Effects of potassium fertilization on winter wheat under different production practices in the North China Plain

Field Crops Research 140 (2013) 69–76

Contents lists available at SciVerse ScienceDirect

Field Crops Research journal homepage: www.elsevier.com/locate/fcr

Effects of potassium fertilization on winter wheat under different production practices in the North China Plain Junfang Niu a,∗ , Weifeng Zhang b , Shuhua Ru c , Xinping Chen b , Kai Xiao d , Xiying Zhang a , Menachem Assaraf e , Patricia Imas e , Hillel Magen e , Fusuo Zhang b,∗∗ a Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China b Center for Resources, Environment and Food Security, China Agricultural University, Key Laboratory of Plant-Soil Interactions, Ministry of Education, Beijing 100193, China c Institute of Agricultural Resources and Environment, Hebei Academy of Agriculture and Forestry Sciences, Shijiazhuang 050051, China d College of Agronomy, Agricultural University of Hebei, Baoding 071001, China e International Potash Institute, Baumgärtlistrasse 17, P.O. Box 569, CH-8810 Horgen, Switzerland

a r t i c l e

i n f o

Article history: Received 22 February 2012 Received in revised form 12 October 2012 Accepted 13 October 2012 Keywords: Potassium Winter wheat (Triticum aestivum L.) Production practices Potassium balance

a b s t r a c t Haplic Luvisols with low to medium grade of potassium occur in major agricultural regions of north China. Moreover, unbalanced fertilization has rapidly depleted soil available potassium (K) and hence caused significant yield response to K fertilization in many intensive farming systems. Our specific objectives in this study were to determine winter wheat (Triticum aestivum L.) response to K fertilization on Haplic Luvisols in the North China Plain (NCP) as affected by conventional as well as high-yielding production practices. Four field experiments were conducted in the NCP. The factorial study compared three levels of K fertilization (K0 = no K; K1 = medium K rate; K2 = high K rate) and two levels of production practices: conventional (CP) and high yielding (HP). A significant positive wheat yield response to K fertilization was obtained under both CP and HP at all site-years. On average, K fertilization significantly increased all three yield components measured, namely kernel number per spike, spike number per hectare and kilo-grain weight. Overall, HP outperformed CP in terms of wheat grain and biomass yield. Nutrient use efficiency of N and P was increased by K application, especially under HP. Overall, HP surpassed CP with regard to partial factor productivity of N and K (PFPN and PFPK) across the four site-years, whereas the opposite trend was found for partial factor productivity of P (PFPP) due to increasing P input. Negative K balances were observed in all of the treatments in both years and under both production practices, especially under HP. Economic profits were achieved under both production practices, but there were no significant differences between CP and HP on average, across four site-years. Therefore, farmers who are planting wheat on Haplic Luvisols in the NCP must take account of the K fertility of their soils for sustainable crop production. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Agricultural intensification through the use of high-yielding crop cultivars, chemical fertilizers and pesticides, irrigation, and mechanization has been responsible for dramatic increases in grain production in developing countries during the past three decades (Matson et al., 1998). There is, however, a growing global

∗ Corresponding author. ∗∗ Corresponding author at: Center for Resources, Environment and Food Security, China Agricultural University, Yuanmingyuan West Road 2, Beijing 100193, China. Tel.: +86 10 6273 2499; fax: +86 10 6273 1016. E-mail addresses: [email protected], [email protected] (F. Zhang). 0378-4290/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fcr.2012.10.008

challenge of meeting increased food demand while protecting environmental quality, and this challenge must especially be met in cropping systems that produce maize (Zea mays L.), rice (Oryza sativa L.), and wheat (Cassman et al., 2002). The NCP is one of the most important areas in China for cereal production, accounting for about 48% of the wheat and 39% of the maize produced in the entire country. The intensive farming in this region features a continuous wheat–maize cropping system which requires careful management of soil nutrients. Intensive agriculture has dramatically increased grain production in developing countries, but yield records in the dominant food-producing regions indicate a large gap between the current and potential yields of wheat (Neumann et al., 2010) which is an important crop because it contributes to food security in China.

70

J. Niu et al. / Field Crops Research 140 (2013) 69–76

Obtaining an increased and sustainable wheat yield will probably require integrated measures that includes K fertilization to maintain soil fertility. Potassium is one of the essential nutrient elements for plants; it is involved in the processes of osmoregulation and cell extension, stomatal regulation, activation of enzymes, protein synthesis, photosynthesis, phloem loading, and transport and uptake (Marschner, 1995; Pettigrew, 2008). Potassium fertilization is, however, uncommon in the NCP, primarily due to the relatively high soil test K as surveyed in the 1980s (National Extension Center of Agricultural Technique in China, 2004). In reality, it has often been reported that continuous wheat–maize cropping with unbalanced fertilization has rapidly depleted the soil available K (Jin, 1994; Liu et al., 2000) and significant crops yield response to K fertilization occurred (Jin, 1994; Huang et al., 2009). A county-wide study in Hebei province in the NCP found that available K decreased by 51.3 and 70.3 mg kg−1 from 1980 to 1999 in rainfed and irrigated lands, respectively (Kong et al., 2006). K deficiency is a worldwide problem (Dobermann et al., 1998) and the K status of agricultural soils is also decreasing across the globe, from Europe to Africa, to Asia, and North America (Tan et al., 2012). Although decreasing yields from withholding K usually have emerged slowly compared to nitrogen (N) and phosphorus (P) (Zhao et al., 2010), K nutrient management has become a major research topic. Numerous studies have focused on crop response to K fertilization as affected by soil properties, application methods, and planting systems (Borges and Mallarino, 2001; Vyn and Janovicek, 2001; Arabi et al., 2002; Schneider et al., 2003; Rehm and Lamb, 2004; Huang et al., 2009; Roshani and Narayanasamy, 2010). It is the biological yield (the dry matter produced), however, that largely determines the amounts of minerals absorbed by crops (Osaki et al., 1991). High-yielding crops with high biological yield absorb large amounts of nutrients to satisfy healthy plant growth (Osaki et al., 1991; Sepat et al., 2010). Soil K depletion was greater for hybrid rice than for inbred rice due to higher yields (Zhang et al., 2011b). The higher yields now commonly obtained must impose a greater drain on K reserves in the soil (Gething, 1993). Therefore, the yield level will be one factor explaining different responses to K fertilization. Nutrient management recommendations may change with yield levels and profit maximization in crop production. Due to high spatial variability in soil K content, the forms and availability to plants of soil K, i.e. potential K-supplying capacity, were related to mineralogy in different soil types (Darunsontaya et al., 2012). Numerous studies on soil K has focussed mainly on K fixation (Zhang et al., 2009) and K quantity/intensity relationships in different soil types (Zhang et al., 2011a). Srinivasarao et al. (2007) categorized K management in different soils based on potassium reserves and production systems. However, it is not clear that K affects cereal crop yields in high-yielding and conventional production systems. Haplic Luvisols are distributed mostly in Shandong and eastern Liaoning peninsulas and Taihang and Yanshan mountains in Hebei province among Haplic Cambisols in the NCP (Xiong and Li, 1987). They are of low to medium grade K in major agricultural regions of north China (Xie, 2000; Huang et al., 2009). The overall goal of this study was to develop a K fertilizer recommendation and evaluation system for high grain yield on Haplic Luvisols in the NCP and offer proposals for K management in soils with medium and relatively low K content and in other areas with intensive farming such as the NCP. High-yielding cropping practices were devised to increase yields. Our specific objectives were: (i) to determine yield response to K fertilizer as affected by conventional as well as high-yielding production practices; (ii) to quantify the effects of K fertilization on N and P use efficiency; and (iii) to evaluate K fertilizer recommendations based on soil nutrient balances and economic profits from high-yielding production practices. Maize and winter wheat were studied because they are the main crops

in the NCP. We previously reported that maize yield response and economic profit from applied K were greater under HP than CP at most sites in the NCP (Niu et al., 2011). The results for winter wheat are presented in this paper. 2. Materials and methods 2.1. Experimental sites The climate of the NCP is warm-temperate, subhumid, continental monsoon with cold winters and hot summers. The annual cumulative mean temperature for days with mean temperatures >10 ◦ C is 4326.6 ◦ C averaged over 45 years from 1961 to 2005 (Tan et al., 2010), and the annual frost-free period is 175–220 d. Winter wheat is usually planted in early October after the harvest of summer maize and is harvested in the middle of June. About 70–80% of the annual precipitation is concentrated during the summer maizegrowing season from June to September. Only 20–30% occurs from October to early June during the wheat season. This would correspond, for example, to an average of about 482 mm yr−1 at the Luancheng Agro-Eco Experimental Station of the Chinese Academy of Sciences, located in the central part of the plain, for the years between 1982 and 2002 (Zhang et al., 2005). The amount and distribution pattern of rainfall vary widely from year to year, however, as affected by the continental monsoon climate. Depending on the amount of rainfall, winter wheat typically receives three irrigation applications, namely before winter, at shooting stage, and at flowering stage. The field experiments were conducted in two agricultural fields at Tangxian (TX) and Zhengding (ZD1) during 2005–2006 and in two additional agricultural fields at Qingyuan (QY) and Zhengding (ZD2) during the 2006–2007. The locations and characteristics of the four experimental site-years are provided in Table 1. 2.2. Experimental design At each site a factorial experiment was conducted in a split-plot randomized complete block design with three replicates. Factors were production practice (two levels) and K application rate (three levels). Main plots were production practices, including CP and HP. Under CP farmers were interviewed and production practices typical for the local area were followed, namely selection of the winter wheat cultivar, plant density, plant spacing, and fertilizer rate. High-yielding practice in this study was to increase chemical P inputs. Other practices under HP were the same as those under CP at each site. Under CP and HP the P fertilizer rates were 150 and 225 kg P2 O5 ha−1 , respectively. The subplots of 24 m2 (4 m × 6 m) were K application rate: K0 (control, no K applied), K1 (medium rate, 75 kg K2 O ha−1 ), and K2 (high rate, 150 kg K2 O ha−1 ). The rate of N fertilizer supplied was 225 kg N ha−1 at each site whether under CP or under HP. Fertilizers applied were urea (46% N), diammonium phosphate (48% P2 O5 and 16% N), and muriate of potash (60% K2 O). At each site one half of the N fertilizer and all the P and K were supplied at sowing and the other half of N as top dressing at shooting stage. The cultivars of winter wheat at TX, ZD1, QY and ZD2 were Shixin733, Shimai12, Shixin828 and Shixin828, respectively. At each site-year, winter wheat was sown at a seed rate of 300 × 104 ha−1 and spaced at 0.15 m. All sites had summer maize as the preceding crop. At all site-years winter wheat typically received three irrigation applications, i.e. before winter, at shooting stage, and at flowering stage to ensure adequate water to satisfy the requirements of plant growth during the whole growth period. We did not observe extreme weather events in any of the years of this study. Fertilization practices usually included two applications, one at planting and the other around the jointing stage. Top dressing at

J. Niu et al. / Field Crops Research 140 (2013) 69–76

71

Table 1 Locations and characteristics of four experimental site-years in the North China Plain. Years

Site

Code

Soil type (FAO)

pH

Organic matter (g kg−1 )

Total N (g kg−1 )

Available N (mg kg−1 )

Olsen P (mg kg−1 )

Exchangeable K (mg kg−1 )

2005–2006

Tangxian Zhengding1 Qingyuan Zhengding2

TX ZD1 QY ZD2

Haplic Luvisol Haplic Luvisol Haplic Luvisol Haplic Luvisol

8.0 7.6 8.1 7.6

14.6 15.3 14.3 15.3

0.80 0.90 0.88 0.86

48.4 55.0 58.6 55.0

11.8 13.8 10.3 13.6

82.6 76.3 88.2 76.3

2006–2007

the jointing stage was applied with the irrigation. Weeds were well controlled through spray herbicides and manually removed. Pest and disease stress was controlled by spray insecticide and fungicide before the stem elongation stage and after anthesis. No obvious water, weed, pest or disease stress was observed during the wheat growing season. 2.3. Sampling and measurement At maturity wheat plants in an area of 1 m2 in the center of each plot were harvested manually. The spike number in the sampling site was counted to calculate the spike numbers per hectare. The plant heights and the spike length were measured on 50 plants per plot at each site. The numbers of total spikelets, fertile spikelets, sterile spikelets and kernel number for each spike were surveyed. Dry weights of stems and grains were determined after separation. The aboveground biomass per hectare was calculated based on the dried plant samples. The yield per hectare was calculated based on the weight of grains after air drying. Thousand kernel weights (TKW) were determined. The harvest index (HI) was calculated as the fraction of grain dry matter divided by the total aboveground biomass on a hectare basis. After grinding, the dried material was passed through a 0.5-mm sieve. About 0.25 g of the ground plant samples was digested in 70% concentrated H2 SO4 and 30% H2 O2 following the procedure outlined by Bao (2000). The K concentrations were determined with a flame spectrophotometer (Cole-Parmer 2655-00, Vernon Hills, IL). Total K uptake per plant was calculated by multiplying the concentration and aboveground biomass for all plots. Partial factor productivity was obtained to indicate the nutrient use efficiency of the applied N, P, and K, and was calculated as grain yield (kg) per unit (kg) of N, P2 O5 , and K2 O applied. In addition, the K use efficiency was also assessed by: (i) agronomic efficiency (AEK), calculated as the increase in grain yield from applied nutrients relative to the control treatment in the same production practice (kg grain kg−1 K2 O applied via fertilizer); (ii) apparent recovery efficiency (REK), defined as the percentage of added K2 O that was recovered in the aboveground plant biomass at the end of the cropping season; and (iii) K use efficiency (KUE), which is the ratio of the amounts of absorbed K to the sum of K supplied from the soil and fertilizer, calculated as PFPK =

GYi FK2 O

GYi − GYCK AEK = FK2 O

applied in the ith treatment (kg K2 O ha−1 ), and Ksoil is the K supplied by the soil (kg K2 O ha−1 ), i.e. the amount of K supplied to the crops by the soil when no K fertilizer was applied, which is equal to UCK in the control treatments. Soil samples were collected at all sites before the start of wheat sowing. Composite soil samples (10 cores per site) were collected from the top 30 cm of the soil profile for separate analysis. The samples were dried at 40 ◦ C and crushed to pass through a 2-mm sieve for chemical analysis. Organic matter, total N, available N, Olsen-P, exchangeable K and pH were determined for each site following procedures recommended for the NCP by Bao (2000). Organic matter was analyzed by the chromic acid titration method, total N by the Kjeldahl method, available N by the alkali hydrolysis and diffusion method, available P by the NaHCO3 method, and exchangeable K by the HN4 OAC extraction and flame photometer method. Soil pH was determined with a pH electrode at a soil/water ratio of 1:2.5. The partial K balance (kg K2 O ha−1 ) in the soil was defined as the quantity of K fertilizer applied minus the quantity of K removed by the wheat plants (grain and straw); no other inputs or outputs were considered. The economic profit from applied K (EPK) was calculated as the difference between the income through wheat yield increments relative to the control subjected to the same production practice and the cost of K fertilizer. The value cost ratio (VCR) of the applied K was defined as the ratio of the income through yield increments relative to the control subjected to the same production practice and the cost of additional K fertilizer, calculated as EPK = [(GYi − GYCK ) × Pg ] − FK PF

(5)

(GYi − GYCK ) × Pg FK PF

(6)

VCR =

where Pg is the price of wheat grain at a specific site (yuan kg−1 ), FK is the amount of K fertilizer applied (kg ha−1 ), and PF is the price of K fertilizer at a specific site (yuan kg−1 ). 3. Statistical methods A two-way ANOVA was used to test for main effects and interactions between production practices and K application rates. The SAS System for Windows Release 8.2 (SAS Institute, Cary, NC) was used for all statistical analysis.

(1) 4. Results (2)

4.1. Wheat yield, yield components and spikelet traits A significant positive response of grain yield to K fertilization was obtained under both CP and HP at all site-years except for the K1 treatment at ZD1 under HP (Table 2). Overall, K fertilization under CP increased grain yield and biomass by 11.6–19.7% and 7.4–14.7%, respectively, and under HP by 6.6–21.2% and 6.4–15.0%, respectively (calculated from data in Table 2). The highest grain yields were obtained at the higher K rate (K2) at all sites; however, grain yields did not increase significantly under the K2 compared to the K1 treatment at TX under HP and at ZD1 under both production practices (Table 2). At each site HP surpassed CP during all four

REK =

Ui − UCK FK2 O

(3)

KUE =

Ui Ksoil + FK2 O

(4)

where GYi is the grain yield (kg ha−1 ) of the ith treatment (i = 1–6), GYCK is grain yield of the control treatment subjected to the same production practice (kg ha−1 ), Ui is K uptake in the ith treatment (kg K2 O ha−1 ), UCK is K uptake in the control treatment under the same production practice (kg K2 O ha−1 ), FK2 O is the amount of K2 O

72

J. Niu et al. / Field Crops Research 140 (2013) 69–76

Table 2 Wheat yield components, grain yield, biomass and harvest index (HI) as affected by K fertilization under different production practices. Site

TX

ZD1

QY

ZD2

Average

Treatment

K0 K1 K2 K0 K1 K2 K0 K1 K2 K0 K1 K2 K0 K1 K2

Kernel no. spike−1

Spike no. ha−1 (×106 ) Kilo-kernel weight (g)

Grain yield (Mg ha−1 )

Biomass (Mg ha−1 )

HI

CP

HP

CP

HP

CP

HP

CP

HP

CP

HP

CP

HP

30.6b 32.5a 32.7a 30.1b 31.9ab 32.2a 28.8c 30.2b 31.4a 29.5c 31.6b 32.6a 29.8c 31.6b 32.2a

32.4a* 33.3a 33.7a 31.8a 32.1a 32.6a 30.3c* 32.1b 33.2a 31.2b* 32.8a 33.2a 31.4b* 32.6a 33.2a

5.69b 5.94a 6.06a 6.78a 6.81a 6.84a 6.59c 6.79b 6.91a 6.74c 6.84b 6.98a 6.45c 6.60b 6.70a

5.78c* 6.11b 6.39a 7.13a* 7.26a 7.30a 6.74b* 6.92a 7.02a 7.11b* 7.18b 7.30a 6.69c* 6.87b 7.00a

39.5b 40.3ab 41.5a 37.6b 40.0a 40.4a 40.7c 42.0b 42.6a 40.4b 41.6ab 42.2a 39.6b 41.0a 41.7a

40.2b 40.9ab 42.4a 38.3b 39.8a 40.7a 41.6b* 43.1a 43.5a 41.3c* 42.3b 43.7a 40.4c* 41.5b 42.6a

5.84c 6.61b 6.99a 6.53b 7.39a 7.57a 6.56c 7.33b 7.84a 6.83c 7.64b 8.14a 6.44c 7.24b 7.64a

6.40c* 7.08ab 7.76a 7.39b* 7.88ab 8.24a 7.22c* 8.14b 8.61a 7.79c* 8.48b 9.00a 7.20c* 7.90b 8.40a

13.2b 14.6a 15.2a 14.5b 15.6ab 16.4a 14.3b 15.8a 16.4a 15.2b 16.8a 17.4a 14.3c 15.7b 16.4a

14.2b* 15.1ab 16.3a 15.0b 16.3a 16.7a 16.4b* 17.4a 18.0a 16.9c* 18.3b 19.2a 15.6c* 16.8b 17.5a

0.44a 0.46a 0.46a 0.45a 0.47a 0.46a 0.46a 0.46a 0.48a 0.45b 0.45b 0.47a 0.45a 0.46a 0.47a

0.45a 0.47a 0.47a 0.49a* 0.48a 0.49a 0.44b 0.47a 0.48a 0.46a* 0.46a 0.47a 0.46b* 0.47ab 0.48a

Means in a column from each site followed by different letters are significantly different at P ≤ 0.05. * Significant difference at P ≤ 0.05 between CP and HP from each site.

site-years in terms of grain yield, and the same results occurred as for biomass yield except for ZD1 (Table 2). Yield components kernel number per spike, spike number per hectare and kilo-kernel weight showed different results at each site-year. Under CP, the medium (K1) and higher (K2) treatment increased significantly kernel number per spike at all site-years except at ZD1 under CP. However, under HP only at half of the site-years were the same results found (Table 2). K input significantly enhanced spike number per hectare at three out of four site-years except for ZD1 under both K levels and both production practices. K input had positive effects on kilo-grain weight of wheat, especially at the higher K treatment (K2) with significantly results (Table 2). On average, K fertilization increased all three yield components significantly; moreover, HP surpassed CP in terms of all three parameters (Table 2). HI was significantly affected by production practice and by higher K rate (K2) only under HP on average (Table 2). Under both production practices K input increased plant height at two and all of four site-years at K1 and K2 levels, respectively (Table 3). K fertilization had a significant positive effect on spike length at three out of four site-years in the K1 and K2 treatments under both production practices. At medium K treatment (K1), K input had no significant influence on total spikelets per spike under both production practices except for ZD1 under HP (Table 3). However, at higher K treatment (K2) K fertilization increased total

spikelets per spike significantly at three and two out of four siteyears under CP and HP, respectively. Under CP, K input increased fertile spikelets per spike significantly at three and all of four siteyears under the K1 and K2 levels, respectively. However, under HP, K fertilization increased fertile spikelets per spike significantly at one and three out of four site-years at the K1 and K2 treatment, respectively (Table 3). Under both production practices medium K input had no significant effect on sterile spikelets per spike. However, at K2 treatment K supply decreased sterile spikelets per spike significantly at three and two out of four site-years under CP and HP, respectively (Table 3). Furthermore, HP outperformed CP at three out of four site-years in terms of plant height (Table 3). However, CP surpassed HP at three out of four site-years in terms of sterile spikelets per spike. There were no significant differences in terms of total spikelets per spike under both production practices (Table 3).

4.2. K uptake and nutrient use efficiency The higher K fertilizer rate (K2) significantly increased the grain K concentration at three of the four site-years whether under CP or under HP, but the medium K rate (K1) there was no significant effect except at QY and ZD2 under CP (Table 4). Under CP, K fertilization had no significant effect on straw K concentration whether

Table 3 Plant height, spike length and spikelet traits of winter wheat under different production practices. Site

Treatment

TX

K0 K1 K2 K0 K1 K2 K0 K1 K2 K0 K1 K2 K0 K1 K2

ZD1

QY

ZD2

Average

Plant height (cm)

Spike length (cm)

Total spikelet spike−1

Fertile spikelet spike−1

Sterile spikelet spike−1

CP

HP

CP

HP

CP

HP

CP

HP

CP

HP

70.32b 71.54ab 72.08a 68.39b 69.86ab 70.68a 72.88c 74.15b 75.85a 72.93b 75.60a 76.48a 71.13b 72.79a 73.77a

71.51b* 72.45a 72.78a 69.56b* 70.96ab 71.77a 74.56b* 76.82a 77.75a 74.19b 75.67ab 76.31a 72.45c* 73.98b 74.65a

6.71b 7.03a 6.94a 7.82a 7.95a 8.22a 7.64b 8.05a 8.16a 7.44b 8.02a 8.15a 7.40b 7.76a 7.87a

7.04a* 7.26a 7.19a 7.91b 8.28a 8.36a 8.07b 8.27a 8.34a 7.97b 8.26a 8.37a 7.75b* 8.02a 8.07a

15.51a 16.03a 16.36a 16.83b 17.22b 17.83a 16.51b 17.34ab 17.81a 17.34b 17.90ab 18.33a 16.55b 17.12ab 17.58a

16.35a 16.39a 16.37a 16.27b 17.86a 17.88a 17.36a 17.63a 17.77a 17.57b 17.76ab 18.14a 16.89b 17.41a 17.54a

12.02b 13.10a 13.56a 13.12b 13.83ab 14.62a 12.91b 14.29a 15.01a 13.85b 14.61a 15.13a 12.98b 13.95a 14.58a

13.67a 13.78a 13.85a 13.22b 15.45a 15.82a 14.52b* 14.96ab 15.23a 14.17b 14.71b 15.37a 13.89b* 14.73a 15.07a

3.49a* 2.94b 2.80b 3.71a* 3.39a 3.21a 3.60a 3.05b 2.80b 3.50a* 3.29b 3.20b 3.57a* 3.17b 3.00b

2.68a 2.61a 2.52a 3.05a 2.41a 2.06a 2.84a 2.66b 2.54b 3.40a 3.05ab 2.77b 2.99a 2.68b 2.47b

Means in a column from each site followed by different letters are significantly different at P ≤ 0.05. * Significant differences at P ≤ 0.05 between CP and HP cultivation practices.

J. Niu et al. / Field Crops Research 140 (2013) 69–76

73

Table 4 K uptake by winter wheat plants as affected by K fertilization under different production practices. Site

Treatment

TX

K0 K1 K2 K0 K1 K2 K0 K1 K2 K0 K1 K2

ZD1

QY

ZD2

Grain K (%)

Straw K (%)

K uptake (kg K2 O ha−1 )

KUE (kg kg−1 ) CP

HP

0.72a 0.56b

0.72a 0.57a

0.78a 0.64b

0.79a 0.66b

0.71a 0.54b

0.70a 0.54b

0.69a 0.53b

0.70a 0.52b

CP

HP

CP

HP

CP

HP

0.56a 0.58a 0.59a 0.55b 0.59ab 0.63a 0.51b 0.54a 0.56a 0.52b 0.56a 0.57a

0.53a 0.56a 0.56a 0.53b 0.55ab 0.60a 0.51b 0.54ab 0.55a 0.53b 0.54ab 0.56a

1.45a 1.48a 1.48a 1.55a 1.57a 1.59a 1.30a 1.28a 1.27a 1.30a 1.28a 1.27a

1.43a 1.46a 1.47a 1.53b 1.55ab 1.58a 1.36a* 1.31ab 1.28b 1.30a 1.29a 1.27a

169.0b 187.5a 195.1a 205.2c 230.7b 246.7a 161.4b 178.9a 184.1a 163.5a 174.2a 182.0a

175.7a 189.9a 204.3a 222.7c* 246.7b 268.2a 193.8b* 198.5ab 202.6a 162.0b 176.4a 178.8a

Means in a column from each site followed by different letters are significantly different at P ≤ 0.05. Significant differences at P ≤ 0.05 between CP and HP cultivation practices.

*

at medium or higher K treatments. Under HP, however, there were no consistent results (Table 4). Under CP, K application enhanced K uptake by wheat plants significantly at all site-years in addition to ZD2 (Table 4). Under HP, K input increased K uptake by whole wheat plants significantly at two and three out of four site-years at K1 and K2 treatments, respectively. There were no significant differences in grain K concentration between CP and HP at all site-years, and the same results were found for straw K concentration except at QY (Table 4). At half of the four site-years (ZD1 and QY), potassium uptake under HP was significantly greater than that under CP (Table 4). Potassium use efficiency (KUE) decreased significantly with increasing K application rate whether under CP or HP at all siteyears except at TX under HP (Table 4); moreover, there were no significant differences between HP and CP (Table 4). At both K levels, K fertilization apparently enhanced the PFP of N compared with the control that received no K fertilizer, at all site-years under both production practices except for at ZD1 under HP (Table 5). The same was true for the PFP of P (Table 5). The PFP of applied K (PFPK) increased at three of the four site-years under HP compared with CP (Table 5). However, K application and production practices had no significant effect on agronomic efficiency of applied K (AEK) or on apparent recovery efficiency (REK) except at QY. Whether under CP or HP, the PFPK at all sites declined significantly with increased K levels. On average, HP surpassed CP

with regard to PFPN and PFPK across the four site-years (Table 5), whereas the opposite result to PFPP was found (Table 5). 4.3. Economic performance and soil K balance In general, K application led to economic profits at all sites in both years and under both production practices, ranging from 442 to 1567 yuan ha−1 (Table 6). Economic profits were significantly higher under HP than CP at only one of the four site-years. On average, there were no significant differences between the K1 and K2 treatments within the same production practice. In all cases, K application and production practices had no significant effect on the VCR which ranged from 2.4 to 4.8. However, on average the VCR decreased significantly at higher K rate (K2) compared to the medium K input (K1) under CP but there were no significant differences between the two K levels under HP (Table 6). Negative partial K balances were found for all K treatments in both years and production practices at all sites (Fig. 1). Moreover, HP apparently surpassed CP in negative partial K balances at two of four site-years (ZD1 and QY) (Fig. 1). 5. Discussion Crop yield response to K fertilization is related to the potential potassium-supplying power of soils (Huang et al., 2009; Schneider

Table 5 Partial factor productivity of applied N, P and K (PFPN, PFPP and PFPK), K agronomic efficiency (AEK) and K apparent recovery efficiency (REK) as affected by potassium fertilization under different production practices. Site

Treatment

TX

K0 K1 K2 K0 K1 K2 K0 K1 K2 K0 K1 K2 K0 K1 K2

ZD1

QY

ZD2

Average

PFPN (kg kg−1 )

PFPP (kg kg−1 )

PFPK (kg kg−1 )

CP

HP

CP

HP

CP

HP

CP

26.0c 29.4b 31.1a 29.0b 32.9a 33.6a 29.2c 32.6b 34.9a 30.3c 34.0b 36.2a 28.6c 32.2b 33.9a

28.4c* 31.5b 34.5a 31.5b* 35.0ab 36.6a 32.1c* 36.2b 38.3a 34.6c* 37.7b 40.0a 31.7c* 35.1b 37.4a

39.0c* 44.1b 46.6a 43.6b* 49.3a 50.4a 43.8c* 48.8b 52.3a 45.5c* 51.0b 54.3a 42.9c* 48.3b 50.9a

28.4c 31.5b 34.5a 31.5b 35.0ab 36.6a 32.1c 36.2b 38.3a 34.6c 37.7b 40.0a 31.7c 35.1b 37.4a

– 88.2a 46.6b – 98.6a 50.4b – 97.7a 52.3b – 101.9a 54.3b – 96.6a 50.9b

– 94.4a* 51.7b – 105.1a 55.0b – 108.6a* 57.4b – 113.1a* 60.0b – 105.3a* 56.0b

– 10.3a 7.6a – 11.5a 6.9a – 10.2a 8.5a – 10.9a 8.8a – 10.7a 8.0a

Means in a column from each site followed by different letters are significantly different at P ≤ 0.05. * Significant differences at P ≤ 0.05 between CP and HP cultivation practices.

AEK (kg kg−1 )

REK (kg kg−1 ) HP

– 9.1a 9.1a – 6.6a 5.7a – 12.2a 9.2a – 9.2a 8.1a – 9.3a 8.0a

CP

HP

– 0.25a 0.17a

– 0.19a 0.19a

0.34a 0.28a

0.32a 0.20a

0.23a* 0.15a

0.06a 0.06a

0.14a 0.12a

0.19a 0.11a

0.24a 0.18a

0.19a 0.14a

74

J. Niu et al. / Field Crops Research 140 (2013) 69–76

Table 6 Economic profits and value cost ratio (VCR) as affected by potassium fertilization under different cultivation practices. Site

TX ZD1 QY ZD2 Average

Treatment

K1 K2 K1 K2 K1 K2 K1 K2 K1 K2

Economic profit (yuan ha−1 )

VCR

CP

HP

CP

HP

829a 1102a 957a 949a 893b 1395a 978a 1453a 914a 1225a

708a 1402a 442a 699a 1143a* 1567a 782a 1296a 769a 1241a

4.3a 3.2a 4.8a 2.9a 3.7a 3.1a 4.0a 3.2a 4.2a 3.1b

3.8a 3.8a 2.8a 2.4a 4.5a 3.4a 3.4a 3.0a 3.6a 3.2a

Production price and fertilizer price were 1.4 yuan kg−1 and 2.0 yuan kg−1 KCl at all sites in 2005–2006. In 2006–2007, production price and fertilizer price were 1.6 yuan kg−1 and 2.6 yuan kg−1 KCl. Mean values in a column from each site followed by different letters are significantly different at P ≤ 0.05. * Significant differences at P ≤ 0.05 between CP and HP cultivation practices.

et al., 2003). Haplic Luvisols of low to medium grade potassium are found in the major agricultural regions of north China (Xie, 2000; Huang et al., 2009). Soil available K concentrations at the four experimental sites ranged from 72.3 to 82.6 mg kg−1 (Table 1), with in the range of moderate lack of available potassium as defined by Zhou et al. (2011). In this study a significant positive response to K fertilization in terms of wheat grain yield was obtained under both CP and HP at all site-years (Table 2), which was related to the low soil K level. Yield increase was due to increasing the yield components spike number per hectare, kernel number per spike and kilo-kernel weight. On average, K fertilization significantly increased all three yield components (Table 2). Potassium is one of the essential nutrient elements for wheat plants and plays important roles in the processes of osmoregulation and cell extension, stomatal movement, activation of enzymes, protein synthesis, photosynthesis, phloem loading, and transport and uptake (Marschner, 1995; Pettigrew, 2008). Under both production practices, K input increased plant height at two and all of four site-years at K1 and K2 levels, respectively (Table 3). K fertilization had significant positive effects on spike length at three out of four site-years at the K1 and K2 treatment and under both production practices. On

Fig. 1. Potassium balance in field experiments on wheat in 2005–2006 (upper) and 2006–2007 (lower) in the North China Plain (TX, Tangxian; ZD1, Zhengding1; QY, Qingyuan; ZD2, Zhengding2) under conventional production practices (CP) and high-yielding production practices (HP) receiving no K fertilizer (K0) or medium (K1) or high (K2) K fertilizer rates. The partial K balance in the soil was defined as the quantity of K fertilizer applied minus the quantity of K removed by the maize plants (grain and straw); no other inputs or outputs were considered. Bars denote standard errors of the mean from each site, n = 3. Mean values from each site with different letters are significantly different at P ≤ 0.05 under the same production practices. *Significant difference at P ≤ 0.05 between CP and HP from each site; otherwise no significant differences occurred.

average, K increased total spikelets per spike and fertile spikelets per spike and decreased the sterile spikelets per spike at the higher K application rate (Table 3). In all site-years, HP surpassed CP in terms of grain yield, and the same results occurred as for biomass yield except at ZD1 (Table 2). HI was significantly affected by production practice and by higher K rate (K2) only under HP on average (Table 2). In this study larger P fertilizer input was the high-yielding production practice compared to CP. Yield increase by P fertilization was primarily due to production of spikes per hectare from more prolific tillering (Sweeney et al., 2000), but K fertilization increased yield by increasing kernel weight (Sweeney et al., 2000). In this study HP outperformed CP in terms of spike numbers per hectare at all siteyears (Table 2). The same result was true in terms of the kilo-kernel weight on average (Table 2). Numerous long-term experiments have shown that a balanced supply of N, P, and K can increase crop yield (Wang et al., 2007, 2010). A highly positive interaction between P and K was reported by Chapman and Mason (1969). Interactions between P and K were clearly evident in the current study and in a previous study (Xie, 2000). This may be one of the primary reasons for the greater response to applied K under HP than CP. Balancing the N/P/K ratio by increasing the input of K fertilizers is a practical way to increase N agronomic efficiency and to minimize the environmental impacts of N fertilization (Zhu and Chen, 2002). It appears that K application alleviates the N pollution problem by inducing a higher rate of N fertilizer uptake by crops (Ardjasa et al., 2002). In the present study the average PFP of N (PFPN) increased by 12.6 and 18.5% under CP and by 10.7 and 18.0% under HP at the K1 and K2 levels, respectively (calculated from data in Table 5). In general, the PFP of N increased with increasing K input under the same production practice, which indicates positive interactions between N and K (Table 5). The value of PFPN increased significantly with high-yielding production practices compared to CP due to higher wheat yields (Table 5). Under HP, the PFP of P were inferior to the values under CP as a result of increasing P inputs under HP (Table 5). Potassium uptake by wheat plants increased significantly with potassium fertilization except for TX under HP and ZD2 under CP (Table 4). The PFP of K fertilizer increased with high production practices due to increasing wheat yields (Table 5). However, K application and production practices had no significant effect on agronomic efficiency of applied K (AEK) or on apparent recovery efficiency (REK) except for QY (Table 5). These K use efficiency results under HP and CP differ from maize plants findings reported by Niu et al. (2011). Overall, in the maize experiment PFPK and AEK increased under HP, as did REK (Niu et al., 2011).

J. Niu et al. / Field Crops Research 140 (2013) 69–76

Intensive crop production in combination with unbalanced fertilization has already resulted in depletion of soil K across large areas of China (Jin et al., 1999; Yang et al., 2004). In the present study, at all sites in both years and under both production practices, K deficits in the soil were serious (Fig. 1). Deficiency of K in crop production usually appears following increases in N and P fertilizer applications and neglect of K fertilization (Ju et al., 2005). Our results suggest that K fertilizer at rates of 75–150 kg K2 O ha−1 would greatly mitigate the present depletion of soil K (Fig. 1). Positive economic profits were achieved under both production practices but there were no significant differences between CP and HP on average, across four site-years (Table 6). Therefore, farmers who are planting winter wheat on Haplic Luvisols must take account of the K fertility of their soils for sustainable crop production. In contrast, maize yield responses and economic profits from applied K were greater under HP than CP at most sites in a previous study in the North China Plain (Niu et al., 2011). The critical K concentration in the tissue water was different (110 mM for maize and 130 mM for wheat) and the critical K concentration in the soil solution varied between soils (Schneider et al., 2003). Based on the results from a pot experiment and long-term field trials, Huang et al. (2009) predicted that significant wheat yield responses to potassium would be observed in these soils with medium or relatively low potassium-supplying power in recent years and insignificant wheat yield responses to potassium in the soils with relatively high potassium-supplying power, whereas significant maize yield responses to potassium would be observed in most soils in north China. Therefore, in the wheat–maize rotation system in the NCP, the contribution of K fertilizers to maize yield was greater than to wheat in soils with higher potassium-supplying power and this suggests that maize could be given priority over wheat when determining K application rates in intensive crop production systems with high inputs. Nutrient recommendations should not be based on the yield response of single crops only, but also on the aftereffects on nutrient availability for succeeding crops (Dai et al., 2010). Due to the K fertilization experiments on winter wheat and maize carried on different sites, studies on crop yield response to continuous K fertilization in the whole wheat–maize cropping system and after-effects of K fertilization in the intensive cropping system in the NCP require further investigation.

6. Conclusions In conclusion, a significant positive wheat yield response to K fertilization on Haplic Luvisols was obtained under both CP and HP at all site-years. Overall, HP outperformed CP in terms of wheat grain and biomass yield. On average, K fertilization significantly increased all three yield components, namely kernel number per spike, spike per hectare and kilo-grain weight. Nutrient use efficiency of N and P increased with K application, especially under HP. On average, HP surpassed CP with regard to PFPN and PFPK across the four site-years, whereas the opposite trend occurred in PFPP due to increased P input. Negative K balances were observed in all of the treatments in both years and under both production practices, especially under HP. Positive economic profits were achieved under both production practices but there were no significant differences between CP and HP on average across four site-years. Therefore, whether under conventional cropping system or under intensive high-yielding cropping systems, farmers who are planting winter wheat on Haplic Luvisols must take into account the K fertility of their soils for sustainable crop production. These results will be of vital importance to K management in intensive agricultural areas with high N and P fertilizer inputs and decreasing medium or low K soil contents. The effect of K fertilization on crop yields under high-yielding and

75

conventional production practices should be verified in different soil types in further studies and the application and extension of these results should be continued.

Acknowledgments We thank the International Potash Institute (IPI), the Chinese Ministry of Agriculture (no. 2006-G60) and the Innovative Group Grant of the National Science Foundation of China (no. 30821003) for financial support. We thank Professor Peter Christie (Agri-Food & Biosciences Institute, North Ireland) for careful correction of the manuscript.

References Arabi, M.I.E., MirAli, N., Jawhar, M., 2002. Effect of foliar and soil potassium fertilisation on wheat yield and severity of Septoria tritici blotch. Aust. Plant Path. 31, 359–362. Ardjasa, W.S., Tomonori, A., Ho, A., Ken-Ichi, K., Makoto, K., 2002. Fate of basal N and growth of crops cultivated under cassava-based intercropping system with reference to K application rate. Soil Sci. Plant Nutr. 48, 365–370. Bao, S.D., 2000. Soil Agricultural–Chemical Analysis. China Agric. Press, Beijing. Borges, R., Mallarino, R.B., 2001. Deep banding phosphorus and potassium fertilizer for corn managed with ridge tillage. Soil Sci. Soc. Am. J. 65, 376–384. Cassman, K.G., Dobermann, A., Walters, D., 2002. Agroecosystems, nitrogen-use efficiency, and nitrogen management. Ambio 31, 132–140. Chapman, F.M., Mason, J.L., 1969. Effect of phosphorus and potassium fertilizers on the agronomic characteristics of spring wheat and their interaction on grain yield. Can. J. Soil Sci. 49, 343–347. Dai, X.Q., Zhang, H.Y., Spiertz, J.H.J., Yu, J., Xie, G.H., Bouman, B.A.M., 2010. Crop response of aerobic rice and winter wheat to nitrogen, phosphorus and potassium in a double cropping system. Nutr. Cycl. Agroecosyst. 86, 301–315. Darunsontaya, T., Suddhiprakarn, A., Kheoruenromne, I., Prakongkep, N., Gilkes, R., 2012. The forms and availability to plants of soil potassium as related to mineralogy for upland Oxisols and Ultisols from Thailand. Geoderma 170, 11–24. Dobermann, A., Cassman, K.G., Mamaril, C.P., Sheehy, J.E., 1998. Management of phosphorus, potassium, and sulfur in intensive, irrigated lowland rice. Field Crop Res. 56, 113–138. Gething, P.A., 1993. Improving Returns from Nitrogen Fertilizer: The Potassium–Nitrogen Partnership. IPI Res. Topics 13, 2nd Rev. ed. Int. Potash Inst., Horgen, Switzerland. Huang, S.W., Jin, J.Y., Tan, D.S., 2009. Crop response to long-term potassium application as affected by potassium-supplying power of the selected soils in Northern China. Commun. Soil Sci. Plant Anal. 40, 2833–2854. Jin, J.Y., 1994. Tendency of potassium deficiency and fertilization in soils in northern part of China. In: Potash and Phosphate Inst. of Canada in Beijing (Ed.), Soil Potassium and Plant Response to K Fertilization in Northern Part of China. China Agrotech Press, Beijing, pp. 8–44 (in Chinese). Jin, J.Y., Lin, B., Zhang, W., 1999. Improving nutrient management for sustainable development of agriculture in China. In: Smaling, E.M.A., Oenema, O., Fresco, L.O. (Eds.), Nutrient Disequilibria in Agroecosystems: Concepts and Case Studies. CABI Publ., Wallingford, UK. Ju, X.T., Zhang, F.S., Bao, X.M., Romheld, V., Roelcke, M., 2005. Utilization and management of organic wastes in Chinese agriculture: past, present and perspectives. Sci. China Ser. C 48, 965–979. Kong, X.B., Zhang, F.R., Wei, Q., Xu, Y., Hui, J.G., 2006. Influence of land use change on soil nutrients in an intensive agricultural region of North China. Soil Till. Res. 88, 85–94. Liu, R.L., Jin, J.Y., Wu, G.R., Liang, M.Z., 2000. The K balance in the soil and effect of potassium fertilizer for crop in North China. Soils Fert. 1, 9–11 (in Chinese). Marschner, H., 1995. Mineral Plant Nutrition of Higher Plants, 2nd ed. Academic Press, London. Matson, P.A., Naylor, R., Ortiz-Monasterio, I., 1998. Integration of environmental, agronomic, and economic aspects of fertilizer management. Science 280, 112–115. National Extension Center of Agricultural Technique in China, 2004. The National Cultivated Land Soil Investigation Report. NECATC, Beijing. Neumann, K., Verburg, P.H., Stehfest, E., Müller, C., 2010. The yield gap of global grain production: a spatial analysis. Agric. Syst. 103, 316–326. Niu, J.F., Zhang, W.F., Chen, X.P., Li, C.J., Zhang, F.S., Jiang, L.H., Liu, Z.H., Xiao, K., Assaraf, M., Imas, P., 2011. Potassium fertilization on maize under different production practices in the North China Plain. Agron. J. 103, 822–829. Osaki, M., Morikawa, K., Shinano, T., Urayama, M., Tadano, T., 1991. Productivity of high-yield crops: II. Comparison of N, P, K, Ca, and Mg accumulation and distribution among high-yielding crops. Soil Sci. Plant Nutr. 37, 445–454. Pettigrew, W.T., 2008. Potassium influences on yield and quality production for maize, wheat, soybean and cotton. Physiol. Plant. 133, 670–681. Rehm, R.G., Lamb, J.A., 2004. Impact of banded potassium on crop yield and soil potassium in ridge-till planting. Soil Sci. Soc. Am. J. 68, 629–636.

76

J. Niu et al. / Field Crops Research 140 (2013) 69–76

Roshani, G.A., Narayanasamy, G., 2010. Effects of potassium on temporal growth of root and shoot of wheat and its uptake in different soils. Int. J. Plant Prod. 4, 25–32. Schneider, A., Castillon, P., Pellerin, S., 2003. Relationships between soil potassium supply characteristics based on soil solution concentration and buffer power and field responses of winter wheat and maize. Plant Soil 254, 269–278. Sepat, R.N., Rai, R.K., Dhar, Shiva, 2010. Planting systems and integrated nutrient management for enhanced wheat (Triticum aestivum) productivity. Indian J. Agron. 55, 114–118. Srinivasarao, C., Vittal, K., Tiwari, K., Gajbhiye, P., Kundu, S., 2007. Categorisation of soils based on potassium reserves and production systems: implications in K management. Aust. J. Soil Res. 45, 438–447. Sweeney, D.W., Granade, G.V., Eversmeyer, M.G., Whitney, D.A., 2000. Phosphorus, potassium, chloride and fungicide effects on wheat yield and leaf rust severity. J. Plant Nutr. 23, 1267–1281. Tan, D., Jin, J., Jiang, L., Huang, S., Liu, Z., 2012. Potassium assessment of grain producing soils in North China. Agr. Ecosyst. Environ. 148, 65–71. Tan, F.Y., Wang, J.L., Song, Y.B., 2010. Characteristics of climate change in the North China Plain for recent 45 years. Meteorol. Monogr. 36, 40–45 (in Chinese). Vyn, T.J., Janovicek, K.J., 2001. Potassium placement and tillage system effects on corn response following long-term no till. Agron. J. 93, 487–495. Wang, X.B., Cai, D.X., Hoogmoed, W.B., Perdok, U.D., Oenema, O., 2007. Crop residue, manure and fertilizer in dryland maize under reduced tillage in northern China: I. Grain yields and nutrient use efficiencies. Nutr. Cycl. Agroecosyst. 79, 1–16. Wang, Y., Wang, E., Wang, D., Huang, S., Ma, Y., Smith, C.J., Wang, L., 2010. Crop productivity and nutrient use efficiency as affected by long-term fertilisation in North China Plain. Nutr. Cycl. Agroecosyst. 86, 105–119.

Xie, J.C., 2000. Potassium in Chinese Agriculture. Hehai University Press, Nanjing, China. Xiong, Y., Li, Q.K., 1987. China Soil, 2nd ed. Science Press, Beijing. Yang, S.M., Li, F.M., Malhi, S.S., Wang, P., Suo, D.R., Wang, J.G., 2004. Long-term fertilization effects on crop yield and nitrate nitrogen accumulation in soil in northwestern China. Agron. J. 96, 1039–1049. Zhang, H., Xu, M., Zhang, W., He, X., 2009. Factors affecting potassium fixation in seven soils under 15-year long-term fertilization. Chin. Sci. Bull. 54, 1773–1780. Zhang, H., Xu, M., Zhu, P., Peng, C., 2011a. Effect of 15-year-long fertilization on potassium quantity/intensity relationships in black soil in Northeastern China. Commun. Soil Sci. Plant Anal. 42, 1289–1297. Zhang, Q., Wang, G., Feng, Y., Qian, P., Schoenau, J.J., 2011b. Effect of potassium fertilization on soil potassium pools and rice response in an intensive cropping system in China. J. Plant Nutr. Soil Sci. 174, 73–80. Zhang, X.Y., Chen, S.Y., Liu, M.Y., Pei, D., Sun, H.Y., 2005. Improved water use efficiency associated with cultivars and agronomic management in the North China Plain. Agron. J. 97, 783–790. Zhao, B.Q., Li, X.Y., Li, X.P., Shi, X.J., Huang, S.M., Wang, B.R., Zhu, P., Yang, X.Y., Liu, H., Chen, Y., Poulton, P., Powlson, D., Todd, A., Payne, R., 2010. Long-term fertilizer experiment network in China: crop yields and soil nutrient trends. Agron. J. 102, 216–230. Zhou, X.F., Feng, W., Yang, J.F., Sun, L.M., Du, J.Z., Wang, S.Y., Zhao, Z.L., 2011. The study on the abundance and deficiency indices of phosphorus and potassium of wheat with straw returning in Taihang mountain piedmont plain. Acta Agr. Boreali Sin. 26, 170–174 (in Chinese). Zhu, Z.L., Chen, D.L., 2002. Nitrogen fertilizer use in China: contributions to food production, impacts on the environment and best management strategies. Nutr. Cycl. Agroecosyst. 63, 117–127.