Assessment of variable application rates of biological amendment substances on establishment and growth characteristics of maize plants

Good plant establishment and excellent vigour constitute essential pre-requisites for successful grain production. The sowing of good viable seeds could contribute to increased productivity and ultimately lead to minimal seed cost and high return on investment. These are however dependent on such factors as the possible effects of preand post-seed sowing soil amendments. Hence, a greenhouse experiment was conducted in 2008 to assess the effects of variable rates (50, 75 and 100% of the recommended rates) of industrial manufactured biological amendment substances (IMBAS) (Biozone, Crop care, Gromor, Growmax, K-humate, Lanbac, Molcast, Montys and Promis) on the establishment and growth characteristics of maize seedlings. Inorganic NPK fertilizer and unamended control treatments were included as standards. Results obtained revealed a significant IMBAS as well as IMBAS x rates interaction effects on plant height, number of leaves, total biomass and leaf area. The percent plant emergence in K-humate, Montys and Promis treatments at 50% recommended rate were significantly decreased relative to the standard treatments. Application of most of the IMBAS at 100% of the recommended rate generally decreased plant establishment and phenological characteristics of maize. The study underpins the relevance of in-depth and accurate agronomic evaluation of industrially manufactured growth enhancement materials prior to recommendation for use by farmers.


INTRODUCTION
The desire of every grain producer is to obtain high yields at reduced production costs so as to optimize net returns on investments.Crop establishment and plant vigour represent key factors that influence the success of grain crop production (Hammermeister et al., 2008).Therefore, *Corresponding author.E-mail: baloyitc@arc.agric.za.Tel: +27 18 299 6267.Fax: +27 86 658 9896.
Abbreviations: IMBAS, Industrial manufactured biological amendment substances; CEC, cation exchange capacity; WAS, weeks after seed sowing; LA , leaf area.
ensuring optimal crop establishment is not only a costsaving measure, but could also contribute to increased productivity and reduced seeding rates.Obtaining good plant emergence and establishment on maize (Zea mays L.) fields is however dependent on the growth strength of the root coleoptiles and crust condition, particularly in soils with high clay content (Souty et al., 1992).Seedling emergence could critically be impeded by soil compaction, typically caused by the use of heavy farm machineries, which often lead to increased soil strength and bulk density (Hartge, 1988), and subsequently impedes plant roots, especially at low moisture levels (Hartge, 1988;Lithourgidis et al., 2005).Regardless of the inherent soil conditions, the use of soil amendments either as pre-or post-seed sowing inputs could also impact on seedling emergence (Baloyi et al., 2009).
In many parts of the world, organic wastes that are often used as fertilizer materials exist in prodigious amount due to the increasing human and animal population.Such wastes include farm wastes, sewage sludge, poultry litter and industrial wastes (food, sugar, cotton and rice industry etc.).The steady accumulation of such wastes often constitutes potential sources of land, water and air pollution (Tahir et al., 2006), with their use as nutrient-sources greatly restricted, thereby leading to the subsequent introduction of chemical fertilizers (Tahir et al., 2006).While few of the organic wastes are utilized to a limited extent for crop production, most are either burnt or remained unutilized, especially in developing countries (Shah and Anwar, 2003).These practices have not only posed serious threat to the environment, but had also resulted in the loss of useful nutrients-pool, which otherwise could be made available to plants (Ikerra et al., 1999;Kang and Shanon, 2001;Akinnifesi et al., 2007).
Nonetheless, the direct application of organic wastes on farmlands has many drawbacks since un-composted organic materials have wider carbon/nitrogen (C/N) ratio than the composted organic materials (Zia et al., 2003).Consequently, they are often not suitable for soil health (Tahir et al., 2006) due to the possible immobilization of applied N, making it unavailable to plants (Ahmed et al., 2006).Moreover, organic wastes are being used either as composted or non-composted materials in large quantities in conventional practice for increased crop productivity (Nevens and Reheul, 2003;Wolkowski, 2003;Terrance et al., 2004).Composting is one of the major recycling processes in which biodegradable organic materials are converted into formless humus-like substances that can be easily and more friendly handled, stored and applied to land without negative environmental impacts (Gallardo-Larva and Nogades, 1987;Tahir et al., 2006).Dried cured composts are generally superior to un-composted materials having more concentrated nutrients, narrower C/N ratios and also being effectively free from pathogens, weed seeds and other potential contaminants that could cause pollution (Ahmed et al., 2006).
The integrated use of organic and inorganic plant nutrient sources may not only recycle organic wastes that could potentially cause environmental pollution, but could also conserve a rich pool of nutrients resource and hence reduce the sole dependence on chemical fertilizers (Ahmed et al., 2006;Tahir et al., 2006).The complementary use of organic materials with inorganic fertilizers increases the potential of organic fertilizers, improves the efficiency of inorganic fertilizers (Heluf, 2002), and also reduces nutrients losses (Guar and Geeta, 1993;Makumba et al., 2007).A study on N-enriched compost supplemented with 57 kg N/ha using urea, gave comparable effectiveness to a full urea dose applied at 114 kg/ha (Tahir et al., 2006).Similarly, the application of inoculated organic fertilizer (bio-fertilizer) supplemented with 57 kg N/ha significantly increased the growth and yield of tomato when compared to a full dose of N-fertilizer (Tahir et al., 2006).Thus, the recent industrial conversion of composted organic materials into value-added single product as plant growth promoter through a novel approach of enrichment or blending of bio-fertilizers with inorganic fertilizers or plant growth promoting rhizobacteria (Tahir et al., 2006), constitute an alternative strategy for increased use of organic fertilizers.The use of such biological growth promoter has been reported to considerably increase grain yield (Ndakidemi et al., 2006;Kutu and Asiwe, 2010).
In South Africa, various organic-based fertilizer materials are being manufactured in industries and promoted for use as growth enhancement substances.Recommendation on the use of these industrially manufactured organic-based fertilizers herein refers to as industrially manufactured biological amendment substances (IMBAS), sometimes involve partial and/or total replacement of NPK.These products are rigorously promoted and marketed for farmers' use without sufficient agronomic information on their efficiency.This study was therefore carried out to evaluate the possible effects following the use of IMBAS, which possess growth enhancement stimulus potential on the establishment and selected phenological traits of maize seedlings.It also compared the performance of the different rates of application of the IMBAS with the conventional inorganic fertilizers applied at optimum rate.

Description of the experiment and layout
A glasshouse pot trial was conducted at the Agricultural Research Station at Grain Crops Institute, Potchefstroom, South Africa (26°S; 27°E) during 2008-summer sowing season, in over six weeks period.The temperature of the glasshouse was maintained between 18 and 27°C throughout the period of the study using an electrical fan and wet wall cooling system.Treatments consisted of the different IMBAS evaluated at 50, 75 and 100% of the recommended rates by suppliers and/or manufacturers.The different IMBAS used in this study were locally produced and they included Biozone, Crop care, Gromor, Growmax, K-humate, Lanbac, Molcast, Montys and Promis.These were applied based on manufacturers' recommendation as contained in Table 1.Optimum recommended rates for NPK inorganic fertilizer and unamended control treatments were included as standard checks.Nitrogen and phosphorus fertilizers were applied at the blanket rates of 80 kg N/ha and 43.5 kg P/ha using limestone ammonium nitrate and superphosphate, respectively.Soil laboratory analysis results used for the study gave 192 mg K/kg, which indicated a sufficiency level and was thus excluded in the fertilization programme.
Soil used for the study was collected from surface 0 -20 cm depth, air dried and sieved through a 2 mm stainless steel sieve.Results of the selected physico-chemical properties of the soil revealed 34% clay content, pH (H2O) 6.6, 5.7 mg/kg total mineral N, 5.6 mg/kg Bray-1 P, 0.82% organic carbon and a cation exchange capacity (CEC) value of 14.7 cmol (+)/kg.Except for the foliar applied materials, each treatment including inorganic fertilizer was thoroughly mixed with 4-kg soil and transferred into plastic pots (20 cm high x 17 cm in diameter).The soil-filled pots containing each IMBAS and inorganic fertilizer treatments along with unamended control were replicated four times and arranged on the glasshouse floor in a completely randomized design.Two uniformly sized maize seeds (cv.PAN 6479) were sown in each pot at a depth of 5 cm.Prior to seed sowing, each pot was watered to approximately 90% field capacity using deionised water, and allowed to equilibrate for 24 h.Plants were supplied with 400 ml of deionised water at three days intervals during the 6 weeks study period, while weeds were manually removed when necessary.

Trial monitoring and data capturing
Percent plant emergence was measured at 3 weeks after seed sowing (WAS), while phenological growth traits such as plant height and number of leaves per plant were measured at 3 and 6 WAS.Additional phenological growth traits of leaf area and total biomass yield were measured at 6 WAS prior to plant harvesting and termination of the trial.Plant height was measured using a steel tape from above the soil surface until the longest extended mature leaf (Alexander et al., 2004), whereas leaf numbers per plant were manually counted.Leaf area (LA) was determined from an intact leaf by multiplying the product of leaf length and breadth by a factor of 0.75 (Saxena and Singh, 1965).Biomass yield was determined by cutting the whole plant from the soil surface using a sharp knife and oven-drying at 70°C until a constant weight was attained.The percent plant emergence and phenological traits determined were subjected to analysis of variance using Statistix 8.1 and differences in treatment means were separated using Tukey HSD test at 5% probability level.

Effect of variable IMBAS application on seedling emergence
Application of the different IMBAS rates exerted inconsistent but significant (P < 0.05) effect on maize plant emergence (Table 2).While the application of the different IMBAS decreased the percent plant emergence relative to the two standard checks, the variable rates of Growmax and Biozone gave inconsequential effect (Table 2).However, the 50% application rate of Crop Care gave equally high percent plant emergence as the two standard treatments.The reduced percent plant emergence obtained in Promis treated pots was severe at 100% recommended rate pots, possibly due to the production of excessive organic acids during the decomposition of the organic constituents of the IMBAS (Shiga, 1997).The application of 75% recommended rate in Montys, Molcast and K-humate treated pots also gave 100% plant emergence as obtained with the two standard treatments.Furthermore, 100% plant emergence was obtained at both 50 and 75% application rates in Gromor and Lanbac treated pots.Hence, the application of 50% recommended rate in Crop Care, Gromor and Lanbac promoted excellent and comparable percent plant emergence as the standards, while the 75% rate guaranteed similar results in Montys, Molcast and K-humate.Generally, the use of the different IMBAS at 100% rate had a depressive effect on plant emergence when compared to NPK fertilizer and unamended control treatments.

Effect on plant height and number of leaves per plant
There was a significant treatment x rate interaction effect on plant height at 3 WAS, while significant differences were observed only for the main effects (rate and IMBAS) at 6 WAS.Plants from pots in which Crop Care and Molcast were applied at 50% of the recommended rate were approximately 25 and 14%, respectively taller than those from NPK applied pots at 3 WAS (Table 2).However, plant height obtained at 6 WAS in pots with 75% recommended application rates in both Crop Care and Molcast was 50% taller than the NPK standard check.Similarly, plant height from Growmax and Lanbac amended pots were comparable but generally taller than those from Gromor, Montys and Promis as well as NPK amended pots.The taller plants obtained in these IMBAS amended than the NPK check pots may be related to beneficial effects associated with the use of these products, which may have resulted in higher N release and uptake.However, the variable effects of the IMBAS may be attributed to the variable N release characteristics of the different products, which might be dependent on the quality of the materials used for the production of the different IMBAS.High quality organic materials decompose very fast thus releasing N for possible immediate plant use (Mafongoya et al., 1998) and thus promote faster plant growth.Low quality organic materials on the other hand possess slow decomposition and N release characteristics that could possibly result in poor synchrony of mineralized N with plant uptake (Mafongoya et al., 1998) and ultimately lead to the reduced plant growth and negative effects associated with some of the IMBAS treated pots.Similar findings were reported by Materechera and Morutse (2009) following application of chicken manure in maize trial.Nonetheless, plants from Molcast and Promis amended pots applied at 100% of the recommended rate had stunted growth with plants in Molcast pots either showing spindled leaves and/or did not emerge entirely while some died with visual necrotic effects on their growing tips.These observations differed from similar study reported by Ahmed et al. (2006) possibly because of differences in the quality of the organic material constituents utilized for this study.
There was significant (P < 0.05) treatment x rates interaction effects on plant height at 3 WAS as well as on mean number of leaves per plant at 6 WAS (Table 3).Significantly higher (P < 0.05) mean number of leaves per plant was obtained at 6 WAS in all IMBAS applied at 50 and 75%, recommended rates than the NPK treatment, except in Molcast, Montys and Promis.Generally, the application of 100% of the recommended rate for all the IMBAS though resulted in significantly decreased mean number of leaves per plant but had values comparable to that obtained from NPK pots.

Leaf area and plant biomass production as affected by the different treatments
There was significant (P < 0.01) interaction between IMBAS and application rates on maize leaf area and biomass production obtained at 6 WAS (Tables 2 and 3).Plants from pots treated with Crop Care, Molcast, Lanbac and Promis at 50% recommended rate gave significantly higher leaf area relative to higher application rates and the NPK standard (Table 2).There was a generally higher leaf area and hence canopy cover was observed with the 50 and 75% application rates in virtually all the IMBAS, except Promis, which indicates evidence of good photosynthates assimilation and resulted in higher vegetative growth (Ibeawuchi et al., 2008).The slow development of maize canopies may limit light interception and potential productivity (Westgate et al., 1997).
Plants from pots that received Molcast and Crop Care at 50% recommended application rate both gave considerably higher dry biomass yield than any other treatment (Table 2).This could possibly be attributed to better plant growth, greater canopy architecture and leaf area expansion that possibly influenced favourable dry matter accumulation and partitioning to the leaves during the early stage of plant development (Tollenaar and Wu, 1999).Dry biomass accumulation from Molcast (15.7 g/pot) and Crop care (14.1 g/pot) treated pots represented approximately 293 and 253% higher biomass yield, respectively, than the value obtained from NPK treated pots (Table 2).The significantly higher biomass yields of Molcast and Crop Care treated plants than all other treatments may be attributed to the presence of zinc (Zn), which constituted vital micro-nutrient in these IMBAS.Proper zinc nutrition increases biomass production (Khan et al., 2004), while favourable phosphorus (P)/Zn ratio and possibly the synergistic effect under low soilphosphorus condition typical of the soil used in this study could have promoted balanced nutrition, which ultimately favoured root development, better nutrient uptake and vigorous plant growth (Gutierrez-Boem and Thomas 1999;Zhu et al., 2001;Rajaie et al., 2009).

Conclusions
The different application rates of IMBAS had profound effects on plant establishment and growth characteristics of maize relative to the conventional NPK fertilized and unfertilized soil.Plant emergences were significantly reduced in pots treated with Molcast and Promis at 100% recommended rate.Application of nearly all the IMBAS beyond 75% of the recommended rate exerted deleterious effects on plant emergence and selected growth indices.While the 50 and 75% rates appeared sufficient for most of the IMBAS, the most appropriate rate is dependent on the IMBAS type utilized.These results validate the importance of thorough agronomic assessment and proper documentation of these materials and other biological soil amendments prior to recommendation for use by farmers.

Table 1 .
Details of the recommended application of the various IMBAS utilized in the study as prescribed by product manufacturer.

Table 2 .
Plant emergence and phenological characteristics of maize measured at 3 and 6 weeks after sowing as affected by application of IMBAS rates.
SE, Standard error; *!, percentage of the optimum recommended rate.

Table 3 .
Variance ratio of testing differences for seedling emergence and selected phenological growth characteristics of maize.