Effect of sesbania green manure on availability of some nutrients in calcareous soil

Introduction

As it is known to most soil scientists and researchers in Iraq and the world that phosphorus fertilizers and micro-nutrients added to calcareous soils, including Iraqi soils, are subject to adsorption and fixation processes due to the presence of carbonate minerals, especially calcium carbonate (Lindsay, 1979; Taalab et al., 2019) [13,26] , or what is known as lime, whose percentage in Iraqi soils ranges from 20 to 30% or more (Buringh, 1960) [4] , where affect distinctly the soil properties related to plant growth, whether they are physical, such as soil-water relations, and soil crusting, or chemicals such as the availability of plant nutrients.So in calcareous soils where pH is high and CaCO3 is dominated, plants suffer low availability of P and K and other nutrients would cause problems more serious than their deficiencies. The increasing availability of these nutrients is one of the important objectives in plant nutrition (Khalefa, 2007) [10] . And due to the importance of phosphorus and the micronutrients in the growth and yield of various plants, especially in calcareous soils and the lack of their availability, it was necessary to think about finding some suitable techniques for fertilization in calcareous soils, including green fertilization, which is expected to reflect positively on the efficiency of absorption of phosphorus, iron, zinc, manganese and copper nutrients, in addition to nitrogen and potassium, which reduces its loss in calcareous soils, and thus improves the growth and yield of plants. (Cakmak, 2008; Marschner, 1995; Malakouti and Tehrani, 2005; Sanchez and Swaminathan, 2005) [5,15,14,24] . Sesbania plant (Sesbania SP.) belongs to the leguminosae family, a leaf is a major compound, stamens in a flower are many and fruit is horn contains many of seeds, it is used as low windbreaks and in improving soil properties (Biag et al., 2005). The sesbania plant is considered one of the plants that highly fixing of atmospheric nitrogen, some countries of the world have great interest this plant. It has been used as a green fertilizer in the fields of rice in Philippines because the ability of this plant to tolerate salinity, increase biomass, organic carbon content and nitrogen fixation (Biag et al., 2005). (Meena and Majumdar, 2016) [16] found the use of green manure in agriculture lead to increased grain production for agricultural crops and maintaining soil properties. Also (Razaq et al., 2016) [23] found that the incorporation of grounded sesbania dry matter in soil markedly enhanced the reclamation process as indicated by the yield of barley and improvement of soil properties. Green manuring can enhance agricultural sustainability by improving nutrient preservation (Dinnes et al., 2002) [7] . Mixing leguminous green manure crops into the soil releases organic materials such as organic acids, amino acids, sugars and vitamins during crop growth as well as after decomposition (Shukla et al., 2011) [25] . Many crops can be used as green manure; however, the choice of green manure crop depends on several factors such as prevailing climatic conditions, crop cultivation system, the availability of seeds and other factors (Rao, 2014) [22] . The mineral composition of leguminous and its content of elements is different depending on the species, time of crop growth and growth condition (Verma et al., 2015) [27] . Mixing leguminous green manure crops in the soil it undergoes to decomposition and mineralization process (Meena et al., 2018) [18] . The invert mineralization process of green manure is the transformation of C and N from the mineral to organic form, the most important soil factors that influence this are: soil texture and structure, soil interaction, microbial activity and soil nutrient status (Dhakal et al., 2015) [6] . Green manure leads to rapid mineralization compared to grain residues because the low C/N ratio, low lignin content and high amount of easily degradable substances (Gil and Fick, 2001) [9] . Besides improving soil properties, green manure help reduce insect pests, disease occurrences and weed management (Kumar et al., 2014) [12] . The continued use of green manure leads to the accumulation of OM in soil, which improves the physical properties of soil and amounts of organic and amino acids, sugars and vitamins (Shukla et al., 2011) [25] .

The green manure has effects on the chemical properties of soil, especially the pH of soil by adding organic acids and generating CO2 during the decomposition of OM which leads to decrease in pH of soil from the proton released by compost (Buragohainet et al., 2017). Reducing organic matter leads to decrease iron and fluoride oxides that which lead to high pH in soil, due to the oxidation of Fe and proteins produced during OM decomposition (Meena et al., 2017) [17] . The researcher (Pooniya et al., 2012) [20] conducted field experiments on summer green manure crops, were found that the highest residues of added green manure resulted in the recycling of 180.5, 22.6 and 267.8 kg/ha-1 of N, P, K respectively. This research aim to find an appropriate level of green residues for sesbania plants to increase the availability of some nutrients in calcareous soil through conducting of laboratory incubation experiment and then move to field application as a large scale. Sesbania residues were added after cutting into small pieces at three levels (0%, 1%, 1.5% and 2% w/w), experiment was laid out according to randomized complete block design (RCBD) with three replicates, while maintaining soil moisture at field capacity using river water with EC of 1.50 dS.m-1, observing the degree of decomposition and the chemical analysis of nutrients is conducted after two months of namely the first period, and four months namely the second period from the beginning of incubation experiment. 20 g of urea was added to each treatment when preparing the experiment, as well as the same amount of urea was added to each treatment a month after the incubation period to increase the speed of decomposition. Soil samples were taking from each treatment and dried in an oven for 24 hours at 105 °C. Soil samples were chemically analyzed according to methods in (Page et al., 1982) [19] , where the EC, pH was measured using 1:1 solution by EC and pH meters. Organic Carbon by (Walkley & Black, 1934) [28] method. Available phosphorous by using a solution of 0.5M NaHCO3 and determined it using spectrophotometer. N available (NH4 + NO3) were determined using a 2M KCl solution by Kjeldahl instrument. Potassium content determined using ammonium acetate solution NH4CHCO2 by Atomic Absorption. Trace elements Cu, Mn, Zn and Fe were determined using DTPA solution by the Atomic Absorption Spectrometer (AAS) as described in (page et al., 1982) [19] . The chemical and Physical properties of soil used in the experiment are presented in Table 1 before adding sesbania plants residues. Some of nutrients content in Sesbania plants as following: total C 27.9%, total N 1.92% and total P 0.12%.

Materials and Methods

Incubation experiment

Field experiment

A field experiment was carried out in the 2013-2014 season at Al-Latifia Research Station of Agricultural Research Directorate, Ministry Of Sci. and Technology to study the effect of adding sesbania residues at field scale on the productivity of the barley crop. The experiment was designed according to randomized complete block design (RCBD), with three replications, area of each plot 6 m2. Sesbania plant residues were incorporated with the soil surface at levels (0%, 1%, 1.5% and 2% w/w). All plots received Nitrogen in 40 kg rate per hectare as urea, for increase the rate of organic matter decomposition in soil (Razaq et al., 2016) [23] . All experimental units were continuously irrigated within the limits of field capacity for a period of four months to continue the process of decomposing organic waste. Barley planted with seeds rate of 100 kg. ha -1 on lines and the distance between them was 30 cm. Urea and phosphate fertilizers were added at the recommended dose. Plants were irrigated with river water as needed. At the maturity stage, plants were harvested, and grain yield was determined.

Results and Discussion

Effect of incubating Sesbania residues on organic carbon content and availability of some nutrients

The results of tables 2 and 3 show that, the incubation of Sesbania plants residues led to a statistically significant (p<0.05) increase of organic carbon content in soil and the highest value in treatment 2% level of residues, for the first and the secend periods after incubation, the lowest value was at the control treatment (0%), and the increase rate was 45% and 50% for the level 2% in comparison to control for the 1 st and 2 nd period after sesbania residues applied respectively. This is consistent with (Fageria, 2007, and Razaq et al., 2016) [8,23] , who indicated that green manure from leguminous plants plays a major role in improving and accumulating organic carbon in the soil after plant residues addition. Also in the same tables show, the effect of incubation of sesbania residues on the available nutrients content in the soil after two and four months of incubation periods, in the table 2, after two month an available nutrients content in the soil increased statistically significant at (p<0.05), and in the 2% level of residue, gave the highest rate, this increase was 24%, 35%, 54%, 33%, 99%, 95% and 222% of nitrogen, phosphorous, potassium, iron, copper, manganese and zinc respectively compared with the control treatment. As in period two (Table 3), Also the results show a statistically significant increased at (p<0.05), in the treatment 2% level of residue, gave the highest rate of nutrients content in the soil, this increase was 50%, 39%, 33%, 114%, 77%, 18%,165% and 115% of nitrogen, phosphorous, potassium, iron, copper, manganese and zinc, respectively over control treatment. This is consistent with (Krishnaprabu, S., 2019) [11] where he found an increase in the nutrients of the rice plant by 59% N, 47% P and 8% K, when fertilizing with a green manure of the sesbania plant compared to non-fertilizer. In addition to the content of N and C, a green manure crops may also contain a large number of nutrients and other trace nutrients (Meena, 2018) [18] . In general, the results show that, with increasing the time or period of incubation of sesbania plant green residues up to four months, there were increased soil organic-C content, and soil available nutrients content of N, P, K, Fe, Cu, Mn, and Zn. On other hand, at the 2nd period N content was decreased strongly, while the copper and zinc content decreased slightly. This may be due to don't added a second activator dose of nitrogen fertilizer during the second period to increase the efficiency of decomposition of organic matter to improve the content of available nitrogen and other nutrients. The behavioral of organic carbon content and availability of some nutrients gives an indication that the decomposition of organic materials added after two and four months has passed leading to release of organic carbon and release most of the available nutrients content to the soil. This is confirmed by many researchers about the role of sesbania plant in improving soil properties (Biag and Zia, 2006; Qadir and Oster, 2002; Razaq et al., 2016) [1,22,24] .

Effect of Sesbania plant residues on barley yield

Table (4) shows the effect of adding Sesbania residues at levels (1%, 1.5% and 2% w/w) in the surface layer of the soil on the grain yield of barley, as it led to an increase in grain yield by 19.00%, 22.86% and 29.47% respectively, compared to the control treatment. The results show, an increase in grain yield with an increase in the level of addition, which is a result of improving soil properties and nutrients, and confirms the results of Tables 2 and3. This is consistent with (Krishnaprabu, S., 2019) [11] , where he indicated an increase of 11% in production of grain yield for the rice with used of Sesbania residues as a green fertilizer added to the soil compared to control treatment without adding the residue.

Conclusions and recommendations

Adopting a legume green manure crop such as Sesbania as a green fertilizer is perfect because it is fast-growing, succulent, easy to decompositions and produces a large amount of biomass with low moisture requirements and it is a tolerant plant for salinity. Green manure is considered to ensure environmental sustainability by maintaining soil productivity over a long time by protecting the soil from erosion and nutrient content. The results indicated that the use of 2% of Sesbania plant residues led to an increase in the soil content of organic carbon and other nutrients, as well as an increase in grain yield of barley over to 30%. Based on the above, we suggest, when the incubation period exceeds more than two months, it is preferable to give a stimulating fertilizer dose of nitrogen to increase the efficiency of decomposition of organic matter and stimulate the micro-organisms responsible for that, and thus improve the content of organic carbon and ready-made nutrients in the soil. This proposal should be applied when moving to a broad field application.

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