Published in Agron J 91:650-656 (1999)
© 1999 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Agronomy Journal 91:650-656 (1999)
© 1999 American Society of Agronomy
SOIL MANAGEMENT
Soil Nitrogen Amendment Effects on Nitrogen Uptake and Grain Yield of Maize
B.L. Maa,
Lianne M. Dwyera and
Edward G. Gregoricha
a Eastern Cereal and Oilseed Res. Ctr. (ECORC), Agric. & Agri-Food Canada, Research Branch, Central Exp. Farm, Ottawa, ON, Canada K1A 0C6
mab{at}em.agr.ca
Received for publication October 1, 1998.
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ABSTRACT
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Efficient use of soil N amendments in maize (Zea mays L.) production is necessary to maximize producer's economic returns and to maintain soil and water quality. A 5-year field experiment was conducted on a Brandon loam soil (fine loamy, mixed, mesic Typic Endoaquoll) (Orthic Humic Gleysol) with the objective of measuring N uptake and grain yield of two maize hybrids under different N amendments [no amendment, NH4NO3 at 100 and 200 kg N ha-1, and stockpiled and rotted dairy manure at 50 and 100 Mg ha-1 (wet wt.)] to determine differences in N use efficiency (NUE) and its components, N uptake efficiency and N utilization efficiency. The N amendments increased the grain yield (by an average of 20%) and NUE (by an average of 17.5%) of a modern hybrid (Pioneer `3902') more than that of an old hybrid (`Pride 5'). The difference method that was used to estimate N recovery indicated that, over the course of the study, Pioneer 3902 took up 48% of inorganic fertilizer N and 20% of the manure N, compared with 42 and 16%, respectively, for Pride 5. Manure application resulted in total N uptake comparable to the 200 kg N ha-1 treatment. Grain yields of manure treatments in 1993 and 1994 were generally lower (5–15%) than the 200 kg N ha-1 treatment. During the latter periods (1995 and 1996) of the study with repeated application under continuous maize, all manure treatments produced grain yields equal to or slightly greater (6–13%) than the fertilizer treatment. Dairy manure application increased N uptake and grain yield of maize. The NUE, based on added mineral N levels, for all manure treatments was greater than for the 200 kg N ha-1 treatment.
Abbreviations: NUE, nitrogen use efficiency
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INTRODUCTION
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NITROGEN USE EFFICIENCY (NUE) has been defined in terms of units of economic yield per unit of soil N (Moll et al., 1982). It is expressed in several ways in the literature. In general, NUE is defined as the total plant N divided by the amount of N applied (e.g., Liang and MacKenzie, 1994). To differentiate plant N uptake from N utilization, Moll et al. (1982) developed a method to partition NUE (per-plant gram of yield produced per gram of available soil N) into N uptake efficiency (gram of plant N per gram of available soil N), which is analogous to the aforementioned NUE of Liang and MacKenzie (1994), and N utilization efficiency (gram of yield per gram of plant total N). In many agronomic studies, variations in total plant N parallel variations in yield and thus N uptake efficiency dominates NUE (Dwyer et al., 1993; Ma and Dwyer, 1998). Maize yield response to soil available N is a function of both N uptake from the soil and utilization of N within the plant to produce grain (Dwyer et al., 1993; Moll et al., 1982). As the economic and environmental costs of excessive N fertilization rise, there is a greater interest in identifying suitable combinations of hybrids and N amendments that result in efficient N use. Application of dairy manure has the potential not only to affect crop yields but also to influence the amount and rate at which soil N is made available to the plant, and thereby, NUE.
In agricultural soils, available N (mainly NH+4 and NO-3) accounts for <2% of total soil N (Keeney and Nelson, 1982). Addition of dairy manure not only increases the soil inorganic N pool, but perhaps more importantly, increases the seasonal soil N mineralization available to the plant (Chang et al., 1993; Murwira and Kirchmann, 1993; Westerman and Kurtz, 1973). Crop yield is usually increased by manure application, because of increased plant nutrient availability and improved soil structure (Chang et al., 1993). However, there is also evidence that application of dairy manure before planting is not as effective as inorganic N fertilizer in increasing crop yields (Brinton, 1985; Murwira and Kirchmann, 1993; Paul and Beauchamp, 1993).
In Ontario, Canada, spreading manure in the fall and early winter is not recommended, because of the potential for runoff to surface water (OMAFRA, 1997). Nonetheless, in short-season to intermediate growing-season areas of the northeastern USA and eastern Canada, manure is often applied prior to fall ploughing, especially on heavy soils, so as not to delay planting in spring, despite potential N losses over winter via leaching (OMAFRA, 1997). However, there is a period of time after application of manure during which N immobilization occurs (Murwira and Kirchmann, 1993). If fall-applied manure includes straw bedding, with a wide C:N ratio, N immobilization may tie up mineral N during late fall and spring so that, by early summer, N is released from manure via mineralization and nitrification processes. In contrast, spring application of such manure could result in yields lower than those with fertilizer N treatments, because of N immobilization (Brinton, 1985; Murwira and Kirchmann, 1993; Paul and Beauchamp, 1993).
A multiyear field experiment was conducted to evaluate maize grain yield and N uptake and utilization under different soil N amendments, including inorganic fertilizer, stockpiled and rotted manure, and an unfertilized control, and to identify differences in responses of two hybrids to these soil N amendments.
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Materials and methods
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An experiment was conducted on a Brandon loam soil (fine loamy, mixed, mesic Typic Endoaquoll) (Orthic Humic Gleysol, in the Canadian classification) for five years, 1992 to 1996, at the Central Experimental Farm at Ottawa, ON, Canada (45°22' N, 75°43' W). The soil contained an average of 34% clay, 27% silt, and 39% sand, with a pH of 6.5 (1:1 in water). The preceding crop was red clover (Trifolium pratense L.). The experiment was a randomized complete block design arranged in a split plot with three replications. Seven N treatments (no amendment, NH4NO3 at 100 and 200 kg N ha-1, and stockpiled and rotted dairy manure at 50 and 100 Mg ha-1 wet wt.) were assigned to the whole plot. Two maize hybrids, an older lower yielding hybrid (Pride 5) with demonstrated intolerance to stress conditions (Tollenaar, 1991), and a modern hybrid of the same maturity (Pioneer 3902), were the subplot.
Plots were fertilized preplanting with P and K according to soil test recommendations. The manure consisted of dairy cow feces and urine and a large amount of straw, because the dairy herd and barn were in a public area and used for demonstration purposes. Manure was collected and either stockpiled on a concrete slab or placed on slotted concrete slabs for aeration to compost the manure.
The appearance of the stockpiled manure was relatively unchanged from the time of collection until the time of application (>6 months), but the appearance of the rotted manure suggested that it had undergone some decomposition but was not fully composted. Over the study period, the rotted manure consistently had a lower moisture content and higher NO-3–N concentrations than stockpiled manure, which indicates that nitrification had occurred in the rotted manure. The C:N ratio of the rotted manure was, on average, smaller than that of the stockpiled manure (Table 1)
. The total mineral N in the manures varied from year to year, averaging 42 ± 12 (mean ± standard deviation) for the low rate and 83 ± 24 kg ha-1 for the high rate of stockpiled manure. For rotted manure, the mean values were 59 ± 13 for the low rate and 119 ± 25 kg ha-1 for the high rate. Stockpiled manure had a higher moisture content than rotted manure. Thus, larger amounts of inorganic and organic N were applied with rotted manure than with stockpiled manure treatments each year (Table 1).
During the first year of the experiment stockpiled manure was the only manure applied. Manures were spread in the spring, before planting from 1992 to 1994, then prior to fall ploughing from 1994 and 1995. The rate of manure was accurately measured each year either by calibrating the manure spreader (collecting manure samples on plastic sheets of a known area or by weighing the manure spreader prior to applying the manure). The manure was incorporated with a moldboard plow to a depth of approximately 20 cm within 24 h after application. Fertilizer N as NH4NO3 was broadcast and raked into the soil shortly after planting each year. The hybrids were planted at a density of 57600 plants ha-1 in the third or fourth week of May each year. The subplot was 8 m long and consisted of 12 rows with 0.762-m spacing. A variety of herbicides was applied for weed control: in 1992, metolachlor [2-chloro-N (2-ethyl-6-methylphenyl)-N-(2-methyoxy-1-methylethyl)acetamide]; in 1993, metolachlor, cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile}, and atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine]; in 1994 and 1995, dimethenamid {2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)acetamide}, cyanazine, and atrazine; and in 1996, glyphosate [N-(phosphonomethyl)glycine], flumetsulan {N-(2,6-difluorophenyl)-5-methyl[1,2,4]triazolo[1,5-
]pyrimidine-2-sulfonamide}, metolachlor, and metolachlor plus atrazine (Primextra Lite, United Agri Products). Additional hand weeding was used to control escaped weeds in all years.
Soil samples were taken at four depth increments (0–15, 15–30, 30–60, and 60–90 cm) using a hydraulic coring system in late April to early May (spring sample) and early November (fall sample) each year. All soil samples were immediately air-dried, then ground and extracted with 2 M KCl. Mineral N (NH+4 and NO-3) concentrations were analyzed colorimetrically (Keeney and Nelson, 1982) on a TRAACS 800 Auto-Analyzer (Bran-Luebbe, Analyzing Technologies, Elmsford, NY).
Crop dry matter was measured at five times in 1993 and 1994: 6-leaf (V6) (Ritchie and Hanway, 1993); tasselling, or approximately 1 wk before anthesis (VT); 2 wk after anthesis; 5 wk after anthesis; and at final harvest. It was measured at two times (VT and final harvest) in 1995 and 1996. At each sampling, 10 plants from each plot were randomly selected and separated into leaves, stalks, other reproductive components, and kernels, which were dried at 80°C for 3 to 4 d to obtain constant weight. After dry weight was recorded for all components, subsamples were taken and ground to pass a 1-mm screen. Total N concentration of each sample was determined by automated dry combustion–gas chromatography using a Carlo Erba T1500 Elemental Analyzer (Carlo Erba, Milan, Italy). At final harvest, grain yield was determined from a 6-m2 area and reported on a 155 g kg-1 moisture basis each year.
Nitrogen use efficiency (NUE) and its components, N uptake efficiency and N utilization efficiency, were calculated according to Moll et al. (1982) on a kg ha-1 basis. For spring-applied N amendments, available soil N was calculated as spring soil mineral N plus mineral N applied. In the case of manure treatments, applied mineral N was the mineral N as measured at the time of application. For fall-applied manure (1994 and 1995), available soil N for 1995 and 1996 growing season was calculated as previous fall soil inorganic N plus mineral N of the manure as measured at the time of application. This procedure aimed to express efficiencies of use of different N amendments as comparably as possible, and with minimum assumptions. Thus, although manure included a larger reservoir of organic mineralizable N (Table 1), because the timing and extent of mineralization varied with weather conditions (Ma et al., 1999), efficiencies were all expressed relative to measured preplant soil mineral N levels.
The common NUE or more specifically N recovery, was also calculated for comparison purposes using the difference method—i.e., the difference in plant total N (kg ha-1) at final harvest between fertilized (manure or inorganic fertilizer) and unfertilized treatments over the total N added (kg ha-1) of the manure or inorganic fertilizer.
Yield, plant N uptake and NUE data were subjected to analysis of variance (SAS Inst., 1990) each year. The whole data set was tested to see if a pooled analysis was possible across years—i.e., to see if both Error a (for testing N amendment differences) and Error b (for testing hybrid differences) variances were homogeneous (P 
0.05) using Bartlett's test (Steel and Torrie, 1980). Treatment means were separated according to the F-protected least squares difference test (P 0.05).
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Results and discussion
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Grain Yield
Both hybrid and soil N amendment main effects were significant for grain yield each year except 1992, whereas there was no N x hybrid interaction for any parameter measured (data not shown). The combined analysis of variance across the five years could not be performed due to the heterogeneity of the error terms for testing soil N amendments (P > 0.05).
Compared with the unfertilized control treatment, both fertilizer and manure application increased grain yield each year except 1992, the initial study year, when treatments had no significant effect on grain yield (Table 2)
. We attribute the lack of response to N amendments in 1992 to the high level of soil mineral N (120 kg N ha-1 pre-planting in the 0- to 90-cm depth increment) associated with the preceding legume crop and also to the cool and wet conditions in 1992, especially in July and August (Table 3) , which may have favored soil N mineralization (Ma et al., 1999) and slowed plant growth and N uptake for all treatments. The nonhomogeneous variation in grain yields across years reflected climatic fluctuations (Table 3) and prevented a combined analysis. Nonetheless, the trend across years is apparent: with repeated application of manure, yield benefit from manure application increased substantially compared with fertilizer N treatments.
For example, grain yields of manure treatments in 1993 and 1994 were generally lower (5–15%) than the 200 kg N ha-1 treatment. During the latter periods of the study (1995 and 1996), following repeated application under continuous maize, grain yields for both stockpiled and rotted manures were close to the 200 kg N ha-1 treatment, at the low rate, or slightly greater (6–13%) at the high rate. This trend could be attributed to the switch from spring-applied to fall-applied manure and/or to nutrient build-up due to repeated applications. McLaughlin and coworkers (1998) demonstrated that improvement in soil structure and water infiltration following repeated application of dairy manure enhanced soil tilth and improved the rooting environment. Manure N immobilization in the late fall and early spring may have played an important role, which is now under investigation. The benefit from fertilizer N decreased over time and the productivity of the unfertilized control treatment declined substantially to about 60% of that in the 200 kg N ha-1 treatment. The high level of initial soil N due to the preceding legume crop may explain the greater yield for unfertilized control treatment and the reduced response to soil N amendments in earlier years of the study. The decline in yields across years was due at least in part to the monoculture cropping, which may have led to an imbalance in soil plant nutrients, build-up of pest levels, or both.
Comparison of grain yields between 1992 and 1996 (Fig. 1)
indicates that all manure treatments increased grain yields over time by 15 to 50%. Comparison of the two hybrids indicates that Pioneer 3902 had a larger increase in yield than Pride 5 when soil N was high, and less reduction in yield when soil N was limiting. On average, Pioneer 3902 yielded more than the older Pride hybrid by 15 to 30% in each year of this study (Table 2). Within a N level, hybrid differences in grain yield were as great as 60%, with the larger differences in yield occurring at lower N levels (data not shown). These findings are consistent with other findings that breeding for yield improvement increased maize stress tolerance over time (Duvick, 1992; Dwyer et al., 1993; Ma and Dwyer, 1998).
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Fig. 1 Changes in grain yield between 1992 and 1996 as affected by soil N amendments. SMH and RMH, stockpiled manure and rotted manure, high rate (100 Mg ha-1 wet wt.); SML and RML, stockpiled manure and rotted manure, low rate (50 Mg ha-1 wet wt.). Within hybrids, bars marked with the same letter are not significantly different at P 0.05
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There was often no difference in yield between 100 and 200 kg N ha-1. Plant total N at harvest was significantly greater for the 200 kg N ha-1 than for the 100 kg N ha-1 treatment in only one of the five years (Table 4)
, suggesting that a larger portion of the N taken up by the crop was derived from the native soil organic N when suboptimum N was applied, as has been demonstrated elsewhere (e.g., Westfall et al., 1996). Soils receiving the low rate of manure contained approximately half the mineral N (42–59 kg N ha-1; Table 1) of the 100 kg N ha-1 treatment at spring preplant time, and grain yields on these soils were similar to that for the 200 kg N ha-1 treatment after several years of manure application (Table 2). Because mineral N in the low rate of manure was only 42 to 59 kg N ha-1 (Table 1), plant total N must have also been supplied from mineralization of organic N in the manure and in the soil.
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Table 4 Plant total N (excluding roots) at final harvest for each N amendment averaged across two cultivars and three replications
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Plant Nitrogen Uptake
The magnitude of plant N uptake was significantly different between the two hybrids and among the soil N amendments (Fig. 2) . In all cases, however, plant N uptake during the growing season followed a sigmoid shape. It took 6 to 7 wk, or >30% of the growing season, to reach the V6 stage, yet the amount of N uptake at V6 was only 10 to 20% of the final total plant N. Nitrogen uptake increased dramatically from V6 until 2 wk after silking, another 6-wk period, with approximately 50 to 60% of the final plant N taken up by 2 wk after silking. Thereafter, N uptake was slow and eventually ceased (Fig. 2). In general, by anthesis the plant took up 50 to 75% of its total N; by harvest, some N taken up pre-anthesis and stored in the vegetative components must have been remobilized and incorporated into the kernels as a large portion of vegetative N was lost between anthesis and harvest. Depending on the year, soil N amendment, and hybrid, the remobilized N accounted for as little as 20% to as much as 100% of kernel N (Fig. 3)
. Pioneer 3902 generally had a smaller proportion of kernel N remobilized from the rest of the plant, implying a larger proportion of N uptake from the soil during grain filling. By harvest time, the grain accumulated a total of 60 to 160 kg N ha-1 for Pioneer 3902, depending on soil N treatment, compared with 40 to 110 kg N ha-1 for Pride 5.
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Fig. 2 Plant N uptake during the growing season as a fraction of plant total N at harvest in 1993 and 1994. SMH and RMH, stockpiled manure and rotted manure, high rate (100 Mg ha-1 wet wt.); SML and RML, stockpiled manure and rotted manure, low rate (50 Mg ha-1 wet wt.). LSD (0.05) values are for comparison among N amendments within sampling dates
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Fig. 3 Kernel N content and N losses from vegetative parts between anthesis (W1B) and harvest (HVT) in 1995 and 1996 of two maize hybrids as affected by soil N amendments. SMH and RMH, stockpiled manure and rotted manure, high rate (100 Mg ha-1 wet wt.); SML and RML, stockpiled manure and rotted manure, low rate (50 Mg ha-1 wet wt.). Bars with different letters are significantly different (P 0.05) based on F-protected LSD (0.05) test
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Nitrogen Use Efficiency
Based on Moll's calculation (Moll et al., 1982), Pioneer 3902 on average had a NUE 17.5% greater than Pride 5. The trend in NUE with soil N amendment was the same for the two hybrids: NUE declined substantially as soil available N increased (Fig. 4) . Although large amounts of total C and total N were added to the soil from the manure, soil mineral N levels in manure treatments were in most cases lower than in the inorganic fertilizer N treatments (Table 5)
. Thus, based on soil mineral N levels at preplanting, NUE for manure treatments almost always appeared to be greater than for the 200 kg N ha-1 treatment. Most of the time (12 out of 16 hybrid–soil N amendment comparisons), the stockpiled manure treatment had greater NUE than the rotted manure treatment.
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Fig. 4 Moll's NUE, N uptake efficiency (NUptE) and N utilization efficiency (NUtiE) of Pioneer 3902 as affected by soil N amendments from 1993 to 1996. SMH and RMH, stockpiled manure and rotted manure, high rate (100 Mg ha-1 wet wt.); SML and RML, stockpiled manure and rotted manure, low rate (50 Mg ha-1 wet wt.). LSD (0.05) values given with the symbols for years are for comparison among N amendments within years
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Unlike grain yield, NUE was greatest in 1995 and lowest in 1993. The weather conditions were similar in the two years (Table 3), with a total precipitation of 385 mm (May to September) in 1993 and 451 mm in 1995. Monthly average temperatures were also similar in both growing seasons. Spring soil mineral N in the rotted manure treatments was similar at the low rate and substantially greater at the high rate in 1993 compared with the fall residual soil mineral N in 1995 (Table 5). In 1993, when manure was applied in the spring, there was likely a period of time when the availability of mineral N was not synchronized with plant demand. In this year, most of the N in the manure was not immediately available to the crop but was probably immobilized. In this situation, additional fertilizer N would be required for initial crop demand. In contrast, manure applied before fall ploughing in 1994 resulted in a large amount of mineralized N (total mineral N at the 0- to 20-cm depth was 20 to 30 kg ha-1) at V6 in 1995, and this was available during the crop's exponential growth phase (Ma et al., 1999). The slightly lower NUE values in 1996 than in 1994 are consistent with the fact that 1994 was the year with the highest yield (Table 2). In general, both stockpiled and rotted manure at the low rate, with approximately 50 kg ha-1 of mineral N (half the 100 kg N ha-1 in the inorganic fertilizer treatment), resulted in NUE values substantially higher than the 200 kg N ha-1 treatment (Fig. 4).
In terms of the common terminology for NUE (or N recovery) using the conventional difference method, both soil N amendment and hybrid significantly affected NUE, while there was no interaction in any of the years studied (data not shown). As noted above, large portions of organic N in the manure resulted in substantially less N recovery than did fertilizer treatments (Fig. 5)
. The substantially lower N recovery values for all treatments in 1993 were due to the large N uptake by plants in the unfertilized treatment. Thus, the conventional method of determining NUE from the difference method did not reflect soil mineralization–immobilization turnover (Liang and MacKenzie, 1994) and led to overestimation of fertilizer use efficiency and underestimation of manure use efficiency. Nonetheless, Pioneer 3902 resulted in an average of 48% N recovery for the inorganic fertilizer and 20% N recovery for the manure, compared with 42 and 16% for Pride 5. These values are closely similar to previous findings with manure (Paul and Beauchamp, 1993). A similar trend in NUE was found in an adjacent experiment in which an 15N-labeling approach was used (Ma and Dwyer, 1998).
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Fig. 5 Nitrogen use efficiency based on the difference in plant N uptake between unfertilized and fertilized treatments divided by the total N applied. SMH and RMH, stockpiled manure and rotted manure, high rate (100 Mg ha-1 wet wt.); SML and RML, stockpiled manure and rotted manure, low rate (50 Mg ha-1 wet wt.). Bars with different letters are significantly different (P 0.05) based on F-protected LSD (0.05) test
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Differences in N uptake efficiency paralleled differences in the overall NUE. At harvest, on average, 1.16 kg N was taken up by Pioneer 3902 for every 1.0 kg available soil N (residual plus N amendment) at planting, compared with 0.95 kg N uptake by Pride 5. Nitrogen uptake efficiency was greatest in 1995 and least in 1993 (Fig. 4). Nitrogen utilization efficiency varied greatly across growing seasons without any apparent pattern, suggesting that this is an insensitive variable for differentiation of treatment effects.
The greater plant N uptake in manure treatments than in the 200 kg N ha-1 treatment was due not only to the direct contribution of mineral N from the manure (Table 5), but also to the N released from the manure organic N and native soil organic and inorganic N (Ma et al., 1999). Because of the slow release of N from manure and the increased uptake of N during the exponential phase of plant growth, manure treatments, especially at low rates, resulted in greater NUE. The reduced soil mineral N after harvest for manure treatments at low rates was also associated with less N loss to the environment through leaching over winter, although N losses over winter from fall-applied manure at the high rates approached only half the N losses during the growing season from the 200 kg N ha-1 treatment (Ma et al., 1999).
In summary, NUE was greatest when manure was applied at the low rate. The difference in timing of availability of mineral N from fertilizer and manure treatments demonstrated in this study and also by others (Murwira and Kirchmann, 1993; Paul and Beauchamp, 1993) suggests that a combination of the two amendments is the most economical and environmentally sustainable fertilization strategy. Hybrid differences in N uptake reflect hybrid differences in the ability to take up N during grain filling. Selection of hybrids that maintain uptake capacity as late as possible in the season should be coupled with a fertilization strategy that maintains high levels of soil mineral N during the grain-filling period.McLaughlin Dwyer Ma Gregorich Topp 1998; SAS Institute 1990
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ACKNOWLEDGMENTS
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We wish to thank Drs. D.W. Stewart and Y.K. Chan for careful and constructive review of this manuscript. The excellent technical assistance of D. Balchin, L. Evenson, D. Meredith, T. Pare, C. Lafontaine, and the field staff of the Agronomy Division of ECORC of Agriculture and Agri-Food Canada is gratefully acknowledged.
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NOTES
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ECORC contribution No. 991376.
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REFERENCES
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J. S. Paschold, B. J. Wienhold, D. L. McCallister, and R. B. Ferguson
Crop Nitrogen and Phosphorus Utilization following Application of Slurry from Swine Fed Traditional or Low Phytate Corn Diets
Agron. J.,
June 16, 2008;
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997 - 1004.
[Abstract]
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[PDF]
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G. R. Munoz, K. A. Kelling, K. E. Rylant, and J. Zhu
Field Evaluation of Nitrogen Availability from Fresh and Composted Manure
J. Environ. Qual.,
May 1, 2008;
37(3):
944 - 955.
[Abstract]
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M. Zhang, R. Gavlak, A. Mitchell, and S. Sparrow
Solid and Liquid Cattle Manure Application in a Subarctic Soil: Bromegrass and Oat Production and Soil Properties
Agron. J.,
October 3, 2006;
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1551 - 1558.
[Abstract]
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C. K. Reddy, E. Z. Nyakatawa, and D. W. Reeves
Tillage and Poultry Litter Application Effects on Cotton Growth and Yield
Agron. J.,
November 1, 2004;
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[Abstract]
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A. Herrmann and F. Taube
The Range of the Critical Nitrogen Dilution Curve for Maize (Zea mays L.) Can Be Extended Until Silage Maturity
Agron. J.,
July 1, 2004;
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[Abstract]
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T. D. Loecke, M. Liebman, C. A. Cambardella, and T. L. Richard
Corn Response to Composting and Time of Application of Solid Swine Manure
Agron. J.,
January 1, 2004;
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[Abstract]
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T. D. Loecke, M. Liebman, C. A. Cambardella, and T. L. Richard
Corn Growth Responses to Composted and Fresh Solid Swine Manures
Crop Sci.,
January 1, 2004;
44(1):
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[Abstract]
[Full Text]
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B.L. Ma, L. M. Dwyer, and E. G. Gregorich
Soil Nitrogen Amendment Effects on Seasonal Nitrogen Mineralization and Nitrogen Cycling in Maize Production
Agron. J.,
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[Abstract]
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TOP
ABSTRACT
INTRODUCTION
