Fertilizer inputs, nutrient balance, and soil nutrient-supplying power in intensive, irrigated rice systems. II: Effective soil K-supplying capacity

Based on the analysis of soil K status in 11 long-term fertility experiments in Asia, two approaches for assessing the K-supplying power of lowland paddy soils were evaluated to predict total K uptake by irrigated rice. A regression model combining commonly used static soil test parameters that appeared to integrate measures of K release from nonexchangeable forms as well as chemical factors affecting K activity in soil solution explained 72% of the crop K uptake in NP and NPK treatments. However, this approach would require determination of six soil properties and it does not provide a direct measure of K release dynamics. The second approach used mixed-bed ion exchange resin capsules to measure K release during 2-wk anaerobic incubation. The resin method provided an integrative measure of soil K status and the factors controlling K transformation and diffusion rates, which are embodied in two kinetic parameters describing the dynamics of rapid- and slow-phase K release. The resin method was sensitive to past fertilizer history and the resulting buildup or depletion of soil K reserves and it was a better predictor of total K uptake in the NP and NPK plots (r²=0.82) than static soil tests. The results also indicated that high (Ca+Mg)/K ratios may contribute to K deficiency in rice soils.     

Nutrient budgeting for phosphorus and potassium in a long-term fertilizer trial

Influence of N, P and K application through inorganic and organic fertilizers on P and K removal in crop plants, changes in soil fertility status and their balance in the soil-plant (maize-wheat-cowpea fodder) studied for the first 22 years of a long-term experiment at Punjab Agricultural University farm, Ludhiana, India. The results showed that P uptake by wheat was about 1.5 times that of maize, whereas K uptake by wheat was only 1.1 times that of maize. The apparent P recovery by both maize and wheat depended on the rates of N, P and K application. Fertilizer rates greater than the recommended (150% NPK) resulted in lower P recoveries. At optimum level of N, P and K application (100% NPK) the mean P recovery (for 22 years) was 30.3% (±5.47) in wheat as compared to 20% (±11.35) in maize. The apparent P recovery in maize declined as the number of cropping years progressed. In 100% NPK plots, it declined from 45.6% in 1973 to 12.5% in 1992. The decline in P recovery was due to the accumulation of plant available P in the soil which increased from the initially low status to high-very high due to continuous application of P fertilizer. The application of FYM in conjunction with 100% NPK led to significantly greater accumulation of available P as compared to 100% NPK treatment alone despite the higher amount of total P removal in the former treatment than that from the latter. A trifle build-up in available K was observed in K amended plots notwithstanding the negative balance of K based on the approach of input-output relationship. The release of K from non-exchangeable form contributed towards K uptake by the crops. The results suggested the need for modifying the existing K fertilizer recommendations to compensate for gradual loss of native soil K fertility.     

Crop yield, nitrogen uptake and nitrate-nitrogen accumulation in soil as affected by 23 annual applications of fertilizer and manure in the rainfed region of Northwestern China

Application of chemical fertilizers and farmyard manure affects crop productivity and improves nutrient cycling within soil–plant systems, but the magnitude varies with soil-climatic conditions. A long-term (1982–2004) field experiment was conducted to investigate the effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizers and farmyard swine manure (M) on seed and straw yield, protein concentration, and N uptake in the seed and straw of 19-year winter wheat (Triticum aestivum L.) and four-year oilseed (three-year canola, Brassica napus L. in 1987, 2000 and 2003; one-year flax, Linum usitatisimum L. in 1991), accumulation of nitrate-N (NO₃-N) in the soil profile (0–210 cm), and N balance sheet on a Huangmian soil (calcaric cambisols, FAO) near Tianshui, Gansu, China. The two main plot treatments were without and with farmyard swine manure (M); sub-plot treatments were control (Ck), N, NP, and NPK.␣The average seed yield decreased in the order MNPK ≥ MNP > MN ≥ NPK ≥ NP > M > N > Ck. The average effect of manure and fertilizers on seed yield was in the order M > N > P > K. The seed yield increase was 20.5% for M, 17.8% for N, 14.2% for P, and 2.9 % for K treatment. Seed yield response to fertilizers was much greater for N and P than for K, and it was much greater for no manure than for manure treatment. The response of straw yield to fertilization treatments was usually similar to that of seed yield. The N fertilizer and manure significantly increased protein concentration and N uptake plant. From the standpoint of increasing crop yield and seed quality, MNPK was the best fertilization strategy. Annual applications of N fertilizer and manure for 23 successive years had a marked effect on NO₃-N accumulation in the 0–210 cm soil profile. Accumulation of NO₃-N in the deeper soil layers with application of N fertilizer and manure is regarded as a potential danger, because of pollution of the soil environment and of groundwater. Application of N fertilizer in combination with P and/or K fertilizers reduced residual soil NO₃-N significantly compared with N fertilizer alone in both no manure and manure plots. The findings suggest that integrated and balanced application of N, P, and K fertilizers and␣manure at proper rates is important for protecting soil and groundwater from potential NO₃-N pollution and for maintaining high crop productivity in the rainfed region of Northwestern China.     

Crop yields and soil organic carbon fractions as influenced by straw incorporation in a rice–wheat cropping system in southeastern China

In agro-ecosystems, the relationship between soil fertility and crop yield is mediated by manure application. In this study, an 8-year field experiment was performed with four fertilizer treatments (NPK, NPKM₁, NPKM₂, and NPKM₃), where NPK refers to chemical fertilizer and M₁, M₂, and M₃ refer to manure application rates of 15, 30, and 45 Mg ha^?1 year^?1, respectively. The results showed that the NPKM (NPKM₁, NPKM₂, and NPKM₃) treatments produced greater and more stable yields (4.95–5.45 Mg ha^?1 and 0.59–0.75) than the NPK treatment (4.01 Mg ha^?1 and 0.50). Crop yields under the NPKM treatments showed two trends, with a rate of decrease of 0.48–0.83 Mg ha^?1 year^?1 during the first 4 years and a rate of increase of 0.10–0.25 Mg ha^?1 year^?1 during the last 4 years. The soil organic carbon (SOC) significantly increased under all treatments. The estimated annual SOC decomposition rate was 0.35 Mg ha^?1 year^?1 and the equilibrium SOC level was 6.22 Mg ha^?1. Soil total nitrogen (N), available N, total phosphorus (P) and available P under the NPKM treatments increased by 0.15–0.26, 15–33, 0.17–0.66 and 45–159 g kg^?1, respectively, compared with the NPK treatment. Manure application mainly influenced crop yield by affecting the soil TN, available N, and available P, which accounted for up to 64% of the crop yield variation. Taken together, applying manure can determine or at least improve the effects of soil fertility on crop yield in acidic soils in South China.     

Detectability of15N-depleted fertilizer N in soil and plant tissue during a corn-rye crop rotation

Use of¹⁵N-depleted fertilizer materials have been primarily limited to fertilizer recovery studies of short duration. The objective of this study was to determine if¹⁵N-depleted fertilizer N could be satisfactorily used as a tracer of residual fertilizer N in plant tissue and various soil N fractions through a corn (Zea mays L.) -winter rye (Secale cereale L.) crop rotation. Nitrogen as¹⁵N-depleted (NH₄)₂SO₄ was applied at five rates (0, 84, 168, 252, and 336 kg N ha^–1) to corn. Immediately following corn harvest a winter rye cover crop treatment was initiated. Residual fertilizer N was easily detected in the soil NO ₃ ^- -N fraction following corn harvest (140-d after application). Low levels of exchangeable NH ₄ ⁺ -N (<2.5 mg kg^–1) did not permit accurate isotope-ratio analysis. Fertilizer-derived N recovered in the soil total N fraction following corn harvest was detectable in the 0 to 30-cm depth at each N rate and in the 30 to 60 and 60 to 90-cm depths at the 336 kg ha^–1 N rate. Atom %¹⁵N concentrations in the nonexchangeable NH ₄ ⁺ -N fraction did not differ from the control at each N rate. Nitrogen recovery by the winter rye cover crop reduced residual soil NO ₃ ^- -N levels below the 10 kg ha^–1 level needed for accurate isotope-ratio analysis. Atom %¹⁵N concentrations in the soil total N fraction (approximately one yr after application) were indistinguishable from the control plots below the 168, 252, and 336 kg ha^–1 N rate at the 0 to 30, 30 to 60, and 60 to 90-cm depths, respectively. Recovery of residual fertilizer N by the winter rye cover crop was verified by measuring significant decreases in atom %¹⁵N concentrations in rye tissue with increasing N rates. The greatest limitation to the use of¹⁵N-depleted fertilizer N as a tracer of residual fertilizer N in a corn-rye crop rotation appears to be its detectibility from native soil N in the total N pool.Research partially supported by grants from the National Fertilizer and Environmental Research Center/TVA and the Virginia Division of Soil and Water Conservation.     

Evaluation of current fertilizer practice and soil fertility in vegetable production in the Beijing region

A survey on current fertilizer practices and their effects on soil fertility and soil salinity was conducted from 1996 to 2000 in Beijing Province, a major vegetable production area in the North China Plain. Inputs of the major nutrients (NPK) and fertilizer application methods and sources for different vegetable species and field conditions were evaluated. Excessive N and P fertilizer application, often up to about 5 times the crop requirement in the case of N, was very common, especially for high-value crops. Potassium supply may have been inadequate for some crops such as leafy vegetables. Urea, diammonium orthophosphate ((NH₄)₂HPO₄) and chicken manure were the major nutrient sources for vegetable production in the region. Over 50% of N, 60% of P and nearly 90% of K applied originated from organic manure. Total N application rate for open-field Chinese cabbage from organic manure and inorganic fertilizers ranged from 300 to 900 kg N ha^–1 on 78% of the farms surveyed. More than 35% of the surveyed greenhouse-grown tomato crops received > 1000 kg N ha^–1 from organic and inorganic sources. A negative K balance (applied K minus K removed by the crop) was found in two-thirds of the surveyed fields of open-field Chinese cabbage and half of the surveyed fields of greenhouse-grown tomato. Plant-available N, P and K increased with increasing length of the period the greenhouse soils had been used for vegetable production. Similarly, soil salinity increased more in greenhouse soils than in open-field soils. The results indicate that balanced NPK fertilizer use and maintenance of soil quality are important for the development of sustainable vegetable production systems in this region.     

6. Ammonium dynamics of puddled soils in relation to growth and yield of lowland rice

The release of non-exchangeable (fixed) NH ₄ ⁺ and the importance of exchangeable NH ₄ ⁺ at transplanting (initial exchangeable NH ₄ ⁺ ) for rice (Oryza sativa L.) growth was studied in representative lowland rice soils of the Philippines.The experiments showed that initial exchangeable ammonium behaved like fertilizer N and thus may serve as a valuable guideline for nitrogen fertilizer application rates when calculated on a hectare basis. By using the¹⁵N tracer technique it was found that nonexchangeable ammonium in soil may contribute to the nitrogen supplying capacity of lowland rice soils. Fixation and release of NH ₄ ⁺ seem to be more dependent on the form of clay minerals than on clay content. In soils rich in vermiculite non-exchangeable ammonium should be considered together with other available N sources such as exchangeable ammonium for N fertilizer recommendations for lowland rice.     

Efficiency of HCl- and H2SO4-acidulated rock phosphates for a rice based cropping system

Pot experiments were conducted with an acid laterite soil and a shallow black calcareous soil to study the effect of initial application of North Carolina and Udaipur rock phosphates, acidulated with HCl or H₂SO₄ to the extent of 25, 50, 75 or 100% of the requirement for complete conversion into superphosphate, on the grain yield and P uptake by crops in rice—wheat and wheat—rice cropping sequences. The products obtained on acidulation with HCl or H₂SO₄ at a given degree behaved similarly. Rock phosphates partially acidulated with HCl or H₂SO₄ to 50–75% could be used successfully for growing rice or wheat on both the soil types. In the rice—wheat sequence, the wheat crop following rice gave very low grain yields compared to the wheat crop in the wheat—rice rotation, while in the wheat—rice rotation the rice crop following wheat gave yields comparable to that of rice in the rice—wheat rotation. The reasons for this differential effect have been made plausible. The studies indicate that a 50–75% H₂SO₄ - or HCl-acidulated rock phosphate may be used as a single application to an upland crop in an upland crop—rice rotation especially on acid soils, where the water soluble fractions of the product are used by the wheat crop. During the process of growth of the upland crop under aerobic soil conditions, the citrate soluble and insoluble fractions undergo such transformations that make it possible for the following rice crop to utilize them under waterlogged conditions.     

Relationship between electroultrafiltration (EUF) extractable nitrogen,grain yield,and optimum nitrogen fertilizer rates for winter wheat

The objective of the investigation was to examine whether there exist relationships between the optimum nitrogen fertilizer rate for winter wheat and soil nitrogen fractions extracted by electroultrafiltration (EUF) from autumn samples of the upper soil layer (0–30 cm). Optimum nitrogen fertilizer rates were derived from grain yield curves of field trials carried out with increasing nitrogen fertilizer rates on 19 different sites in 1985/86 and 1986/87. Most soils were luvisols derived from loess, two soils were brown earths and one a pararendzina. Total Nitrogen fertilizer rates were 0, 40, 80, and 120 kg N/ha applied twice before ear emergence. The final nitrogen rate at ear emergence was the same for all treatments, namely 60 kg N/ha.Optimum nitrogen fertilizer rates were derived from the grain yield curve fitted to a modified Mitscherlich equation. The optimum nitrogen fertilizer rates were correlated with the nitrogen fractions extracted by EUF. The regression equation thus obtained showed that NO ₃ ^- , the organic N fraction (EUF Norg), and the EUF Norg-quotient each had a highly significant impact on the optimum nitrogen fertilizer rate. The higher the amounts of EUF-N extracted the lower the optimum nitrogen rate. Substituting the EUF Norg-fraction for total nitrogen concentration in the upper soil layer gave a poorer relationship between the optimum nitrogen fertilizer rate and the soil data. In absolute terms the EUF Norg-fraction had by far the greatest impact on calculating the optimum nitrogen fertilizer rate. The investigation shows that the EUF method is a suitable technique for the determination of available soil nitrogen from which optimum nitrogen fertilizer rates can be derived for winter wheat cultivated under soil and climatic conditions typical for cereal growing areas in central Europe.     

Site-specific nutrient management in rice in Eastern India using a modeling approach

Rice is the staple food of about 50% of the world’s population. Rice yields in many parts of south Asia, however, are declining due to conventional blanket and imbalanced use of fertilizers. Fertilizer application based on quantitative approaches such as simulation modeling can assist in improving yields and nutrient use efficiency in rice. Field experiments were conducted in 20 sites in Eastern India to assess the soil supply, requirement and internal efficiency of N, P, K and Zn in rice. The data were used to calibrate the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model for site-specific, balanced fertilizer recommendations. The parameters of maximum accumulation (a) and dilution (d) of N (31, 87), P (192, 678), K (33, 81) and Zn (32488, 153125) in plants were developed, which can be used as the standard parameters in the QUEFTS model for rice. The relationships between chemical properties and nutrient supplying capacity of soil were also established. Grain yield of rice showed good correlation with N (R ² = 0.95**), P (R ² = 0.71**), K (R ² = 0.98**) and Zn uptake (R ² = 0.57*). The NPK ratio to produce 1 Mg grain yield of rice was derived to be 6.5:1.0:6.8. Running the calibrated model with observed field data from different locations in India with different amounts of N, P, K and Zn produced a good fit between measured and calculated yields. The results suggested that the validated QUEFTS model could be used for calculating fertilizer requirements and improved site-specific and balanced fertilizer management in rice.     

Greenhouse gas intensity and net annual global warming potential of cotton cropping systems in an extremely arid region

A long-term fertilizer experiment investigating cotton-based cropping systems established in 1990 in central Asia was used to quantify the emissions of CO₂, CH₄ and N₂O from April 2012 to April 2013 to better understand greenhouse gas (GHG) emissions and net global warming potential (GWP) in extremely arid croplands. The study involved five treatments: no fertilizer application as a control (CK), balanced fertilizer NPK (NPK), fertilizer NPK plus straw (NPKS), fertilizer NPK plus organic manure (NPKM), and high rates of fertilizer NPK and organic manure (NPKM+). The net ecosystem carbon balance was estimated by the changes in topsoil (0–20 cm) organic carbon (SOC) density over the 22-year period 1990–2012. Manure and fertilizer combination treatments (NPKM and NPKM+) significantly increased CO₂ and slightly increased N₂O emissions during and outside the cotton growing seasons. Neither NPK nor NPKS treatment increased SOC in spite of relatively low CO₂, CH₄ and N₂O fluxes. Treatments involving manure application showed the lowest net annual GWP and GHG intensity (GHGI). However, overuse of manure and fertilizers (NPKM+) did not significantly increase cotton yield (5.3 t ha^?1) but the net annual GWP (?4,535 kg CO₂_eqv. ha^?1) and GHGI (?0.86 kg CO₂_eqv. kg^?1 grain yield of cotton) were significantly lower than in NPKM. NPKS and NPK slightly increased the net annual GWP compared with the control plots. Our study shows that a suitable rate of fertilizer NPK plus manure may be the optimum choice to increase soil carbon sequestration, maintain crop yields, and restrict net annual GWP and GHGI to relatively low levels in extremely arid regions.     

Crop response of aerobic rice and winter wheat to nitrogen,phosphorus and potassium in a double cropping system

In the aerobic rice system, adapted rice cultivars are grown in non-flooded moist soil. Aerobic rice may be suitable for double cropping with winter wheat in the Huai River Basin, northern China plain. Field experiments in 2005 and 2006 were conducted to study the response of aerobic rice and winter wheat to sequential rates of nitrogen (N), phosphorus (P) and potassium (K) in aerobic rice—winter wheat (AR-WW) and winter wheat—aerobic rice (WW-AR) cropping sequences. Fertilizer treatments consisted of a complete NPK dose, a PK dose (N omission), a NK dose (P omission), a NP dose (K omission), and a control with no fertilizer input. Grain yields of crops with a complete NPK dose ranged from 3.7 to 3.8 t ha⁻¹ and from 6.6 to 7.1 for aerobic rice’ and ‘winter wheat’, respectively. N omissions caused yield reductions ranging from 0.5 to 0.8 t ha⁻¹ and from 1.6 to 4.3 t ha⁻¹ for rice and wheat, respectively. A single omission of P or K did not reduce rice and wheat yields, but a cumulative omission of P or K in a double cropping system significantly reduced wheat yields by 1.2–1.6 t ha⁻¹. N, P and K uptake of both crops were significantly influenced by fertilizer applications and indigenous soil nutrient supply. Nutrient omissions in a preceding crop reduced plant N and K contents and uptake additionally to direct effects of the fertilizer treatments in wheat, but not in rice. Apparent nutrient recoveries (ANR) differed strongly between ‘aerobic rice’ and ‘winter wheat’; in rice: for N it ranged from 0.30 to 0.32, for P from 0.01 to 0.06, and for K from 0.03 to 0.19 and in wheat: for N from 0.49 to 0.71, for P from 0.09 to 0.15, and for K from 0.26 to 0.31. Further improvements of crop productivity as well as nutrient-use efficiencies, should be brought about by developing cropping systems, by an appropriate choice of adapted cultivars, by a site- and time-specific fertilizer management and by eliminating other yield-limiting factors. It is concluded that nutrient recommendations should not be based on the yield response of single crops only, but also on the after-effects on nutrient availability for succeeding crops. A whole cropping system approach is needed.     

Pathways of dissolved unreactive phosphorus loss under long-term crop straw and manure application

Dissolved unreactive phosphorus (DUP) loss can increase the risk of water organic and inorganic compound pollution. Because DUP loss under different fertilizers has not been evaluated, selecting a fertilizer that decreases losses but maintains yields remains challenging. Therefore, we compared DUP losses via overland flow, leaching, and sediment in lysimeter plots (8 m?×?4 m?×?0.6 m) with mineral and organic fertilizers for two years. The six treatments, with three replicates, included no fertilizer (CK), mineral fertilizer (NPK), pig manure only (OM), pig manure combined with NPK (OMNPK), crop straw only (RSD), and crop straw combined with NPK (RSDNPK). The results showed that leaching accounted for 54–89% and was the major route for DUP loss. Compared with NPK (0.074 kg ha^?1 year^?1), in the OM and OMNPK, the annual DUP losses via leaching were substantially increased by 11.1% and 8.6%, respectively, whereas they were decreased by 13.2% and 6.2% in the RSD and RSDNPK treatments, respectively. There was a significant positive linear relationship between the soil P surplus and the annual total DUP loss loading (r?=?0.80, p?=?0.05). Compared with the NPK (43.44 kg ha^?1 year^?1), the values of the soil P surplus under the RSD and RSDNPK treatments were greatly reduced by 122.6% and 14.5%, thereby decreasing the annual total DUP loss by 34.5% and 26.4%, respectively. In conclusion, pig manure application can increase DUP leaching risk, whereas the combination of mineral fertilizers and crop straw residues can decrease the DUP loss without compromising the crop yield.

     

Dryland wheat yield dependence on rainfall,applied N and mulching in preceding maize

To evaluate the response of dryland wheat (Triticum aestivum L.) to mulching in preceding maize and fertilizer N application field experiments were conducted for six years (1980–86) with maize-wheat sequence on a sandy loam soil in northern India. Four rates of N application viz. 0, 40, 60 and 80 kg N ha^–1 in wheat were combined with three mulch treatments viz. no mulch (M₀), paddy straw mulch (M_p) and basooti (Premma mucronate) mulch (M_b) applied at the rate of 4 tons ha^–1 on dry weight basis applied three weeks before harvest of maize. Mulching (M_p and M_b) increased (profile) stored moisture at wheat seedling by 31 to 88 mm. M_b also increased NO₃-N content by 33 to 42 kg ha^–1 in 0–120 cm profile over M₀ and M_p. Over the years, M_p increased wheat yield by 11 to 515 kg ha^–1 and M_b by 761 to 879 kg ha^–1. Wheat yield response to mulching was related to rainfall pattern during its growth season. Significant response to mulching was obtained only in years when rainfall during vegetative phase of the crop was low. Amount and distribution of rainfall during two main phases of crop development affected the N use efficiency by wheat. On an average, each cm of rain substituted for 3.5, 4.6 and 6.5 kg of applied N ha^–1 under M₀, M_p and M_b, respectively. Split rainfall for two main phases of crop growth, available stored water at seeding, fertilizer N and profile NO₃-N content accounted for 89 per cent variability in wheat yield across years and mulching treatments.     

Effect of P-K-fertilizer with a low Cl content on the yield and quality of aromatic and sun-cured tobacco

The effect of a phosphate rock—sulfuric acid—potassium chloride-complex fertilizer with a low chloride content (PKLCl) on the yield and quality of aromatic and sun-cured tobacco was studied. In areas where the soil is deficient in Cl and/or the rainfall is sufficient to leach the chloride below the plants' root zone, an application of PKLCl, together with a N fertilizer substitute for NPK complex fertilizer (K from K₂SO₄), can be administered to the tobacco. The PKLCl was able to increase the yield and improve the quality of cured-leaf tobacco, while the Cl content in the cured-leaf was still below 2% for sun-cured tobacco and below 1% for aromatic tobacco.     

Ammonium nitrogen uptake by rice grown in acid sulfate soil under controlled redox conditions

A study was conducted to determine plant growth and ammonium fertilizer nitrogen uptake by rice (Oryza sativa, L.) in acid sulfate soils (Sulfic Tropaquept) as affected by soil redox conditions. Rice seedlings of acid sulfate soil-tolerant and sensitive varieties (IR 46 and IR 26, respectively) were grown in laboratory microcosms for 3 weeks in soil suspensions incubated at four separate Eh levels (+500, +250, +50, and-150 mV). Growth of both varieties decreased as soil Eh decreased. Uptake of both added¹⁵N labelled (NH₄)₂SO₄ and native soil nitrogen also decreased with decreasing soil Eh. Percent N from fertilizer in the plant tissues increased with decreasing soil Eh. Nitrogen uptake was greater in IR 46 as compared to IR 26. A greater amount of fertilizer N and native soil N remained in the soil suspension under a highly reduced condition compared to an oxidized condition indicating that more ammonium N was utilized by the rice plants under the oxidized than the highly reduced conditions. The growth of the soil tolerant rice variety (IR 46) was more superior to that of the sensitive rice variety (IR 26) under oxidized (+500 mV) and moderately reduced (+250 to +50 mV) than highly reduced (-150 mV) conditions. Greater uptake of soil and fertilizer nitrogen was measured under the soil redox conditions in which adequate plant growth was recorded. Strongly reducing soil redox conditions adversely affected plant growth which in turn limited nitrogen uptake.     

Effect of NPK fertilization on the mineral nutrition and yield of three coconut genotypes

Annual application of NPK fertilizers over a 18 year period to coconut on red sandy loam soils resulted in a minimal increase in mineralisable N, but in a marked increase in available P and K. Plant N levels, however, reflected the improved N nutrition but did not reach sufficiency levels found elsewhere. An available P status of 15 ppm in the control plots kept leaf P at sufficiency levels. P fertilizers did not increase the P content of leaves. K fertilizers raised the K leaf content to sufficiency levels. Doubling the M₁ fertilizer rates of 500 g N, 220 g P and 830 g K per palm per year had no effect on N, P and K levels in the palm leaves.Changes in K levels of the leaves had antagonistic effects on leaf Mg (r = – 0.68^**) and leaf Na (r = – 0.87^**). As this effect brings leaf Mg close to deficiency values palms receiving K might need additional Mg as well.The findings and interpretation of soil and leaf analysis data were confirmed by large yield responses to application of NPK fertilizers. Genetic differences between palms in their response to levels of nutrient supplies were apparent. The CDO × WCT hybrid outyielded the high yielding WCT variety especially when NPK was given at the M₁ level. The response in yield to applied fertilizers was linear for WCT and curvilinear for the hybrids CDO × WCT and WCT × CDO.     

Nitrate distribution and accumulation in an Ustochrept soil profile in a long term fertilizer experiment

Distribution and accumulation of NO₃—N, down to 210 cm depth, in the soil profile of a long term fertilizer experiment were studied after 16 cycles of cropping (maize-wheat-fodder cowpea). The application of fertilizer N without P and K or in combination with only P resulted in higher NO₃—N concentration in the soil profile than the application of N with P and K. With an annual application of 320 kg N ha^–1 alone, a peak in NO₃—N accumulation occurred at 135 cm soil depth. However, with the application of NPK, no peak in NO₃—N distribution was discernible and its content at most of the sampling depths was either less than or equal to N and NP treatments. The annual application of 10 tons farm yard manure (FYM) per ha along with NPK resulted in a relatively lower NO₃—N content in the sub soil. The amount of NO₃—N accumulation in the soil profile decreased as the cumulative N uptake by the crops increased. Application of fertilizer amounts greater than that of the recommended (100% NPK) resulted in low percent N recoveries in crops and greater NO₃—N accumulation in the soil profile.     

Long term effects of fertilization on carbon and nitrogen sequestration and aggregate associated carbon and nitrogen in the Indian sub-Himalayas

An understanding of the dynamics of soil organic carbon (SOC) as affected by farming practices is imperative for maintaining soil productivity and also for restraining global warming by CO₂ evolution. Results of a long-term (30 year) experiment in the Indian Himalayas under rainfed soybean (Glycine max L.)—wheat (Triticum aestivum L.) rotation was analyzed to determine the influence of mineral fertilizer and farmyard manure (FYM) application at 10 Mg ha⁻¹ on SOC and total soil nitrogen (TSN) stocks and distribution within different aggregate size fractions. Fertilizers (NP, NK and NPK) and FYM in combination with N or NPK were applied before the soybean crop every year and no nutrient was applied before the wheat crop. Results showed that addition of FYM with N or NPK fertilizers increased SOC and TSN contents. The overall gain in SOC in the 0- to 45-cm soil depth interval in the plots under NPK + FYM treatment over NPK was 17.18 Mg C ha⁻¹ in 30 year. The rate of conversion of input C to SOC was about 19% of each additional Mg C input per hectare. SOC content in large size aggregates was greater than in smaller size aggregates, and declined with decreased aggregate size. Thus, long-term soybean–wheat rotation in a sandy loam soil of the Indian Himalayas sequestered carbon and nitrogen. Soil organic C and TSN sequestration in the 0.25- to 0.1-mm size fraction is an ideal indicator of long-term C and N sequestration, since this fraction retained maximum SOC/TSN stock.