Azosprillium based integrated nutrient management for conserving soil moisture and increasing sorghum productivity

In this field study, we evaluated the utilization of Azosprillium with organic amendments and urea in winter sorghum productivity in order to achieve the best results with minimum nitrogen utilization in Vertisols under different rainfall situations of SAT, India. Results showed that the organic materials application conserved more rainwater in top 0.60 m soil profile. Across three years of study, Azospirillum seed inoculation had a positive effect on sorghum production and produced 13% more sorghum grain and straw yields compared to 0 kg N ha –1 . Sorghum grain yields were 44% higher when seeds were treated with Azospirillum and applied with 50% recommended rate of nitrogen (RRN) through urea and 50% RRN through organic materials (50:50 ratio of Leucaena loppings and farm yard manure) compared to control. Water use efficiency (WUE) was 42% greater with Azospirillum seed treatment and application 50% RRN through organic materials and 100% RRN through urea over control. Interference drawn in this study clearly indicates that low cost technology of Azospirillum seed treatment has to be adopted for higher sorghum grain yields. However, it is recommended to apply N through organic and fertilizer N in the ratio of 50:50 RRN along with Azospirillum seed treatment for sustainable sorghum yields and greater water productivity in the Vertisols of SAT, India.


INTRODUCTION
The global human population will reach around 10 billion by 2050. To meet the needs of growing population, the pressure on the reduced land area will increase to produce more food, fibre and fuel by greater use high yielding crop cultivars, fertilizers and employing new production technologies at farm level (Johri et al., 2003). In India, nearly 60% of cultivated area is rainfed that contributes for 45% of agricultural production (Venkateswarlu, 2008a, b). Vertisols are major soils in rainfed eco-system of SAT in south India. These soils are sometimes more hungry than thirsty as low soil fertility is one of the major factor limiting crop productivity. These Vertisols are universally deficient in N and nearly 40% in P thus requires proper management to sustain productivity. Low rainfall (508 mm average of 56 years) and its uneven distribution; poor economic status of dryland farmers, high costs and timely unavailability of fertilizers and organic amendments in recent years resulting in lesser application than the recommended rate. This practice leads to higher rate of nutrients depletion than their replenishment that declines the soil health and consequently reduces crop productivity over the years (Math and Patil, 2013). Decreased availability of organic amendments, increased cost of chemical fertilizers and organic amendments farmers are forced to pay nearly double the cost of fertilizers during 2012 to 2013 alone in India. Frequent droughts due to greater variation in rainfall as a result of climate change resulting in higher cost of production and decreased net returns per unit area. Adverse effect of water stress on productivity of rainfed crops especially during drought years can be minimized by use of organic materials as soil amendments. These amendments conserve rainwater in situ; enhance nutrients supply and increase N use efficiency of applied fertilizers (Reddy et al., 2004;Patil and Sheelavantar, 2009). To meet crop nutrient requirements exclusively through organic amendments alone requires large quantity of materials which is uneconomical due to its high cost and low availability. Application of chemical fertilizers alone does not bring significant increase in crop yields on sustainable basis over the years as these fertilizers supply only limited nutrients.
In addition, continued use of chemical fertilizers causes health and environmental hazards such as ground and surface water pollution by nitrate leaching. So reducing the amount of nitrogen fertilizers applied to the field without a nitrogen deficiency will be the main challenge in field management. One of the possible options to reduce the use of chemical fertilizer could be using of organic materials. It is generally acknowledged that organic materials play an important role in maintaining a high level of soil fertility. The positive influence of organic fertilizers on soil fertility, on crop yield and quality has been demonstrated in the works of many researchers (Suresh et al., 2004;Naeem et al., 2006;Dauda et al., 2009). Increase in price of chemical fertilizers and organic amendments forcing the farmers in the region to use alternative low cost inputs like biofertilizers.
Biofertilizers play an important role in plant nutrient management, particularly in rainfeds where farmers wants to reduce the fertilizer application through biofertilizers that costs them low. Applications of biofertilizers improves soil organic matter content, enzymes, microbial population and decrease the negative effect of chemical fertilizer and also increase yields of crops on sustainable basis (Alizadeh and Ordookhani, 2011;Jala-Abadi et al., 2012). Among the plant growth promoting rhizobacterium (PGPR) species, Azospirillum spp. is well known for its ability to excrete. Earlier research indicates that cereal crops in general, and sorghum and pearlmillet in particular have a variety of N fixing bacteria in its rhizosphere, including Azospirillum and Azotobacter which releases growth promoting substances like phytohormones such as indole acetic acid, gibberellins, cytokinins and auxins. For instance, these phytohormones fixes nearly about 10 to 25 kg N ha -1 thus increasing root biomass and grain yield (Kumar and Gautam, 2004;Fuentes-Ramirez and Caballero-Mellado, 2005).
In view of the present existing situation,it is more essential to adopt Integrated plant nutrient supply system (IPNS) system for sustainable crop productivity by the farmers who have greater concerns on soil health. Under IPNS, balanced use of organic amendments along with chemical fertilizers including micronutrients and biofertilizers results in improved soil fertility and crop productivity through fertilizer use efficiency (Singh et al., 2004;Guggari and Kalghatagi, 2005;Jala-Abadi et al., 2012).
Sorghum is one of the major rainfed cereal crop cultivated in 41 Mha that produces 64.20 Mt, with a productivity hovering around 1.6 tons per ha. Unlike in other parts of world, sorghum is cultivated in both rainy and postrainy seasons in India. In India sorghum is cultivated in 7.69 Mha that produces around 7.29 Mt with a low productivity of 948 kg ha -1 (Tonapi et al., 2011). Quality of rainy season sorghum is poor and is mainly used for animal and poultry consumption. Postrainy season sorghum grain is mostly consumed by human beings and is a staple food of dryland dwellers in central and south India. Sorghum is cultivated on stored soil water in profile during winter season. Deficit soil moisture and low availability of required quantity of nutrients at critical crop growth stages of sorghum reduces crop yields in Vertisols of Deccan Plateau region in India. To enhance winter sorghum productivity, various agronomic management practices have been designed and evaluated, however the information on IPNS with biofertilizers is scarce under different rainfall situations.
In view of this situation, the present field study aims to explore the effect of bio-organic and organic materials and chemical fertilizers on rainwater conservation, water use efficiency and sorghum productivity during winter season.

Soil and site characteristics
A field study was conducted for three years (2000 to 2001 to 2002 to 2003) at CSWCRTI's Research farm, Bellary, India (15°09 ' N latitude, 76°51 ' E longitude, and at an altitude of 445 m above msl). Experimental soils were classified as Typic-Pellusterts of Bellary series derived from granite, gneiss and schist. Clay content increased with depth from 44% on surface to 50% at 0.90 m. Infiltration rate of these soils is 0.8 mm h -1 with bulk density of 1.25 Mg m -3 (Black, 1965). These soils pH is 8.6, electrical conductivity is 0.14 dS m -1 and organic carbon content is 3.83 g kg -1 (Piper, 1966). The available N of these soils is low 159 kg ha -1 (Subbaiah and Asija, 1956), medium available P of 21 kg as P2O5 ha -1 (Jackson, 1967) and high available K of 550 kg as K2O ha -1 (Muhr et al., 1965). Chickpea was cultivated at study site during 1999 to 2000.

Treatment details
A field study was conducted with 10 treatments combinations of N applied through organic materials, urea and PGPR Azospirillum brasilense. The treatments details includes, that is, T1-0 kg RRN ha -1 (Control), T2-Azospirillum, T3-50% recommended rate of nitrogen (RRN) through organic material, T4-50 RRN through organic material + Azospirillum, T5-50% RRN through urea, T6-50% RRN through urea + Azospirillum, T7-100% RRN through urea, T8-100% RRN through urea + Azospirillum, T9-50% RRN through urea +50% RRN through organic material + Azospirillum and T10-100% RRN through urea + 50% RRN through organic material + Azospirillum. This study is conducted in a randomized block design with three replications. The organic N is applied through Leucaena loppings and farmyard manure (50% each) on N content basis (Table 1). Leucaena loppings and farmyard manure were incorporated in soil during second and third week of August, respectively in top 10 cm soil depth as per the treatments. Seeds were treated with PGPR A. brasilense prior to sowing and N was applied through urea as per treatments at sowing along with recommended rate of P2O5, that is, 40 kg ha -1 . Sorghum (

Computation of soil water and water use efficiency
Profile soil moisture was gravimetrically recorded at every 0.15 m soil depth up to 0.60 m soil depths in each treatment prior to sowing and at 30, 60 and 90 days after sowing (DAS) and at harvest. Soil moisture utilized was computed as the difference of soil moisture at sowing, at 30, 60 and 90 DAS and at harvest. Consumptive use of water was determined by recording difference in values of soil moisture content (mm) in top 0.60 m of soil between any two stages, by adding rainfall and subtracting runoff during the relevant period (Patil, 2013;Patil and Sheelavantar, 2006). No drainage or deep percolation was observed at Bellary during the crop growth period and hence it was not accounted for calculation of consumptive use of water during three years of study period. Runoff that was measured by using multi-slot device from adjacent study plot was used for this study in 10 treatments of 3 replications, that is, total 30 treatments for assessing each treatment runoff. Difference in soil water was added to arrive at consumptive use of water in mm by using the formula, n CUW =  (SMa-SMb) + Rainfall -Runoff, i=1 Where CUW = Consumptive use of water (mm), SMa = Soil moisture content in top 0.60 m soil at stage a, SMb = Soil moisture content in top 0.60 m soil at stage b, Rainfall and Runoff as recorded between stage a and b. The stages a and b are sowing, 30 days after sowing (DAS), 60 DAS, 90 DAS and harvest. The economic sorghum yield, i.e., grain yield was divided by CUW (mm) to work out the water use efficiency (WUE). The WUE is expressed in kg ha -1 mm -1 .

Growth and yield components of sorghum
Average plant height (base to the tip of the head) is computed from five randomly selected plants from each plot and expressed in meter. Biometric characterization of sorghum head was computed by measuring head length (base to tip) and head girth (perimeter at the centre of the head) of five randomly selected plants from each plot and expressed in centimeter. Weight of the head and grain yield per plant were recorded after drying for 10 days. The sample of 1000 grains were randomly drawn from individual treatment in all three replications were weighed and expressed in grams. The grains per head was estimated using the formulae, 1 2 Grains weight per head 3 Number of grains per head = × 1000 4 1000-grains weight 5 6 The Harvest index (HI) is computed using the formulae (Donald 1962). 7 Economic yield 8 Harvest index = × 100 9 Total biological yield 10 The Harvest index (HI) is computed using the formulae (Donald 1962 The Harvest index (HI) is computed using the formulae (Donald 1962). 7 Economic yield 8 Harvest index = × 100 9 Total biological yield 10

Statistical analysis
All the field data in this study was analyzed using MSTAT-C statistical package (Gomez and Gomez, 1984). When analysis of variance indicated significant difference, LSD test was used for comparing the differences between the treatments.

Years
During 2001 the rainfall of 566.6 mm that fell in 31 rainy days was 12% higher. In addition, the antecedent rainfall  (Table 4). Even the trend in straw production was similar to grain and is attributed to production of taller plants with more leaves higher dry matter production in both leaves and stem (  (Hagbabayi et al., 2011;Ghanbari et al., 2013). Lower consumptive use with more grain production per each unit of water utilized during 2000 to 2001 produced greater WUE of 8.53 kg ha -1 mm -1 and it was higher by 23 and 14% compared to 2002 to 2003 and 2001 to 2002, respectively (Table 4). In arid and semi arid regions abiotic stresses such as water stress, salinity, high light, temperature, flooding, toxic metals, wounding and biotic stresses including pests and pathogens reduced plant growth and yield (Glick et al., 2007;Ghanbari et al., 2013). Grain yield of maize reduced due to water stress (Sajedi et al., 2009;Habibi et al., 2010;Farajzadeh et al., 2011;Ghanbari et al., 2013).

Treatments
Azospirillum seed treatment produced 7% more grain yield compared to control during 2001 to 2002 with higher rainfall and its uniform distribution. During 2000 to 2001 with a higher rainfall of 550.9 mm and its uneven distribution, sorghum grain yield was higher by 13%, while in a drought year with lower annual rainfall of 432.6 mm during 2002 the sorghum grain yield was 23% higher with Azospirillum seed treatment compared to 0 kg N ha -1 during 2002 to 2003. Across three years, sorghum grain and straw yields were higher by 13% with Azospirillum seed treatment over control (Table 4). These results indicate that a simple low cost technology of seed treatment with Azospirillum is more beneficial during drought years with less soil water availability at different stages of sorghum compared to normal and higher rainfall years. Seed inoculation of wheat varieties with biofertilizers showed a significantly increased vegetative growth and grain yield (Narula et al., 2001;Jala-Abadi et al., 2012). Higher sorghum yields with Azospirillum inoculation was probably attributed to the biosynthesis and secretion of bacterial Indole-3-Acetic Acid (IAA) (Johri et al., 2003;Fuentes-Ramirez and Caballero-Mellado, 2005). Bacterial IAA stimulates plant root production, especially lateral roots with greater root hairs and improves their development (Meunchang et al., 2004). Okon and Kapulnik (1986) also pointed out that colonization of plant root by Azospirillum might enhance permeability of N, P, and K ions into roots. The plant growth promoting rhizobacterium (PGPR) enhances uptake of soil nutrients by host plant (Salamone et al., 1997;Fuentes-Ramirez and Caballero-Mellado, 2005). Higher grain yield of winter sorghum with Azospirillum inoculation compared to 0 kg N ha -1 was attributed to production of greater dry matter in head due to greater head and grain weight per plant, higher values of 1000 grains weight and higher head length and head girth ( Table 4).
The sorghum grain yield enhanced from 13 to 38% with application of 50% RRN through organic material along with Azospirillum (T 4 ), while increase was higher and varied from 33 to 47% with application of 50% RRN through urea along with Azospirillum (T 6 ) during different years of study. Further, increase in N application from 50% to 100% through urea along with Azospirillum (T 8 ) increased grain yield marginally compared to control during all the three years of study (Table 3 and Figure 1). In pooled data, mean grain yield of three years in T 8 was 40% higher compared to control (Reddy and Sudhakarbabu, 1996). In addition to N fixation, Azospirillum improves plant growth through production of phytohormones leading to better plant growth with greater photosynthate production and its translocation to reproductive parts (Fuentes-Ramirez and Caballero-Mellado, 2005;Arbad et al., 2008;Prasad, 2008;Khan et al., 2010). Higher head and grain weight per plant with higher values of head length, head girth and 1000-grains weight produced higher grain yield in T 4 , T 6 and T 8 treatments compared to control during all three years of this study. Application of bacterial inoculants at higher soil moisture with zinc sulphate increased maize cob weight (Ghoorchiyani et al., 2011;Mostafavi et al., 2012;Ghazvineh and Yousefi, 2012).
Applying 50% RRN through urea and 50% RRN through organic materials and seed treatment with Azospirillum (T 9 ) produced significantly higher grain yield varying from 32 to 66%, while increase in N application through urea to 100% (T 10 ), sorghum grain yield was 37 to 67% higher compared to 0 kg N ha -1 during study period and in pooled data (Table 3 and Figure 1). These results indicates that Azospirillum seed inoculation fixes around 10-25 kg N ha -1 and could save nearly 50% of recommended rate of N through urea in winter sorghum (Prasad, 2008). Occurrence of moisture stress from flower initiation to maturity due low soil water availability in profile and higher N through urea negatively interacted during a drought  T1  T2  T3  T4  T5  T6  T7  T8  T9 T1  T2  T3  T4  T5  T6  T7  T8  T9 T1  T2  T3  T4  T5  T6  T7  T8  T9  T10  Treatments Grain yield (kg/ha)  T1  T2  T3  T4  T5  T6  T7  T8  T9  T10   Treatments Grain yield (kg/ha) Pooled Figure 1. Grain yield (kg ha -1 ) and soil water (cm) in 0.60 m soil profile as influenced by integrated nutrient supply system in winter sorghum in Vertisols of Bellary, India.  decreased sorghum grain yields from 1728 kg ha -1 under T 9 to 1719 kg ha -1 in T 10 . Straw yield during study period and in pooled data was higher and it varied from 32 to 61% in T 10 compared to control (Table 3 and Figure 1).
Higher grain and straw yield in T 9 and T 10 were attributed to more rainwater conservation and its availability in soil profile from sowing to 60 days after sowing and increased the use efficiency of applied N fertilizer either through organic/inorganic materials/Azospirillum (Figure 1). Higher soil water and nutrient availability at different stages of sorghum produced better plant growth with greater dry matter translocation to head from leaf and stem during physiological maturity thus producing greater head weight plant -1 , grain weight plant -1 , 1000-grains weight, head length and diameter in T 9 and T 10 (Kundu et al., 2009;Thakur et al., 2009). Greater grain and straw yields in T 9 and T 10 were also attributed to balanced supply of nutrients through organic and inorganic materials with increased N use efficiency as reported earlier by Singh and Agarwal (2005), Kumar et al. (2005), Laddha et al. (2006) and Jala-Abdi et al. (2012). In Vertisols of Bijapur, India, adoption of moisture conservation practices with increased N application up to 50 kg ha -1 produced greater dry matter accumulation plant -1 resulting in higher grain and straw yield in sorghum (Math and Patil, 2013;Patil et al., 2011). Application of farmyard manure at 5 t ha -1 and 30 kg N ha -1 along with Azospirillum seed inoculation resulted in greater pearlmillet yield over other treatments as reported by Kumar and Gautam (2004). Results of this study clearly indicate that N application through either organic, inorganic or microbial cultures alone were not beneficial compared to their combination in increasing cereals yields and was attributed to soil and rainwater conservation and supply of all nutrients at required rates at different sorghum growth stages. In corn and sorghum also biological fertilizer was not sufficient but integrated application of biological and chemical fertilizers produced significant increase in yield (Amujoyegbe et al., 2007;Rizwan et al., 2008;Haghighi et al., 2010).
Greater dry matter translocation from leaves and stem to head at physiological maturity producing 7% higher HI with application of 50% RRN through urea, 50% RRN through organic materials and Azospirillum seed treatment compared to control during all three years of study and in the pooled data. Conserved rainwater in soil profile was better utilized for grain production thus producing higher WUE during 2000-01 compared to 2001 to 2002 and 2002 to 2003. In pooled data, WUE was 12% higher with Azospirillum seed inoculation over control. The WUE across three years of study increased from 16% (T 3 ) to 21% (T 4 ), 29% (T 5 ) to 37% (T 6 ) and 35% (T 7 ) to 39% (T 8 ) with Azospirillum seed treatment compared to application of organic or inorganic materials at same rate. The water use efficiency (WUE) was also greater by 41 and 42% with application of 50% RRN through urea, 50% RRN through organic materials and seed treatment with Azospirillum (T 9 ) and application of 100% RRN through urea, 50% RRN through organic materials with Azospirillum seed treatment (T 10 ), respectively compared to control (Table 3 and Figure 1). Higher WUE with urea alone compared to application of same quantity of N through organic materials or in combination of urea and organic materials was attributed to lower consumptive use of water with application of urea alone. Organic materials conserved more rainfall with higher soil water in profile resulting in higher consumptive use with lower WUE.

Conclusions
Organic materials conserved rainwater in-situ. Azospirillum seed inoculation produced 13% greater sorghum yields and was economically more beneficial during drought years compared to normal rainfall situations. Poor farmers with animal components apply available organic amendments with low cost Azospirillum for greater winter sorghum yields. Resourceful farmers apply available organic amendments at farm along with 50% RRN through urea during normal rainfall years and top dress 20 kg N ha -1 with urea during October second fortnight during above normal rainfall situations with better soil fertility and sustained sorghum yields in Vertisols of SAT, India. Azospirillum seed inoculation alone increased the WUE by 12% and further integrated nutrient management improved the water productivity in winter sorghum up to 41%.