Pig slurry as a nutrient source in wheat / corn succession

Submitted on June 18 , 2015 and accepted on March 29 , 2016. 1 Universidade Federal de Santa Maria, Departamento de Ciências Agronômicas e Ambientais, Frederico Westphalen, Rio Grande do Sul, Brasil. claudirbasso@gmail.com; marlo.bison@gmail.com; santi_pratica@yahoo.com.br; rodrigosilva@smail.ufsm.com Autor para correspondência: marlo.bison@gmail.com Pig slurry as a nutrient source in wheat/corn succession


INTRODUCTION
Wheat and corn are staple foods for mankind and corn is also important raw material in the formulation of feed for pig and poultry farming.In recent decades, there has been a significant demand for these grains in the domestic market, driving technologies towards increasing yield and quality of the grains.Brazil is not self-sufficient in wheat production and this is caused by a lot of insecurity of the framers due to either lack of a guaranteed minimum price, or by adverse weather in the South region, its leading producer.Crop failure or low prices may not be enough to pay even the production costs, in which 40% is consisted of modern inputs (Brum & Heck, 2005).On the other hand, corn is important for crop rotation.The increase in grain production, is due more to vertical productivity associated to new technologies than the actual increase in the cultivated area.Fertilizers have the most impact on the final cost of corn production (Araujo et al., 2004), which has high demand for nitrogen fertilization (Gomes et al., 2007;Duete et al., 2008), because nitrogen (N) is a vital plant nutrient, responsible for the formation of various organic compounds and activation of enzymes (Malavolta, 2006).Despite the requirement of nitrogen not being as high in wheat compared to corn (Commission of Chemistry and Soil Fertility -CQFS 2004), an adequate supply of N has been considered vital for desirable industrial quality of grains (Cazetta et al., 2008;Pinnow et al., 2013).
The production chain of swine is one of the major income-generating activities in small farms in southern Brazil, and more recently, it has been expanding to the central west region of the country, which is a significant region in corn production, the main component in animal diet.However, due to the intensification of swine farming in these regions, there is a high supply of pig slurry (PS) which, according to Konzen (1983), consists of the animal hairs, feces, urine, leftover feed, water from troughs and cleaning of the stalls, and other residues resulting from the adopted management practices.
PS has fertilizing and pollutant potential, and caution in its use with agricultural crops has already been documented, especially as a source of N, phosphorus (P) and potassium (K) (CQFS, 2004;Ceretta et al., 2005;Konzen, 2006;Seidel et al., 2010;Correa et al., 2011;Costa et al., 2011;Cassol et al., 2012).Besides being a way of disposing this waste, its use in agricultural crops is a way of alleviating pollutant potential and providing the cycling of these nutrients within their own production units.
In this sense, some studies have aimed to evaluate the effect of PS on the production of cover crops in winter (Ceretta et al., 2005;Aita et al., 2006), on the decomposition of straw on the surface (Aita et al., 2006;Giacomini et al., 2008), on soil nutrients and chemical properties (Lourenzi et al., 2011;Lourenzi et al., 2013) and on the dynamics of transformation of nitrogen in the soil (Aita et al., 2006;Aita & Giacomini, 2008).However, little is known of its nutritional value in two important gramineae, seen as major exporters of nutrients and grown in succession.Therefore, the aim of this study was to evaluate the effect of PS as fertilizer on plant growth and yield in wheat/corn succession.

MATERIAL AND METHODS
The experiment was conducted on field in the period of June 2012 to March 2013.The soil of the experimental area is classified as Rhodic Eutrudox, (Embrapa, 2006) and the climate as subtropical climate with hot summers (CFa) according to Köppen classification system (Moreno, 1961).Rainfall during the period is presented in Figure 1.
The area where the experiment was conducted had been cultivated under no-tillage system over the last 10 years, the last year remaining under fallow.In March 2013, three months before the sowing of wheat and the installation of the experiment, sampling was conducted in soil layer 0-10 cm and it presented the following characteristics: pH (1:1 in water) = 4.8; SMP index = 5.5; clay = 650 g kg -1 , organic matter = 29 g kg -1 ; potassium = 252 mg dm -3 , calcium = 3.4 cmol c dm -3 ; magnesium = 1.7 cmol c dm -3 , aluminum = 1.0 cmol c dm -3 , phosphate = 13.00 mg dm -3 .Seeking to increase pH to 6.0, liming was also done in March as recommended (CQFS, 2004), followed by subsoiling and plowing operations.
The experimental design was in randomized blocks with six treatments and four replications structured in plots of 9 m 2 .The treatments were three doses of PS (40, 80, 160 m³ ha -1 ), mineral NPK, and no fertilization, as the bottom control.Mineral NPK fertilization was quantified as recommended for each crop (CQFS, 2004) with an expected yield of 3.0 Mg ha -1 for wheat and 12 Mg ha -1 for corn.Urea (175 kg ha -1 ), triple superphosphate (150 kg ha -1 ) and potassium chloride (100 kg ha -1 ) were used as the source of NPK, respectively.PS was obtained from a swine production unit in the region, whose characterization and respective amounts of N, P (P 2 O 5 ) and K (K 2 O) added to each treatment and crop is shown in Table 1.The treatments were applied by casting after sowing of crops, while N coverage was done at wheat tillering (30 days after emergence) and V4 for corn.
The sowing of wheat (cultivar Quartzo, classified as bread wheat, of medium cycle and plant height) was manual, in rows spaced at 0.17 meters, density of 300 viable seeds per square meter.The sowing of corn (DKB 250 VT Pro) was spaced at 0.45 m, performed manually, with a density of 6.30 seeds per linear meter, thus ensuring population of 70,000 plants ha -1 after thinning.
The dry matter (DM) of the shoots at flowering was evaluated, which for wheat was measured when 50% of the plot had spikes in bloom, and for corn when 50% of the spikes had exposed stigmas.For wheat, this assessment was made by cutting the plants close to the ground in an area of 0.25 m² in each plot.For corn, sampling was done on five random plants in the plot.Samples were taken to a circulating air oven at 65 °C until constant weight.After being dried, the samples were weighed and crushed in electric forage, and homogenized; a sub sample was then removed and referred to the laboratory for tissue analysis to determine the content of N, P and, K.In the laboratory, samples were ground in a Willey grinder, proceeding to the wet digestion method described by Tedesco et al. (1995).
Close to harvest, ten random plants of the plot were evaluated as regards plant height (PH), having the ground level and the insertion of the flag leaf as reference for both crops.For wheat, the number of grains per spike (G/S), and for corn, stem diameter (SD) were measured with a digital caliper at the height between the first and second node of the stem.
For wheat, the plants were harvested in an area of 2.72 m² from the center of each plot, and for corn, cobs were collected from ten random plants, disregarding the borders of the plot.The determination of yield was calculated after threshing, cleaning and correction of humidity (13%), considering the harvested area of wheat and the number of plants harvested for corn.The weight of a thousand grains (TGW) was determined for both crops using four replications of 100 units of each plot and for wheat, the hectoliter weight (HW) was measured through a specific device in an unloading grain cooperative in the region.
The analysis of variance was carried out and when significant, the Dunnett test was applied to compare each treatment of PS with each control at 5% error probability (p > 0.05), using the software GENES (Cruz et al., 2006).

RESULTS AND DISCUSSION
As regards dry matter (DM) yield in the shoots of wheat, Table 2 shows an increase of 26, 52 and 33%, respectively, for doses of 40, 80 e 160 m 3 ha -1 , compared to the production without fertilizer application, but not significantly differing from that obtained with mineral fertilizer.The 52% oppose the 34% found by Assmann et al. (2007) in DM yield in oats+rye grass intercropping, and the 104% found by Aita et al. (2006) in black oat in monoculture when using 80 m 3 ha -1 .
This DM response may be associated with the amount of nutrients applied via PS, because even at the lowest dose of PS (40 m 3 ha -1 ), sufficient nutrients were added and nutritional demand of N, P and K in wheat was met, similarly to mineral fertilization (Table 1).Even without significant difference, the highest DM yield in the shoots of wheat was achieved with the dose of 80 m 3 ha -1  , which would approximate doses of 65 and 86 m 3 ha -1 , respectively found by Aita et al. (2006) and Ceretta et al. (2005), and maximum technical efficiency in the black oat yield.
In corn, there was no difference in DM yield among doses of pig slurry and mineral fertilizer control.However, compared to control without fertilizer, there was an increase in DM yield of 35.03, 44.25 and 44.35% for doses of 40, 80 e 160 m³ ha -1 of PS, respectively.It was observed that, by doubling the amount of PS from 80 to 160 m³ha -1 , the increase in DM yield was insignificant, which, according to Ceretta et al. (2005), nutritional inefficiency occurs by PS with the increase of the dose, as found by doubling the dose of 40 to 80 m³ha -1 .Using 63.3 m³ ha -1 of PS as the source of 140 kg N ha -1 in growing wheat on oat straw, Giacomini & Aita (2008) did not find any difference in DM yield compared with mineral fertilization.However, in comparing these studies, it is interesting to note that soil, straw, hybrid and PS between both are different.In addition, the treatment of only 40 m³ ha -1 of PS presented a similar response to the mineral control, as opposed to the necessary 63.3 m³ ha -1 of the authors.This can also be associated with the amount of readily available N (ammonium) supplied via the PS, which was 57.9 kg ha -1 in the work of Giacomini & Aita (2008) and 74.4 kg ha -1 in the present work.
The number of G/S in wheat crop did not differ with the application of PS compared to any of the controls.If the high input of nitrogen by PS is considered, Teixeira Filho et al. (2010) found no response in number of G/S when nitrogen fertilization in irrigated wheat crop was studied.However, Cazetta et al. (2008) and Espindula et al. (2010) found positive linear response to the number of G/S with increasing doses of N in wheat up to 120 kg ha -1 .
Wheat PH had an increase of 5.5 cm at the dose of 160 m³ ha -1 of PS compared to mineral fertilizer control (Table 2).This response, by increasing doses of N via PS, corroborates the work of Espindula et al. (2010) who found linear and positive response of wheat PH with increased supply of N. Greater plant height is possibly associated not only to the high input of readily available N (411.2kg ha -1 ), in relation to the demand of the crop (60 kg ha -1 ), but may also be more closely related to the anticipation of N supply.It depends on the PS having been all applied at sowing in relation to mineral NPK, corroborating the results of Teixeira Filho et al. (2008) in which all the nitrogen was applied in early sowing of wheat, as not all genotypes respond to different doses of N.
Corn PH was not lower in the PS treatments compared to mineral NPK.However, compared to the control without fertilizer, it was equal to the treatment with 40 m³ ha -1 of PS and superior to the others.The variable SD was superior when applying 160 m³ ha -1 of PS, supporting Mata et al. (2010) who found a gain in the use of cattle manure, Table 2: DM (Dry matter yield -kg ha -1 ), PH (plant height cm), G/S (grains per spike num.) and SD (stem diameter -mm) of the wheat/corn succession fertilized with mineral NPK and PS (pig slurry)

DM* PH G/S DM PH SD
No fertilizer (1)  4,023.7 (-2)  82.5 33.2 8,416.8 (-2) 212.9 (-2)  19.8 40 m 3 ha - No fertilizer control, (2) Mineral NPK control; *Means followed by: (+2) significant and higher than the mineral NPK control, (+1) significant and higher than no fertilizer control; (-2) significant and lower than mineral NPK by Dunnett test at 5% probability.et al. (2008) and Soratto et al. (2010) found positive response to this variable with increasing N supply, including a favorable correlation with grain yield, justifying that well-nourished corn plants use the stem as a reserve structure for the supply of grains.Although, such nutritional benefit was observed, attention is brought to the importance of a balanced supply of nutrients most required by the crop, and not only a single nutrient, as shown in Table 1, where the treatment showed excess of N and a low addition of P compared to the culture demand.

Treatments
With regard to the accumulation of N, P and K by the DM, it can be inferred in general concerning the cultures and the three elements, that the dose of 80 m³ ha -1 of PS favors accumulation of these nutrients in relation to the two controls (Table 3), with higher accumulation than the control without fertilization and not lower than the mineral fertilization control.
These results show the fertilizing potential of PS with satisfactory accumulation of nutrients in DM, as evidenced by Aita et al. (2006).It was also observed that the accumulation of such nutrients increased as quantities of PS were doubling.However, the supply of 160 m³ ha -1 did not provide greater accumulation than the mineral fertilizer control, showing a loss of efficiency in the absorption of these elements, which could encumber yield with the transportation of waste, and enhance environmental hazards.Cerreta et al. (2005) found a positive response for the accumulation of N, P and K with increasing doses of PS in black oat/corn/turnip succession.
Regarding the variables of production of wheat grain, fertilization with PS influenced only the TGW variable, for which the treatments of 80 and 160 m³ ha -1 provided a higher value than the mineral NPK control (Table 4).If the high input of N is considered in these two treatments with 205.6 and 411.2 kg ha -1 , respectively, shown in Table 1, the results oppose those of Espindula et al. (2010) and Teixeira Filho et al. (2010), who found a negative linear correlation between increased levels of N and TGW.This justifies that higher N availability increases the number of G/S, which may compete for photoassimilates and lack for grain filling.The author raised yet another hypothesis that the increased supply of N increases plant mass, causing selfshading and loss of photosynthetic efficiency of plants, a fact that was not observed in this experiment, as noted in DM yield shown in Table 2. PS probably favored N uptake by the plant until the period of grain filling, depending on the slow net mineralization as verified by Fioreze et al. (2012) for very clayey soil.
Wheat PH was not influenced by the treatments (Table 4), although the increased supply of N could reflect in a decrease in PH (Cazetta et al., 2008;Teixeira Filho et al., 2010), depending on the increase of G/S and decrease of TGW, as discussed in the preceding paragraph.However, the largest TGW may have been responsible for annulling the decline of PH.
Wheat productivity did not differ statistically (Table 4), which can be due to the fact that the area remained fallow in the previous year.Sartor et al. (2012) obtained linear increments in wheat yield with increasing doses of PS up to 60m 3 ha -1 in three crops, and with this dose, obtaining higher yield than mineral fertilization, with an average of 2,8; 10.55 kg ha -1 in the three crops, very similar to the treatment of 40 m 3 ha -1 of this study.
Corn did not differ in TGW and yield among treatments of PS and the controls (Table 4).Seidel et al. (2010) found no difference in the corn yield with PS in relation to mineral fertilization, suggesting that it is an effective alternative for the farmer.Costa et al. (2011) did not obtain satisfactory corn yield grown after fertilized wheat, respectively, with 25 and 38 m 3 ha -1 of PS, although in the first year, when grown after wheat, the corn development was favored due to residual fertilization of that given to wheat.However, Further studies should address the efficiency of PS doses, as reported by Ceretta et al. (2005), and Cassol et al. (2005).The latter authors found a maximum technical efficiency at the dose of 143 m 3 ha -1 , but warn that it is not feasible to achieve it, as 59 m 3 ha -1 would be needed to increase the remaining 10%.

CONCLUSIONS
Compared with the mineral NPK source, PS is an efficient alternative and can be used as a source of nutrients in wheat/corn succession.  (1No fertilizer control, (2) Mineral NPK control; *Means followed by: (+2) significant and higher than the mineral NPK control by Dunnett test at 5% probability.

Figure 1 :
Figure 1: Distribution of rainfall during the study period.Data collected from the meteorological station INMET (National Institute of Meteorology), located 1000 meters from the experiment.

Table 1 :
Characteristics of pig slurry in N (total N and N-NH 4 + ), P (P 2 O 5 ), K (K 2 O), DM (Dry matter), pH, density and respective amounts added to the system by each treatment in the fertilization of wheat and corn Rev. Ceres, Viçosa, v. 63, n.3, p. 412-418, mai/jun, 2016compared to mineral fertilization.The highest SD demonstrates an adequate nutrition of crop because Cruz

Table 3 :
Sartor et al. (2012) and K by DM ((Dry matter) of wheat and corn shoots, fertilized with mineral NPK and PS (pig slurry))Sartor et al. (2012)found a positive response with increasing doses up to 60 m³ ha -1 of PS, reaching a 55% increase in yield compared to the zero dose, with very close values to mineral fertilization.A yield increase of 2.86, 10.33 and 10.60% is observed, compared to control without fertilization for treatments of 40, 80 and 160 m 3 ha - 1 of PS, respectively.Attention is brought to the low increment provided when the dose of 80 is doubled to 160 m 3 ha -1 .