Faqir Hussain

Carbon availability and microbial biomass in soil under an irrigated wheat-maize cropping system receiving different fertilizer treatments

Abstract Seasonal changes in carbon availability and microbial biomass were studied in soil under an irrigated wheat-maize cropping system receiving different fertilizter treatments over the past 10 years. Treatments included N-100 and N-200 (urea at 100 and 200kgNha–1 year–1, respectively), FYM-16 and FYM-32 (farmyard manure at 16 and 32tha–1 year–1, respectively) and a control (unfertilized). Aerobically mineralizable carbon (AMC; C mineralized after 10 days aerobic incubation at 30°C) increased (13–16%) under wheat at both rates of urea whereas under maize it increased (22%) only with the lower rate of urea. Farmyard manure also increased the content of soil AMC under both crops, the effect being two- to threefold higher under wheat than under maize. Urea application caused an 32–78% increase in the specific respiratory activity (SRA) under wheat but caused an 11–50% decrease during the maize season. Farmyard manure also resulted in a higher SRA under both crops but only at the higher application rate. Under wheat, microbial biomass C (MBC) decreased in urea-treated plots but showed a slight increase at the higher rate of FYM. During the maize season, MBC was higher under both urea (42–46%) and FYM (36–47%) treatments as compared to the control. Microbial biomass turnover rate was highest for FYM-32 (2.08), followed by FYM-16 and urea treatments (1.35–1.49); control plots showed a turnover rate of 0.82. The higher AMC and SRA during the active growth period of wheat than that of maize indicated that root-derived C from wheat was higher in amount and more easily degradable.

Microbial biomass and mineralization-immobilization of nitrogen in some agricultural soils

SummaryThe chloroform fumigation-incubation method (CFIM) was used to measure the microbial biomass of 17 agricultural soils from Punjab Pakistan which represented different agricultural soil series. The biomass C was used to calculate biomass N and the changes occurring in NH4+-N and NO3−-N content of soils were studied during the turnover of microbial biomass or added C source. Mineral N released in fumigated-incubated soils and biomass N calculated from biomass C was correlated with some N availability indexes.The soils contained 427–1240 kg C as biomass which represented 1.2%–6.9% of the total organic C in the soils studied. Calculations based on biomass C showed that the soils contained 64–186 kg N ha−1 as microbial biomass. Immobilization of NCO3−-N was observed in different soils during the turnover of microbial biomass and any net increase in mineral N content of fumigated incubated soils was attributed entirely to NH4+-N.Biomass N calculated from biomass C showed non-significant correlation with different N availability indexes whereas mineral N accumulated in fumigated-incubated soils showed highly significant correlations with other indexes including N uptake by plants.

Water-use efficiency and carbon isotope discrimination of Acacia ampliceps and Eucalyptus camaldulensis at different soil moisture regimes under semi-arid conditions

Acacia ampliceps Maslin and Eucalyptus camaldulensis Dehnh. were grown for one year in lysimeters at three soil moisture regimes: 100 % (well-watered), 75 % (medium-watered) and 50 % (low-watered) of total plant available water. Biomass yield of both species increased with increase in soil moisture. Water-use efficiency (WUE) of E. camaldulensis decreased and that of A. ampliceps increased markedly with decrease in available soil moisture. A. ampliceps showed 4 − 5 times more biomass yield than E. camaldulensis grown at similar soil moisture. A. ampliceps showed almost 5, 9 and 12 times higher WUE than E. camaldulensis under low-, medium- and well-watered treatments, respectively. Significant negative correlation of δ13C with WUE (r = −0.99) was observed in A. ampliceps. In contrast, δ13C of E. camaldulensis showed a significant positive correlation with WUE (r = 0.82).

Influence of Salinity on Nitrogen Transformations in Soil

Laboratory experiments were carried out to study the influence of various salinity levels [1 (control), 9 (medium), 17 (high), and 27 dS m–1(strong)] on nitrogen (N) transformations in soil fertilized with urea and ammonium sulfate. Generally, soil salinization affected the normal pathway of N transformations. The results showed that salinity (medium to high) inhibited the second step of nitrification, causing nitrite (NO2 −) accumulation in soil. The inhibition was more severe in cases of high level of salinity. The greatest salinity level caused inhibition of even the first step of nitrification, leaving more ammonium (NH4)-N accumulation in soil. Severity in nitrification inhibition was observed with increase in salinity and rate of N application, which declined with time. Ammonium accumulation with increased salinity caused N losses in the form of ammonia (NH3) volatilization. After 14 days, the NH3 losses were 1.4-, 2-, and 5-fold greater at 9, 17, and 27 dS m–1 than that of the control (1 dS m–1). After 42 days, the losses reached up to 6-fold more than the control at the greatest salinity level. Initially (up to 14 days), NH3 losses were more from urea than from ammonium sulfate, whereas at the later stages (42 days), the losses were almost equal from both the fertilizers. The overall results revealed significant adverse effects of salinity on N transformations in soil.

Determination of biomass N in some agricultural soils of Punjab, Pakistan

Microbial biomass N was measured in 18 agricultural soils collected from Punjab, Pakistan using a chloroform fumigation extraction method (CFEM), a chloroform extraction method (CEM), and a chloroform fumigation-incubation method (CFIM) using anaerobic incubation. In CFEM, the soil samples were exposed to chloroform vapour for 24 h followed by estimation of the K2SO4-extractable N whereas in CEM, soil samples were directly extracted with K2SO4 containing 10% chloroform. In the CFIM, fumigated and unfumigated samples were incubated for 15 days under anaerobic conditions and the NH4-N accumulated in the soils was used to calculate biomass N.The biomass N determined by CEM accounted for 2.8 to 13.8% of the total soil N; the average value for all soils was 6.9%, an almost similar variation (2.6 to 14.8%) was observed for the CFEM. The biomass N determined by the two methods was highly correlated (r=0.89,P<0.01). Biomass N estimated by CFIM in soils incubated under anaerobic conditions accounted for 6.1 to 13.6% of the total soil N but showed no significant correlation with biomass N determined by either CFEM or CEM.

IMPROVEMENT IN YIELD AND QUALITY OF KINNOW (CITRUS DELICIOSA X CITRUS NOBILIS) BY POTASSIUM FERTILIZATION

Citrus, especially Kinnow, fruit yield and quality in Pakistan is not competitive with other countries, which could be mainly attributed to a lack of good nutrient management for citrus orchards. Many of the soils under these orchards have been reported as deficient in potassium (K). Therefore, work was initiated for improving citrus fruit yield, size, and quality through K nutrition management. Experiments were conducted in four districts of Punjab including Faisalabad, Toba Tek Singh, Jhang, and Sargodha and four rates of potash, i.e., 0, 50, 75 and 100 kg dipotassium oxide (K2O) ha−1 were applied using sulfate of potash (SOP) along with recommended rates of phosphorus (P) and nitrogen (N). Soils of all the selected sites were clay loam or sandy clay loam and deficient in K. The leaf analysis also showed that all the selected orchards were deficient in K. Application of K increased the fruit yield and quality but K at100 kg K2O ha−1 was more effective in increasing the fruit weight and size, and peel thickness than other K rates in all the selected orchards. Juice volume and percentage significantly increased when K was applied at 75 kg K2O ha−1 at all sites. Nutrient uptake like K, P, and N enhanced with the increase in K application rate, however, the highest calcium (Ca)+ magnesium (Mg) was recorded at 50 kg K2O ha−1. The results indicated that all rates of K application improved the fruit yield and quality and reduced fruit dropping, however, 75 kg K2O ha−1 rate was more effective as juice volume and percentage, total soluble solid (TSS)/acid ratio and nutrient uptake showed significant improvement.

Phytoremediation of Saline Soils for Sustainable Agricultural Productivity

Salinization of soils is one of the major factors which severely affect the agricultural productivity worldwide. Due to salinity, more than half a billion hectares of land are not being properly used for crop production. Thus, there is a need to search means to improve saline soils so that such soils could support highly productive and meaningful land-use systems to meet the current challenges of global food security. Although permanent solution of soil salinity problem necessitates a sound drainage system to manage the rising water table, this option, being energy- and cost-intensive cannot be employed on a large scale on vast areas. Phytoremediation or biological approach, i.e., plant-based strategies for improvement of deteriorated soils is an appropriate option. Phytoremediation of saline soils can be done by cultivating suitable plant species as well as by Exploiting the ability of plant roots to improve the dissolution and enhance levels of Ca in soil solution to efficiently remove Na from the soil cation exchange complex and leach it from the root zone. During the amelioration process, soil-aggregates stability, root proliferation, soil hydraulic properties and availability of nutrients to plants are also improved. Such improvement in soil properties facilitates cultivation of less tolerant plants, improves the environment in general, and the climatic conditions by enhancing carbon sequestration.

Evaluation of acid permanganate extraction as an index of soil nitrogen availability

SummaryA chemical measure of soil nitrogen (N) availability has been evaluated. The method involved the estimation of initial mineral N, plus mineralizable N released with 0.05N KMnO4 in 1NH2SO4. The results obtained correlated highly significantly with the N uptake by wheat plants (r=0.72,P<0.01).

Evaluation of alkaline permanganate method and its modification as an index of soil nitrogen availability

SummaryTo find out a rapid and reliable procedure for estimating soil available nitrogen (N), the standard alkaline-permanganate extraction and its modification to include soil NO3 were evaluated. The N values obtained with the standard method showed a poor correlation with the mineral N of incubation test and plant uptake (r=0.36 and 0.37 respectivelyP<0.05 in both the cases) whereas the results obtained with the modified method gave highly significant correlations (r=0.84 and 0.76 respectively.P<0.01 in both the cases). The data supplied further verification of the modified alkaline-permanganate method for assessing N availability in soils.

MODULATION IN YIELD AND JUICE QUALITY CHARACTERISTICS OF CITRUS FRUIT FROM TREES SUPPLIED WITH ZINC AND POTASSIUM FOLIARLY

Citrus, especially K innow (Citrus deliciosa × Citrus nobilis), fruit yield and quality in Pakistan is not competitive with that of other countries which could be mainly attributed to the lack of good nutrient management for citrus orchards. The yield losses in this fruit crop occur mainly due to heavy fruit dropping. Experiments to overcome these problems were conducted at four different sites one each in Faisalabad, Toba Tek Singh, Jhang and Sargodha districts of Punjab, Pakistan. The soil and leaf chemical analysis showed severe deficiency of Zn and our pervious results have shown that soil amendment with potassium (K) at 75 K2O kg ha−1 improved the citrus fruit yield and quality at all selected sites. In the present experiments, effect of foliar application of Zn and K alone or in combination was studied on nutrient uptake, fruit yield, fruit dropping and juice quality. The fruit trees were pretreated with a selected K level of sulfate of potash (SOP) or muriate of potash (MOP), i.e., 75 kg K2O ha−1 along with recommended nitrogen (N) and phosphorus (P) doses. Zinc [Zn, 1% zinc sulfate (ZnSO4) solution], K [1% potassium sulfate (K2SO4) solution] and Zn + K (solution containing 0.5% each of ZnSO4 and K2SO4) were sprayed at the onset of spring and flush of leaves or flowers, fruit formation and at color initiation on fruit. Overall, application of Zn, K or Zn + K was effective in improving the nutrient uptake, yield and quality parameters of citrus fruit at all sites. Fruit dropping was also reduced by the foliar spray of Zn, K or Zn + K but the most promising results were recorded with foliar spray containing both Zn and K.