Scientific abstracts

High-Yield Maize Production in Relation to Potassium Uptake Requirements in China

Understanding maize (Zea mays L.) grain yield in relation to K uptake requirements is essential for devising optimized K fertilizer management practices and agricultural policies to increase grain yield for food security. A database comprising 953 measurements was created using 56 on-farm and research station experiments during 2000 to 2012 in the North China Plain (NCP) to determine K uptake requirements and patterns of K accumulation pre- and post-silking with different yield levels. The K requirement Mg^–1 grain yield (K_req.) in the K = Opt. treatment was 15.0 kg, which was lower than 20.0 kg in the K > Opt. treatment. In the Optimal K treatment, average K_req. values were 15.0, 14.8, 14.8, and 15.7 kg for grain yields ranging from <8.0, 8 to 10, 10 to 12, and >12.0 Mg ha^–1, respectively. The relative consistency of K_req. values with increasing grain yield was mainly attributed to an offset in the increase in stover K (from 14.0 to 18.1 g kg^–1), an increase in harvest index (HI) from 0.49 to 0.54, and the stability of grain K concentrations (about 3.2 g kg^–1). Higher percentages for K accumulation at the post-silking stage were observed with >12 Mg ha^–1 (24%) and 10 to 12 Mg ha^–1 (22%) compared to <10 Mg ha^–1 (9%). In conclusion, maintaining adequate K supply and post-silking K accumulation is essential for achieving high-yield maize production.

Potassium Fertilization - An Effective Mitigator of Unused Nitrogen in Forage Sorghum

Forages tend to accumulate elevated levels of nitrate when fields are heavily fertilized with nitrogenous fertilizers or are environmentally stressed due to drought, cold, frost, hail, etc. Elevated levels of nitrate have detrimental effects on animal health and are regarded as a causative factor for several mass cattle-death incidents. It was observed that nitrate concentration in Sorghum bicolor L. obtained from local fields of Uttar Pradesh (Ghaziabad and Meerut) and Haryana (Gurgaon and Faridabad) exceeded the safe limit (2,500 mg of nitrate kg^-1 of fresh wt.) i n a significant number of samples (31.7%) studied. Given this, the investigation was conducted in earthen pots to determine nitrate contents in 16 genotypes of S. bicolor L. A significant difference in nitrate content was observed among genotypes, many of which accumulated nitrate to toxic levels. POP-52 (V9), a high nitrate reductase (HNR) genotype and EB-15 (V7), a low nitrate reductase (LNR) genotype of sorghum were selected to study the effect of potassium (K) application on nitrate accumulation in specially designed PVC-drums. The minimum nitrate concentration (V9=816.6 mg/kg fresh wt. and V7=2691.8 mg/kg fresh wt.), coupled with maximum NR activity (V9=9.916 μmol NO₂^-1h^-1g^-1 fresh wt. and V7=5.018 μmol NO₂^-1h^-1g^-1 fresh wt.) were observed in 60 day old K60 treated plants. K application reduced the nitrate concentration by 35.24% in V9 and by 25.54% in V7 genotypes by increasing nitrate reductase (NR) activity by 86.23% in V9 and lesser increase of 32.07% in V7 genotype of sorghum at 30 days. A two-fold (approx.) decrease in nitrate concentration was observed at K60 in both genotypes from 30 to 60-days-after-sowing. K application also reduced considerably the nitrate in the leachate indicating that K is effective in mitigating nitrate pollution in plants and soil. The data emphasizes the importance of K in increasing the nitrogen use efficiency and of balanced fertilization in combating the nitrate-related implications on human beings, animals and environment.

Potassium Fertiliser Enhances the Salt-Tolerance of Common Bean (Phaseolus vulgaris L.)

Sodium chloride (NaCl) is the most abundant salt that contributes to soil salinity. The response of plants to excess NaCl is complex, involving changes in their morphology, physiology, and metabolism. Potassium (K) is not only an essential macronutrient for plant growth and productivity, but it is also a primary osmoticum for maintaining the low water potential of plant tissues. A pot experiment was conducted in the wirehouse of the National Research Centre, Cairo, Egypt, during the 2010-2011 season, to examine the potential role of K fertiliser in alleviating the deleterious effects of NaCl-salinity on some physiological and biochemical traits of two recombinant inbred lines (RILs) of common bean (Phaseolus vulgaris L.; RIL 147 and RIL 115).The results showed that salinity levels of 25 mM (S1) and 50 mM NaCl (S2) caused significant decreases in the numbers of pods per plant, the fresh weight (FW) and dry weight (DW) of pods per plant, shoot DW per plant, as well as in the level of photosynthetic pigments, compared to plants irrigated with tap water (S0). A dose of 150 mg K₂O kg^-1 soil (K2) mitigated these harmful effects of salinity on common bean yield and on the content of photosynthetic pigments. Both salinity levels (S1 and S2) and treatment K2 caused significant increases in proline, free amino acid, and soluble carbohydrate concentrations, as well as peroxidase and polyphenol oxidase activities, relative to the corresponding control plants. In contrast, both RILs show a decrease in their phenolic compound concentrations due to salinity and/or the application of K2 compared to control plants (i.e., treatment S0K1; where K1 = 25 mg K₂O kg^-1 soil). The K⁺:Na⁺ ion ratio decreased significantly as the salinity level increased, and increased significantly under treatment K2. We conclude that treatment K2 mitigated the adverse effects of salinity (NaCl) through the effect of K⁺ ions enhancing the levels of photosynthetic pigments, anti-oxidant enzyme activities, osmoprotectant concentrations, and the K⁺:Na ion ratio, all of which were reflected in an improvement in plant performance.

Effect of Potassium Application on Wheat (Triticum aestivum L.) Cultivars Grown Under Salinity Stress

Effect of potassium application on wheat plants (two cultivars), one sensitive (Gemiza 9) and the other cv. tolerant (Sakha 93) grown under salinity stress was studied. A pot experiment were carried out during two successive winter seasons (2009/2010 and 2010/2011) under greenhouse conditions at the National Research Centre, Dokki, Giza, Egypt. The treatments used were: irrigated with (tap water), 40, 80 and 120 mM NaCl and two levels of potassium fertilizers (25 and 150 mg K₂O/kg soil) in the form of potassium sulfate (48-50% K₂O) were added to soil. When plants age reached 65 days, samples were drawn for vegetative growth criteria, photosynthetic pigments (chlorophyll (a), (b) and carotenoids). Polyphenoloxidase (PPO), peroxidase (POX) and superoxide dismutase (SOD). Soluble sugar, starch and total phenols, macro elements and Na⁺ as well as yield were determined. The results showed that NaCl-stress triggered significant inhibitory effects on wheat plant growth, photosynthetic pigments especially for sensitive cv. Application of 150 mg K₂O fertilizer to the soil exerted certain alleviative effects on these indices in wheat cultivars, especially tolerant one (Sakha 93). Activities of the enzymes Polyphenoloxidase (PPO), peroxidase (POX), superoxide dismutase (SOD) and soluble sugar and total phenols were significantly increased by salinity at 80 and 120 and K application at level 150 mg K₂O/kg soil. Potassium application could play an important role in alleviation of injury of wheat irrigated with salinized water depend on the level of salinity. The yield of both cultivars significantly decreased as the level of salinity increased. Potassium fertilizer level of 150 mg K₂O/kg soil was effective in lessening the harmful effect of salinity, especially at lower levels on yield.

Exogenous Application of Proline Alleviates Salt-Induced Oxidative Stress in Phaseolus vulgaris L. Plants

Two field experiments on common bean (Phaseolus vulgaris L.) plants were conducted at three sites having different levels of salinity (EC = 1.84, 6.03, or 8.97 dS m^-1) and considered to be low, moderate, or highly saline soil, respectively. The aim was to examine the effects of three successive exogenous applications of 5.0 mM proline, applied as foliar sprays at 20, 30, and 40 d after sowing (DAS) to each plant at each site. Bean plants were sampled 50 DAS and the effects of the proline sprays on various growth parameters, levels of photosynthetic pigments, endogenous proline, ascorbic acid, nitrate, nitrite, and mineral nutrient (P, K, Na) concentrations, and anti-oxidant enzyme activities were measured in order to understand the mechanism(s) of salt tolerance in proline-treated bean plants. Exogenous applications of 5 mM proline alleviated oxidative stress and enhanced the growth of all treated common bean plants. Proline also increased the activities of the anti-oxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), as well as the concentrations of carotenoids, ascorbic acid, and endogenous proline. Spray applications of proline increased the concentrations of P and K⁺, and decreased Na⁺ ion concentrations, in salt-affected plants. Thus, the K⁺:Na⁺ ratio increased. Based on these findings, we recommend the use of proline as a commercial formulation to enhance plant growth and production in common bean plants grown under saline conditions.

Potassium Mobilization and Transformation in Red Paddy Soil as Affected by Rice

A rhizobox experiment was conducted to study the effect of growing rice (Oryza sativa L.) on the movement and transformation of K in a red paddy soil. Results showed that K uptake by rice reduced the concentrations of soil water-soluble K (Sol-K), exchangeable K (Ex-K), and non-exchangeable K (Nonex-K) in the root zone. Soil Sol-K in non-root-zone compartment close to the root zone (0–6 cm) migrated toward the root zone, and soil Ex-K (0-4 cm) and soil Nonex-K (0–3 cm) was released into soil solution. As the rice growth progressed, soil Sol-K, Ex-K, and Nonex-K in the root zone and soil Sol-K in non-root-zone compartment close to the root zone (0-6 cm) continued to decrease. Decreases of soil Ex-K and Nonex-K in non-root-zone compartment extended from the root to 6 and 5 cm into the bulk soil, respectively. At the late grain-filling stage, soil Sol-K concentration in the root zone and non-root-zone compartment (0-6 cm) declined, and then remained stable, whereas Sol-K in the non-root zone (6-7 cm) kept diffusing toward the root zone. Soil Ex-K and Nonex-K in the root zone and non-root-zone compartment continued to reduce, and the decrease distance of soil Nonex-K was extended to 6 cm. Within the whole season, soil Ex-K and Nonex-K were the main forms of K available to the plants, followed by Sol-K. The information obtained in this study indicated that K fertilizer should be added to the place around the root zone.

Phosphorus and Potassium Distribution and Adsorption on Two Florida Sandy Soils

Phosphorus and K are critical nutrients in citrus production whose deficiency or excess can affect yield, fruit quality, and water quality. However, no study has been conducted to understand the nutrient distribution in the root zone using intensive fertigation practices in Florida’s sandy soils. Thus, experiments were conducted to: (i) compare the performance of intensively managed drip and microsprinkler fertigation systems with conventional grower practices; and (ii) determine P and K adsorption based on recommended fertilizer application rates on Candler (hyperthermic, uncoated Lamellic Quartzipsamments) and Immokalee (sandy, siliceous, hyperthermic Arenic Alaquods) fine sands. Phosphorus and K were applied and tracked with time and distance from point of application. Soil P on Immokalee soil was 27 to 163% higher in the irrigated zone for drip and restricted microsprinkler fertigation than the unirrigated zone and up to 70% greater in the 0- to 15-cm depth of the irrigated zone than conventional microsprinkler practices. Soil K was 5 to 61% greater in the upper 0- to 15-cm of the irrigated zone with drip and microsprinkler fertigation than conventional microsprinkler practices on Immokalee fine sand. Soil P and K on Candler also differed by fertilization method, depth, and between irrigated and unirrigated zones. The linearized P sorption coefficients for Candler were three- to fourfold greater than the corresponding depths for Immokalee, while sorption coefficients for K were similar for the two soils. It is unlikely that P or K would present a water quality concern as strictly related to irrigation practice. The P application rate for Candler should be lowered for young trees (<3 yr old).

Residual Effects of Potassium to Cotton on Corn Productivity under No-Tillage

The long-term residual effects of K applications to preceding cotton (Gossypium hirsutum L.) on subsequent corn (Zea mays L.) is largely unknown under no-tillage. A cotton field experiment was conducted on a no-tilled Loring silt loam (fine-silty, mixed, active, thermic Oxyaquic Fragiudalf) at Jackson, TN, during 1995 to 2008 with the K treatments of 0, 28, 56, 84, 112, 140, and 168 kg ha^-1applied to the same plots each year. From 2009 through 2011, corn was no-till planted on the previous cotton trial without further K fertilization. Incremental gains in corn leaf K responses were consistent with increases in the K application rate for previous cotton. A significant quadratic relationship was observed between corn yields and K application rates in 2010 and 2011 with corn yield peaking at the K rate of 94 kg ha^-1 in 2010 and 84 kg ha^-1 in 2011. Potassium removal by grain ranged from 2.54 to 3.55 kg K Mg^-1 of grain yield. For the 28 kg K ha^-1 rate and those higher K rates, soil K buffering capacity followed an exponential decline as the initial soil test K level increased. Surface broadcasting of K fertilizer at the recommended rate of 56 kg K ha^-1 or above to preceding cotton for 14 yr and relying on the residual K fertilizer for the subsequent corn for at least 3 yr without further K fertilization might be a viable K management practice on high K fields under no-tillage.

Mineral Micronutrient Content of Cultivars of Field Pea, Chickpea, Common Bean, and Lentil Grown in Saskatchewan, Canada

The mineral content of pulses grown in Saskatchewan, Canada, was examined for magnesium, potassium, iron, zinc, manganese, copper, selenium, and in some cases nickel and calcium. Eight to 18 cultivars of each of field pea (Pisum sativum), common bean (Phaseolus vulgaris), chickpea (Cicer arietinum), and lentil (Lens culinaris) were grown at several locations in southern Saskatchewan in 2005 and 2006 in randomized complete block designs with three replicates. Mineral content was examined by atomic absorption spectrometry. The pulses were found to contain significant proportions of the recommended daily allowance (RDA) for all the tested minerals except calcium. In many cases a 100 g (dry weight) portion of the crop provided over 50% of the RDA. For selenium, pulses grown in some locations provided 100% of the RDA. The effect of location was highly significant in most instances, while that of year and cultivar were generally less so. Pairwise differences among cultivars were examined by Tukey’s test. Where possible, crops grown side by side were compared.

Drought Resistance of Warm-Season Putting Green Cultivars on U.S. Golf Association Root Zones with Varied Potassium

Drought resistance of putting green cultivars is receiving increased attention due to irrigation restrictions. Potassium, which reduces turfgrass tolerance to environmental stresses when deficient, is often applied at rates equal to or greater than N in an attempt to increase its efficacy. Drought resistance for recently established 'TifDwarf' (TD) and 'TifEagle' (TE) bermudagrasses [Cynodon dactylon (L.) Pers. × C. transvaalensis Burt Davy], 'SeaDwarf' (SD) seashore paspalum (Paspalum vaginatum Swartz), and 'PristineFlora' (PF) zoysiagrass [Zoysia japonica Stued. by Zoysia tenuifolia (L.) Merr.] was evaluated under varied irrigation and K levels on a U.S. Golf Association (USGA)-specified research green. Irrigation treatments were applied in the spring and fall of 2009 and spring 2010, and included 25, 50, and 100% of potential evapotranspiration (ETo), as calculated using the Blaney-Criddle equation. Nitrogen at 4.9 g m^-2 30 d^-1 and K (as KCl) in 1N:1K, 1N:2K, 1N:3K, and 1N:4K fertilization ratios were applied at the beginning of each experiment. All cultivars had objectionable wilting (>10%) at 25% ETo in 2009, although PF and SD had least in the fall. In 2010 PF and SD did not exhibit objectionable wilting at any irrigation level. At 50% ETo, TD and TE wilted objectionably in all experiments, as did PF in the fall of 2009. In 2010, the bermudagrasses exhibited objectionable wilting under daily irrigation at 100% ETo. Increasing K in relation to N failed to increase drought resistance for the cultivars studied. The bermudagrasses had the least drought resistance and PF and SD the most.

Farmers’ Use of Nutrient Management: Lessons from Watershed Case Studies

Nutrient enrichment of water resources has degraded coastal waters throughout the world, including in the United States (e.g., Chesapeake Bay, Gulf of Mexico, and Neuse Estuary). Agricultural nonpoint sources have significant impacts on water resources. As a result, nutrient management planning is the primary tool recommended to reduce nutrient losses from agricultural fields. Its effectiveness requires nutrient management plans be used by farmers. There is little literature describing nutrient management decision-making. Here, two case studies are described that address this gap: (i) a synthesis of the National Institute of Food and Agriculture, the Conservation Effects Assessment Project, and (ii) field surveys from three nutrient-impaired river basins/watersheds in North Carolina (Neuse, Tar-Pamlico, and Jordan Lake drainage areas). Results indicate farmers generally did not fully apply nutrient management plans or follow basic soil test recommendations even when they had them. Farmers were found to be hesitant to apply N at university-recommended rates because they did not trust the recommendations, viewed abundant N as insurance, or used recommendations made by fertilizer dealers. Exceptions were noted when watershed education, technical support, and funding resources focused on nutrient management that included easing management demands, actively and consistently working directly with a small group of farmers, and providing significant resource allocations to fund agency personnel and cost-share funds to farmers. Without better dialogue with farmers and meaningful investment in strategies that reward farmers for taking what they perceive as risks relative to nutrient reduction, little progress in true adoption of nutrient management will be made.

Effects of Long-Term Fertilization on Soil Carbon and Nitrogen in Chinese Mollisols

Three field experiments were conducted to examine the influence of long-term (30–31 yr) effect of fertilizer applications on soil C and N in the mollisols of Northeast China. Each experiment represented a different latitude range: low latitude (LatL), middle latitude (LatM) and high latitude (LatH). Four types of fertilizer applications were considered: (i) CK: unfertilized (control); (ii) NPK: balanced application of inorganic fertilizer nitrogen, phosphorus, potassium; (iii) M: application of organic manure; and (iv) NPKM: fertilizer nitrogen, phosphorus, potassium, plus organic manure. Compared with CK treatments, applications of fertilizers increased soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), microbial biomass carbon (Cmic) and microbial biomass nitrogen (Nmic). On average compared with CK treatments, SOC in the NPK, M, and NPKM treatments increased by 2.74, 22.00, and 27.81%, respectively. Thus, applications of organic manure combined with inorganic fertilizers showed greater effects on the topsoil C and N content than inorganic fertilizers. Under the same fertilizer treatments, SOC, TN, Nmic, and Cmic contents were the lowest at LatM site. Available N content decreased for a latitude sequence of LatH > LatM > LatL for CK, M, and NPKM treatments and LatM > LatH > LatL for the NPK treatments. These results indicate that the magnitude of soil C and N among the three sites was not related to the latitude of the experiments.

Recommended Nutrient Management Practices in the Carbon Sequestration Potential of Cassava (Two Decades Experience from a Long-Term Fertiliser Experiment)

Increasing CO₂ concentration in the atmosphere is considered as the predominant cause of global warming. Agricultural ecosystem has the greatest potential to sequester atmospheric CO₂ into the soil to mitigate global warming. Nutrient management practices involving crop residue and application of recommended fertilisers are viable options to acquire atmospheric CO₂. Cassava is considered as the future food security crop as regards to its biological efficiency coupled with ability to sustain under changing climate especially during drought (by shedding leaves) and to grow well in marginal soils. In this paper, a comparison between Recommended Fertiliser Practice (RFP) and an Absolute Control (AC) with respect to soil organic carbon (SOC) dynamics through leaf dry matter addition is analysed over a period of 20 years (1991-2012). The results obtained from a Long-Term Fertiliser Experiment (LTFE) under Cassava at CTCRI to highlight the C sequestering efficiency of Cassava and thereby global warming. During the first year (1991), the leaf dry matter production was 2.366 t ha^–1 in RFP equivalent to 0.475 μg g^–1 leaf carbon, for which 39.985 μg g^–1 of atmospheric CO₂ was absorbed reducing its concentration to 320.015 μg g^–1 from 360 μg g^–1 and the then SOC status was 0.8% only. After 20 years of continuous application of recommended fertilisers, in 2012, the leaf dry matter production was increased to 5.245 t ha^–1 equivalent to 1.053 μg g^–1 leaf C. To produce this, the utilization of atmospheric CO₂ was 88.64 μg g^–1, reducing the atmospheric CO₂ status to 304.36 μg g^–1. Atmospheric CO₂ acquired by Cassava leaves transformed into leaf C, on leaf shedding has resulted in a concomitant increase in SOC to 0.512% by 20 years indicating the potential of Cassava to sequester atmospheric CO₂ to SOC. In the absolute control, the CO₂ acquisition and concomitant increase in SOC ranged from 25-50% of RFP only. The ultimate effect of sequestering the atmospheric CO₂ by reduction in atmospheric CO₂ and increase in SOC was manifested as increase in tuber yield to the tune of 32.13 t ha^–1 during 2012 from 17.76 t ha^–1 in 1991. Hence, it can be inferred that Cassava under recommended fertiliser management practices can sequester atmospheric CO₂ into SOC and mitigate global warming to a great extend.

Potassium Nutrition and Management in Indian Agriculture Issues and Strategies

Growing population in India demands more food in near future and continues further. This pressurises Indian agriculture to produce more from shrinking arable land. Balanced nutrition plays a key role in augmenting crop production. Potassium, one of the most important macronutrient, has greater influence on plant physiology and sturdiness for stress conditions. But, low status of K in Indian soils resulted from exclusion of K in balanced nutrition lead to mining of soil reserve K. Soil K status depends on soil mineralogy, fertilizer K application and through other K sources (organic manures, tank silt, irrigation water etc.). Therefore, while interpreting soil K status, non-exchangeable K is to be considered. Hence, this paper deals with categorization of soils both district wise and agro-ecological region wise for exchangeable and non-exchangeable K. Based on this crop recommendations were made and crop response also studied. Positive results were observed in different crops and cropping systems across agro-ecological regions. This further supports the inclusion of non-exchangeable K in soil K fertility interpretation and recommendation for crops based on categories of both exchangeable and non-exchangeable K.

Site-Specific Nutrient Management (SSNM) in Thailand

A site-specific nutrient management (SSNM) research project was started in Thailand in 1997 by Professor Dr. Tasnee Attanandana and colleagues. The project focused on a lowcost technology with high efficiency and the protocols that can easily be followed by farmers. Soil classification was prepared in a simple way so that Thai farmers can identify their own soil. A soil test kit has been invented which allows farmers to analyze soil nutrients (NPK) by themselves. DSSAT and PDSS models were used to generate nitrogen (N) and phosphorus (P) requirements, and a specific model for potassium (K) requirement was developed. Nutrient requirement data from crop modeling was processed by simple formulas to generate fertilizer recommendation that provides the highest return under specific conditions. After the experimental trials, the project led to the steps of technology transferring and programming of SSNM for maize (SimCorn) in 2001. After the success of SSNM for maize, in 2005, the project expanded into SSNM for rice (SimRice) and sugarcane (SimCane). During this time, the project emphasized the independency of farmers. In 2008, the Land Development Department generated the Onfarm program following the policy of the Ministry of Agriculture and Cooperatives. The Onfarm program used the data from the SSNM projects together with the fertilizer recommendation based on soil test by the Department of Agriculture. As a result, the Onfarm program recommended fertilizers for major crops in Thailand. At present, a new research team is conducting the SSNM for chili.

Effective Fertilizer Management Practises for High Yield Rice Production of Granary areas in Malaysia

High yield targets in modern rice farming should be supported by effective and efficient fertilizer management practices. Over-dependence on blanket subsidy fertilizer recommendation is unable to produce high yield. Site-specific balanced fertilizer recommendation option by FERTO package is able to enhance crop performance, subsequently achieving high yield target. The significant yield increment (up to 300%) using FERTO package recommendation is accomplished because due consideration is given to four basic principles of fertilizer management, i.e. nutrient quantity, nutrient access, indigenous soil fertility status, and balanced crop requirement. Sitespecific approach of the FERTO package recommendation is complex. Therefore, FERTO package recommendation is more applicable to large-scale commercialized rice production. Thus, for policy formulation, FERTO package recommendation has to be transformed into formulation according to cropping zones. Development of fertilizer formulation according to cropping zone is more practical and can easily be managed by fertilizer suppliers and rice estate managers. The formulation can also be adopted by progressive small-scale farmers. Fourteen fertilizer formulations for specific management zones within the granary areas were identified in this study. The formulation is able to enrich proportionate vegetative and reproductive growth for high rice-yield performance. However, the application of FERTO package recommendation rate can be further enhanced by using straight fertilizers in place of the present subsidy mixture or compound fertilizers. These straight fertilizers are much cheaper compared to the mixture or compound fertilizers in the market. Therefore, the adoptions of FERTO package using straight fertilizers will reduce cost of production and ultimately increase net farm returns.