Aul Mj*,Shhz Munwr Mhi,Ai Niz,Ai Mhmoo,Ehsn-Ul-Hq,Nm AhmShhi Jvi,Ati Mhmoo

aSugarcane Research Institute Faisalabad,Ayub Agricultural Research Institute,Punjab,Pakistan

bSoil Fertility Research Institute,Lahore,Ayub Agricultural Research Institute,Punjab,Pakistan

cInstitute of Soil Chemistry and Environmental Sciences,Ayub Agricultural Research Institute,Punjab,Pakistan

dAyub Agricultural Research Institute,Punjab,Pakistan

eProvincial Reference Fertilizer Testing Laboratory,Raiwind Lahore,Punjab,Pakistan

fKey Laboratory of Clean Utilization Technology for Renewable Energy,Ministry of Agriculture,College of Engineering,China Agricultural University,Beijing 100083,China

Keywords:P-enriched compost Maize Wheat Farmyard manure P-uptake

ABSTRACT Crop phosphorus(P)deficiency and poor utilization of added P is a major agricultural problem due to reduced solubility of soil P and rapid fixation or precipitation of applied P fertilizer in alkaline and calcareous soils.The effects of P-enriched compost and single superphosphate(SSP)fertilization on maize and wheat yields and P use efficiency in a maize–wheat rotation system were studied for three years.On a three-year average,grain yields of maize and wheat after application of P-enriched compost were increased by 18%and 24%,respectively,in comparison with sole addition of a recommended dose of SSP fertilizer.P-enriched compost additiontosoil increasedmaizeand wheat yieldsby 12%and 17%,respectively,compared toP fertilizer plus FYM incorporation.Soil available P concentration and P uptake were affected significantly by the addition of P-enriched compost.On average,increases in P recovery,use efficiency,and agronomic efficiency of 52%,18%,and 43%were recorded in maize and increases of 50%,23%,and 49%inwheat.P-enrichedcompostapplicationyielded 30%and 32%higher economic returns in maize and wheat than SSP fertilization alone.

1.Introduction

Phosphorus(P)is a major component of animal and plant life,playing energetic roles in several metabolic mechanisms of cerealcropsand vegetables[1].In Pakistan,intensive cultivation of cereal crops(maize and wheat)is dependent on the use of mineral P fertilizers.The addition of farmyard manure(FYM)to soil as source of nutrients has become obsolete in most rural areas,becauseofthe separation ofland cultivation from livestock operations.Globally,maize and wheat are the most important cereal crops and also the main source of farmer income and staple food in Pakistan[2–4].However,the yield per hectare of maize and wheat is very low compared to that in other producing countries[5].Among many factors limiting crop yield,low available P is one of the major ones[5].Farmers have added large quantities of mineral P fertilizers over many years to increase crop yields.However,most of the P added with fertilizers is fixed in the year of application by precipitation and adsorption reactions.The availability of the remaining P fraction to subsequent crops via desorption or dissolution,and the effectiveness of any adsorbed P fertilizer,decline over time,particularly in alkaline calcareous soils with high P sorption power[5].P availability to crops could be increased by addition of organic or inorganic fertilizers such as manures,composts,and different mineral P fertilizers.Composting and mixing of organic manures with P fertilizers and rock phosphate has been reported to increase P availability[6].The present study was conducted to develop a new P-enriched compost(PEC)as a more efficient P fertilizer for alkaline calcareous soils than conventional P fertilizers and to estimate the effects of PEC on P use,recovery,and agronomic efficiency as well as on maize and wheat grain yields in a maize–wheat rotation system.

2.Materials and methods

2.1.Study site and methods of planting

Field experiments were conducted in the research field of the Soil Chemistry Section,Ayub Agricultural Research Institute,Faisalabad,Pakistan for three consecutive years(2011–2012,2012–2013,and 2013–2014).The soil of the field area is a sandy clay loam.Soil samples were collected with a soil auger at 0–30 cm depth for the determination of physicochemical properties in July 2011 before maize cultivation.The soil was alkaline in pH with low organic matter and P,but sufficient in potassium(K)(Table 1).The climate of the research area is semi-arid with cold winters and hot,dry summer seasons.The rainfall pattern was erratic during the experimental period.Maize–wheat was the cropping rotation,with maize receiving furrow and wheat receiving flood irrigation.Seed beds were prepared with a rotavator,followed by cultivation at optimum moisture level.A cultivator was used for final seed bed preparation,followed by planking.Maize was sown on ridges and wheat on a flat surface.

2.2.Preparation of PEC and description of treatments

To compare the efficiency and economics of PEC,four treatments were applied:T1,control(CK),T2,recommended dose(RD)of NPK,T3,RD of NPK+FYM at the rate of 1 Mg ha-1(RD NPK+FYM),T4,RD of NK+P-enriched compost(RD NK+PEC).FYM used in these treatments was analyzed and contained N(0.72%),P(0.51%)and K(0.59%),respectively.All treatments were repeated three times.Recommended rates of N(from urea)P(from single superphosphate)and K(from potassium sulfate)fertilizers were added in the respective amounts of 275,125,and 75 kg ha-1in maize and 120,90,and 60 kg ha-1in wheat.Full doses of P and K and half doses of N fertilizers were applied at final land preparation before maize and wheat planting,with the remaining half of N fertilizer applied in maize 45 days after germination and in wheat at tillering stage.For preparation of PEC,the recommended rate of single superphosphate fertilizer was mixed with farmyard manure at 1 Mg ha-1followed by sprinkling with water placement in pits,and covering with polyethylene plastic sheeting 45 days before crop sowing.Water was sprinkled weekly on the mixture,followed by mixing and covering again with plastic sheeting.The prepared PEC was incorporated in the soil at the time of final land preparation before sowing of maize and wheat crops.

2.3.Crop management and yield determination

The maize crop was grown in kharif(summer season)and after harvesting of maize,the wheat crop was grown in rabi(winter season).In the maize field,weeds were controlled by application of a post-emergence herbicide,atrazine,at 500 mL ha-1,and insect pests were controlled with 20 kg ha-1furadan[5].In each cropping season,maize grain yield was determined as follows:a37 m2area was manually harvested and the plants were left in the field for five days,then bundled and stacked in the sun for four or five weeks for drying.After drying,the ears were husked and let dry in the sun for a few days before threshing.The yield components of maize grain yield,namely number of kernels ear-1,number of kernel rows ear-1,and 100-kernel weight(g),were recorded.

Table 1–Initial soil properties of the field used for experimentation.

For determination of grain and straw wheat yield,an area of 9 m2was harvested by hand from the centers of all plots.Yieldcontributing traits,including number of spikes m-2,number of grains spike-1and 1000-grain weight(g)were recorded.

2.4.Plant and soil analysis

The pH of a soil paste and electrical conductivity of a soil extract was measured following Majeed et al.[7]and Jackson[8].P was measured with a spectrophotometer following sodium bicarbonate extraction[8].Soil organic matter content was estimated following Ryan et al.[9].Ammonium acetate was used for soil extraction and flame photometry was used for K determination[10,11].The dry plant material was digested with acid to determine phosphorus[5,11].

2.5.Calculation of P use efficiency and its components

P uptake,PUE(P use efficiency),PAE(P agronomic efficiency)and PRE(P recovery efficiency)were calculated following[2,5]:

2.6.Statistical and economic analysis

All data were analyzed with Statistics 8.1(statistix.software.informer.com).Least significant differences(LSD,P≤0.05)were used to compare treatment means[12].The relationship between grain yield and soil available P was assessed by exponential regression.Each year's repeated data from each treatment during the three years of the experiment were pooled,based on input prices,gross income and total expenditure were used to estimate the economic feasibility of PEC application for increasing maize and wheat grain yields and net economic returns[2].

3.Results and discussion

3.1.Yield and its attributes

The planting of maize and wheat in a maize–wheat cropping rotation with application of P fertilizer at rates 125 and 90 kg P ha-1isacommon practicein Punjabprovince,Pakistan.This practice was compared with the addition of FYM at 1 Mg ha-1and with recommended P fertilizer and PEC application,with the aim of determining whether or not PEC application increased crop yield.In 2011–2013,the PEC application resulted in significantly(P≤0.05)higher maize and wheat yields as compared to control treatments.The maximum maize grain yields,8.43,8.69,and 9.05 Mg ha-1(Table 2)and wheat grain yields,4.80,4.95,and 4.78 Mg ha-1(Table 3)were realized when RD NK+PEC was applied in 2011,2012,and 2013,respectively,followed by treatments in which RD NPK+FYM were applied.The minimum grain yields of maize and wheat were recorded in the control(CK)treatment.Over the three years,average maize and wheat grain yields were increased by 18%and 24%respectively by application of RD NK+PEC relative to sole application of RD of NPK fertilizer.Further,RD NK+PEC application increased maize and wheat yields by respectively 12%and 17%as compared to RD NPK+FYM application.Incorporation of FYM with RD NPK fertilizer did not significantly affect grain yields in comparison with sole RD NPK fertilizer.Grain yield of wheat was significantly increased when inorganic fertilizer was mixed with organic materials[13,14].Similarly,a significantly higher maize grain yield was observed when mixtures of organic and inorganic fertilizer were added to soil[15].On average over the three years(Table 4),RD NK+PEC addition increasedthenumberofkernel rows ear-1,numberof kernels ear-1and 100-kernel weight(5.6%,8.4%,and 7.2%,respectively)over RD NPK fertilizer application.A strong association was observed between number of kernels ear-1and soil available P with maize grain yield(Fig.1).The maximum numbers of grains spike-1,47,54,and 52 in therespective 2011–2012,2012–2013,and 2013–2014 were recorded in the RD NK+PEC treatment and the minimum in the control(Table 5).Overall,5.6%,6.2%,and 21.4%higher 1000-grain weight,number of spikes m-2,and number of grains spike-1,respectively,were recorded in RD NK+PEC than RD NPK treatments.For wheat as for maize,positive correlations were found between number of grains spike-1and soil available P(Fig.2).

Table 2–Effect of P-enriched compost on maize grain yield and P uptake.

Table 3–Effect of P-enriched compost on wheat grain yield and P uptake.

Table 4–Effect of P-enriched compost on yield contributing parameters of maize.

Fig.1–Association between number of corn kernels ear-1and soil available P.

Table 5–Effect of P-enriched compost on yield-contributing parameters of wheat.

The1000-grain weightofwheatwassignificantly increased by application of mineral fertilizers together with organic materials[14].P fertilizer enriched with organic material led to higher availability of phosphorus to plants than mineral P fertilizer alone[16].The higher grain yield of crops following PEC treatment may be due to increased soil microbial activities and higher availability of nutrients[16,17].

Fig.2–Associations between number of grains spike-1and soil available P.

Table 6–Effect of P-enriched compost on P recovery,use and agronomic efficiency.

3.2.P uptake in plant dry matter

P uptake in plant dry matter of maize and wheat significantly(P≤0.05)increased relative to the control.Maximum P uptakes(23.62,23.71,and 25.07 kg ha-1)by maize grain and(10.53,8.72,and 9.80 kg ha-1)by stalk were observed under PEC treatment in the three respective years(Table 2).Nonsignificantly different P uptakes in grain were recorded with RD NPK and RD NPK+FYM treatments during the three years;under RD NPK,18.40,18.73,and 18.36 kg ha-1and with RDNPK+FYM,20.85,19.84,and 20.79 kg ha-1phosphorus uptake by maize grain was observed(Table 2).These results also showed that higher P uptakes by wheat grain and straw were achieved with RD NK+PEC than with RD NPK+FYM application(Table 3);values of 12.80,13.35,and 12.42 kg ha-1in grain and 4.68,4.12,and 5.04 kg ha-1in straw were recorded in the respective 2011–2012,2012–2013,and 2013–2014 cropping seasons,both significantly higher than those under control treatments.Similarly,Taalab et al.[18]reported that plant P uptake was increased by the combination of rock phosphate with organic manure.P uptake and dry matter yield of crops were improved by application of chemical fertilizer enriched with organic manure[6].On average over the three years,the application of PEC to maize led to 30%and 17%higher P uptakes in grain and stalk and in wheat to 29%and 35%higher P uptakes in grain and straw,respectively,than sole RD NPK fertilizer application.Comparison of RD NK+PEC and RD NPK+FYM application showed that 18%higher P uptake in maize grain,8%higher P uptake in maize stalk and similarly 18%higher P uptake in wheat grain and 3%higher P uptake in straw,were recorded with PEC addition relative to RD NPK+FYM application.Thus,P fertilizer enriched with organic manure significantly increased plant P uptake and yield of crops,in accord with previous findings[6].

Table 7–Effect of P-enriched compost on post-harvest soil available P,EC,and pH.

3.3.P use,recovery,and agronomic efficiency

The maximum P use efficiencies,67,69,and 72 kg kg-1in maize and 53,55,and 53 kg kg-1in wheat during the 2011,2012,and 2013 cropping seasons,respectively,were found with the addition of PEC,whereas the minimum P use efficiency was found with the application of RD NPK treatments(Table 6).On average the application of PEC in the respective maize and wheat led to 18%and 23%higher P use efficiency than sole P fertilizer application.Similarly,greater P recovery efficiency was noted for PEC than for RD NPK+FYM treatments.The highest P recovery efficiencies,0.15,0.16,and 0.19 kg kg-1in maize and 0.13,0.14,and 0.14 kg kg-1in wheat,were recorded with the applications of PEC during the 2011,2012,and 2013 cropping seasons,respectively(Table 6).Similarly,higher P agronomic efficiency,29,36,and 41 kg kg-1in maize and 28,32,and 32 kg kg-1in wheat during the 2011,2012,and 2013 cropping periods,were observed with PEC application(Table 6).On average,29%higher P recovery,12%higher P use,and 28%higher P agronomic efficiency in maize and 23%,17%,and 33%higher P recovery,use,and agronomic efficiency in wheat were observed under PEC treatments than under P fertilizer plus FYM application.This effect may be explained by increased dissolution of insoluble phosphate fertilizer and native soil P by PEC,resulting in increased P release into the soil solution[19].

3.4.Post-harvest soil analysis and cost-benefit ratio

Over the three years,there was no marked effect on soil pH and ECevalues by the different treatments(Table 7).However,availability of soil P was significantly greater following addition of PEC than in the control in both maize and wheat crops(Table 7).An increasing trend was observed for soil available P with the application of RD NK+PEC as comparedto RD NPK and CK treatments.Averaged over the three years,soil available P was 5.34%and 5.65%higher after maize and wheat harvests,respectively,under RD NK+PEC than under sole RD NPK application.This finding may be due to the lower insolubilization or precipitation of added P fertilizer in PEC than of that in RD NPK fertilizer.Similarly,Biswas[20]reported an increase in soil available P following enriched compost application,as compared to application of mineral fertilizer alone.Three years of averaged maize and wheat yields were used for calculating net incomes and cost-benefit ratios.The highest net incomes and maximum cost-benefit ratios were achieved by PEC application,followed by RD NPK+FYM application(Table 8).In relative terms,a 21%higher net income in maize and 23%higher net income in wheat were achieved with PEC than with RD NPK+FYM application.

Table 8–EffectofP-enrichedcompost onnet incomeand cost-benefitratio ofmaize and wheat.

4.Conclusion

RD NK+PEC application increased maize and wheat yields as compared to RD NPK+FYM application.Soil available phosphorus and P uptake were increased significantly by addition of PEC than control.On average,30%in maize and 32%in wheathigher economic returnswererecorded withP-enriched compost than with sole SSP fertilizer addition.Thus,the use of P-enriched compost is more effective for crop production.Further studies should investigate the effects of application of composts made from different organic manures with P fertilizer on plant P availability and on the growth of crops in different agro-ecological zones.

Acknowledgments

The farm manager of the Soil Chemistry Section,Ayub Agricultural Research Institute,Faisalabad,is gratefully acknowledged for providing the field area,fertilizers and seeds of crops for this study.The reviewers are thanked for helping to improve the manuscript.