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Effect of Conservation Tillage Practices on Soil Phosphorus Nutrition in an Apple Orchard
November 2016. Horticultural Plant Journal, 2 (6): 331–337.
Horticultural Plant Journal Available online at www.sciencedirect.com The journal’s homepage: http://www.journals.elsevier.com/horticultural-plant-journal
Effect of Conservation Tillage Practices on Soil Phosphorus Nutrition in an Apple Orchard YANG Xiaozhu, LI Zhuang, and CHENG Cungang * Institute of Pomology, Chinese Academy of Agricultural Sciences, Xingcheng, Liaoning 125100, China Received 28 August 2016; Received in revised form 16 October 2016; Accepted 2 November 2016 Available online 16 February 2017
Abstract Soil phosphorus (P) is an essential and limiting element for plant growth, which is significantly affected by different approaches to soil management. In order to reveal the effect of different management approaches on soil P and phosphatase activity in 0–20 cm and 20–40 cm soil, this research was conducted to study variations in the characteristics of P and phosphatase activity under 3-year tillage without mulching (CK), notillage with corn straw mulching (NTSM) and no-tillage with grass (NTG) in Liaoning apple orchard. The results showed that NTSM and NTG could significantly increase soil P content (P < 0.05) as compared with CK. However, the effect was different between NTSM and NTG; with the NTSM approach, the improvement in the P content in 20–40 cm was remarkable, and in the NTG approach, the improvement in the soil surface P content was significant. At the same time, soil phosphatase activity significantly increased (P < 0.05) under NTSM and NTG. The soil surface and 20–40 cm phosphodiesterase (PD) activity was enhanced under the two management approaches, however, the effect of NTG was stronger than NTSM. In addition, NTSM was more conducive to increasing alkaline phosphomonoesterase (AlP), and NTG was more conducive to increasing acid phosphomonoesterase (AcP). Our findings highlight the variation of dominant mechanisms involved in soil P with different mulching materials application. NTSM and NTG could have the potential to increase P content and phosphatase activity, and provide a basis for using this method to improve P phytoavailability and reduce the application of soil fertilizer. Keywords: apple orchard; phosphorus; phosphatase activity; corn straw mulching; grassing
1. Introduction Hilly areas are traditional fruit producing areas which, due to a mountain climate and special soils, produce sweet fruits. However, it is difficult to manage this type of cultivated land primarily because the soil nutrient supply is decreasing in many mountain apple orchards (Bai et al., 2010). In addition, unreasonable orchard management measures, such as excessive fertilizers that actually make soil structure worse, reduce nutrient content and the ability of the soil to generate a sufficient supply of nutrients. Soil nutrients, and especially the retention and supply capacity of soil phosphorus (P), are an important foundation for maintaining agricultural productivity and orchard soil fertility. However, P nutrients are liable to be adsorbed, fixed and precipitated by soil solid constituents (Chintala et al., 2014), forming an organic P composition which is difficult for the plant to use.
Organic P could be available for organisms’ uptake only under the hydrolysis of phosphatase (Zhu et al., 2016). Therefore, understanding the P form, content and phosphatase activity in apple orchard soils is of strategic importance for improving organism P nutrition. Soil phosphatase is a kind of specific enzyme that hydrolyzes soil organic P, an activity that affects the transformation and bio-availability of soil P (Zhang et al., 2012a). Additionally, some studies have indicated that corn straw mulching and natural grassing were effective methods for improving soil quality because these management strategies could protect soil status, raise water utilization ratio, restrain violent changes in soil temperature and increase soil organic matter content (Wen et al., 2011; Wei et al., 2014a). Therefore, corn mulching and natural grassing were the most important agricultural management measures for controlling water and soil erosion and
* Corresponding author. Tel.: +86 429 3598158 E-mail address: [email protected] Peer review under responsibility of Chinese Society for Horticultural Science (CSHS) and Institute of Vegetables and Flowers (IVF), Chinese Academy of Agricultural Sciences (CAAS) http://dx.doi.org/10.1016/j.hpj.2016.11.005 2468-0141/© 2016 Chinese Society for Horticultural Science (CSHS) and Institute of Vegetables and Flowers (IVF), Chinese Academy of Agricultural Sciences (CAAS). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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improving fertility conditions. However, the effects of longtime corn straw mulching and natural grassing on apple orchard soil P nutrients and phosphatase activity are still unknown. In this study, we selected the 3-year mountain apple orchard soils with corn straw mulching and natural grassing in order to study how soil P and phosphatase activity were affected. The objective was to explore the mechanism of soil P nutrition under corn straw mulching and natural grassing, which is important for improving agricultural practices, as well as effects on the environment and other natural resources. 2. Materials and methods 2.1. Study site The study site was located at the Apple Experiment Station of Chinese Academy of Agricultural Sciences (CAAS) in Western Liaoning (41°06′N, 119°13′E), China. The selected apple tree was the 5-year-old ‘Fuji’, which was a typical cultivar in Western Liaoning. The apple orchard area was 16 675 m2 with consistent tillage management conditions. Plant row and spacing was 4 m × 3 m. Background fertilizer inputs in this area were about 20 kg of organic fertilizer per tree in autumn and 3–6 kg of N fertilizer per tree in summer. The area had a good regional representation and an important network with low hilly land on a mountain geographic position. The annual precipitation and the mean annual temperature were 550 mm and 8.2 °C, respectively, where the climate was affected by a semi-humid, north temperate zone and continental monsoon, characterized by relatively hot, humid summers and cold, dry winters. The soil type was Alfisol. Site conditions were consistent, as the site was regularly managed. 2.2. Experiment design From October 2012 to October 2015, the 667 m2 study area was planted as a randomized block design with three replications of three treatments: 3-year tillage without mulching (CK), no-tillage with corn straw mulching (NTSM) and no-tillage with grass (NTG). Each treatment area was 60 m2 with 5 trees (3 trees for test and 2 trees for guarding). The details of trial processing are provided in Table 1. The amount of straw applied was 50 kg per tree with total P of 1.8 g·kg−1, and based on the dry basis of covered grass to achieve an amount of 50 kg per tree with total P of 2.3 g·kg−1. The dominant species of grasses were Setaria viridis (L.) Beauv, Echinochloa crusgalli (L.) Beauv, Chloris virgata Swartz as well as 10 other species. 2.3. Soil sample Soil sample collection was conducted in early August (in the growing season) of 2015. In the orchard, 5 soil samples of
0–20 cm and 20–40 cm (>1 kg) were collected from each tree canopy drip (1.5–2 m away from the tree trunk) and then passed through a 2 mm sieve after removing stones and coarse roots. A portion of the sieved soils (≥200 g) was kept at 4 °C for the analysis of soil phosphatase activities for one month, and the rest of the soil was air-dried and stored at room temperature for the chemical analysis. 2.4. Determination of soil properties Soil pH was determined at a 1:5 soil/deionized water ratio using a glass electrode (Shen et al., 2013). Soil moisture was determined by 105 °C drying. The measurement for organic matter content followed the methods, as described in Page (1982). Soil total nitrogen (TN) was determined by the Kjeldahl method. Soil mineral elements (potassium — K; calcium — Ca; magnesium — Mg; iron — Fe; manganese — Mn; copper — Cu: zinc — Zn; boron — B) were assayed using nitric acid (HNO3) digestion, then measured by ICP-AES (Thermo Electron ICP-6000) (Resner et al., 2015). Total P (TP) was determined by the combustion method and the molybdenum blue colorimetric method at 880 nm (Walker and Adams, 1958). Inorganic P (IP) was extracted with 0.5 mol·L−1 H2SO4 (1:25 soil-to-solution ratio for 16 h) and measured by Kuo’s method (Kuo, 1996). Organic P (OP) was calculated by subtracting the inorganic P from the TP. Available P (AP) was extracted with 0.5 mol·L−1 NaHCO3 by the Olsen method (Ryan et al., 2007). The activities of phosphatases were analyzed using fresh soil as described by Tabatabai (1994). The acid phosphomonoesterase (AcP) activity was determined by measuring the release of p-nitrophenol by incubating 1 g of soil at 37 °C for 1 h with 0.2 mL of toluene, 4 mL of buffer (pH 6.5), and 1 mL of 50 mmol p-nitrophenyl phosphate. The enzymatic activity was expressed as mg p-nitrophenol∙kg−1 soil·h−1. The activity of alkaline phosphomonoesterase (AlP) was determined with the pH 11.0 buffer. The activity of phosphodiesterase (PD) was determined by a similar procedure but with bis-p-nitrophenyl phosphate as the substrate, and the buffer was adjusted to pH 8.0. 2.5. Data analysis The soil data were calculated based on the oven-dried (105 °C) weight. The significance of differences in the chemical properties and phosphatase activities of the soil was analyzed by Oneway ANOVA with Duncan’s test at the P = 0.05 level. All of the statistical analyses were conducted using SPSS 16.0 software. Origin 8.0 was used to plot the data.
Table 1 Treatment description Abbreviation
Treatment
Original conditions CK NTSM
Tillage without mulching No-tillage with corn straw mulching
NTG
No-tillage with grass
Description of treatment The background value at the time of start of experiment Orchard wiping off weeds and conventional tillage Corn straw mulching on the soil surface for three successive years after autumn harvest in the test site Natural grass growing techniques cutting grass three times a year (in June, August and October, respectively) mulching on the soil surface for successive three years in the test site
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Table 2 Main physicochemical properties under different treatments Treatment
Soil sample position/cm
pH
Soil moisture/%
Organic matter/(g·kg−1)
Total nitrogen/(g·kg−1)
Original conditions
0–20 20–40 CK0–20 CK20–40 NTSM0–20 NTSM20–40 NTG0–20 NTG20–40
6.5 ± 0.1 ab 6.3 ± 0.3 b 6.5 ± 0.2 ab 6.2 ± 0.2 b 6.8 ± 0.3 a 6.5 ± 0.1 ab 6.7 ± 0.1 a 6.4 ± 0.2 b
15.4 ± 0.3 ab 13.2 ± 0.2 b 15.1 ± 0.4 ab 13.7 ± 0.4 b 17.6 ± 0.6 a 16.9 ± 0.5 a 16.8 ± 0.3 a 15.7 ± 0.5 ab
31.6 ± 1.1 ab 24.0 ± 0.9 b 31.4 ± 1.0 ab 23.7 ± 1.2 b 38.6 ± 0.8 a 31.9 ± 0.9 ab 37.5 ± 0.7 a 30.6 ± 1.0 ab
1.9 ± 0.2 ab 1.1 ± 0.1 b 1.8 ± 0.1 ab 1.2 ± 0.4b 2.1 ± 0.2 a 1.4 ± 0.3 b 1.9 ± 0.4 ab 1.3 ± 0.3 b
CK NTSM NTG
Note: CK, tillage without mulching; NTSM, no-tillage with corn straw mulching; NTG, no-tillage with grass. Values of soil properties are means ± standard deviation (SD, n = 3), and different lowercase letters indicate significant differences (P < 0.05) in the values using One-way ANOVA with Duncan’s test.
Table 3 Soil mineral elements under different treatments Macro element/(g·kg−1)
Micro element/(mg·kg−1)
Treatment
Soil sample position/cm
K
Ca
Mg
Fe
Mn
Cu
Zn
B
Original conditions
0–20 20–40 CK0–20 CK20–40 NTSM0–20 NTSM20–40 NTG0–20 NTG20–40
1.1 ± 0.1 ab 1.0 ± 0.2 b 1.1 ± 0.1 ab 0.9 ± 0.1 b 1.3 ± 0.3 a 1.4 ± 0.1 a 1.2 ± 0.2 ab 1.1 ± 0.1 ab
10.7 ± 0. 8a 9.8 ± 0.5 b 10.5 ± 0.8 a 9.9 ± 0.6 b 10.4 ± 0.7 a 10.0 ± 0.6 ab 10.9 ± 0.8 a 10.2 ± 0.6 ab
2.6 ± 0.2 ab 2.8 ± 0.3 ab 2.4 ± 0.1 b 2.7 ± 0.2 ab 3.1 ± 0.5 a 2.9 ± 0.3 a 2.9 ± 0.2 a 3.0 ± 0.4 a
83.1 ± 6.3 b 76.3 ± 5.9 c 84.9 ± 6.7 ab 82.4 ± 6.2 b 90.7 ± 7.8 a 87.1 ± 7.0 ab 91.5 ± 8.3 a 92.6 ± 8.5 a
133.4 ± 11.4 b 142.2 ± 12.0 b 135.7 ± 11.4 b 139.1 ± 11.7 b 148.9 ± 12.5 ab 145.3 ± 12.2 ab 150.4 ± 13.1 a 154.1 ± 13.8 a
13.9 ± 2.6 a 13.0 ± 2.1 b 13.4 ± 2.2 ab 13.3 ± 2.1 ab 13.7 ± 2.3 a 13. 1 ± 2.0 b 14.0 ± 2.8 a 13.5 ± 2.2 ab
17.5 ± 2.5 b 16.9 ± 2.1 b 17.8 ± 2.5 ab 17.4 ± 2.5 b 18.7 ± 3.1 a 18.2 ± 2.9 ab 18.4 ± 2.9 a 18.0 ± 2.6 ab
37.3 ± 4.8 b 37.7 ± 5.1 b 39.1 ± 5.6 ab 38.6 ± 5.3 ab 39.8 ± 5.9 a 39.5 ± 5.7 a 40.3 ± 6.0 a 39.7 ± 5.8 a
CK NTSM NTG
Note: CK, tillage without mulching; NTSM, no-tillage with corn straw mulching; NTG, no-tillage with grass. Values of soil properties are means ± standard deviation (SD, n = 3), and different lowercase letters indicate significant differences (P < 0.05) in the values using One-way ANOVA with Duncan’s test.
3. Results 3.1. Effects of the corn straw and grass mulching on soil physicochemical properties and mineral elements Soil physicochemical properties had small changes in original conditions and CK (Table 2). Corn straw and grass mulching increased soils’ main properties significantly (P < 0.05), however, the effect of corn straw was more obvious. The increment rate of pH was 5%–6%, soil moisture was about 2%, organic matter
was 7%–34% and TN was 13%–16%. After a 3-year corn straw and grass mulching, soil mineral element concentrations (K, Mg, Fe, Mn, Zn and B) were effectively increased which compared to original conditions and CK (Table 3), while the change of Ca and Cu concentrations was unobvious. 3.2. Effects of corn straw and grass mulching on soil P content Corn straw and grass mulching significantly affected the change of soil P content (P < 0.05) in different soil layers (Fig. 1).
Fig. 1 Soil P content variation under different treatments Different lowercase letters above the bar indicate significant differences (P < 0.05) in different soils.
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YANG Xiaozhu et al. Table 4 The increased percentage of P content under different treatments
Table 5 The increased percentage of phosphatase activity under different treatments
Treatment
Total phosphorus (TP)
Inorganic phosphorus (IP)
Organic phosphorus (OP)
Available phosphorus (AP)
Treatment Acid Alkaline Phosphodiesterase phosphomonoesterase phosphomonoesterase (PD) (AcP) (AlP)
NTSM0–20 NTSM20–40 NTG0–20 NTG20–40
12 116 71 38
10 236 40 14
14 58 111 50
−1 105 −14 86
53 NTSM0–20 NTSM20–40 19 NTG0–20 196 NTG20–40 149
Natural grass and corn straw had obviously different influences on soil P content: corn straw could significantly increase the soil P content in the 20–40 cm soil of apple trees, while grass affected the soil P content in the 0–20 cm soils except AP. After a 3-year corn straw mulching management, the increment rate of soil P was −1% to 236% in which the greatest value was in the 20–40 cm soils, and after a 3-year grass management, the increment rate of soil P was −14% to 111% of which the greatest value was in the 0–20 cm soils (Table 4). TP content had greatest increment (116%) in NTSM20–40 and least change (12%) in NTSM0–20; IP content had greatest increment (236%) in NTSM20–40 and least change (10%) in NTSM0–20; OP content had greatest increment (111%) in NTG0–20 and least change (14%) in NTSM0–20; AP content had greatest increment (105%) in NTSM20–40 and least change (−14%) in NTG0–20. 3.3. Effects of corn straw and grass mulching on soil phosphatase activity After corn straw and grass mulching, soil phosphatase activity increased significantly. The increment rate was as
126 173 31 91
149 81 154 104
follows: AcP > AlP > PD (Fig. 2). Corn straw increased AlP activity markedly and grass significantly affected AcP activity, however, the two managements both increased PD activity. The 3-year corn straw mulching made soil phosphatase activity increase at 19%–173% (Table 5), and after the 3-year grass mulching, the increment rate of phosphatase activity was 31%–196%. AcP activity had greatest increment (196%) in NTG0–20 and least change (19%) in NTSM20–40; AlP activity had greatest increment (173%) in NTSM20–40 and least change (31%) in NTG0–20; PD activity had greatest increment (154%) in NTG0–20 and least change (81%) in NTSM20–40. 3.4. Relationships among soil property, P content and phosphatase activity Soil OM, TN, IP, AcP and AlP were strongly and positively correlated with soil pH (Table 6). The TP, OP and AP were significantly and positively correlated with SM. Phosphatase activity (AlP and PD) and TN had significantly positive correlations with soil OM. Soil P contents (OP, IP and AP) were positively correlated with soil TP.
Fig. 2 Soil phosphatase activity variation under different treatments Different lowercase letters above the bar indicate significant differences (P < 0.05) in different soils.
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Table 6 Correlation coefficients among soil physicochemical properties, soil P content and phosphatase activities in different treatments
pH SM OM TN TP OP IP AP AcP AlP PD
pH
SM
OM
TN
TP
OP
IP
AP
AcP
AlP
PD
1 0.538 0.882* 0.853* 0.589 0.306 0.842* 0.755 0.873* 0.846* 0.791
1 0.497 0.256 0.863* 0.886* 0.771 0.864* 0.132 0.702 0.541
1 0.882* 0.702 0.368 0.737 0.597 0.794 0.867* 0.857*
1 0.350 0.840* 0.569 0.418 0.769 0.618 0.630
1 0.816* 0.833* 0.823* 0.335 0.803 0.677
1 0.517 0.622 0.030 0.692 0.601
1 0.970** 0.587 0.765 0.603
1 0.436 0.717 0.531
1 0.732 0.768
1 0.970**
1
Note: SM, soil moisture; OM, organic matter; TN, total nitrogen; TP, total phosphorus; OP, organic phosphorus; IP, inorganic phosphorus; AP, available phosphorus; AcP, acid phosphomonoesterase; AlP, alkaline phosphomonoesterase; PD, phosphodiesterase.* and ** indicate correlations are significant at the 0.05 and 0.01 levels, respectively.
4. Discussion 4.1. Effects of different conservation tillage practices on soil properties and mineral elements Previous research reported that corn straw mulching and grass could improve the stability of soil aggregate and increase the soil water retention so as to improve soil structure and quality (Zhang et al., 2012c). Our results indicated that soil moisture was significantly increased in mountain apple orchard soils after mulching corn straw and grass, which was in accordance with findings from previous studies (Wen et al., 2011). They further suggested that the results were caused by forming a physical isolation layer on the soil surface after mulching corn straw and grass, which decreased the evaporation of water and temperature. In addition, soil mineral element concentrations (K, Mg, Fe, Mn, Zn and B) were increased obviously after the 3-year corn straw and grass mulching. Similar results were also reported by Huo et al. (2011) and Kumar et al. (2014). When using these agricultural management approaches, soil properties and mineral elements were increased significantly which indicated that soil quality was improved effectively. The content of soil organic matter was higher in the 0–20 cm soils than in the 20–40 cm soils, however, the increasing rate of soil organic matter was higher in the 20–40 cm soil (29%– 35%) than in the 0–20 cm soils (19%–23%) after the 3-year organic material mulching. These could be attributed to the accumulation rate of organic matter because of the rapid growth and metabolism of the roots after mulching corn straw and grass (Kumar et al., 2014). Actually, organic materials were an important organic fertilizer source after rotting, which could provide a variety of nutrients for fruit tree growth (Zhang and Wen, 2012d). No fresh organic materials were used to supplement the soil; only the cultivation pattern was changed. Improvements to soil organic matter were limited, so long-term corn and grass mulching could be administered to ensure soil nutrient supplements over time (Messiga et al., 2015). 4.2. Effects of different conservation tillage practices on soil P content Corn straw mulching resulted in a significant increase in soil P content in the 20–40 cm soils, which was in accordance with
the change of soil organic matter. These results could be attributed to two factors: (1) corn straw mulching enhanced the fruit trees’ rapid growth, and further, the soil P pool was increased effectively (Fan et al., 2013); and (2) straw and no-tillage could cause an increase in the effect of soil P eluviation, which could be due to the increment of soil biological macropore, leading P to a deeper depth and further accumulation in the rhizosphere zone (Fan et al., 2012; Schotanus et al., 2013). Moreover, the increasing rate of soil AP presented −1%, which could be attributed to the immobilization effect of soil microorganisms to P in 0–20 cm soils (Zhang et al., 2012b) because straw mulching and no tillage increased microbial biomass and microbes could immobilize more AP when microbes obtained a carbon source from corn straw simultaneously (Zhang et al., 2012c). Natural grass and corn straw had a different effect on soil P content. Natural grass increased the content of TP, OP and IP in the 0–20 cm soils; however, the effect of natural grass was weaker than corn straw in the 20–40 cm soils. Moreover, the increasing rate of soil AP presented −14% in the 0–20 cm soils, which could be the result of the immobilization effect of soil microorganisms to P after natural grass. This effect was stronger than corn straw because grass mulching on soil augmented soil microorganisms’ activity significantly, yet microorganisms could immobilize more P when acquiring a carbon source (Ouni et al., 2013). According to the results, we found that corn straw mulching was more conducive to the increase of soil P content in the fruit trees’ 20–40 cm soils, while natural grass was better for increasing soil P content in the surface soils (0–20 cm). The reasons might be the grass roots and tree roots competed with the P nutrient after natural grass in the surface soils, then the nutrient was returned to the surface soils after the grass rotting (Kumar et al., 2014). However, there was no root competition after straw mulching and tree root grew fast in the 20–40 cm and the nutrient kept in the 20–40 cm soils (Messiga et al., 2015). 4.3. Effects of different conservation tillage practices on soil phosphatase activity Our results showed that corn straw mulching increased soil phosphatase activity significantly. These results could be attributed to three factors: (1) the long-term application of organic material (such as corn straw) could carry a large number of
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enzymes which might be the direct source of soil phosphatase activity (Shen and Chen, 2005); (2) the increase in enzyme substrate, which could promote soil phosphatase activity boosting after corn straw mulching (Deng and Tabatabai, 1997; Wang et al., 2011); and (3) the increase in microbial biomass because of corn straw, which could provide a sufficient carbon source; therefore, soil microbial activity was strengthened so that soil phosphatase activity increased because most of the soil phosphatase is derived from microorganisms (Browman and Tabatabai, 1978; Turner and Haygarth, 2005). Compared with AcP and PD, AlP activity had a greater increment which was related to soil pH. These results showed that corn straw mulching could gradually improve soil acidification, and indicated that the improvement of the soil environment enhanced the AlP activity (Zhang et al., 2012a). AlP played a more important role in regulating the bio-availability of P nutrition than other phosphatases (Sakurai et al., 2008). Therefore, corn straw mulching had a positive effect on improving the biological effectiveness of soil P. The PD activity increased in the 0–20 cm and 20–40 cm soils after corn straw and grass mulching, however, the effect of grass was stronger than corn straw. Furthermore, corn straw mulching was more conducive to the increase of AlP activity, while natural grass was better for increasing AcP activity. These results, mainly attributed to AcP, come from the secretion of fungi and plant roots which are directly related to grass roots (Turner and Haygarth, 2005). However, AlP was believed to result entirely from microorganisms because corn straw could bring abundant microorganisms (Sakurai et al., 2008; Wei et al., 2014b). Thus, corn straw and grass had different effects on soil phosphatase activity, which could provide a basis for the theory that the improvement of soil fertility is dependent on soil types. 4.4. Factors impacting soil P distribution in different treatments The results indicated that SM was significantly positively correlated with TP, OP and AP contents under corn mulching and grass which suggested that water was the most important factor affecting P nutrition in Western Liaoning and corn mulching and grass could increase soil water effectively under drought condition. Soil enzymes have been regarded as very good indicators of the changes in the soil properties because of their sensitivity to soil management practices (Roldan et al., 2005). Our results showed that AlP and PD had significantly positive correlation with soil OM. These results were attributed to soil enzymes that mainly come from the soil microorganism metabolites and plant root secretion, with the increase of grass root system growth, root system secretions and microbial content were increased in soil, leading to enzyme activity increased in the soil surface (Yao et al., 2006; Duarte et al., 2008; Reboreda and Caçador, 2008). 5. Conclusions Soil quality was effectively improved by corn mulching and grass, in which SM, TN, OM, pH and mineral elements were increased. In contrast, the effect of corn mulching was better than that of grass. Further, soil P content and phosphatase activity both increased markedly. The results indicate that corn straw and
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grass could be responsible for an increment of soil P content and phosphatase activity. There are better clear effects of these managements on mountain orchard soil P nutrient increasing which reveals that corn mulching and grass could replace phosphate fertilizer. Future studies should be focused on reducing phosphate fertilizer application to soil, and pay more attention to OP mineralization and sustainable utilization of apple orchard soils in mountain areas. Acknowledgments This research was financed by the National High-Technology Project (2013AA102405). References Bai, G.S., Du, S.N., Li, M.X., Geng, G.J., Zhang, R., 2010. Influencing factors on apple development in Loess Hilly and Gully region of Northern Shaanxi. Ecol Econ, 233: 60–64. (in Chinese) Browman, M.G., Tabatabai, M.A., 1978. Phosphodiesterase activity of soils. Soil Sci Soc Am J, 42: 284–290. Chintala, R., Schumacher, T.E., McDonald, L.M., Clay, D.E., Malo, D., Papiernik, S.K., 2014. Phosphorus sorption and availability from biochars and soil/ biochar mixtures. Clean Soil Air Water, 42: 626–634. Deng, S.P., Tabatabai, M.A., 1997. Effect of tillage and residue management on enzyme activities in soils: III. Phosphatases and arylsulfatase. Biol Fert Soils, 24: 141–146. Duarte, B., Reboreda, R., Caçador, I., 2008. Seasonal variation of extracellular enzymatic activity and its influence on metal speciation in a polluted salt marsh. Chemosphere, 73: 1056–1063. Fan, R.Q., Zhang, X.P., Liang, A.Z., Shi, X.H., Chen, X.W., Bao, K.S., Yang, X.M., Jia, S.X., 2012. Tillage and rotation effects on crop yield and profitability on a black soil in Northeast China. Can J Soil Sci, 92: 463–470. Fan, R.Q., Zhang, X.P., Yang, X.M., Liang, A.Z., Jia, S.X., Chen, X.W., 2013. Effects of tillage management on infiltration and preferential flow in a black soil, Northeast China. Chinese Geogr Sci, 23: 312–320. Huo, Y., Zhang, J., Wang, M.C., Yao, Y.C., 2011. Effects of inter-row planting grasses on variations and relationships of soil organic matter and soil nutrients in ear orchard. Sci Agric Sin, 44: 1415–1424. Kumar, R., Sood, S., Sharma, S., Kasana, R.C., Pathania, V.L., Singh, B., Singh, R.D., 2014. Effect of plant spacing and organic mulch on growth, yield and quality of natural sweetener plant Stevia and soil fertility in Western Himalayas. Int J Plant Prod, 8: 311–334. Kuo, S., 1996. Phosphorus, in: Bridgham, J.M. (Ed.), Methods of Soil Analysis. Part 3. ASA and SSSA, Madison, WI, pp. 869–919. Messiga, A.J., Sharifi, M., Munroe, S., 2015. Combinations of cover crop mixtures and bio-waste composts enhance biomass production and nutrients accumulation: a greenhouse study. Renew Agr Food Syst, 31: 1–9. Ouni, Y., Lakhdara, A., Scelza, R., Scotti, R., Abdelly, C., Barhoumi, Z., Rao, M.A., 2013. Effects of two composts and two grasses on microbial biomass and biological activity in a salt-affected soil. Ecol Eng, 60: 363–369. Page, A.L., 1982. Methods of Soil Analysis. Chemical and Microbiological Properties. American Society of Agronomy, Madison, WI. Reboreda, R., Caçador, I., 2008. Enzymatic activity in the rhizosphere of Spartina maritima: potential contribution for phytoremediation of metals. Mar Environ Res, 65: 77–84. Resner, K., Yoo, K., Sebestyen, S.D., Aufdenkampe, A., Hale, C., Lyttle, A., Blum, A., 2015. Invasive earthworms deplete key soil inorganic nutrients (Ca, Mg, K, and P) in a Northern hardwood forest. Ecosystems, 18: 89– 102. Roldan, A., Salinas-Garcia, J.R., Alguacil, M.M., Diaz, E., Caravaca, F., 2005. Soil enzyme activities suggest advantages of conservation tillage practices in sorghum cultivation under subtropical conditions. Geoderma, 129: 178– 185.
Effect of Conservation Tillage Practices on Soil Phosphorus Nutrition in an Apple Orchard Ryan, J., Estefan, G., Rashid, A., 2007. Soil and Plant Analysis Laboratory Manual. ICARDA, Syria. Sakurai, M., Wasaki, J., Tomizawa, Y., Shinano, T., Osaki, M., 2008. Analysis of bacterial communities on alkaline phosphatase genes in soil supplied with organic matter. Soil Sci Plant Nutr, 54: 62–71. Schotanus, D., van der Ploeg, M.J., van der Zee, S., 2013. Spatial distribution of solute leaching with snowmelt and irrigation: measurements and simulations. Hydrol Earth Syst Sci, 17: 1547–1560. Shen, C.C., Xiong, J.B., Zhang, H.Y., Feng, Y.Z., Lin, X.G., Li, X.Y., Liang, W.J., Chu, H.Y., 2013. Soil pH drives the spatial distribution of bacterial communities along elevation on Changbai Mountain. Soil Biol Biochem, 57: 204–211. Shen, J.P., Chen, L.J., 2005. Response of soil phosphatase activities to fertilization, planting and tillage systems. Chinese J Soil Sci, 36: 622–627. (in Chinese) Tabatabai, M.A., 1994. Soil enzymes, in: Weaver, R.W., Angle, J.R., Bottomley, P.S. (Eds.), Methods of Soil Analysis. Part 2: Microbiological and Biochemical Properties. Soil Science Society of America, Madison WI, pp. 775–833. Turner, B.L., Haygarth, P.M., 2005. Phosphatase activity in temperate pasture soils: potential regulation of labile organic phosphorus turnover by phosphodiesterase activity. Sci Total Environ, 344: 27–36. Walker, T., Adams, A.R., 1958. Studies on soil organic matter: I. influence of phosphorus content of parent materials on accumulations of carbon, nitrogen, sulfur, and organic phosphorus in grassland soils. Soil Sci, 85: 307–318. Wang, J.B., Chen, Z.H., Chen, L.J., Zhu, A.N., Wu, Z.J., 2011. Surface soil phosphorus and phosphatase activities affected by tillage and crop residue input amounts. Plant Soil Environ, 57: 251–257.
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Wei, K., Chen, Z.H., Zhang, X.P., Liang, W.J., Chen, L.J., 2014b. Tillage effects on phosphorus composition and phosphatase activities in soil aggregates. Geoderma, 217–218: 37–44. Wei, K., Chen, Z.H., Zhu, A.N., Zhang, J.B., Chen, L.J., 2014a. Application of 31P NMR spectroscopy in determining phosphatase activities and P composition in soil aggregates influenced by tillage and residue management practices. Soil Till Res, 138: 35–43. Wen, X.X., Yin, R.J., Gao, M.S., Ai, S.L., 2011. Spatiotemporal dynamics of soil enzyme activities and microbes apple orchard soil under different mulching management. Acta Agric Bore Occi Sin, 20: 82–88. (in Chinese) Yao, X.H., Hang, M., Lü, Z.H., Yuan, H.P., 2006. Influence of acetamiprid on soil enzymatic activities and respiration. Eur J Soil Biol, 42: 120–126. Zhang, A.M., Chen, Z.H., Zhang, G.N., Chen, L.J., Wu, Z.J., 2012a. Soil phosphorus composition determined by 31P NMR spectroscopy and relative phosphatase activities influenced by land use. Eur J Soil Biol, 52: 73–77. Zhang, B., He, H.B., Ding, X.L., Zhang, X.D., Zhang, X.P., Yang, X.M., Filley, T.R., 2012b. Soil microbial community dynamics over a maize (Zea mays L.) growing season under conventional- and no-tillage practices in a rainfed agroecosystem. Soil Till Res, 124: 153–160. Zhang, S.X., Li, Q., Zhang, X.P., Wei, K., Chen, L.J., Liang, W.J., 2012c. Effects of conservation tillage on soil aggregation and aggregate binding agents in black soil of Northeast China. Soil Till Res, 124: 196–202. Zhang, Z.X., Wen, Q.L., 2012d. Effects of maize straw mulching on soil physical properties in spring wheat fields. J Trit Crop, 32: 1006–1010. (in Chinese) Zhu, Y.R., Wu, F.C., Feng, W.Y., Liu, S.S., Giesya, J.P., 2016. Interaction of alkaline phosphatase with minerals and sediments: Activities, kinetics and hydrolysis of organic phosphorus. Colloid Surface A, 495: 46–53.
Horticultural Plant Journal Available online at www.sciencedirect.com The journal’s homepage: http://www.journals.elsevier.com/horticultural-plant-journal
Effect of Conservation Tillage Practices on Soil Phosphorus Nutrition in an Apple Orchard YANG Xiaozhu, LI Zhuang, and CHENG Cungang * Institute of Pomology, Chinese Academy of Agricultural Sciences, Xingcheng, Liaoning 125100, China Received 28 August 2016; Received in revised form 16 October 2016; Accepted 2 November 2016 Available online 16 February 2017
Abstract Soil phosphorus (P) is an essential and limiting element for plant growth, which is significantly affected by different approaches to soil management. In order to reveal the effect of different management approaches on soil P and phosphatase activity in 0–20 cm and 20–40 cm soil, this research was conducted to study variations in the characteristics of P and phosphatase activity under 3-year tillage without mulching (CK), notillage with corn straw mulching (NTSM) and no-tillage with grass (NTG) in Liaoning apple orchard. The results showed that NTSM and NTG could significantly increase soil P content (P < 0.05) as compared with CK. However, the effect was different between NTSM and NTG; with the NTSM approach, the improvement in the P content in 20–40 cm was remarkable, and in the NTG approach, the improvement in the soil surface P content was significant. At the same time, soil phosphatase activity significantly increased (P < 0.05) under NTSM and NTG. The soil surface and 20–40 cm phosphodiesterase (PD) activity was enhanced under the two management approaches, however, the effect of NTG was stronger than NTSM. In addition, NTSM was more conducive to increasing alkaline phosphomonoesterase (AlP), and NTG was more conducive to increasing acid phosphomonoesterase (AcP). Our findings highlight the variation of dominant mechanisms involved in soil P with different mulching materials application. NTSM and NTG could have the potential to increase P content and phosphatase activity, and provide a basis for using this method to improve P phytoavailability and reduce the application of soil fertilizer. Keywords: apple orchard; phosphorus; phosphatase activity; corn straw mulching; grassing
1. Introduction Hilly areas are traditional fruit producing areas which, due to a mountain climate and special soils, produce sweet fruits. However, it is difficult to manage this type of cultivated land primarily because the soil nutrient supply is decreasing in many mountain apple orchards (Bai et al., 2010). In addition, unreasonable orchard management measures, such as excessive fertilizers that actually make soil structure worse, reduce nutrient content and the ability of the soil to generate a sufficient supply of nutrients. Soil nutrients, and especially the retention and supply capacity of soil phosphorus (P), are an important foundation for maintaining agricultural productivity and orchard soil fertility. However, P nutrients are liable to be adsorbed, fixed and precipitated by soil solid constituents (Chintala et al., 2014), forming an organic P composition which is difficult for the plant to use.
Organic P could be available for organisms’ uptake only under the hydrolysis of phosphatase (Zhu et al., 2016). Therefore, understanding the P form, content and phosphatase activity in apple orchard soils is of strategic importance for improving organism P nutrition. Soil phosphatase is a kind of specific enzyme that hydrolyzes soil organic P, an activity that affects the transformation and bio-availability of soil P (Zhang et al., 2012a). Additionally, some studies have indicated that corn straw mulching and natural grassing were effective methods for improving soil quality because these management strategies could protect soil status, raise water utilization ratio, restrain violent changes in soil temperature and increase soil organic matter content (Wen et al., 2011; Wei et al., 2014a). Therefore, corn mulching and natural grassing were the most important agricultural management measures for controlling water and soil erosion and
* Corresponding author. Tel.: +86 429 3598158 E-mail address: [email protected] Peer review under responsibility of Chinese Society for Horticultural Science (CSHS) and Institute of Vegetables and Flowers (IVF), Chinese Academy of Agricultural Sciences (CAAS) http://dx.doi.org/10.1016/j.hpj.2016.11.005 2468-0141/© 2016 Chinese Society for Horticultural Science (CSHS) and Institute of Vegetables and Flowers (IVF), Chinese Academy of Agricultural Sciences (CAAS). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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improving fertility conditions. However, the effects of longtime corn straw mulching and natural grassing on apple orchard soil P nutrients and phosphatase activity are still unknown. In this study, we selected the 3-year mountain apple orchard soils with corn straw mulching and natural grassing in order to study how soil P and phosphatase activity were affected. The objective was to explore the mechanism of soil P nutrition under corn straw mulching and natural grassing, which is important for improving agricultural practices, as well as effects on the environment and other natural resources. 2. Materials and methods 2.1. Study site The study site was located at the Apple Experiment Station of Chinese Academy of Agricultural Sciences (CAAS) in Western Liaoning (41°06′N, 119°13′E), China. The selected apple tree was the 5-year-old ‘Fuji’, which was a typical cultivar in Western Liaoning. The apple orchard area was 16 675 m2 with consistent tillage management conditions. Plant row and spacing was 4 m × 3 m. Background fertilizer inputs in this area were about 20 kg of organic fertilizer per tree in autumn and 3–6 kg of N fertilizer per tree in summer. The area had a good regional representation and an important network with low hilly land on a mountain geographic position. The annual precipitation and the mean annual temperature were 550 mm and 8.2 °C, respectively, where the climate was affected by a semi-humid, north temperate zone and continental monsoon, characterized by relatively hot, humid summers and cold, dry winters. The soil type was Alfisol. Site conditions were consistent, as the site was regularly managed. 2.2. Experiment design From October 2012 to October 2015, the 667 m2 study area was planted as a randomized block design with three replications of three treatments: 3-year tillage without mulching (CK), no-tillage with corn straw mulching (NTSM) and no-tillage with grass (NTG). Each treatment area was 60 m2 with 5 trees (3 trees for test and 2 trees for guarding). The details of trial processing are provided in Table 1. The amount of straw applied was 50 kg per tree with total P of 1.8 g·kg−1, and based on the dry basis of covered grass to achieve an amount of 50 kg per tree with total P of 2.3 g·kg−1. The dominant species of grasses were Setaria viridis (L.) Beauv, Echinochloa crusgalli (L.) Beauv, Chloris virgata Swartz as well as 10 other species. 2.3. Soil sample Soil sample collection was conducted in early August (in the growing season) of 2015. In the orchard, 5 soil samples of
0–20 cm and 20–40 cm (>1 kg) were collected from each tree canopy drip (1.5–2 m away from the tree trunk) and then passed through a 2 mm sieve after removing stones and coarse roots. A portion of the sieved soils (≥200 g) was kept at 4 °C for the analysis of soil phosphatase activities for one month, and the rest of the soil was air-dried and stored at room temperature for the chemical analysis. 2.4. Determination of soil properties Soil pH was determined at a 1:5 soil/deionized water ratio using a glass electrode (Shen et al., 2013). Soil moisture was determined by 105 °C drying. The measurement for organic matter content followed the methods, as described in Page (1982). Soil total nitrogen (TN) was determined by the Kjeldahl method. Soil mineral elements (potassium — K; calcium — Ca; magnesium — Mg; iron — Fe; manganese — Mn; copper — Cu: zinc — Zn; boron — B) were assayed using nitric acid (HNO3) digestion, then measured by ICP-AES (Thermo Electron ICP-6000) (Resner et al., 2015). Total P (TP) was determined by the combustion method and the molybdenum blue colorimetric method at 880 nm (Walker and Adams, 1958). Inorganic P (IP) was extracted with 0.5 mol·L−1 H2SO4 (1:25 soil-to-solution ratio for 16 h) and measured by Kuo’s method (Kuo, 1996). Organic P (OP) was calculated by subtracting the inorganic P from the TP. Available P (AP) was extracted with 0.5 mol·L−1 NaHCO3 by the Olsen method (Ryan et al., 2007). The activities of phosphatases were analyzed using fresh soil as described by Tabatabai (1994). The acid phosphomonoesterase (AcP) activity was determined by measuring the release of p-nitrophenol by incubating 1 g of soil at 37 °C for 1 h with 0.2 mL of toluene, 4 mL of buffer (pH 6.5), and 1 mL of 50 mmol p-nitrophenyl phosphate. The enzymatic activity was expressed as mg p-nitrophenol∙kg−1 soil·h−1. The activity of alkaline phosphomonoesterase (AlP) was determined with the pH 11.0 buffer. The activity of phosphodiesterase (PD) was determined by a similar procedure but with bis-p-nitrophenyl phosphate as the substrate, and the buffer was adjusted to pH 8.0. 2.5. Data analysis The soil data were calculated based on the oven-dried (105 °C) weight. The significance of differences in the chemical properties and phosphatase activities of the soil was analyzed by Oneway ANOVA with Duncan’s test at the P = 0.05 level. All of the statistical analyses were conducted using SPSS 16.0 software. Origin 8.0 was used to plot the data.
Table 1 Treatment description Abbreviation
Treatment
Original conditions CK NTSM
Tillage without mulching No-tillage with corn straw mulching
NTG
No-tillage with grass
Description of treatment The background value at the time of start of experiment Orchard wiping off weeds and conventional tillage Corn straw mulching on the soil surface for three successive years after autumn harvest in the test site Natural grass growing techniques cutting grass three times a year (in June, August and October, respectively) mulching on the soil surface for successive three years in the test site
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Table 2 Main physicochemical properties under different treatments Treatment
Soil sample position/cm
pH
Soil moisture/%
Organic matter/(g·kg−1)
Total nitrogen/(g·kg−1)
Original conditions
0–20 20–40 CK0–20 CK20–40 NTSM0–20 NTSM20–40 NTG0–20 NTG20–40
6.5 ± 0.1 ab 6.3 ± 0.3 b 6.5 ± 0.2 ab 6.2 ± 0.2 b 6.8 ± 0.3 a 6.5 ± 0.1 ab 6.7 ± 0.1 a 6.4 ± 0.2 b
15.4 ± 0.3 ab 13.2 ± 0.2 b 15.1 ± 0.4 ab 13.7 ± 0.4 b 17.6 ± 0.6 a 16.9 ± 0.5 a 16.8 ± 0.3 a 15.7 ± 0.5 ab
31.6 ± 1.1 ab 24.0 ± 0.9 b 31.4 ± 1.0 ab 23.7 ± 1.2 b 38.6 ± 0.8 a 31.9 ± 0.9 ab 37.5 ± 0.7 a 30.6 ± 1.0 ab
1.9 ± 0.2 ab 1.1 ± 0.1 b 1.8 ± 0.1 ab 1.2 ± 0.4b 2.1 ± 0.2 a 1.4 ± 0.3 b 1.9 ± 0.4 ab 1.3 ± 0.3 b
CK NTSM NTG
Note: CK, tillage without mulching; NTSM, no-tillage with corn straw mulching; NTG, no-tillage with grass. Values of soil properties are means ± standard deviation (SD, n = 3), and different lowercase letters indicate significant differences (P < 0.05) in the values using One-way ANOVA with Duncan’s test.
Table 3 Soil mineral elements under different treatments Macro element/(g·kg−1)
Micro element/(mg·kg−1)
Treatment
Soil sample position/cm
K
Ca
Mg
Fe
Mn
Cu
Zn
B
Original conditions
0–20 20–40 CK0–20 CK20–40 NTSM0–20 NTSM20–40 NTG0–20 NTG20–40
1.1 ± 0.1 ab 1.0 ± 0.2 b 1.1 ± 0.1 ab 0.9 ± 0.1 b 1.3 ± 0.3 a 1.4 ± 0.1 a 1.2 ± 0.2 ab 1.1 ± 0.1 ab
10.7 ± 0. 8a 9.8 ± 0.5 b 10.5 ± 0.8 a 9.9 ± 0.6 b 10.4 ± 0.7 a 10.0 ± 0.6 ab 10.9 ± 0.8 a 10.2 ± 0.6 ab
2.6 ± 0.2 ab 2.8 ± 0.3 ab 2.4 ± 0.1 b 2.7 ± 0.2 ab 3.1 ± 0.5 a 2.9 ± 0.3 a 2.9 ± 0.2 a 3.0 ± 0.4 a
83.1 ± 6.3 b 76.3 ± 5.9 c 84.9 ± 6.7 ab 82.4 ± 6.2 b 90.7 ± 7.8 a 87.1 ± 7.0 ab 91.5 ± 8.3 a 92.6 ± 8.5 a
133.4 ± 11.4 b 142.2 ± 12.0 b 135.7 ± 11.4 b 139.1 ± 11.7 b 148.9 ± 12.5 ab 145.3 ± 12.2 ab 150.4 ± 13.1 a 154.1 ± 13.8 a
13.9 ± 2.6 a 13.0 ± 2.1 b 13.4 ± 2.2 ab 13.3 ± 2.1 ab 13.7 ± 2.3 a 13. 1 ± 2.0 b 14.0 ± 2.8 a 13.5 ± 2.2 ab
17.5 ± 2.5 b 16.9 ± 2.1 b 17.8 ± 2.5 ab 17.4 ± 2.5 b 18.7 ± 3.1 a 18.2 ± 2.9 ab 18.4 ± 2.9 a 18.0 ± 2.6 ab
37.3 ± 4.8 b 37.7 ± 5.1 b 39.1 ± 5.6 ab 38.6 ± 5.3 ab 39.8 ± 5.9 a 39.5 ± 5.7 a 40.3 ± 6.0 a 39.7 ± 5.8 a
CK NTSM NTG
Note: CK, tillage without mulching; NTSM, no-tillage with corn straw mulching; NTG, no-tillage with grass. Values of soil properties are means ± standard deviation (SD, n = 3), and different lowercase letters indicate significant differences (P < 0.05) in the values using One-way ANOVA with Duncan’s test.
3. Results 3.1. Effects of the corn straw and grass mulching on soil physicochemical properties and mineral elements Soil physicochemical properties had small changes in original conditions and CK (Table 2). Corn straw and grass mulching increased soils’ main properties significantly (P < 0.05), however, the effect of corn straw was more obvious. The increment rate of pH was 5%–6%, soil moisture was about 2%, organic matter
was 7%–34% and TN was 13%–16%. After a 3-year corn straw and grass mulching, soil mineral element concentrations (K, Mg, Fe, Mn, Zn and B) were effectively increased which compared to original conditions and CK (Table 3), while the change of Ca and Cu concentrations was unobvious. 3.2. Effects of corn straw and grass mulching on soil P content Corn straw and grass mulching significantly affected the change of soil P content (P < 0.05) in different soil layers (Fig. 1).
Fig. 1 Soil P content variation under different treatments Different lowercase letters above the bar indicate significant differences (P < 0.05) in different soils.
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YANG Xiaozhu et al. Table 4 The increased percentage of P content under different treatments
Table 5 The increased percentage of phosphatase activity under different treatments
Treatment
Total phosphorus (TP)
Inorganic phosphorus (IP)
Organic phosphorus (OP)
Available phosphorus (AP)
Treatment Acid Alkaline Phosphodiesterase phosphomonoesterase phosphomonoesterase (PD) (AcP) (AlP)
NTSM0–20 NTSM20–40 NTG0–20 NTG20–40
12 116 71 38
10 236 40 14
14 58 111 50
−1 105 −14 86
53 NTSM0–20 NTSM20–40 19 NTG0–20 196 NTG20–40 149
Natural grass and corn straw had obviously different influences on soil P content: corn straw could significantly increase the soil P content in the 20–40 cm soil of apple trees, while grass affected the soil P content in the 0–20 cm soils except AP. After a 3-year corn straw mulching management, the increment rate of soil P was −1% to 236% in which the greatest value was in the 20–40 cm soils, and after a 3-year grass management, the increment rate of soil P was −14% to 111% of which the greatest value was in the 0–20 cm soils (Table 4). TP content had greatest increment (116%) in NTSM20–40 and least change (12%) in NTSM0–20; IP content had greatest increment (236%) in NTSM20–40 and least change (10%) in NTSM0–20; OP content had greatest increment (111%) in NTG0–20 and least change (14%) in NTSM0–20; AP content had greatest increment (105%) in NTSM20–40 and least change (−14%) in NTG0–20. 3.3. Effects of corn straw and grass mulching on soil phosphatase activity After corn straw and grass mulching, soil phosphatase activity increased significantly. The increment rate was as
126 173 31 91
149 81 154 104
follows: AcP > AlP > PD (Fig. 2). Corn straw increased AlP activity markedly and grass significantly affected AcP activity, however, the two managements both increased PD activity. The 3-year corn straw mulching made soil phosphatase activity increase at 19%–173% (Table 5), and after the 3-year grass mulching, the increment rate of phosphatase activity was 31%–196%. AcP activity had greatest increment (196%) in NTG0–20 and least change (19%) in NTSM20–40; AlP activity had greatest increment (173%) in NTSM20–40 and least change (31%) in NTG0–20; PD activity had greatest increment (154%) in NTG0–20 and least change (81%) in NTSM20–40. 3.4. Relationships among soil property, P content and phosphatase activity Soil OM, TN, IP, AcP and AlP were strongly and positively correlated with soil pH (Table 6). The TP, OP and AP were significantly and positively correlated with SM. Phosphatase activity (AlP and PD) and TN had significantly positive correlations with soil OM. Soil P contents (OP, IP and AP) were positively correlated with soil TP.
Fig. 2 Soil phosphatase activity variation under different treatments Different lowercase letters above the bar indicate significant differences (P < 0.05) in different soils.
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Table 6 Correlation coefficients among soil physicochemical properties, soil P content and phosphatase activities in different treatments
pH SM OM TN TP OP IP AP AcP AlP PD
pH
SM
OM
TN
TP
OP
IP
AP
AcP
AlP
PD
1 0.538 0.882* 0.853* 0.589 0.306 0.842* 0.755 0.873* 0.846* 0.791
1 0.497 0.256 0.863* 0.886* 0.771 0.864* 0.132 0.702 0.541
1 0.882* 0.702 0.368 0.737 0.597 0.794 0.867* 0.857*
1 0.350 0.840* 0.569 0.418 0.769 0.618 0.630
1 0.816* 0.833* 0.823* 0.335 0.803 0.677
1 0.517 0.622 0.030 0.692 0.601
1 0.970** 0.587 0.765 0.603
1 0.436 0.717 0.531
1 0.732 0.768
1 0.970**
1
Note: SM, soil moisture; OM, organic matter; TN, total nitrogen; TP, total phosphorus; OP, organic phosphorus; IP, inorganic phosphorus; AP, available phosphorus; AcP, acid phosphomonoesterase; AlP, alkaline phosphomonoesterase; PD, phosphodiesterase.* and ** indicate correlations are significant at the 0.05 and 0.01 levels, respectively.
4. Discussion 4.1. Effects of different conservation tillage practices on soil properties and mineral elements Previous research reported that corn straw mulching and grass could improve the stability of soil aggregate and increase the soil water retention so as to improve soil structure and quality (Zhang et al., 2012c). Our results indicated that soil moisture was significantly increased in mountain apple orchard soils after mulching corn straw and grass, which was in accordance with findings from previous studies (Wen et al., 2011). They further suggested that the results were caused by forming a physical isolation layer on the soil surface after mulching corn straw and grass, which decreased the evaporation of water and temperature. In addition, soil mineral element concentrations (K, Mg, Fe, Mn, Zn and B) were increased obviously after the 3-year corn straw and grass mulching. Similar results were also reported by Huo et al. (2011) and Kumar et al. (2014). When using these agricultural management approaches, soil properties and mineral elements were increased significantly which indicated that soil quality was improved effectively. The content of soil organic matter was higher in the 0–20 cm soils than in the 20–40 cm soils, however, the increasing rate of soil organic matter was higher in the 20–40 cm soil (29%– 35%) than in the 0–20 cm soils (19%–23%) after the 3-year organic material mulching. These could be attributed to the accumulation rate of organic matter because of the rapid growth and metabolism of the roots after mulching corn straw and grass (Kumar et al., 2014). Actually, organic materials were an important organic fertilizer source after rotting, which could provide a variety of nutrients for fruit tree growth (Zhang and Wen, 2012d). No fresh organic materials were used to supplement the soil; only the cultivation pattern was changed. Improvements to soil organic matter were limited, so long-term corn and grass mulching could be administered to ensure soil nutrient supplements over time (Messiga et al., 2015). 4.2. Effects of different conservation tillage practices on soil P content Corn straw mulching resulted in a significant increase in soil P content in the 20–40 cm soils, which was in accordance with
the change of soil organic matter. These results could be attributed to two factors: (1) corn straw mulching enhanced the fruit trees’ rapid growth, and further, the soil P pool was increased effectively (Fan et al., 2013); and (2) straw and no-tillage could cause an increase in the effect of soil P eluviation, which could be due to the increment of soil biological macropore, leading P to a deeper depth and further accumulation in the rhizosphere zone (Fan et al., 2012; Schotanus et al., 2013). Moreover, the increasing rate of soil AP presented −1%, which could be attributed to the immobilization effect of soil microorganisms to P in 0–20 cm soils (Zhang et al., 2012b) because straw mulching and no tillage increased microbial biomass and microbes could immobilize more AP when microbes obtained a carbon source from corn straw simultaneously (Zhang et al., 2012c). Natural grass and corn straw had a different effect on soil P content. Natural grass increased the content of TP, OP and IP in the 0–20 cm soils; however, the effect of natural grass was weaker than corn straw in the 20–40 cm soils. Moreover, the increasing rate of soil AP presented −14% in the 0–20 cm soils, which could be the result of the immobilization effect of soil microorganisms to P after natural grass. This effect was stronger than corn straw because grass mulching on soil augmented soil microorganisms’ activity significantly, yet microorganisms could immobilize more P when acquiring a carbon source (Ouni et al., 2013). According to the results, we found that corn straw mulching was more conducive to the increase of soil P content in the fruit trees’ 20–40 cm soils, while natural grass was better for increasing soil P content in the surface soils (0–20 cm). The reasons might be the grass roots and tree roots competed with the P nutrient after natural grass in the surface soils, then the nutrient was returned to the surface soils after the grass rotting (Kumar et al., 2014). However, there was no root competition after straw mulching and tree root grew fast in the 20–40 cm and the nutrient kept in the 20–40 cm soils (Messiga et al., 2015). 4.3. Effects of different conservation tillage practices on soil phosphatase activity Our results showed that corn straw mulching increased soil phosphatase activity significantly. These results could be attributed to three factors: (1) the long-term application of organic material (such as corn straw) could carry a large number of
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enzymes which might be the direct source of soil phosphatase activity (Shen and Chen, 2005); (2) the increase in enzyme substrate, which could promote soil phosphatase activity boosting after corn straw mulching (Deng and Tabatabai, 1997; Wang et al., 2011); and (3) the increase in microbial biomass because of corn straw, which could provide a sufficient carbon source; therefore, soil microbial activity was strengthened so that soil phosphatase activity increased because most of the soil phosphatase is derived from microorganisms (Browman and Tabatabai, 1978; Turner and Haygarth, 2005). Compared with AcP and PD, AlP activity had a greater increment which was related to soil pH. These results showed that corn straw mulching could gradually improve soil acidification, and indicated that the improvement of the soil environment enhanced the AlP activity (Zhang et al., 2012a). AlP played a more important role in regulating the bio-availability of P nutrition than other phosphatases (Sakurai et al., 2008). Therefore, corn straw mulching had a positive effect on improving the biological effectiveness of soil P. The PD activity increased in the 0–20 cm and 20–40 cm soils after corn straw and grass mulching, however, the effect of grass was stronger than corn straw. Furthermore, corn straw mulching was more conducive to the increase of AlP activity, while natural grass was better for increasing AcP activity. These results, mainly attributed to AcP, come from the secretion of fungi and plant roots which are directly related to grass roots (Turner and Haygarth, 2005). However, AlP was believed to result entirely from microorganisms because corn straw could bring abundant microorganisms (Sakurai et al., 2008; Wei et al., 2014b). Thus, corn straw and grass had different effects on soil phosphatase activity, which could provide a basis for the theory that the improvement of soil fertility is dependent on soil types. 4.4. Factors impacting soil P distribution in different treatments The results indicated that SM was significantly positively correlated with TP, OP and AP contents under corn mulching and grass which suggested that water was the most important factor affecting P nutrition in Western Liaoning and corn mulching and grass could increase soil water effectively under drought condition. Soil enzymes have been regarded as very good indicators of the changes in the soil properties because of their sensitivity to soil management practices (Roldan et al., 2005). Our results showed that AlP and PD had significantly positive correlation with soil OM. These results were attributed to soil enzymes that mainly come from the soil microorganism metabolites and plant root secretion, with the increase of grass root system growth, root system secretions and microbial content were increased in soil, leading to enzyme activity increased in the soil surface (Yao et al., 2006; Duarte et al., 2008; Reboreda and Caçador, 2008). 5. Conclusions Soil quality was effectively improved by corn mulching and grass, in which SM, TN, OM, pH and mineral elements were increased. In contrast, the effect of corn mulching was better than that of grass. Further, soil P content and phosphatase activity both increased markedly. The results indicate that corn straw and
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