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 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.., 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 ( and Yicheng sites) were classifi mg/kg (Zhongxiang and Yicheng 100 and 150 mg/ soils; those with available K content between , , 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 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, , 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.