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Twenty surface soil samples were collected from different paddy fields of thoubal district, Manipur to determine status and different forms of zinc in the soils. All the soil samples were acidic in nature with mean value of pH 5.49. The mean value of electrical conductivity was 0.07 dSm-1. The mean value of organic carbon was 2.13%. The mean cation exchange capacity, available nitrogen, available phosphorus and available potassium were 17.37 [cmol(p+)kg-1], 315.16 kg ha-1, 26.39 kg ha-1 and 240.11 kg ha-1 respectively. The studied soils were fine-textured that is clay in the textural class. The mean value of available (DTPA extractable) zinc was 0.82 mg kg-1. The DTPA extractable zinc show positive and significant correlation with CEC. A negative and significant correlation was observed with pH. On the basis of average concentration, the distribution of zinc in the soil order was: WSEX-Zn (0.38 mg kg-1) < CRYOX-Zn (1.31 mg kg-1) < MnOX-Zn (1.95 mg kg-1) < AMOX-Zn (3.04 mg kg-1) < OCx-Zn (3.16 mg kg-1) < Res-Zn (82.79 mg kg-1). All the zinc fractions showed positive correlation with EC, OC, CEC, available nitrogen, available potassium, clay; and negative correlation with pH and available phosphorus. WSEX-Zn and Res-Zn showed the lowest and highest concentration among the all zinc fractions, respectively. Different zinc fractions were found to be correlated to eachother, suggesting the dynamic nature of the equilibrium existing between them. The highest correlation among zinc fractions was found between residual and total zinc indicating the dependence of these forms on each other.

A field investigation was carried out during kharif seasons of 2016 and 2017 at research farm of College of Agriculture, Central Agricultural University, Imphal, to study the influence of integrated nutrient management on dry matter production, yield and NPK content of transplanted rice. The treatments were laid out in a randomized block design and replicated thrice using the rice variety (CAU-R1). Among the different treatments, higher dry matter production and N content in rice were found significantly in T8 (100% RDN from urea + 10 tonnes Azolla ha-1) on 30th, 60th and 90th DAT. At harvest, significantly higher content of N in grain was observed in T10 (75% RDN from urea + 25% RDN from FYM + 10 tonnes Azolla ha-1) while treatments T8 and T10 showed the similar effect in straw N content. However, statistically higher P concentration was recorded in T11 (50% RDN from urea + 50% RDN from FYM + 10 tonnes Azolla ha-1) throughout the growing period and also in grain and straw at harvest time. T12 (25% RDN from urea + 75% RDN from FYM + 10 tonnes Azolla ha-1) noted the highest K concentration in grain followed by T11 while K content in straw was highest in both the treatments T11 andT12. In contrary to P content, the K content recorded in grain was low under different treatments. Critical analysis of the pooled data showed that soil treated with 75% RDN from urea + 25% RDN from FYM + 10 tonnes Azolla ha-1(T10) yielded significantly higher grain and straw yield of rice.

The critical limit of nitrogen in soil and plant (CAU R-1) was determined through a pot culture experiment with twenty five soils of Imphal West district of Manipur, India for predicting the response of rice to nitrogen application. All the soil samples were clayey in texture and acidic in reaction with the mean pH value of 5.16, electrical conductivity ranged from 0.06 to 0.14 dSm-1 with an average of 0.1 dSm-1, organic carbon content from 1.06 to 2.62 % with mean value of 2.03%, cation exchange capacity of the soils from 12.20 to 20.20 meq/100g with mean value of 16.06 meq/100g. Available nitrogen content in soils varied from 185.00 to 331.06 kg N/ha with an average value of 267.24 kg N/ha. Available nitrogen in the soils was positively and significantly correlated with plant N content (r=0.653**), dry matter yield (r=0.556**), plant N uptake (r=0.726**) in control pots. There was also a positive and significant correlation between available N and bray’s per cent yield (r = 0.519**). The critical limit of available N was established at 257 kg N/ha for soil and 1.04 % for 45 days old rice plants. Soil containing N below this critical limit may respond economically to N fertilization for growing rice.

An experiment was conducted to study the effect of row spacing and phosphorus levels on growth, yield and economics of grass pea (Lathyrus sativus L.) during rabi season of 2011-12 and 2012-13 at the Research Farm, College of Agriculture, Central Agricultural University, Imphal, Manipur, India. The factorial R.B.D. comprised of two spacings (20 x 10cm and 30 x 10 cm) and five levels of phosphorus (0, 20, 30, 40 and 50 kg P2O5 ha-1) with three replications. Although wider spacing (30 cm x 10 cm) resulted in greater number of pods/plant (12.05) and seeds/pod (4.43) but higher grain yield (739 kg/ha) was recorded with closer spacing (20 cm x 10 cm) probably due to greater plant population in per unit area.

An experiment was conducted on an alkaline clay loam soil of Golagamdi, India during 2005-2006 to study the effect of Farm Yard Manure and pressmud on fertility status of alkali soil under maize-wheat cropping sequence. The treatment consist of three levels of organic manure M0- no manure; M1- FYM at the rate of 10 tha-1; M2- Pressmud at the rate of 5 tha-1 and six fertilizer levels; F0- no fertilizer; F1- 75% of recommended N and P; F2-100% of recommended N and P; F3- 75% of recommended N and P+S+Zn+Fe; F4-100% of recommended N and P+S+Zn+Fe; F5- 100% of recommended N and P+foliar spray of 1% multi-micronutrient. The direct effect of FYM (M1) and pressmud (M2) reduced pH of soil. The maximum pH (8.26) was recorded from control after the harvest of wheat and the lowest (8.17) from F5. The highest EC (0.38 dS m-1) was recorded from F5 followed by F4 (0.37 dS m-1) and the lowest from control (0.27 dS m-1). The pressmud was more effective in reducing soil pH and increasing the EC than by FYM. The application of FYM (M1) and pressmud (M2) increased the available N, P, S, Fe, Zn, Cu and Mn in soil. The available N, S, Fe and Zn content under pressmud application was more than the FYM. However, the residual effect of FYM (M1) maintained higher available P (71.49 kg ha-1), K, Zn than PM (M2). Residual effect of the pressmud (M2) showed maximum available S (27.99 mg kg-1) as compared to FYM (M1) (15.86 mg kg-1). M2F3 and M2F4 treatment combinations performed better than other combinations regarding the S and Zn content of soil. The direct effect of pressmud was higher in case of Fe content than FYM. The residual effect of both FYM (1.02 mg kg-1) and pressmud (1.01 mg kg-1) significantly increased DTPA extractable Mn content in soil over control (3.27 mg kg-1) after wheat harvest. Direct effect of FYM on maize was found slightly depressed DTPA extractable Cu contents as compared to pressmud. However, the Cu content was increased again after the harvest of wheat. Key words: Farm yard manure (FYM), pressmud, residual effect, electrical conductivity (EC), maize-wheat cropping.

Evaluation of nutrient status in soil is important for nutritional, environmental and economical aspects. Phosphorus is a very important nutrient for leguminous crops. In order to evaluate the phosphorus availability, six soil test methods were carried out for predicting response of soybean to phosphorus application on twenty surface soils (0 - 15 cm) of Imphal East District, Manipur were studied. The suitability of these extractants was in the descending order: Bray P1 > Mehlich P1 > Bray P2 > Troug P > Olsen P > Morgan P. Bray’s P1 extractable phosphorus showed the highest and positive correlations with phosphorus content (control), phosphorus uptake (control), Bray’s percent yield and uptake. Therefore, this extractant may be used as an index of available phosphorus for soybean (JS-335) grown on acid soils of Imphal East District, Manipur, the critical level being 13 ppm (mg kg-1). The critical limit of phosphorus concentration in plant at 40 days of planting was 0.22%. Key words: Phosphorus, acid soils, Bray’s percent yield, soybean, critical limit.

The experiment was laid out in randomized block design with three replications and eight weed control treatments viz., weedy check, polythene mulching as pre emergence (PE), pendimethalin30EC (PE), chlorimuron ethyl 9g ha-1as post emergence (POE), quizalofop ethyl 50g ha-1 (POE), imazethapyr 100g ha-1 as early post emergence (EPOE), one hand weeding at 40 days after sowing (DAS) and two hand weeding at 20 and 40 DAS. The results showed that polythene mulching had the lowest weed dry matter due to effectively suppression of weed emergence. It was followed by twice hand weeding at 20 and 40 days after sowing. Weed index was found to be the highest with weedy check (42.10%) followed by the pre-emergence application of pendimethalin (19.09%). The effect of herbicide applied as pre-emergence was subdued at this belated stage, which may possibly be on account of longer period after application and restricted effective residual period. Plant height, number of pods per plant and grain yield of soybean was found to be highest in the treatments twice hand weeding at 20 and 40 DAS as well as polythene mulching. However, the net return and B:C ratio was lower in comparison to imazethapyr and quizalofop ethyl due to higher cost of labour and polythene material respectively. On an average, the application of imazethapyr as early post emergence (3.17) and quizalofop ethyl (3.02) gave significantly highest B:C ratio than the other treatments for soybean.

Profile distribution of DTPA-extractable micronutrient cations (Zn, Cu, Fe and Mn) and their relationship with various soil properties were studied in eighteen profiles of citrus orchard of Ukhrul district of Manipur. The content of DTPA-extractable Zn, Cu, Fe and Mn were higher in surface horizons and decreased with depth in most of the profiles and ranged from 0.08 to 0.76, 0.01 to 0.34, 8.0 to 54.0 and 1.6 to 20.4 mg Kg−1, respectively. Surface horizons contain sufficient amount of DTPA-extractable micronutrient cations except Zn. Distribution of Mn was influenced positively with EC in the first (0–20 cm) and second layer (20–40 cm), Cu was influenced inversely by organic carbon and positively by EC, Zn was influenced positively with CEC and Fe was influenced by clay content of the soils. Multiple regression analysis indicated that DTPA-extractable Zn, Cu, Fe and Mn were influenced by CEC, EC, clay and EC to the level of 0.25, 0.63, 0.25 and 0.41, respectively. However, only clay and EC contributed significantly towards these nutrient cations.

In an field experiment conducted on pea (Pisum sativum L.) during rabi season of 2013–14 in acid soil of Senapati district, Manipur, India phosphorus was given in the form of single super phosphate and levels of P2O5 kg ha-1 (0, 40 and 60) had significant influence on total dry matter yield, phosphorus concentration in plants and phosphorus uptake by plant. Six extractants were tried viz. Bray 1, Bray 2, Mehlich 1, Mehlich 3, Troug and Olsen to assess the available phosphorus status of the acid soils. The suitability of these extractants was in the descending order: Bray 1> Troug> Bray 2> Mehlich 3> Olsen (pH-8.5)> Mehlich 1. Bray's P 1 extractable phosphorus showed the highest and positive correlations with dry matter yield (control) phosphorus content (control), phosphorus uptake (control), Bray's percent yield and uptake. Therefore this extractant may be used as an index of available phosphorus for pea (Arkel) grown on acid soils of Senapati district, Manipur, the critical level being 14 ppm (mg/kg). The critical limit of phosphorus concentration in plant at 40 days of planting was 0.42% according to the graphical procedure of Cate and Nelson (1965) using a scattered diagram.

Among the different contaminants in the environment, heavy metals (HMs) are unique due to the fact that they cannot be broken down to non-toxic forms. According to the reports published worldwide, these metals are released into the environment by both natural and anthropogenic sources, especially, mining and industrial activities, and automobile exhausts (for lead). They leach into underground waters, moving along water pathways and eventually depositing in the aquifer, or are washed away by run-off into surface waters thereby, resulting in water and subsequently soil pollution. The HM contamination is increasing day by day because of increase in population, industrialization and urbanization. Therefore, posing a serious threat to health and environment. Researchers worldwide have used different methods for removing these hazardous elements. Although, these methods for cleaning up of contaminated environment including soil and water are usually expensive and do not give optimum results. Currently, phytoremediation is an effective and affordable technology used to remove inactive metals and metal pollutants from contaminated soil and water. It includes phytoextraction, rhizofiltration, phytostabilization, phytovolatization, and phytodegradation/ phytotransformation. This technology is ecofriendly and exploits the ability of plants to remediate pollutants from contaminated sites. More than 400 plant species have been identified to have potential for soil and water remediation. Among them, Thlaspi, Brassica, Sedum alfredii H., and Arabidopsis species have been mostly studied. Our paper aims to cover the causes of HM pollution and phytoremediation technology, including HM uptake mechanism and several reports describing its application at field level.