Zero Tillage Plus Residue Management and K Fertilization Effect on Cotton Yield and K Use Efficiency in Wheat-Cotton System

Zero tillage straw retained with optimum K is an important strategy to increase cotton ( Gossypium hirsutum L.) yield and K efficiency in wheat ( Triticum aestivum L.)-cotton system. A 2 years field experiment was conducted during 2018, and 2019 to study the impact of [zero tillage straw as such on soil surface (ZT SAS ) and zero tillage straw burnt (ZT SB )] and five K rates were 0, 20, 40, 60 and 80 kg ha -1 on cotton yield and K use efficiency. Results indicated that bolls/plant –1 , weight per boll, seed cotton yields, ginning out turn and K agronomic efficiency were highest with 60-80 kg K ha –1 . Interactions revealed that ZT SAS with 60-80 kg K ha –1 had higher bolls/plant, bolls weight, seed cotton yields and ginning out turn compared to ZT SB . K agronomic efficiency indices decreased with increasing K rate. ZT SAS with 20 kg K ha –1 gave greater K agronomic efficiency than other combinations. ZT SAS with 60-80 kg potassium per hectare may be a sustainable and environmentally safe strategy to enhance cotton yield and soil fertility . from combined input of ZT with straw retained and k fertilizer application at 60 kg K ha -1 . This shows that retention of crop residues has led to the increase in the K contents of soil and microbial activity which is clear indication of an improvement in soil health (Pankhurst et al. 2002; Nie et al. 2007). In the present study, we tried to optimize K management under zero tillage methods in order to improve cotton yield in wheat-cotton system.


INTRODUCTION
Zero tillage plus straw retained as such on surface (ZTSAS) is a suitable tillage method that increased soil fertility and cotton production as compared to zero tillage straw burnt, ZTSB (Ishaq et al., 200;Hulugalle et al., 2004). Zero tillage (ZT) impacted soil, water and environment. ZT with wheat residues is feasible and economical in wheat, cotton rotation (Wang, 2006). Zero tillage plus residues is the possible alternative to builds up organic matter in the surface of soil, increase moisture absorption capability, improve soil prosperities and increased cotton yield (Boquetet al., 2004). ZT plus residues enhanced SOM and potassium in the soil (Doganet al., 2009). Cotton scientists said that ZT with residue mulch gave higher size of aggregates, stability and total organic carbon in soil aggregates than ZT straw burnt (Mert et al., 2006). Higher accumulation of organic matter in the soil, greater fertilizer use efficiency and optimum moisture accessibility increased cotton yield under zero tillage straw retained (Nyakatawa and Reddy, 2000;Blaise, 2011).
Potassium is a major macro fertilizer that needed in large quantity and significantly affect cotton production and K agronomic efficiency (Kumar and Goh 2000;Torbertet al., 2002;Xuet al., 2009;Usman et al., 2014). Cotton crop requires optimum potassium for maximum production. Higher and lower K rates greatly influenced cotton yield and efficiency (Kumar et al., 2000;Singh et al., 2006;Jan et al., 2012;Wang et al., 2007). Potassium deficiency resulted in number of bolls per plant and boll weight that reduced cotton yield. (Sijtsma et al.,(1998, Tewolde et al.,(2008),and Reddy et al.,(2012). Potassium uptake could be improved through zero tillage and nutrients availability (Su et al. 2008;Sharma et al. 2002;Beri et al., 2003;Hu, W et al., 2015;Singh et al., 2005;Xu, et al., 2009). K use efficiency depends on fertilizer application rate and soil tillage methods Nyakatawa et al., 2001;Norsworthy et al., 2010;Potter et al., 2011;Cassman et al., 200;Minton et al., 1991;Pettigrew et al., 2008). K use in conational cotton sown after is decidedly un-productive (Kienzler, 2010;Dong et al., 2012), having less N recovery efficiency (Reddy et al., (2009) and Reddy et al., (2001). Research findings showed that the zero tillage straw retained with proper nitrogen use has shown to be a possible alternative for sustainable cotton crop production in irrigated wheatcotton systems (Zhang, et al., 2007;Wang, et al., 2012;Yang, et al., 2014). The experiment was carried out with the aim of zero tillage with residues management and K levels on cotton yield and K agronomic efficiency in arid environment of Dera Ismail Khan.

Ginning out turn (%)
Lint percent was affected significantly by ZT, potassium and interactions were not significant (Table-3). ZTSAS produced greater ginning out turn %age than ZTSB. Maximum GOT was obtained from 80 kg K ha -1 (Table 8).
Interactions indicated that optimum lint percentage could be recorded with 80 kg K ha -1 under ZTSAS.

Potassium Agronomic Efficiency (KAE)
Potassium agronomic efficiency as the yield (kg ha -1 ) increase for each kg K applied (kg ha -1 ) is the most important K use efficiency to producers. KAE was significantly affected by ZT and K and ZT × K interactions (Table 3). ZTSAS resulted in higher KAE than ZTSB. Potassium application at 20 kg ha -1 had the greatest agronomic efficiencies, while 80 kg K ha -1 had the lowest KAE (Table 9). Mean values for ZT × K interactions revealed that ZTSAS in combination with 20 kg K ha -1 gave an optimum NAE.

DISCUSSION
Zero tillage cotton sown into standing residues of wheat is done on experimental basis in Pakistan. Though, cotton growers take eager attention in ZT cotton establishment after wheat harvest due to lower cost of production and profitable cotton yield (Su et al. 2008;Sharma et al., 2002). Research data revealed that higher bolls per plant observed in ZTsas. Because the plants on the ZTsas plots had more numbers of fruiting sites were greater than those observed in the ZTSB (SB-straw burnt). Consequently, ZTsas had greater boll number and weight per boll than ZTSB. Thus, higher seed cotton was recorded under ZTsas than under ZTSB. Enhanced boll retention and weight per boll in ZTsas could be due to other factors such as improved soil K and soil organic matter, differences in nutrient supply and/ or conserved soil moisture. Greater boll numbers and boll weight under ZTsas contributed to yield improvements compared to the ZTSB Nyakatawa et al., 2001;Norsworthy et al., 2010;Potter et al., 2011;Cassman et al., 200;Minton et al., 1991;Pettigrew et al., 2008;Kienzler, 2010;Dong et al., 2012). Highest plant height were under ZTsas with optimum K level ( Beri et al., 2003;Hu, W et al., 2015). In long-term study on conservation tillage, significant yield differences were observed in upland cotton (Gormus,&Yucel , 2002) The study offers great yield variations in cotton genotype under conservation tillage. In addition, improved soil moisture content due straw mulch and better soil physical conditions might have contributed to more number of bolls and yield improvements in ZTsas than ZTSB (Singh et al., 2005;Xu, et al., 2009). Readet al.,(2006 and Oosterhuis(2010) obtained greater yield due to better soil hydrothermal regime under zero tillage and K at 80 kg ha -1 . In this research work, Seed cotton yields was significantly encouraged by ZTsas plots compared to plots ZT straw burnt. Seed cotton yield of the residue burnt plots was lowered significantly compared with the straw retained treatments due to the distinctive decrease of bolls, weight per boll and GOT % age (Kumar et al., 2000;Singh et al., 2006;Jan et al., 2012;Wang et al., 2007;Readet al., 2006;Oosterhuis, 2010). Our results revealed that lower cotton yield in residue burnt treatments, probably due to loss of mainly organic carbon (C) and huge losses of nitrogen (up to 70%), Phosphorus (26%) and mainly Potassium (20 %) and the death of useful soil flora and micro-organisms (Kumar and Goh 2000;Torbertet al., 2002;Xuet al., 2009). While greater seed cotton-yields in residues retained plots maybe due to improved nutrient accessibility in crop residues and right fertilizer management in soil through the adjustment of abundant micro-organisms after returning of wheat residues to the cotton fields (Sijtsma et al., 1998;Tewolde et al.,2008;Reddy et al., 2012;Reddy et al., 2009;Reddy et al., 2001). In the first cotton growing year, the micro-organisms might have feed on more nutrients such as potassium and Carbon to meet their own growth need, thus, lesser bolls, weight boll -1 and lastly decreased seed cotton yield have reported. However, in the 2 nd cotton sowing season, optimum use of soil resources by ZTsas sown cotton and decomposed residues that released fertilizer resulting in higher seed cotton (Zhang, et al., 2007;Wang, et al., 2012;Yang, et al., 2014). Optimum K management in cotton sown in ZTsas with wheat residues retained have increased seed cotton yield due to higher enzymatic activities in boll formation Nyakatawa et al., 2001;Norsworthy et al., 2010;Potter et al., 2011). Our results showed K at 60-80 kg ha -1 produced number bolls per plant and heavier boll weight as compared other K treatments (Kaddah, 1997;Kushwaha et al., 2001;Nehra et al., 2005). Enhanced yields in ZTsas with 60-80 kg K ha -1 were probably due to increased K supply, improved decomposition of wheat straw that enhances biological activity, better cotton root growth because of improved soil structure and enhanced soil moisture content by way of better infiltration rates (Cassman et al., 200;Minton et al., 1991;Pettigrew et al., 2008;Davis-Carter et al., 1992). Results also showed that ZTsas with wheat residues retention in combination with 80 kg K ha -1 had comparatively higher Potasssium agronomic efficiency than ZTSB. This result was probably due to more efficient K delivery, and lower losses of K from the system as against ZTSB (Prasad and Power 1991;Unger et al., 1997;Tursonov. 2009;Ishaq et al., 200;Javed et al., 2009;Huang et al., 2001). An optimum yield response could be achieved from combined input of ZT with straw retained and k fertilizer application at 60 kg K ha -1 . This shows that retention of crop residues has led to the increase in the K contents of soil and microbial activity which is clear indication of an improvement in soil health (Pankhurst et al. 2002;Nie et al. 2007). In the present study, we tried to optimize K management under zero tillage methods in order to improve cotton yield in wheat-cotton system.