Usha Kiran Chopra

Effect of soil covers on growth and yield of irrigated wheat planted at two dates

Abstract A field study was conducted to evaluate the effect of soil covers, viz. control (C), transparent polyethylene (TP), black polyethylene (BP) and rice straw (RS), on growth and yield of irrigated wheat planted on 30 November (S1) and 6 January (S2) during 1978–1979, and 19 November (S1) and 24 December (S2) during 1979–1980. The TP cover expedited seedling emergence, caused a higher rate of dry matter accumulation, advanced inflorescence emergence and lengthened the grain filling period, resulting in a greater number of fertile tillers and grains per head and higher grain yield. These favourable effects on growth and yield of wheat relative to the control were associated with significant increases in 14.30 h soil temperature at 0–15 cm depth during the first 6 weeks after planting. Consistent with the smaller increase in soil temperature under BP, growth and yield advantage were less. With the decrease in soil temperature under RS, growth and yield were significantly less. The positive or negative effect of a soil cover on grain yield was of greater magnitude for S2 than for S1 since temperatures were lower during early growth. The results indicated the possibility of increasing the grain yield of late planted wheat by covering soil with TP sheet during early growth.

Assessment of plant nitrogen stress in wheat Triticum aestivum L. through hyperspectral indices

A field experiment with wheat was conducted with four different nitrogen and four different water stress levels, and hyperspectral reflectances in the 350–2500 nm range were recorded at six crop phenostages for two years (2009–2010 and 2010–2011). Thirty-two hyperspectral indices were determined using the first-year reflectance data. Plant nitrogen (N) status, characterized by leaf nitrogen content (LNC) and plant nitrogen accumulation (PNA), showed the highest R 2 with the spectral indices at the booting stage. The best five predictive equations for LNC were based on the green normalized difference vegetation index (GNDVI), normalized difference chlorophyll index (NDCI), normalized difference705 (ND705) index, ratio index-1dB (RI-1dB) and Vogelman index a (VOGa). Their validation using the second-year data showed high R 2 (>0.80) and ratio of performance to deviation (RPD; >2.25) and low root mean square error (RMSE; <0.24) and relative error (<10%). For PNA, five predictive equations with simple ratio pigment index (SRPI), photochemical reflectance index (PRI), modified simple ratio705 (mSR705), modified normalized difference705 (mND705) and normalized pigment chlorophyll index (NPCI) as predicting indices yielded the best relations with high R 2 > 0.80. The corresponding RMSE and RE of these ranged from 1.39 to 1.13 and from 24.5% to 33.3%, respectively. Although the predicted values show good agreement with the observed values, the prediction of LNC is more accurate than PNA, as indicated by higher RMSE and very high RE for the latter. Hence, the plant nitrogen stress of wheat can be accurately assessed through the prediction of LNC based on the five identified reflectance indices at the booting stage.

Root growth, leaf water potential and yield of irrigated summer mung bean (Phaseolus aureus roxb.) In relation to soil water status and soil temperature under various mulches

Abstract Changes in soil water status and soil temperature under various mulches, and the associated effects on root growth, leaf water potential (LWP) and grain yield of summer mung bean were evaluated during 1977 and 1978. Irrigation was varied in the two years to produce a range in the severity of water stress. In 1977 pre-irrigation water depletions from field capacity in soil between the surface and a depth of 90 cm were 14.4, 12.4, 8.7 and 9.2 cm under no mulch (M 0 ), straw mulch (M s ), black polyethylene mulch (M p ) and polyethylene covered with straw (M ps ), respectively. Corresponding values in 1978 were 8.7, 7.5, 4.8 and 5.1 cm. Soil temperature was comparable under M 0 and M p and averaged 5.6°C higher than under M s and M ps during the crop growth period. A significant increase in root density in the soil layer down to 30 cm occurred in both 1977 and 1978 under M s and only in 1977 under M p . Leaf water potential measured before irrigation on May 18 was lowest under M 0 and highest under M ps followed by M s and M p . Mulching resulted in a significant increase in grain yield. The greatest increase occurred under M ps followed by similar increases under M p and M s . Under conditions of comparable soil water status, it would seem that the higher root density, leaf water potential (LWP) and grain yield under M ps than under M p resulted from the soil temperature mediated effect of the straw mulch. Nearly equal yields under M p and M s , despite a drier soil water regime under M s , also reflected a similar effect. The soil temperature mediated effect of the straw mulch, shown by the difference between M ps and M p , appeared to account for about 50% of the increase in the grain yield. The result indicated the possibility that the grain yield of summer mung bean could be increased by the use of mulches which regulate soil temperature and moisture regimes and favour crop growth.

Nuclear magnetic resonance relaxation characterisation of water status of developing grains of maize (Zea mays L.) grown at different nitrogen levels

Changes in water status of developing grains of maize (Zea mays L.) grown under different nitrogen levels were characterized by nuclear magnetic resonance (NMR) spectroscopy. There were distinct changes in water status of grains due to the application of different levels of nitrogen (0, 120 and 180 kg N ha(-1)). A comparison of the grain developmental characteristics, composition and physical properties indicated that, not only the developmental characteristics like grain weight, grain number/ear, and rate of grain filling increased, but also bound water characterized by the T2 component of NMR relaxation increased with nitrogen application (50-70%) and developmental stages leading to maturation (10-60%). The consistency in the patterns of responses to free water and intermediate water to increasing levels of nitrogen application and grain maturity suggested that nitrogen application resulted in more proportion of water to both bound- and intermediate states and less in free state. These changes are further corroborated by the concomitant increases in protein and starch contents in grains from higher nitrogen treatments as macromolecules like protein and starch retain more amount of water in the bound state. The results of the changes in T2 showed that water status during grain development was not only affected by developmental processes but also by nitrogen supply to plants. This study strongly indicated a clear nutrient and developmental stage dependence of grain tissue water status in maize.

CROPPING SYSTEM EFFECTS ON SOIL QUALITY FOR THREE AGRO-ECOSYSTEMS IN INDIA

Soil quality integrates the effects of soil physical, chemical and biological attributes. Some of them are dynamic in nature and behave differentially in various agro-ecosystems (AESs) and are quantified in terms of a soil quality index (SQI). An attempt has been made in this paper to develop an SQI based on a minimum data set (MDS), which could be used to evaluate the sustainability of the crop production in three varying AESs in India, namely sub-humid, semi-arid and arid. Thirteen indicators were utilized to develop the SQI from the properties measured from the surface soil layer (0–15 cm). Each indicator of the MDS was transformed into a dimensionless score based on scoring functions (linear and non-linear) and integrated into four SQIs. The weighted non-linear index (WNLI) was identified as the most sensitive for all the AESs and was recommended as an index for future assessments. Based on this index, the quantification of soil quality under several cropping systems was carried out for sub-humid, semi-arid and arid AESs and the most suitable cropping system was identified. WLNI was positively and significantly correlated ( R 2 = 0.79, p

Effect of soil temperature alteration by soil covers on seedling emergence of wheat (Triticum aestivum L.) sown on two dates.

SummaryA field study was conducted to evaluate the effect of soil temperature altered by various ways of soil coveringviz control (T1), transparent polyethylene (T2), black polyethylene (T3), rice straw (T4), rice straw applied only during night (T5) and farm yard manure (T6) on seedling emergence of wheat sown on November 30, 1978 and January 6, 1979. Maximum increase in soil temperature occurred under transparent polyethylene cover. Temperature alterations were relatively smaller under other treatments and was minimum under farm yard manure cover. With both sowings, the effect of various ways of soil covering on seedling emergence depended on the magnitude of soil temperature alteration caused by them. It was hastened markedly under transparent polyethylene cover and only slightly under black polyethylene cover. Continuous soil covering with rice straw slowed down seedling emergence while covering only during night hastened it slightly. Farm yard manure cover showed negligible effect on seedling emergence. Seedling emergence response to an increase in soil temperature was higher with second sowing when temperature was relatively lower than with first sowing. The result suggests the possibility of expediting seedling emergence of wheat sown under low temperature condition by transparent polyethylene cover. Seedling emergence was only slightly influenced by other soil covers.