (2) half of the total annual amount of K was equally applied to each crop (K1); (3) the total annual amount of K was applied only to rice but not to wheat (K2(rice)), and (4) only to wheat (K2(wheat)). Each treatment was replicated four times in a completely randomized block arrangement. Each plot has an area of 40 m2. The annual amount of potash was the same, 216 kg K2O ha 1, for all K treatments. The application amount and methods of other fertilizers were the same as farmers used (Chen and Zhou, 1999). 2.2. Potash use efficiency calculation The potash use efficiency of the first cropping year was calculated according to the following formula: K use efficiency ð%Þ ¼ ½ðT 1 þ T 2Þ ðC1 þ C2Þ=ðC1 þ C2Þ*100 Here, the ‘‘T’’ and ‘‘C’’, respectively, mean the K removed with the harvest of crops in K treatments (K1 or K2) and CK treatments (K0); and the ‘‘1’’ and ‘‘2’’ mean the first and
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
67
Table 1 Fertility conditions of the experimented soilsa Site
Liyang Siyang
pH
5.7 8.1
OM (%)
N
0.62 0.32
23.0 11.1
P
K
S
B
Ca
Mg
Cu
Fe
Mn
Zn
43.0 39.1
24.1 77.4
0.00 0.26
1623.2 1863.7
245.4 151.9
4.8 2.1
168.0 31.5
31.9 9.9
2.3 1.6
1
Ag ml
8.9 25.0
a
The critical values of N, P, K, S, Ca, Mg, Cu, Fe, Mn, Zn, and B in the systematic approach are 50, 12, 78.2, 12, 400.8, 121.5, 1, 10, 5, 2, and 0.2 Ag ml 1, respectively (Potash and Phosphate Institute of Canada (PPIC), 1992).
second cropping season, respectively. The K use efficiency of the first 2 years was calculated as follows: K use efficiency ð%Þ ¼½ðT 1 þ T 2 þ T 3 þ T 4Þ ðC1 þ C2 þ C3 þ C4Þ =ðC1 þ C2 þ C3 þ C4Þ*100 The ‘‘3’’ and ‘‘4’’ mean the third and fourth cropping seasons, respectively. The K use efficiency of the first 3 and 4 years is obtained in a similar manner. 2.3. Soil sampling and analysis Soils of 0– 15 cm depth were taken from the field before the trials were conducted and after each cropping season was completed. The soil samples were air-dried and gently ground to pass through a 2-mm sieve in preparation for laboratory analysis. The basic fertility properties of the soil samples were analyzed using the systematic approach (Potash and Phosphate Institute of Canada (PPIC), 1992) by the Sino –Canada Soil and Plant Test Laboratory in Beijing before the experiments (Table 1). Comparing with the critical values from Table 1, N and K were found to be deficient in both soils and B in the soil of Liyang and Zn in the soil of Siyang were rather deficient. 2.4. Soil K fertility analysis The exchangeable and nonexchangeable K of the samples were also determined with the conventional chemical analysis methods, i.e., exchangeable K was extracted with 1 M neutral NH4OAc for 30 min (Jones, 1973), and nonexchangeable K with 1 M boiling HNO3 for 10 min (Pratt, 1965). The potassium was measured using flame spectrophotometry.
3. Results and discussion 3.1. Effect of potash application patterns on crop yield The yields and yield increases of eight cropping seasons for different K treatments in the rice –wheat rotation experiments conducted on the soils in Siyang and Liyang were
68
Treatment First season
Second season
Third season
Fourth season
Fifth season
Sixth season
Seventh season
Eight season
Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) K0 K1 K2(wheat) K2(rice) a
8.00 8.70 8.00 8.97
ba a b a
– 8.8 – 12.2
7.42 8.01 8.29 7.85
c b a b
– 7.9 11.7 5.7
6.60 c – 7.46 ab 13.1 7.06 b 7.0 7.57 a 14.7
4.48 5.16 5.34 5.30
c b a a
15.26 19.39 18.47
7.46 9.06 8.92 9.08
b a a a
21.37 19.59 21.83
Column values followed by the same letter are not significantly different at the 0.05 probability level.
5.94 6.98 7.14 6.85
b a a a
17.49 20.17 15.44
8.33 9.52 8.90 10.1
d b c a
– 14.3 6.8 21.0
4.66 5.54 5.57 5.53
b a a a
– 19.0 19.7 18.8
X.Q. Chen et al. / Geoderma 115 (2003) 65–74
Table 2 Yields and yield increases of eight cropping seasons in the rice – wheat rotation experiment conducted on Aquept in Siyang County
Treatment First season
Second season
Third season
Fourth season
Fifth season
Sixth season
Seventh season
Eight season
Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase Yield Increase (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) (103 kg (%) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) ha 1) K0 K1 K2(wheat) K2(rice) a
7.38 8.56 7.38 8.80
ba a b a
– 16.1 – 19.3
2.85 3.73 3.91 3.56
c – ab 30.7 a 37.2 b 24.7
4.73 6.75 6.65 6.81
b a a a
– 42.8 40.7 44.2
1.90 3.88 4.06 3.88
c b a b
104.48 113.74 104.14
4.43 6.58 6.59 6.67
b a a a
48.43 48.76 50.58
Column values followed by the same letter are not significantly different at the 0.05 probability level.
2.98 4.42 4.71 4.00
c a a b
48.16 58.08 34.18
7.81 9.49 8.55 9.90
d b c a
– 21.6 9.5 26.8
0.395 c – 2.04 a 415.8 2.11 a 434.9 1.36 b 245.3
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Table 3 Yields and yield increases of eight cropping seasons in the rice – wheat rotation experiment conducted on Aqualf in Liyang City
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presented in Tables 2 and 3. The data show that the yields of treatment K2 in each current season, i.e., the yields of crops in the seasons with the total annual amount of potash were always the highest, although with increasing number of cropping seasons, yields for the three K application patterns were not significantly different. The yield increases of crops in the treatments K2(rice) of the four rice seasons or treatments K2(wheat) of wheat seasons were increasing with the increase of cropping years, except for those in the wheat seasons on Liyang soil. These results indicate that the benefit from potash application was inclined to getting larger. It may imply that the potassium fertility of soils with no potash applied was decreasing as cropping seasons increased. During the wheat seasons in Liyang, especially the fourth and sixth cropping seasons, serious drought in the early growing stage of wheat and too much rain and impeded drainage in the latter stage may have induced a great response of wheat yield to potash. The yield increases in all treatments on Liyang soil were always larger than those in corresponding treatments on Siyang soil which might indicate that the soil K-supplying power on Liyang soil was less than that on Siyang soil. Table 4 presents the K use efficiency of the first cropping year, the first 2 years, the first 3 years, and the first 4 years. The data show that the K use efficiency tended to become larger with the increase of the cropping year. Such results are consistent with those of yield increase. In Table 4, the highest use efficiency of potash is observed in K2(rice) treatment and the lowest in the K2(wheat) treatment on both soils. This indicates that applying the same amount of potash only in rice season may provide more benefit than splitting it in both rice and wheat season, and much more than applying it only to wheat. 3.2. Effect of potash application patterns on soil K fertility The variation of the contents of exchangeable and nonexchangeable K in the experiments after one to four cropping years are shown in Figs. 1– 4. Fig. 1 shows that on Siyang soil, the variation of exchangeable K for the same treatments is not very distinct with the increase of cropping year. Applying potash in the current cropping season could correspondingly increase the exchangeable K, however, there’s no significant difference found between the increases caused by the application of whole or half amount of K in the current season. But applying K only in the previous season, the exchangeable K is obviously less than that in the other two K treatments. On Table 4 The K use efficiency of different potash application patterns in the initial one, two, three, and four cropping years on Aquept and Aqualf Soil
Treatment
Aquept
K1 K2(wheat) K2(rice) K1 K2(wheat) K2(rice)
The first year
The initial 2 years
The initial 3 years
The initial 4 years
49.3 39.6 33.9 49.9 23.7 65.4
56.5 44.8 52.3 69.0 47.2 92.1
50.4 46.6 55.9 74.3 57.1 90.4
56.3 54.5 59.2 74.8 62.0 85.9
(%)
Aqualf
a b c b c a
a c b b c a
b c a b c a
b b a b c a
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Fig. 1. Variation of exchangeable K of Aquept after one to four cropping years.
the Aqualf (Fig. 3), with an increase of cropping year, the exchangeable K in K1 and K2(rice) treatments visually decreases, while that in the K2(wheat) treatment varied little. The differences among the three K treatments were distinct. With no K applied, the exchangeable K is significantly decreased in both soils. Such results may imply that K application could increase K-supplying power compared with the K0 treatment, but the K application rate was not big enough to maintain the K fertility of the soils. Fig. 2 illustrates that with the increase of cropping year, the nonexchangeable K of Aquepts slowly declined. When the total annual potash was applied only in the rice season, the nonexchangeable K was always relatively lower. And the gap of nonexchangeable K between soils with or without K applied was widened, mainly caused by the relatively greater decrease of nonexchangeable K of soils in CK treatment. The nonexchangeable K values of soils in all treatments were lower than the original content of soil K indicating that some of the nonexchangeable K were released to maintain the exchangeable K during the growing seasons. The higher nonexchangeable K in the Siyang soil means a higher buffer capacity in K supply. For the Liyang soil, the nonexchangeable K of soils with K1 and K2(wheat) treatments was slightly higher than the original soil, while
Fig. 2. Variation of nonexchangeable K of Aquept after one to four cropping years.
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Fig. 3. Variation of exchangeable K of Aqualf after one to four cropping years.
in K2(rice) treatment, the nonexchangeable K was always lower than that in the other two K treatments indicating that potash application patterns influenced the K-supplying power. The nonexchangeable K in K0 treatment was significantly lower than the original soil, demonstrating K exhaustion without K application in the rotation. Based on these results of exchangeable K, it appears that the K fertility level of the Liyang Aqualf is higher than that of the Siyang Aquepts. However, a more serious K deficiency and a higher crop response to potash indicate that the soil in Liyang has a lower K-supplying power. When the exchangeable K in soil is low enough, the nonexchangeable K may play the leading role in K supplying. On the Siyang soil, the growth of crops promoted the release of soil K mainly supplied by the part of nonexchangeable K. But on the Liyang soil, the content of nonexchangeable K was too low to supply sufficient K to meet the requirement of crops for normal growth and the K needed had to be supplied, in part, by exchangeable K of soils and the potash applied. In the K2(rice) treatment, both the exchangeable and nonexchangeable K were lower than those in the other two K treatments on Siyang and Liyang soils. This is mainly due to the higher K use efficiency of rice. In rice seasons, more potassium can be removed by the crop than by the harvest of the wheat seasons. Such results are not contrary to those of crop yields.
Fig. 4. Variation of nonexchangeable K of Aqualf after one to four cropping years.
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4. Conclusions The results from the 4 years of field experiments conducted on soils at Siyang and Liyang show that different potash application patterns can greatly affect the growth of crops and the soil potassium fertility of the soils. The yield increase and potash use efficiency of crops under different K application patterns show that applying the same amount of potash only in rice season may be more beneficial than splitting it in the rice and wheat seasons, and much more than applying it only to wheat. On the soil of Siyang, with an increase of cropping seasons, the exchangeable K of soils with the same treatment varied little, but the nonexchangeable K was slowly declining. Among the K treatments, both the exchangeable K and nonexchangeable K were higher when applying K only in the wheat season and accordingly lower when K was applied only to rice due mainly to the higher potash use efficiency of rice. On soil at Liyang, the nonexchangeable K changed little with the same treatment along with the increase of cropping year, but the exchangeable K obviously decreased except for the exchangeable K when the total amount of K was applied only in the wheat season. Like on the soil at Siyang, the soil K was lower when the potash was used only on the rice, possibly indicating that the Ksupplying power of the soils at Siyang was larger than that at Liyang. When potash was used only in rice season, the K use efficiency was the highest, however, it also resulted in the lowest soil K fertility. This suggests that the limited K is better applied in the rice season and the K input still should be increased in order to help maintain the soil K fertility at the same time. In order to reduce crop yield risk, it is also recommended that more K should be provided to soils in Liyang.
Acknowledgements Potash and Phosphate Institute of Canada (PPIC) is greatly acknowledged for the fund support.
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