Effect of no‐tillage vs. conventional tillage on soil organic matter and nitrogen contents

Abstract

Four treatments (no‐tillage plus subsoiling, no‐tillage, conventional tillage plus subsoiling, and conventional tillage) were continuously in place for 6 yr and a second set of no‐tillage plus subsoiling and conventional plus subsoiling treatments were continuously in place for 3 yr to study the long‐term effects of conventional and no‐tillage corn on soil organic matter (OM) and N contents. Soil samples were taken at random between the rows and in the rows to a depth of 60 cm, in 5‐cm increments to a depth of 30 cm, and then in 15‐cm increments from the 30 to 60‐cm depth for OM and N determination. No‐tillage resulted in A3 and 20% more Kjeldahl N than conventional tillage in the 0 to 5‐cm soil depth after 6 and 3 yr, respectively. after 6 yr, the 0 to 5‐cm depth had 36% more OM in no‐tillage treatments than in conventional tillage treatments, and soil from no‐tillage treatments averaged 27% more OM than the conventional tillage plus subsoiling treatment at the 0 to 15‐cm soil depth.     

Effects of phosphorus application method and rate on furrow‐irrigated ridge‐tilled grain sorghum

Conservation tillage systems, including ridge‐tillage, have become increasing popular with producers in the central Great Plains because of their effectiveness in controlling soil erosion and conserving water. A major disadvantage of the ridge system is that nutrient placement options are limited by lack of any primary tillage options. The objective of this research was to investigate the effects of method of phosphorus (P) placement and rate on irrigated grain sorghum [Sorghum bicolor (L.) Moench] grown in a ridge‐tillage system on a soil low in available P. This experiment was conducted from 1993 to 1995 on a producer's field near the North Central Kansas Experiment Field at Scandia, Kansas on a Carr sandy loam soil (course, loamy, mixed, calcareous, mesic, Typic Udifuvents). Treatments consisted of fertilizer application methods, surface broadcast, single band starter (5 cm to the side and 5 cm below seed), dual band starter (one band on each side of the row), and knifed in the center of the row middle (38 cm from each adjacent row). Each of these treatments was made at either 22 or 44 kg P₂O₅ ha^‐1, and nitrogen (N) also was included at the rate of 13 kg ha^‐1. Additional treatments were, a combination of 13 kg N and 44 kg P₂O₅ ha^‐1 applied half broadcast and half as a single band starter, a 1:1 N:P₂O₅ ratio (44 kg N and 44 kg P₂O₅ ha^‐1) applied as a single band starter, and a 3:1 ratio (134 kg N and 44 kg P₂O₅ ha^‐1) applied as a single band starter. A no‐P check plot also was included. Broadcast and center‐of‐row middle knife applications were made approximately 1 week before planting. After planting, N was balanced on all plots to give a total of 180 kg ha^‐1. Applied P treatments improved grain yield and nutrient uptake and consistently shortened the time from emergence to mid‐bloom in all 3 years of the experiment. On this low soil test P soil, treatments that subsurface banded P increased grain yield by 1.27 Mg ha^‐1 compared to broadcast treatments. Placing N and P in a single starter band 5 cm to the side and 5 cm below the seed was as effective as placing a band on each side of the row. Knife applying N and P in the center of the row was not as effective as placement beside the row. Single band starter application of N and P in a 1:1 and or 3:1 N:P₂O₅ ratio consistently increased yields and nutrient uptake and shortened the time to mid‐bloom as compared to the single band starter treatment that provided only 13 kg N ha^‐1. Over the 3 years of the study, these 1:1 and 3:1 N:P₂O₅ ratio starters were clearly superior to an other treatments.     

Soil fertility in a long‐term fertilizer trial with different tillage systems

The presented results originate from a field experiment established in 1972 on an Eutric cambisol with two main factors: soil tillage (conventional‐, reduced‐, and no‐tillage) and NPK fertilization. The test plants were maize and winter wheat in two years rotation.

The long‐term soil fertility without and with optimum fertilization, the influence of fertilization, tillage and crop sequence on grain yields, the organic carbon content (C_org) and the nitrate infiltration are discussed.

In the course of years without any NPK fertilization grain yields of maize and winter wheat decreased significantly and reached a minimum level which was modified however by the actual climatic conditions. The analogous yield level of optimum NPK fertilization at maize showed a growing tendence while at wheat it remained mostly constant.

The method of soil tillage influenced grain yield of winter wheat to a lesser extent than the yield of maize. Grain yields of maize and winter wheat were consistently lower with no‐till as compared to reduced or conventional tillage, however the differences with w. wheat were much smaller. The effect of tillage was especially high at N₀ P₀ K₀. Crop rotation had a positive effect on the yields of maize. For winter wheat at N₀ P₀ K₀ oneself was the better forecrop, while at optimum N and PK maize performed a little better. C_orgcontent of soil slightly increased in the course of 25 years not only on the fertilized plots but on the nil plots too. Increasing N‐doses showed only a little effect on the C_org. There was a little positive effect of no‐till on C_org content of soil as well as compared fall ploughing. Soil tillage did not much influence the total amount of nitrate in the soil profile. The distribution of nitrate‐N in the soil profile was more affected by the actual climatical circumstances than by the system of tillage. However big nitrate accumulations were found in the subsoil according to different soil tillage systems at some other times, as well as lack of it, which suppose the possibility of a relative quick nitrate infiltration.     

Nitrogen balance in a soil‐wheat system under plow‐ and no‐tillage in the argentine humid pampa

Abstract

Changing conventional tillage to conservation tillage systems affects nitrogen (N) cycling in agroecosystems. Our objective was to evaluate the role of soil organic pools, specially plant residues, as sources‐sinks of nitrogen in an humid and warm temperate environment cropped to wheat, under plow‐ and no‐tillage. The experimental site was in the Argentine Pampa on a Typic Hapludoll. A balance‐sheet method was used: Nupt+Nres=Nsow+Nmin, where Nupt=N uptake by the crop at harvest; Nsow=soil mineral N as NH₄ and NO₃ at 0–90 cm depth, one month before sowing, plus N added as fertilizer; Nres=residual soil mineral N as NH₄ and NO₃ at 0–90 cm depth, at harvest; Nmin=N mineralized from humus and plant residues during wheat growing period. Nupt did not differ between tillage systems. Nitrogen supply by the mineral N pool, estimated by the difference Nsow‐Nres, was ca. 150 kg N ha^‐1 in both tillage systems. Plant residues decomposed and released N under both treatments. This organic N pool decreased 77% along the crop cycle. Nmin, calculated using the balance equation was 83 kg N ha^‐1, and did not differ between tillage managements, representing 35% of Nupt. This results highlight the importance of the organic pools as sources of N for wheat in the Humid Pampa. They also brink our attention on the importance for evaluate residue decomposition and humus mineralization in warm‐temperate regions when fertilizer requirements are determined, in order to minimize environmental hazard and economic losses by overfertilization.     

Changes in nitrogen and phosphorus concentrations of silicon‐fertilized rice grown on organic soil 1

Rice grown on the organic soils of the Everglades is routinely fertilized with silicon (Si). The objective of this research was to investigate changes in nitrogen (N) and phosphorus (P) concentration in various plant parts in response to Si fertilization. Two cultivars were grown in lysimeters filled with low‐Si soil. Half the lysimeters were fertilized with calcium silicate to provide 2Mg Si ha^‐1 and the other lysimeters remained unfertilized as a control. Nitrogen concentration decreased in all plant parts with Si fertilization. Phosphorus concentration increased with Si. Maturity was earlier in the Si fertilized rice.     

Nitrates in soil after long‐term management for dryland grain sorghum and winter wheat

Abstract

The leaching of phosphorus (P), nitrogen (N), and radionuclides (²³²Th, ²²⁶Ra, ²²⁸Ra, and ⁴⁰K) from Joel sands amended with red mud/gypsum (RMG) at 9 rates (0, 2, 4, 8, 16, 32, 64, 128, and 256 t/ha) was measured using columns. Intense leaching conditions (34 mm/day for 12 days) and a high rate of applied P (320 kg/ha as superphosphate) and N (680 kg/ha as ammonium nitrate) were used to simulate extremes of irrigated vegetable production on the Swan Coastal Plain. Addition of the highest rate of RMG (256 t/ha) reduced leaching of fertiliser P and ammonium‐nitrogen (NH₄‐N) by 85% and 50%, respectively, compared with 0 t/ha after 12 days. At 641 RMG/ha P leaching was reduced 50% compared with 0 t/ha. Nitrate‐nitrogen (NO₃‐N) leaching was not affected by addition of RMG.

Reduced leaching of NH₄‐N was attributed to an increase in cation exchange capacity of the soil with the addition of RMG. Bicarbonate‐extractable P in the soil increased with rate of RMG to >50 μg P/g soil at 256 t/ha. This indicates that soil testing of residual P could be used to reduce P inputs to vegetable crops after soils were amended with RMG. This would further reduce the impact of vegetable production on the water systems of the Swan Coastal Plain and extend the period of effectiveness of RMG amended soils. The increase in ²³²Th specific activity in Joel sand amended with RMG was well below statutory limits even at the highest rate. Neither ⁴⁰K nor ²²⁶Ra were detectable in RMG amended sands up to 2561 RMG/ha. There was no evidence of leaching of ²²⁶Ra or ²²⁸Ra at any rate of RMG. These results suggest that the use of RMG amendment on commercial horticultural properties on the Swan Coastal Plain could be feasible.     

Twelve‐year tillage and crop rotation effects on yields and soil chemical properties in northeast Iowa

Abstract

Long‐term tillage and crop management studies may be useful for determining crop production practices that are conducive to securing a sustainable agriculture. Objectives of this field study were to evaluate the combined effects of crop rotation and tillage practices on yield and changes in soil chemical properties after 12 years of research on the Clyde‐Kenyon‐Floyd soil association in northeastern Iowa. Continuous corn (Zea mays L.) and a corn‐soybean [Glycine max L. (Herr.)] rotation were grown using moldboard plowing, chisel plowing, ridge‐tillage, or no‐tillage methods. Tillage and crop rotation effects on soil pH, Bray P1, 1M NH₄OAc exchangeable K, Ca, and Mg, total C, and total N in the top 200 mm were evaluated. Profile NO₃‐N concentrations were also measured in spring and autumn of 1988. Crop yields and N use efficiencies were used to assess sustainability. Bray P1 levels increased, but exchangeable K decreased for all cropping and tillage methods. Nutrient stratification was evident for no‐tillage and ridge‐tillage methods, while the moldboard plowing treatment had the most uniform soil test levels within the 200 mm management zone. Chisel plowing incorporated fertilizer to a depth of 100 mm. Soil pH was lower with continuous corn than with crop rotation because of greater and more frequent N applications. Profile NO₃‐N concentrations were significantly different for sampling depth and among tillage methods in spring 1988. In autumn the concentrations were significantly different for sampling depth and for a rotation by tillage interaction. Estimated N use efficiencies were 40 and 50 kg grain per kg N for continuous corn, and 48 and 69 kg grain per kg N for rotated corn in 1988 and 1989, respectively. The results suggest that P fertilizer rates can be reduced, but K rates should probably be increased to maintain soil‐test levels for this soil association. Crop rotation and reduced tillage methods such as ridge‐tillage or chisel plowing appear to meet the criteria for sustainable agriculture on these soils.     

Influence of split‐applied nitrogen on grain yield and protein content in ten grain sorghum culti‐vars 1

More information on the response of newly developed or introduced grain sorghum cultivare to split‐applied nitrogen (N) in semi‐arid rainfed agriculture is needed. Therefore, the influence of four split‐applied N schedules (100/0, 66/34, 50/50, and 34/66) on six American (SC 283, SC 274, SC 669, B 66181, SC 33, and RTam 428), and four West African (CSm 63, 1S 6704c, 1S 7173c, and 1S 7419c) grain sorghum cultivars was evaluated. The split‐applied N significantly increased grain yield and percent protein in grain sorghum over a one‐time application of N. The increase in yield and protein content varied among varieties and schedules of N application. Varieties SC 574, RTam 428, and Csm 63 at split‐applied schedules of 66/34, 50/50, and 34/66, respectively, gave the highest yield over one‐time application of N. Similar differences in percent protein in grain among cultivars due to split‐applied N were observed.     

Yield of iron‐sprayed and non‐sprayed strawberry cultivars grown on high ph calcareous soil

Abstract

Iron (Fe) deficiency chlorosis (FeDC) results in extensive reduction in yield of strawberry (Fragaria x ananassa Duch.) grown on high pH calcareous soils. Three cultivars differing in response to FeDC were grown on a high pH (8.2) calcareous soil (25.4% calcium carbonate equivalent in surface 20 cm) in the field (Choueifat, coastal area of Lebanon) to determine the effects of FeDC on fruit yield of cultivars sprayed with FeEDDHA [ferric ethylene‐diiminobis (2‐hydroxyphenyl) acetate]. The unsprayed plots were used as a control. No significant interaction (P<0.05) between cultivars x FeEDDHA spray treatment, and no significant differences (P<0.05) between one and two FeEDDHA spray(s)/week treatment was noted for visual FeDC, fruit number, and fruit yield. Sprayed cultivars once a week produced higher yields than unsprayed ones; overall increases were 33% (13% for ‘Motto’, 30% for ‘Chandler’, and 56% for ‘Douglas'). Even though only slight FeDC was noted on the ‘Motto’ cultivar receiving no Fe EDDHA spray, fruit yields were increased when sprayed with FeEDDHA. However, significant increases in yield for ‘Chandler’ and ‘Douglas’ cultivars with severe FeDC ratings were rioted when sprayed with FeEDDHA.     

Effect of extractable zinc,phosphorus, and soil ph on zinc concentrations in leaves of field‐grown corn

Abstract

The variability in corn yield responses to applications of Zn fertilizer appears to be associated with several complex soil and climatic factors that affect the availability of endogenous soil Zn to the crop under specific conditions. Among the soil chemical properties that influence availability of endogenous Zn are soil pH, organic matter content, and extractable P. Over a period of several years, soil and plant analysis data were collected from 54 field experiments, field trials, and diagnostic visits to producer's fields. These data were subjected to multiple regression analysis, resulting in an equation: Zn_leaf = 37.14 + 1.513 Zn_st ‐4.04 pH_st ‐ 1.791 ln(P_st/100) where Zn_st, pH_st, and P_st were 0.1N HC1 extractable soil Zn (kg/ha), 1:1 soil‐water pH, and Bray's 1 extractable soil P (kg/ha), respectively. These factors accounted for 67% of variation in leaf Zn, which was a large portion of the variability in Zn_leaf considering that climatic conditions, management levels, and varietal differences were uncontrolled in most instances. Using the previously published critical level in the leaf opposite and below the ear as 17 μg Zn/g, these data can be used to set required soil test levels of Zn at different levels of extractable P and soil pH. Inadequate levels of extractable Zn would range from 2.5 (at pH 6.0, P = 70 kg/ha) to, 9.5 kg/ha (at pH 7.5, P = 420 kg/ha).     

Comparison of phosphate rock and triple superphosphate on a phosphorus‐deficient Kenyan soil

Abstract

Soil phosphorus (P) deficiency is a constraint to crop production in many regions of sub‐Saharan Africa, which could be overcome through use of either soluble P fertilizer or sufficiently reactive phosphate rock (PR). A field study was conducted with corn (Zea mays L.) for three growing seasons (18 months) on a P‐deficient, acid soil in Kenya to compare a soluble P source (triple superphosphate, TSP) and relatively reactive Minjingu PR from Tanzania. In the 18 months following application of 250 kg P ha^‐1, bicarbonate extractable inorganic soil P (P_i) was higher for application of TSP than PR, but Pi extracted with a mixed anion‐cation resin was comparable for TSP and PR. Inorganic P extracted by 0.1M NaOH, without prior extraction of resin and bicarbonate P_i, decreased during the 18 months following TSP application, but increased following PR application. After 18 months, about 7% of the added PR‐P remained as Ca‐bound P that was extracted with 1M HCl. The 1M HCl extractable P., however, underestimated residual PR‐P that gradually dissolved and supplied plant‐available P, as indicated by recovery of <40% of PR‐P added to soil in laboratory incubations even though PR solubility in HCl was >90%. Minjingu PR was an effective source of P for corn. Corn yields were comparable for TSP and PR, and the relative agronomic effectiveness of PR averaged 107% in Season 1 and 79% in Season 3. Anion resin and mixed anion‐cation resin appeared to be superior to bicarbonate and NaOH as a soil P test for use with both TSP‐ and PR‐treated soils.     

Carbon,nitrogen, and gaseous profiles in a humid,temperate region,maize field soil under no‐tillage

Abstract

The effect of four consecutive years of tillage method [conventional tillage (CT) or no‐tillage (NT)] and fertilizer N rate (84, 168, 336 kg N·ha^‐1·yr) on soil carbon, nitrogen and and gaseous profiles was examined in a Wharton‐Cookport (Aquic Hapludults‐Aquic Fragiudults) silt loam soil in West Virginia cropped to continuous maize (Zea mays L.). At midseason (July) of the last cropping year, soil mineral N profile differences were generally discernible only at the high N (336 kg·ha^‐1) rate in the topsoil (0‐ to 30‐cm layer). Ammonium (NH₄ ⁺‐N) levels at this time were significantly (p ≤ 0.05) higher under CT, while NO₃ ^‐‐N levels were the same under both tillage methods. However, after silage harvest in September NH₄ ⁺‐N levels were the same under both tillage systems, while NO₃ ^‐‐N levels were significantly higher under CT. Although no significant (p ≥ 0.05) tillage effects were found for TC, the level was increased by ～16% under NT in the surface soil (0 to 15‐cm) layer at the low N (84 kg·ha^‐1) rate treatment. Total N (TN) was significantly (p ≤ 0.05) increased under NT compared to CT only in the soil surface layer at the high N rate treatment. Soils under both tillage methods after cropping appeared to be equally well aerated to the deepest layer (60 cm) as O₂ levels were near atmospheric concentrations, and no gases commonly associated with more anaerobic environments (CH₄, C₂H₄) were detected. Carbon dioxide (CO₂) levels increased 30‐ to 40‐times atmospheric levels in the deepest layers, and were generally higher under NT. The incidence of detectable N₂O (‐0.36 × 10 ^‐2μg·ml^‐1) was two‐ to seven‐times more numerous at the high N rate, and twice as numerous under NT compared to CT. These results generally corroborate previous results for soil mineral N changes as related to tillage method, but not for organic C, N and microbial activity, as has usually been reported, especially for more arid region soils.     

Preliminary investigations on the effects of no‐till corn production methods on specific soil mesofauna populations

Abstract

Moldboard plowing, chisel plowing and no‐till methods were used to produce field corn (Zea mays) in an old grass sod. Grain yields were similar ranging between 13,100 and 14,186 kg/ha. The greatest spread in soil temperatures was only 2.1 C with the plowed soil always being warmest. Mean soil organic matter levels of the surface soil ranged between 1.9 percent on the moldboard plowed plots and 3.3 on the no‐till plots. Ten species of soil Collembola were identified. Collembola and Acarina populations were concentrated in the surface 5 cm of soil and were present in greatest numbers in the No‐Till soil.     

Sampling depth effects on sodium bicarbonate (NaHCO3)‐extractable phosphorus and potassium and fertilizer recommendations

Abstract

Soil test nutrient concentrations vary with depth, especially in perennial cropping systems where fertilizer is broadcast on the soil surface without incorporation. The objective of this study was to determine the effect of fertilizer rate and sampling depth on soil test phosphorus (P) and potassium (K), and P and K fertilizer recommendations for alfalfa (Medicago sativa L.). Five rates of P and K (0, 56, 112, 224, and 336 kg ha^‐1 P₂O₅ and K₂O) were broadcast on established alfalfa stands at three sites with different soil properties and tillage and fertilization histories. In separate plots at one site the same rates of P and K were also incorporated to a depth of 15 cm prior to seeding alfalfa. Soil samples were collected at depths of 0 to 10, 0 to 15, and 0 to 30 cm during the growing season. Fertilizer rates and soil sample depth affected soil test P and K at all sites. Relative to the 30‐cm sample depth, soil test values were higher in fertilized treatments with 10 and 15 cm sample depths due to the concentration of immobile P and K near the soil surface. Sample depths of 10 and 15 cm frequently resulted in lower P and K fertilizer recommendations than those of the 30‐cm depth. Sample depth is an important consideration in routine soil sampling for the purpose of making fertilizer recommendations. If research data used for developing soil test‐based fertilizer recommendation are obtained using a standard sampling depth, routine sampling must also be to the same depth.     

Interactions of gamma‐irradiated sewage,nitrogen and phosphorus for Sorghum on a calcareous soil

Abstract

The interaction of gamma‐irradiated sewage sludge, nitrogen and phosphorus fertilizers on dry matter production, phosphorus concentration and phosphorus uptake of sorghum was examined. Three crops of sorghum were grown in the greenhouse in 19 1 plastic buckets. The phosphorus and sludge treatments were applied at the initiation of the experiment only. Nitrogen was applied to the corresponding nitrogen treatment pots before each of the three croppings.

There was a significant nitrogen x sewage interaction for dry matter production, phosphorus concentration and phosphorus uptake in each harvest. There was a significant phosphorus sewage sludge interaction in the first harvest for phosphorus uptake. All other possible interactions were not statistically significant. The 67 metric ton/ha sludge rate produced nearly the same yield as the nitrogen treatment. In the first harvest, sludge significantly increased plant phosphorus uptake from the fertilizer phosphorus. The phosphorus uptake in sorghum from 472 and 944 kg P/ha from the sludge treatments was comparable to that from 1299 and 2598 kg P/ha from triple superphosphate.     

Salinity effects on growth analysis and nutrient composition in four grain legumes‐rhizobium symbiosis

The effect of salinity on growth response, nitrogen (N) fixation and tissue mineral content was investigated for four legumes: faba bean (Vicia faba L), pea (Pisum sativum L), soybean (Glycine max L), and common bean (Phaseolus vulgaris L). Plants were grown in a vermiculite culture system supplied with a N‐free nutrient solution with the addition of 0, 50, and 100 mM NaCl. Plants were harvested at the beginning of the flowering period and the dry weights of shoots and roots and acetylene reduction activity (ARA) were evaluated at the same time plant tissues were analysed for N, potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) contents.

The depressive effect of saline stress on ARA of nodules was directely related to the salt induced decline in dry weight and N content in shoots. Growth inhibition by NaCl treatments was greater for the pea than for other legumes, whereas the soybean was the most salt‐tolerant Saline stress also affected the N content in shoots and roots. In general the N content accumulated in the shoot and Na in the roots of the four legumes tested, while K accumulated both organs. The acquisition of other macronutrients differed according to the legume species. The legumes most sensitive were P. sativum and V. faba which accumulated Ca in shoot and Mg both in the shoot and the roots. On the contrary, in G. max and P. vulgaris, the two most salt tolerant legumes, accumulated Mg in the roots and Ca in both vegetative organs. Our results suggest a relationship between the salt‐tolerant range in legumes and the macronutrient accumulation in vegetative organs.     

Loss‐on‐ignition as an estimator of soil organic carbon in a‐horizon forestry soils

Abstract

The determination of soil organic matter by wet digestion techniques is a slow and laborious analysis. Loss‐on‐ignition (LOI) provides a simple alternative technique for the estimation of soil organic carbon in non‐calcareous A horizon soils of the Natal midlands and Zululand forestry regions. Using multiple regressional techniques, the relationships between loss‐on‐ignition, Walkley organic carbon and soil texture for 55 soils were determined over a range of ignition temperatures. The relationships hold best for soil samples with relatively low organic carbon contents (< 5%). The optimum temperature for ignition was found to occur at 450°C and resulted in the relationship: Soil organic carbon = 0.284*LOI percent. No advantage is gained through ignition at higher temperatures due to the loss of clay mineral structural water, even if the soil texture is accurately known.     

Availability of phosphorus in a Brazilian Oxisol cultivated with eucalyptus after nine years as influenced by phosphorus‐fertilizer source,rate, and placement

Abstract

This work evaluated the effect of different placement and rates of two phosphorus (P) fertilizers on P‐availability by three methods of extraction, nine years after application to a Brazilian Oxisol cultivated with Eucalyptus camaldulensis. The treatments were applied to 24x18 m plots and 96 seedlings of E. camaldulensis were planted (3.0x1.5 m) in each plot. Single superphosphate (SSP) and rock phosphate (RP) were tested in three rates (100, 200, and 400 kg ha^‐1 of P₂O₅). Each fertilizer was either (1) surface‐applied in bands (0.6 m either side of the rows of trees) and incorporated before planting or (2) incorporated into furrows (0.2 m deep in the tree rows) before planting. As additional treatments, the combination of RP (96 kg ha^‐1 of P₂O₅ applied in broadcast, or bands, or in furrows) + SSP (54 kg ha^‐1 of P₂O₅ localized in the planting hole before planting) were tested. Twelve soil subsamples from two layers (0–15 and 25–40 cm) were taken from each plot (from the planting rows or between the planting rows) and were analyzed for pH in water (1:2.5), available P by Mehlich‐1, Bray‐1 and anionic resin, exchangeable Ca, and Al by 1 mol L^‐1 Kcl. For both methods of fertilizers placement, the highest values of available P were observed in the surface soil and in the planting row, and were strongly related to fertilizer rate. Samples taken between the planting rows did not exhibit treatment effects on available P. The higher values of available P obtained with Mehlich‐1 and the lower eucalyptus plant uptake efficiency of fertilizer‐P from banded RP confirms the fact that this extractant can overestimate the availability of P in soils receiving RP. The use of anion exchange resin in this situation to estimate available P is supported. The results obtained with the localized application of RP indicate root system activity (P and Ca uptake and acidification of rhizosphere) as a factor in increasing fertilizer dissolution rates.     

Application rate and composting method affect the immediate and residual manure fertilizer value in a maize–rice–rice–maize cropping sequence on a degraded soil in northern Vietnam

A field experiment was carried out in northern Vietnam to investigate the effects of adding different additives [rice (Oriza sativa L.) straw only, or rice straw with added lime, superphosphate (SSP), urea or a mixture of selected microorganism species] on nitrogen (N) losses and nutrient concentrations in manure composts. The composts and fresh manure were applied to a three-crop per year sequence (maize–rice–rice) on a degraded soil (Plinthic Acrisol/Plinthaquult) to investigate the effects of manure type on crop yield, N uptake and fertilizer value. Total N losses during composting with SSP were 20% of initial total N, while with other additives they were 30–35%. With SSP as a compost additive, 65–85% of the initial ammonium-N (NH₄-N) in the manure remained in the compost compared with 25% for microorganisms and 30% for lime. Nitrogen uptake efficiency (NUE) of fresh manure was lower than that of composted manure when applied to maize (Zea mays L.), but higher when applied to rice (Oriza sativa L.). The NUE of compost with SSP was generally higher than that of compost with straw only and lime. The mineral fertilizer equivalent (MFE) of manure types for maize decreased in the order: manure composted with SSP?>?manure composted with straw only and fresh manure?>?manure composted with lime. For rice, the corresponding order was: fresh manure?>?manure composted with SSP/microorganisms/urea?>?manure composted with lime/with straw alone. The MFE was higher when 5 tons manure ha^?1 were applied than when 10 tons manure ha^?1 were applied throughout the crop sequence. The residual effect of composted manures (determined in a fourth crop, with no manure applied) was generally 50% higher than that of fresh manure after one year of manure and compost application. Thus, addition of SSP during composting improved the field fertilizer value of composted pig manure the most.     

Effect of different zinc application methods on grain yield and zinc concentration in wheat cultivars grown on zinc‐deficient calcareous soils

The effect of six different zinc (Zn) application methods on grain yield and concentrations of Zn in whole shoots and grain was studied in wheat cultivars (Triticum aestivum, L. cvs. Gerek‐79, Dagdas‐94 and Bezostaja‐1 and Triticum durum, Desf. cv. Kunduru‐1149) grown on severely Zn‐deficient calcareous soils (DTPA‐extractable Zn: 0.12 mg‐kg^‐1 soil) of Central Anatolia which is the major wheat growing area of Turkey. Zinc application methods tested were: a) control (no Zn application), b) soil, c) seed, d) leaf, e) soil+leaf, and f) seed+leaf applications. Irrespective of the method, application of Zn significantly increased grain yield in all cultivars. Compared to the control, increases in grain yield were about 260% with soil, soil+leaf, and seed+leaf, 204% with seed and 124% with leaf application of Zn. In a similar manner, biomass production (dry weight of above‐ground parts) was increased by Zn treatments. The highest increase (109%) was obtained with the soil application and the lowest increase (40%) with the leaf application. Significant effects of Zn application methods were also found on the yield components, i.e., spike number.m^‐2, grain number‐spike^‐1, and thousand kernel weight. Spike number.m^‐2 was affected most by Zn applications, particularly by soil and soil+leaf applications. Concentrations of Zn in whole shoots and grain were greatly affected by different Zn treatments. In plants without added Zn, concentrations of Zn were about 10 mg‐kg^‐1 both in shoots and grain and increased to 18 mg‐kg^‐1 dry weight (DW) by soil application of Zn, but not affected by seed application of Zn. Soil+leaf application of Zn had the highest increase in concentration of Zn in shoot (82 mg‐kg^‐1 DW) and grain (38 mg‐kg^‐1 DW). Soil application of Zn was economical and had long‐term effects for enhancing grain yield of wheat grown on Zn deficient soils. When high grain yield and high Zn concentration in grains are desired, soil+leaf application of Zn was most effective method of Zn application.