Use of manures and organic wastes to improve soil quality and nutrient balances
COMPARISON OF FIELD METHODS TO ASSESS NET N MINERALIZATION IN SOILS UNDER DIFFERENT RATES OF CATTLE-SLURRY APPLICATION AND A MAIZE / ANNUAL RYEGRASS CROPPING SYSTEM Pereira J.1,2*, Coutinho J.3, Moreira N.2, Trindade H.2 Escola Superior Agrária de Viseu, IPV, Quinta da Alagoa, 3500-606 Viseu, Portugal; 2 CITAB, Universidade de Trás-os-Montes e Alto Douro, Ap. 1013, 5001-801 Vila Real, Portugal; 3 Chemistry Centre, Universidade de Trás-os-Montes e Alto Douro, Ap. 1013, 5001-801 Vila Real, Portugal. *Tel:+351 23 2446600, e-mail:
[email protected] 1
1
INTRODUCTION
Knowledge of the amount of N mineralized from manure applied to soil and its availability to crops is extremely important for precise fertilization practices and environment protection. The objectives of our study were to evaluate the effect of cattle-slurry application rate on net N mineralization (NNM) and compare the field methods of soil core incubation with acetylene (SIA) and the sequential in situ incubation of undisturbed soil cores (SIU) to assess N mineralization in an intensive double-cropping forage system producing maize and Italian ryegrass (winter crop) for silage.
2
MATERIALS AND METHODS
The experiment was conducted on a sandy loam soil, between May-1997 and May-2000, on a typical commercial dairy farm located in the main Portuguese dairy region (NW Portugal). A control (T1) and four treatments (T2, T3, T4 and T5) were arranged in a randomized complete block design (RCBD) with three replications as described in Table1. The dimension of each plot was 160 m2 (20m x 8m). Treatments consisted of the application of different rates of cattle-slurry and/or mineral fertiliser at sowing or top-dressed to growing crops (Table 1). The treatments were arranged to compare slurry additions alone or in combination with mineral-N fertiliser, which is the common local practice, and mineral-N fertiliser only. Treatment T4 represents the fertiliser management of many intensive dairy farmers in the NW Portugal. In the summer (May-October) silage maize (Zea mays L.) was grown and in October a winter crop (Lolium multiflorum Lam.) was established. Cattle-slurry was incorporated immediately after each application by disk ploughing, in order to reduce ammonia volatilization. From each application, representative slurry samples were collected and analysed by standard laboratory methods. The main characteristics of the slurry used were the following: total N = 1.8 g N kg-1; NH4+-N = 0.9 g N kg-1; NO3--N < 1.0 mg N kg-1; pH = 8.3 and dry matter = 7.1%. Each experimental plot was maintained under the assigned treatment management for the two previous years and measurements were carried out only in the 3rd year. Net N mineralization in the 0-30 cm soil layer was measured in each treatment (for sub-plots of 15 m2) employing two methods and incubation periods of two weeks for each measurement date. From May-1999 to May2000 NNM was measured using the SIA method (Hatch et al., 1990). For each incubation period and in each plot, five soil cores of 3 cm diameter and 30 cm depth were collected and placed in sealed jars. To facilitate the collection and management of the soil cores for incubation, PVC tubes were used with appropriate dimensions and perforated sidelong to accelerate the diffusion of the acetylene into the soil. Each lid of the jars had two septum seal stoppers through which acetylene was injected to achieve a concentration of 2% (vol/vol) in the headspace of the jar. This acetylene concentration was effective inhibiting the nitrification process. The cores in the jars were incubated for ca. 14 days in holes made in the study area. At the same time and near the place where the cores were picked, soil samples for analysis were collected to the same depth using a probe. For comparison with the SIA method, NNM rates were measured at the same depth, using the SIU technique as described by Stenger et al. (1996). The measurements with this method were made only in treatments T1, T2 and T3 in two periods, namely between June and October-1999 and between Mars and May-2000 (total of 12 incubations). The SIU method consists of the incubation of covered soil cores, combined with measurements of
Use of manures and organic wastes to improve soil quality and nutrient balances
mineral N content (NH4+ and NO3-) in the surrounding unconfined soil at the start and the end of each incubation period. At the start of each incubation period, five PVC tubes not perforated (3 cm diameter) were inserted into the soil to 30 cm depth and then removed at the end of incubation (14 days). The incubated soil cores were covered by a roof (10 x 10 cm) to prevent nitrate leaching. The start and the end of each incubation period were coincident in both methods. Soil samples were homogenised and the humidity, mineral N content and bulk density determined by standard laboratory methods. The mean daily NNM rates were determined through the difference of mineral N at the start and end of each incubation period. Results (for each method) were analysed assuming a two factor RCBD, where the treatments were the main-plots and the incubation periods the split-plot, as described by Little and Hills (1978). The two methods were compared by linear regression. Nitrogen applications in treatments during this study (kg N ha-1).
TABLE 1
Treatment
Time of application
T1 (control) T2
At sowing
T3
At sowing
T4
At sowing
T5
Maize silage (sowing at 2-Jun 99)
Winter crop (sowing at 27-Oct 99)
Cattle-slurry
Mineral fertiliser
Cattle-slurry
Mineral fertiliser
0
0
0
0
0
0
0
0
0
0
50 (total N) 25 (NH4+-N) on 1-Jun 99 140 (total N) 70 (NH4+-N) on 14-Jul 99 50 (total N) 25 (NH4+-N) on 1-Jun 99 140 (total N) 70 (NH4+-N) on 14-Jul 99
150 (total N) 76 (NH4+-N) on 19-Oct. 99
0
0
50 (total N) 25 (NH4+-N) on 12-Fev. 00
0
0
0
50 (total N) 25 (NH4+-N) on 12-Fev. 00
187 (total N) 98 (NH4+-N) on 1-Jun 99 340 (total N) 175 (NH4+-N) on 1-Jun 99 258 (total N) 127 (NH4+-N) on 1-Jun 99
Topdressed
0
At sowing
0
Topdressed
0
3
RESULTS AND DISCUSSION
3.1
N mineralization
Figs 1a and 1b show the pattern of daily NNM rates and N mineral contents in the treatments up to 30 cm depth. As can be seen in treatments T2 and T3 the application of cattle-slurry at the sowing of maize led to an immediately increase of NNM rate reaching maximum values ,of respectively, 1.8 and 2.6 mg N kg-1 d-1. Indeed, high applications of cattle-slurry make available at short term large amounts of mineral N by net mineralization. The highest NNM rates were obtained in treatment T4, which reached a maximum rate of 6.7 mg N kg-1 d-1. Topdressing of mineral N fertiliser to the maize crop led immediately to N immobilization in treatments T4 and T5; the immobilization effect was more pronounced in T4 than in T5. Daily mean NNM rates during maize growth in the treatments T1, T2, T3, T4 and T5 were, respectively, 0.5, 0.8, 1.2, 1.9 and 0.5 mg N kg-1 d-1. However, during the winter crop growth NNM rates were relatively low and constant, showing daily mean values of 0.2, 0.3, 0.3, 0.1 and 0.2 mg N kg-1 d-1, respectively, in T1, T2, T3, T4 and T5. In these treatments, the amounts of N released annually in the soil layer up to 30 cm depth reached, respectively, 313, 477, 637, 602 and 258 kg N ha-1. Apparent NNM from amended treatments (subtracting N released in treatments T1), accounted to 88, 95 and 45% of the total N applied respectively in treatments T2, T3 and T4, while the application of mineral fertiliser in treatment T5 led to N immobilization (-23%). Sims (1995) found annual NNM rates between 40 and 80% when cattle-slurry was applied to soil.
Use of manures and organic wastes to improve soil quality and nutrient balances
T1
T2
T3
T4
a
T5
8
Net N mineralization rate (mg kg-1 d-1)
7 6 5 4 3 2 1 0 -1 -2
13-Mai
29-Abr
15-Abr
01-Abr
18-Mar
04-Mar
19-Fev
05-Fev
22-Jan
08-Jan
25-Dez
11-Dez
27-Nov
13-Nov
30-Out
16-Out
02-Out
18-Set
04-Set
21-Ago
24-Jul
07-Ago
10-Jul
26-Jun
12-Jun
29-Mai
15-Mai
01-Mai
-3
Date
T1
T2
T3
T4
b
T5
100 90
Soil mineral N (mg kg-1)
80 70 60 50 40 30 20 10
13-Mai
29-Abr
15-Abr
1-Abr
18-Mar
4-Mar
5-Fev
19-Fev
22-Jan
8-Jan
25-Dez
11-Dez
27-Nov
13-Nov
30-Out
16-Out
2-Out
18-Set
4-Set
21-Ago
7-Ago
24-Jul
10-Jul
26-Jun
12-Jun
29-Mai
15-Mai
1-Mai
0
Date
FIGURE 1
3.2
(a) Net N mineralization rates measured using soil core incubation with acetylene method (0-30 cm) and (b) soil mineral N content at the start of incubation period (0-30 cm). Vertical bars represent standard errors of the mean (N = 3).
Comparison of the two field methods for NNM estimation
Measurements of NNM rates in treatments T1, T2 and T3 with the two field methods shown that they supply similar estimates of the N mineralization because the measured values did not differ significantly (P > 0.05) (Fig. 2). However, for treatments where cattle slurry was applied (T2 and T3), the regression equations fitted showed that the sequential in situ incubation method of undisturbed soil cores tended to give slightly higher estimates for low values of NNM rates and lower estimates for high values of NNM rates than the soil core incubation method with acetylene.
Use of manures and organic wastes to improve soil quality and nutrient balances
3 y = 0.66x + 0.48 R2 = 0.48, P < 0.05
-1
-1
Sequential in situ incubation (mg N kg d )
3
2
y = 0.65x + 0.49 R2 = 0.37, P < 0.05 T1 T2 T3
2
1 y = 0.88x + 0.15 R2 = 0.79, P < 0.05 1
0 0
1
1
2
2
3 -1
3
-1
Soil core incubation with acetylene (mg N kg d )
FIGURE 2
4
Linear regressions between daily mean net N mineralization rates measured for the two in situ methods.
CONCLUSIONS
Apparent NNM from amended treatments (subtracting N released in control), accounted to 88, 95 and 45% of the total N applied respectively in treatments T2, T3 and T4, while the application of mineral fertiliser in T5 conducted to N immobilization (-23%). To assess N mineralization from slurry applications the field methods of SIA and SIU did not differ significantly for estimating NNM rates. Important amounts of N were released by mineralization due cattle-slurry application to soil. Data obtained in this study may be used for N fertiliser recommendations in order to improve the N efficiency of the double-cropping forage system of NW Portugal.
ACKNOWLEDGEMENTS The authors acknowledge the financial support supplied by IFADAP - Project PAMAF No 3005, Portugal.
REFERENCES Hatch D J, Jarvis S C, Philipps L 1990. Field measurement of nitrogen mineralization using soil core incubation and acetylene inhibition of nitrification. Plant and Soil 124, 97-107. Little T M, Hills F J 1978. Agricultural experimentation. Design and analysis. John Wiley and Sons, New York, USA. pp. 167-227. Sims J T 1995. Organic wastes as alternative nitrogen sources. In: Nitrogen fertilization in the environment. P.E. Bacon (ed.) Marcel Dekker Inc., New York. pp. 487-535. Stenger R, Priesack E, Beese F 1996. In situ studies of soil mineral N fluxes: some comments on the applicability of the sequential coring method in arable soils. Plant and Soil 183, 199-211.
