Better Crops/Vol. 98 (2014, No. 3) 13 ). Yield responses to the responses ). Yield Table 1 Table showing the general K fertilizershowing recommen- Potassium fertilization and K input from crop straw resi- due both contributed to better rice yields, but their impact depended on soil K status ( generalized K or straw treatments alone were similar in size, cantly greater than the check across soil fertil- but not signifi ity levels. Only the fertilizer and straw K treatment generated cantly higher than the check better yields, which were signifi treatment in low and medium K soils. Results Comparisons at a low soil K site left), left), (bottom dation (top right), K plus Straw the zero K check (top right). (bottom and K minus Straw China. When b > Px/Py, C is the recommended amount of K; C China. When b > Px/Py, the recommended amount of K is 0. when b < Px/Py, O 2 ciency ed as high K is fertilizer K rate (kg/ x C) OAc extractable K) of >150 4 ≤
O/ha/yr, in part because of the in part because of the O/ha/yr, x O/ha). The crop straw was me- 2 2 ( bx > C) elds. As a result, soil K defi x + is the regression coeffi cient, C repre- is the regression coeffi a b y =
addy-upland rotations, located mainly in the Yangtze located mainly in the Yangtze addy-upland rotations, form the most important cropping River basin, arguably crops rice and subsequent However, systems in China. is the intercept,
a Oac = ammonium acetate.
The K in crop straw left in the fi eld is a readily available The K in crop straw left in the fi trial sites national soil survey, second According to China’s Linear and plateau K fertilization models (Cerrato and where, y is the grain yield (kg/ha), y = P ( 4
O/ha, 3) 4.5 t/ha wheat straw/winter rape straw (with ~2.1% 2
Abbreviations and notes: N = nitrogen; P = phosphorus; K = potassium; NH P like wheat, rice, or oilseed rape remove large amounts of K oilseed rape remove large amounts like wheat, rice, or kg K from 210 to 360 annually, Generalized fertilizerGeneralized K in China exist for recommendations partly their disproving evidence of a lack of local because use, and partly fertilizer to address limited resources. This research demonstrates K use of the nutrient making good how straw of crop value can help optimize fertilizer and reduce the reliance on strategies K application that promote general- ized fertilizer systems recommendation across large areas. Strategies in Rice Cropping Systems Cropping in Rice Strategies Zhou Xiao-kun Li, and Li Ren, Ri-huan Cong, Jian-wei Lu, Tao By Ji-fu Li, CENTRAL CHINACENTRAL Fertilization Potassium Optimize Can Straw Crop K content), and 4) straw combined with two lower rates of K fertilizer (i.e., 25 and 50 kg K removal of crop straw from fi removal of crop straw due factor for sustained high yields has become a key limiting besides region. However, to relatively low rates of K input in the to consider all potential K it is always important K fertilizer, a region. resources available to farmers within use, especially under source that is released quickly for plant ooded conditions. Changes towards large-scale mechaniza- fl are providing favorabletion in Chinese agricultural production returning crop straw to conditions to expand the practice of a 2011-2012 study (IPNI China, elds. This article examines fi straw on the K nutri- 2012) that measured the impact of crop K application rates. tion of rice, its yield, and optimal fertilizer with available K content (1 N NH (4.5 Yuan/kg) and of rice (2.5 Yuan/kg) during 2011-2012 in and of rice (2.5 Yuan/kg) (4.5 Yuan/kg) mg/kg (Zhongxiang and Yicheng sites) were classifi mg/kg (Zhongxiang and Yicheng 100 and 150 mg/ soils; those with available K content between Xiantao, Honghu, and Zhijiang sites) were clas- kg (Tuanfeng, K content ed as medium K soils; and those with available sifi and Qichun sites) <100 mg/kg (Macheng, Guangshui, Ezhou, ed as low K soils. Earlier on-site investigation re- were classifi from the farmland vealed that crop straws are always removed were carried out in for rice transplanting. Field experiments a randomized block design with six treatments including: 1) zero-K check, 2) the generalized K recommendation of 75 kg K chanically chopped to a length of 10 cm and then incorporated into the soil with the fertilizer. 1990) were used to determine the optimum levels Blackmer, of K fertilization: sents the intersection of the straight line and the plateau, and P is the plateau yield (kg/ha). Px and Py are the prices of K ha), Table 1. Effect of straw incorporation and K fertilization on rice yield and K uptake, Yangtze River Basin. As with the yield re- sponses, K fertilization Yield, Yield increase, Yield increase, K uptake, K uptake K uptake also led to an increase Soil K levels Treatment kg/ha kg/ha % kg/ha increase, kg/ha increase, % in K uptake in rice bio- Check 8,372 ab - - 253 b - - mass in high, medium K† 8,635 ab 1, 263 13.1 285 a 32 12.6 and low K soils (Table High K Straw‡ 8,852 ab 1, 480 15.7 278 a 25 ll9.9 1). Straw input most Straw + K 9,005 ab 1, 633 17.6 293 a 40 15.8 affected crop K uptake Check 8,710 bb - - 265 b - - in low and high K soils and was less effective K 9,460 ab 1, 750 18.6 305 a 40 15.1 Medium K in medium K soils. The Straw 9,023 ab 1,313 13.6 279 b 14 15.3 fertilizer and straw K Straw + K 9,808 ab 1,098 12.6 322 a 57 21.5 treatment produced the Check 7,767 bb - - 170 c - - highest K uptake values K 8,376 ab 1, 609 17.8 194 b 24 14.1 Low K across all soils. Straw 8,019 ab 1, 252 13.2 185 b 15 ll8.8 Impact of Straw Straw + K 8,503 ab 1, 736 l9.5 212 a 42 24.7 † on Potassium General recommendation of 75 kg K2O/ha. All treatments received 165 kg N/ha and 45 kg P2O5/ha. ‡Straw applied at 4.5 t/ha. Means in the same column followed by the same letter are not significantly different at p = Uptake and Yield 0.05. With straw incor- poration, the yield in-
14 creases in different soils varied with K fertilizer rates (Figure High-K y = 0.0346x (r=0.679) A 1a). Linear equations were signifi cant for the plots of yield increase and K application rate for both medium and low K 12 Medium-K y = 0.1258x (r=0.975*) soils, but the correlation was non-linear in high K soils. In Low-K y = 0.0961x (r=0.977*) medium K soils, while the K fertilizer rate increased by 30% 10 (i.e., 50 to 75 kg/ha) the yield only increased from 7.6 to 8.8%. This indicates that surplus K+ ions were absorbed by the rice 8 crop grown on medium K soils. For low K soils, the present generalized recommendation for K fertilizer was found to be 6 inadequate. Similarly, Figure 1b shows the linear equations fi t to 4 Rice yield increase, % plots of the increase in shoot K versus K fertilizer application rate across soil fertility levels. Although the linear correlation 2 was not signifi cant for high K soils, K accumulation tended to increase linearly with K fertilizer application rate in medium 0 and low K soils. There are risks of luxury K absorption, such 020406080 as the change in the K:Mg ratio if the straw is used for fodder K O fertilizer rate, kg/ha 2 (Römheld and Kirkby, 2010), due to excess K application in 30 High-K y = 0.0895x (r=0.798) medium K soils, while in low K soils the need for additional K B input via fertilizer to meet rice production goals is apparent. Medium-K y = 0.2171x (r=0.995**) 25 Optimal Fertilizer Potassium Rates Low-K y = 0.2658x (r=0.994**) in Rice with Straw Incorporation 20 Two 15-year fi eld experiments carried out in the Sichuan Basin indicated that soil K reserves could be used to predict the
15 application rates of K fertilizer (IPNI China, 2012). The yield
O increase, % response data in Figure 1 suggests that the current K fertil- 2
izer recommendation of 75 kg K2O/ha is excessive for high and 10 medium K soils supplied with 4.5 t/ha of incorporated wheat
Shoot K or oilseed rape straw. Yet, on low K soils, the general fertilizer 5 recommendation plus straw is still not adequate to meet the demands of high yielding rice crops. The optimal amount of fertilizer K to be combined with straw is presented according 0 0 20406080to the linear and plateau models (Table 2). For example, in
K2O fertilizer rate, kg/ha high K sites at Zhongxiang and Yicheng, the corresponding optimal rates of K fertilizer were 36 kg/ha and 40 kg/ha, or Figure 1. Relationships between yield increase (A), K uptake (B) and about half of the generalized recommendation. For medium K K fertilizer rate with crop straw incorporation, Yangtze soils, the optimal K fertilizer rate averaged 60 kg/ha or 80% River Basin. * and ** denote significance at p = 0.05 and of the generalized recommendation.
Better Crops/Vol. 98 (2014, No. 3) Crops/Vol. Better p = 0.01, respectively. 14 Better Crops/Vol. 98 (2014, No. 3) 15 ). * 2 O 2 verified June 4, 2014 verified June rate, kg/harate, R Optimum K Optimum 9,658 40.49,852 0.739 56.1 0.963* 8,447 36.1 0.976* 8,400 62.6 0.961* kg/ha 1 1 1 1 Max. yield, kg/ha 8,281 Min. yield, Yicheng 9,423 Zhijiang 8,101 Zhongxiang TuanfengXiantao 9,798Honghu 10,375 9,682 8,333 10,604 62.7 58.6 0.961* 0.955* tion, Yangtze River Basin. River tion, Yangtze Optimal fertilizer Optimal for rice incorpora- straw with K rates Table 2. Table Based on linear and plateau K fertilizationBased on linear and plateau and Black- (Cerrato models 1990). mer, Soil K levels Sites High K Medium K Römheld, V. and E.A. Kirkby. 2010. Plant Soil 335:155-180. and E.A. Kirkby. V. Römheld, IPNI China. 2012. http://china.ipni.net/article/CNP-3019 ( C BBC area within China. O/ha is insuffi increased to ensure cient and needs to be O/ha is insuffi 2 The K nutritional needs of paddy rice can be effectively The K nutritional needs of paddy rice met through the combination of K fertilizer and recycled crop Although K fertilization had better effects on yield and K straw. uptake than straw return alone in medium and low K soils, the opposite was true in high K soils. Using a linear and plateau fertilization model, the optimal K fertilizer rates for high and But medium K soils averaged 38 and 60 kg/ha, respectively. for low K soils, the current generalized recommendation of 75 kg K Cerrato, M.E. and A.M. Blackmer. 1990. Agron. J. 82:138-143. 1990. Agron. J. Cerrato, M.E. and A.M. Blackmer. References Mr. Li is a Ph.D. candidate (e-mail: [email protected]), Dr. Dr. Li is a Ph.D. candidate (e-mail: [email protected]), Mr. Ren is Lecturer, (e-mail: [email protected]), Mr. Lu is Professor and Ms. Zhou is Li is Associate Professor, Dr. Ms. Cong is Lecturer, Hubei, China. Assistant at Huazhong Agricultural University, Research Entire Yangtze River Basin Entire Yangtze Summary both high rice yields and soil K fertility. both high rice yields and soil K fertility.